diff --git a/core/src/main/scala/kafka/api/FetchRequest.scala b/core/src/main/scala/kafka/api/FetchRequest.scala
index 55a5982..c0f80e8 100644
--- a/core/src/main/scala/kafka/api/FetchRequest.scala
+++ b/core/src/main/scala/kafka/api/FetchRequest.scala
@@ -17,16 +17,16 @@
 
 package kafka.api
 
-import java.nio.ByteBuffer
 import kafka.utils.nonthreadsafe
 import kafka.api.ApiUtils._
-import scala.collection.immutable.Map
 import kafka.common.{ErrorMapping, TopicAndPartition}
 import kafka.consumer.ConsumerConfig
-import java.util.concurrent.atomic.AtomicInteger
 import kafka.network.RequestChannel
 import kafka.message.MessageSet
 
+import java.util.concurrent.atomic.AtomicInteger
+import java.nio.ByteBuffer
+import scala.collection.immutable.Map
 
 case class PartitionFetchInfo(offset: Long, fetchSize: Int)
 
@@ -147,7 +147,7 @@ case class FetchRequest private[kafka] (versionId: Short = FetchRequest.CurrentV
   override  def handleError(e: Throwable, requestChannel: RequestChannel, request: RequestChannel.Request): Unit = {
     val fetchResponsePartitionData = requestInfo.map {
       case (topicAndPartition, data) =>
-        (topicAndPartition, FetchResponsePartitionData(ErrorMapping.codeFor(e.getClass.asInstanceOf[Class[Throwable]]), -1, MessageSet.Empty))
+        (topicAndPartition, PartitionData(ErrorMapping.codeFor(e.getClass.asInstanceOf[Class[Throwable]]), -1, MessageSet.Empty))
     }
     val errorResponse = FetchResponse(correlationId, fetchResponsePartitionData)
     requestChannel.sendResponse(new RequestChannel.Response(request, new FetchResponseSend(errorResponse)))
diff --git a/core/src/main/scala/kafka/api/FetchResponse.scala b/core/src/main/scala/kafka/api/FetchResponse.scala
index d117f10..40e9ca9 100644
--- a/core/src/main/scala/kafka/api/FetchResponse.scala
+++ b/core/src/main/scala/kafka/api/FetchResponse.scala
@@ -19,20 +19,21 @@ package kafka.api
 
 import java.nio.ByteBuffer
 import java.nio.channels.GatheringByteChannel
+
 import kafka.common.{TopicAndPartition, ErrorMapping}
 import kafka.message.{MessageSet, ByteBufferMessageSet}
 import kafka.network.{MultiSend, Send}
 import kafka.api.ApiUtils._
 
-object FetchResponsePartitionData {
-  def readFrom(buffer: ByteBuffer): FetchResponsePartitionData = {
+object PartitionData {
+  def readFrom(buffer: ByteBuffer): PartitionData = {
     val error = buffer.getShort
     val hw = buffer.getLong
     val messageSetSize = buffer.getInt
     val messageSetBuffer = buffer.slice()
     messageSetBuffer.limit(messageSetSize)
     buffer.position(buffer.position + messageSetSize)
-    new FetchResponsePartitionData(error, hw, new ByteBufferMessageSet(messageSetBuffer))
+    new PartitionData(error, hw, new ByteBufferMessageSet(messageSetBuffer))
   }
 
   val headerSize =
@@ -41,18 +42,18 @@ object FetchResponsePartitionData {
     4 /* messageSetSize */
 }
 
-case class FetchResponsePartitionData(error: Short = ErrorMapping.NoError, hw: Long = -1L, messages: MessageSet) {
-  val sizeInBytes = FetchResponsePartitionData.headerSize + messages.sizeInBytes
+case class PartitionData(error: Short = ErrorMapping.NoError, hw: Long = -1L, messages: MessageSet) {
+  val sizeInBytes = PartitionData.headerSize + messages.sizeInBytes
 }
 
 // SENDS
 
 class PartitionDataSend(val partitionId: Int,
-                        val partitionData: FetchResponsePartitionData) extends Send {
+                        val partitionData: PartitionData) extends Send {
   private val messageSize = partitionData.messages.sizeInBytes
   private var messagesSentSize = 0
 
-  private val buffer = ByteBuffer.allocate( 4 /** partitionId **/ + FetchResponsePartitionData.headerSize)
+  private val buffer = ByteBuffer.allocate( 4 /** partitionId **/ + PartitionData.headerSize)
   buffer.putInt(partitionId)
   buffer.putShort(partitionData.error)
   buffer.putLong(partitionData.hw)
@@ -80,7 +81,7 @@ object TopicData {
     val partitionCount = buffer.getInt
     val topicPartitionDataPairs = (1 to partitionCount).map(_ => {
       val partitionId = buffer.getInt
-      val partitionData = FetchResponsePartitionData.readFrom(buffer)
+      val partitionData = PartitionData.readFrom(buffer)
       (partitionId, partitionData)
     })
     TopicData(topic, Map(topicPartitionDataPairs:_*))
@@ -91,7 +92,7 @@ object TopicData {
     4 /* partition count */
 }
 
-case class TopicData(topic: String, partitionData: Map[Int, FetchResponsePartitionData]) {
+case class TopicData(topic: String, partitionData: Map[Int, PartitionData]) {
   val sizeInBytes =
     TopicData.headerSize(topic) + partitionData.values.foldLeft(0)(_ + _.sizeInBytes + 4)
 
@@ -151,7 +152,7 @@ object FetchResponse {
 
 
 case class FetchResponse(correlationId: Int,
-                         data: Map[TopicAndPartition, FetchResponsePartitionData])  {
+                         data: Map[TopicAndPartition, PartitionData]) {
 
   /**
    * Partitions the data into a map of maps (one for each topic).
@@ -167,7 +168,7 @@ case class FetchResponse(correlationId: Int,
       folded + topicData.sizeInBytes
     })
 
-  private def partitionDataFor(topic: String, partition: Int): FetchResponsePartitionData = {
+  private def partitionDataFor(topic: String, partition: Int): PartitionData = {
     val topicAndPartition = TopicAndPartition(topic, partition)
     data.get(topicAndPartition) match {
       case Some(partitionData) => partitionData
diff --git a/core/src/main/scala/kafka/cluster/Partition.scala b/core/src/main/scala/kafka/cluster/Partition.scala
index 134aef9..edc8079 100644
--- a/core/src/main/scala/kafka/cluster/Partition.scala
+++ b/core/src/main/scala/kafka/cluster/Partition.scala
@@ -21,7 +21,7 @@ import kafka.admin.AdminUtils
 import kafka.utils._
 import kafka.api.{PartitionStateInfo, LeaderAndIsr}
 import kafka.log.LogConfig
-import kafka.server.{OffsetManager, ReplicaManager}
+import kafka.server.{TopicPartitionRequestKey, LogOffsetMetadata, OffsetManager, ReplicaManager}
 import kafka.metrics.KafkaMetricsGroup
 import kafka.controller.KafkaController
 import kafka.message.ByteBufferMessageSet
@@ -29,7 +29,8 @@ import kafka.message.ByteBufferMessageSet
 import java.io.IOException
 import java.util.concurrent.locks.ReentrantReadWriteLock
 import kafka.utils.Utils.{inReadLock,inWriteLock}
-import scala.collection._
+import scala.Some
+import scala.collection.immutable.Set
 
 import com.yammer.metrics.core.Gauge
 
@@ -39,18 +40,18 @@ import com.yammer.metrics.core.Gauge
  */
 class Partition(val topic: String,
                 val partitionId: Int,
-                var replicationFactor: Int,
                 time: Time,
-                val replicaManager: ReplicaManager) extends Logging with KafkaMetricsGroup {
+                replicaManager: ReplicaManager) extends Logging with KafkaMetricsGroup {
   private val localBrokerId = replicaManager.config.brokerId
   private val logManager = replicaManager.logManager
   private val zkClient = replicaManager.zkClient
-  var leaderReplicaIdOpt: Option[Int] = None
-  var inSyncReplicas: Set[Replica] = Set.empty[Replica]
-  private val assignedReplicaMap = new Pool[Int,Replica]
+  private val assignedReplicaMap = new Pool[Int, Replica]
+  // The read lock is only required when multiple reads are executed and needs to be in a consistent manner
   private val leaderIsrUpdateLock = new ReentrantReadWriteLock()
   private var zkVersion: Int = LeaderAndIsr.initialZKVersion
-  private var leaderEpoch: Int = LeaderAndIsr.initialLeaderEpoch - 1
+  @volatile private var leaderEpoch: Int = LeaderAndIsr.initialLeaderEpoch - 1
+  @volatile var leaderReplicaIdOpt: Option[Int] = None
+  @volatile var inSyncReplicas: Set[Replica] = Set.empty[Replica]
   /* Epoch of the controller that last changed the leader. This needs to be initialized correctly upon broker startup.
    * One way of doing that is through the controller's start replica state change command. When a new broker starts up
    * the controller sends it a start replica command containing the leader for each partition that the broker hosts.
@@ -58,7 +59,6 @@ class Partition(val topic: String,
    * each partition. */
   private var controllerEpoch: Int = KafkaController.InitialControllerEpoch - 1
   this.logIdent = "Partition [%s,%d] on broker %d: ".format(topic, partitionId, localBrokerId)
-  private val stateChangeLogger = KafkaController.stateChangeLogger
 
   private def isReplicaLocal(replicaId: Int) : Boolean = (replicaId == localBrokerId)
 
@@ -72,13 +72,11 @@ class Partition(val topic: String,
   )
 
   def isUnderReplicated(): Boolean = {
-    inReadLock(leaderIsrUpdateLock) {
-      leaderReplicaIfLocal() match {
-        case Some(_) =>
-          inSyncReplicas.size < assignedReplicas.size
-        case None =>
-          false
-      }
+    leaderReplicaIfLocal() match {
+      case Some(_) =>
+        inSyncReplicas.size < assignedReplicas.size
+      case None =>
+        false
     }
   }
 
@@ -114,15 +112,13 @@ class Partition(val topic: String,
   }
 
   def leaderReplicaIfLocal(): Option[Replica] = {
-    inReadLock(leaderIsrUpdateLock) {
-      leaderReplicaIdOpt match {
-        case Some(leaderReplicaId) =>
-          if (leaderReplicaId == localBrokerId)
-            getReplica(localBrokerId)
-          else
-            None
-        case None => None
-      }
+    leaderReplicaIdOpt match {
+      case Some(leaderReplicaId) =>
+        if (leaderReplicaId == localBrokerId)
+          getReplica(localBrokerId)
+        else
+          None
+      case None => None
     }
   }
 
@@ -155,9 +151,7 @@ class Partition(val topic: String,
   }
 
   def getLeaderEpoch(): Int = {
-    inReadLock(leaderIsrUpdateLock) {
-      return this.leaderEpoch
-    }
+    return this.leaderEpoch
   }
 
   /**
@@ -179,14 +173,17 @@ class Partition(val topic: String,
       val newInSyncReplicas = leaderAndIsr.isr.map(r => getOrCreateReplica(r)).toSet
       // remove assigned replicas that have been removed by the controller
       (assignedReplicas().map(_.brokerId) -- allReplicas).foreach(removeReplica(_))
-      // reset LogEndOffset for remote replicas
-      assignedReplicas.foreach(r => if (r.brokerId != localBrokerId) r.logEndOffset = ReplicaManager.UnknownLogEndOffset)
       inSyncReplicas = newInSyncReplicas
       leaderEpoch = leaderAndIsr.leaderEpoch
       zkVersion = leaderAndIsr.zkVersion
       leaderReplicaIdOpt = Some(localBrokerId)
+      // construct the high watermark metadata for the new leader replica
+      val newLeaderReplica = getReplica().get
+      newLeaderReplica.convertHWToLocalOffsetMetadata()
+      // reset log end offset for remote replicas
+      assignedReplicas.foreach(r => if (r.brokerId != localBrokerId) r.logEndOffset = LogOffsetMetadata.UnknownOffsetMetadata)
       // we may need to increment high watermark since ISR could be down to 1
-      maybeIncrementLeaderHW(getReplica().get)
+      maybeIncrementLeaderHW(newLeaderReplica)
       if (topic == OffsetManager.OffsetsTopicName)
         offsetManager.loadOffsetsFromLog(partitionId)
       true
@@ -233,18 +230,8 @@ class Partition(val topic: String,
     }
   }
 
-  def updateLeaderHWAndMaybeExpandIsr(replicaId: Int, offset: Long) {
+  def updateLeaderHWAndMaybeExpandIsr(replicaId: Int) {
     inWriteLock(leaderIsrUpdateLock) {
-      debug("Recording follower %d position %d for partition [%s,%d].".format(replicaId, offset, topic, partitionId))
-      val replicaOpt = getReplica(replicaId)
-      if(!replicaOpt.isDefined) {
-        throw new NotAssignedReplicaException(("Leader %d failed to record follower %d's position %d for partition [%s,%d] since the replica %d" +
-          " is not recognized to be one of the assigned replicas %s for partition [%s,%d]").format(localBrokerId, replicaId,
-            offset, topic, partitionId, replicaId, assignedReplicas().map(_.brokerId).mkString(","), topic, partitionId))
-      }
-      val replica = replicaOpt.get
-      replica.logEndOffset = offset
-
       // check if this replica needs to be added to the ISR
       leaderReplicaIfLocal() match {
         case Some(leaderReplica) =>
@@ -253,8 +240,10 @@ class Partition(val topic: String,
           // For a replica to get added back to ISR, it has to satisfy 3 conditions-
           // 1. It is not already in the ISR
           // 2. It is part of the assigned replica list. See KAFKA-1097
-          // 3. It's log end offset >= leader's highwatermark
-          if (!inSyncReplicas.contains(replica) && assignedReplicas.map(_.brokerId).contains(replicaId) && replica.logEndOffset >= leaderHW) {
+          // 3. It's log end offset >= leader's high watermark
+          if (!inSyncReplicas.contains(replica) &&
+            assignedReplicas.map(_.brokerId).contains(replicaId) &&
+            replica.logEndOffset.messageDiff(leaderHW) >= 0) {
             // expand ISR
             val newInSyncReplicas = inSyncReplicas + replica
             info("Expanding ISR for partition [%s,%d] from %s to %s"
@@ -270,29 +259,29 @@ class Partition(val topic: String,
   }
 
   def checkEnoughReplicasReachOffset(requiredOffset: Long, requiredAcks: Int): (Boolean, Short) = {
-    inReadLock(leaderIsrUpdateLock) {
-      leaderReplicaIfLocal() match {
-        case Some(_) =>
-          val numAcks = inSyncReplicas.count(r => {
-            if (!r.isLocal)
-              r.logEndOffset >= requiredOffset
-            else
-              true /* also count the local (leader) replica */
-          })
-          trace("%d/%d acks satisfied for %s-%d".format(numAcks, requiredAcks, topic, partitionId))
-          if ((requiredAcks < 0 && numAcks >= inSyncReplicas.size) ||
-            (requiredAcks > 0 && numAcks >= requiredAcks)) {
-            /*
-            * requiredAcks < 0 means acknowledge after all replicas in ISR
-            * are fully caught up to the (local) leader's offset
-            * corresponding to this produce request.
-            */
-            (true, ErrorMapping.NoError)
-          } else
-            (false, ErrorMapping.NoError)
-        case None =>
-          (false, ErrorMapping.NotLeaderForPartitionCode)
-      }
+    leaderReplicaIfLocal() match {
+      case Some(leaderReplica) =>
+        // keep the current immutable replica list reference
+        val curInSyncReplicas = inSyncReplicas
+        val numAcks = curInSyncReplicas.count(r => {
+          if (!r.isLocal)
+            r.logEndOffset.messageOffset >= requiredOffset
+          else
+            true /* also count the local (leader) replica */
+        })
+        trace("%d/%d acks satisfied for %s-%d".format(numAcks, requiredAcks, topic, partitionId))
+        if ((requiredAcks < 0 && leaderReplica.highWatermark.messageOffset >= requiredOffset) ||
+          (requiredAcks > 0 && numAcks >= requiredAcks)) {
+          /*
+          * requiredAcks < 0 means acknowledge after all replicas in ISR
+          * are fully caught up to the (local) leader's offset
+          * corresponding to this produce request.
+          */
+          (true, ErrorMapping.NoError)
+        } else
+          (false, ErrorMapping.NoError)
+      case None =>
+        (false, ErrorMapping.NotLeaderForPartitionCode)
     }
   }
 
@@ -302,15 +291,19 @@ class Partition(val topic: String,
    */
   private def maybeIncrementLeaderHW(leaderReplica: Replica) {
     val allLogEndOffsets = inSyncReplicas.map(_.logEndOffset)
-    val newHighWatermark = allLogEndOffsets.min
+    val newHighWatermark = allLogEndOffsets.min(new LogOffsetMetadata.OffsetOrdering)
     val oldHighWatermark = leaderReplica.highWatermark
-    if(newHighWatermark > oldHighWatermark) {
+    if(oldHighWatermark.precedes(newHighWatermark)) {
       leaderReplica.highWatermark = newHighWatermark
-      debug("Highwatermark for partition [%s,%d] updated to %d".format(topic, partitionId, newHighWatermark))
+      debug("High watermark for partition [%s,%d] updated to %s".format(topic, partitionId, newHighWatermark))
+      // some delayed requests may be unblocked after HW changed
+      val requestKey = new TopicPartitionRequestKey(this.topic, this.partitionId)
+      replicaManager.unblockDelayedFetchRequests(requestKey)
+      replicaManager.unblockDelayedProduceRequests(requestKey)
+    } else {
+      debug("Skipping update high watermark since Old hw %s is larger than new hw %s for partition [%s,%d]. All leo's are %s"
+        .format(oldHighWatermark, newHighWatermark, topic, partitionId, allLogEndOffsets.mkString(",")))
     }
-    else
-      debug("Old hw for partition [%s,%d] is %d. New hw is %d. All leo's are %s"
-        .format(topic, partitionId, oldHighWatermark, newHighWatermark, allLogEndOffsets.mkString(",")))
   }
 
   def maybeShrinkIsr(replicaMaxLagTimeMs: Long,  replicaMaxLagMessages: Long) {
@@ -349,7 +342,9 @@ class Partition(val topic: String,
     if(stuckReplicas.size > 0)
       debug("Stuck replicas for partition [%s,%d] are %s".format(topic, partitionId, stuckReplicas.map(_.brokerId).mkString(",")))
     // Case 2 above
-    val slowReplicas = candidateReplicas.filter(r => r.logEndOffset >= 0 && (leaderLogEndOffset - r.logEndOffset) > keepInSyncMessages)
+    val slowReplicas = candidateReplicas.filter(r =>
+      r.logEndOffset.messageOffset >= 0 &&
+      leaderLogEndOffset.messageOffset - r.logEndOffset.messageOffset > keepInSyncMessages)
     if(slowReplicas.size > 0)
       debug("Slow replicas for partition [%s,%d] are %s".format(topic, partitionId, slowReplicas.map(_.brokerId).mkString(",")))
     stuckReplicas ++ slowReplicas
@@ -362,6 +357,8 @@ class Partition(val topic: String,
         case Some(leaderReplica) =>
           val log = leaderReplica.log.get
           val info = log.append(messages, assignOffsets = true)
+          // probably unblock some follower fetch requests since log end offset has been updated
+          replicaManager.unblockDelayedFetchRequests(new TopicPartitionRequestKey(this.topic, this.partitionId))
           // we may need to increment high watermark since ISR could be down to 1
           maybeIncrementLeaderHW(leaderReplica)
           info
@@ -399,14 +396,12 @@ class Partition(val topic: String,
   }
 
   override def toString(): String = {
-    inReadLock(leaderIsrUpdateLock) {
-      val partitionString = new StringBuilder
-      partitionString.append("Topic: " + topic)
-      partitionString.append("; Partition: " + partitionId)
-      partitionString.append("; Leader: " + leaderReplicaIdOpt)
-      partitionString.append("; AssignedReplicas: " + assignedReplicaMap.keys.mkString(","))
-      partitionString.append("; InSyncReplicas: " + inSyncReplicas.map(_.brokerId).mkString(","))
-      partitionString.toString()
-    }
+    val partitionString = new StringBuilder
+    partitionString.append("Topic: " + topic)
+    partitionString.append("; Partition: " + partitionId)
+    partitionString.append("; Leader: " + leaderReplicaIdOpt)
+    partitionString.append("; AssignedReplicas: " + assignedReplicaMap.keys.mkString(","))
+    partitionString.append("; InSyncReplicas: " + inSyncReplicas.map(_.brokerId).mkString(","))
+    partitionString.toString()
   }
 }
diff --git a/core/src/main/scala/kafka/cluster/Replica.scala b/core/src/main/scala/kafka/cluster/Replica.scala
index 5e659b4..e9a2ea5 100644
--- a/core/src/main/scala/kafka/cluster/Replica.scala
+++ b/core/src/main/scala/kafka/cluster/Replica.scala
@@ -19,8 +19,9 @@ package kafka.cluster
 
 import kafka.log.Log
 import kafka.utils.{SystemTime, Time, Logging}
+import kafka.server.LogOffsetMetadata
 import kafka.common.KafkaException
-import kafka.server.ReplicaManager
+
 import java.util.concurrent.atomic.AtomicLong
 
 class Replica(val brokerId: Int,
@@ -28,33 +29,17 @@ class Replica(val brokerId: Int,
               time: Time = SystemTime,
               initialHighWatermarkValue: Long = 0L,
               val log: Option[Log] = None) extends Logging {
-  //only defined in local replica
-  private[this] var highWatermarkValue: AtomicLong = new AtomicLong(initialHighWatermarkValue)
-  // only used for remote replica; logEndOffsetValue for local replica is kept in log
-  private[this] var logEndOffsetValue = new AtomicLong(ReplicaManager.UnknownLogEndOffset)
-  private[this] var logEndOffsetUpdateTimeMsValue: AtomicLong = new AtomicLong(time.milliseconds)
+  // the high watermark offset value, in non-leader replicas only its message offsets are kept
+  @volatile private[this] var highWatermarkMetadata: LogOffsetMetadata = new LogOffsetMetadata(initialHighWatermarkValue)
+  // the log end offset value, kept in all replicas;
+  // for local replica it is the log's end offset, for remote replicas its value is only updated by follower fetch
+  @volatile private[this] var logEndOffsetMetadata: LogOffsetMetadata = LogOffsetMetadata.UnknownOffsetMetadata
+  // the time when log offset is updated
+  private[this] val logEndOffsetUpdateTimeMsValue = new AtomicLong(time.milliseconds)
+
   val topic = partition.topic
   val partitionId = partition.partitionId
 
-  def logEndOffset_=(newLogEndOffset: Long) {
-    if (!isLocal) {
-      logEndOffsetValue.set(newLogEndOffset)
-      logEndOffsetUpdateTimeMsValue.set(time.milliseconds)
-      trace("Setting log end offset for replica %d for partition [%s,%d] to %d"
-            .format(brokerId, topic, partitionId, logEndOffsetValue.get()))
-    } else
-      throw new KafkaException("Shouldn't set logEndOffset for replica %d partition [%s,%d] since it's local"
-          .format(brokerId, topic, partitionId))
-
-  }
-
-  def logEndOffset = {
-    if (isLocal)
-      log.get.logEndOffset
-    else
-      logEndOffsetValue.get()
-  }
-  
   def isLocal: Boolean = {
     log match {
       case Some(l) => true
@@ -62,24 +47,45 @@ class Replica(val brokerId: Int,
     }
   }
 
-  def logEndOffsetUpdateTimeMs = logEndOffsetUpdateTimeMsValue.get()
-
-  def highWatermark_=(newHighWatermark: Long) {
+  def logEndOffset_=(newLogEndOffset: LogOffsetMetadata) {
     if (isLocal) {
-      trace("Setting hw for replica %d partition [%s,%d] on broker %d to %d"
-              .format(brokerId, topic, partitionId, brokerId, newHighWatermark))
-      highWatermarkValue.set(newHighWatermark)
-    } else
-      throw new KafkaException("Unable to set highwatermark for replica %d partition [%s,%d] since it's not local"
-              .format(brokerId, topic, partitionId))
+      throw new KafkaException("Should not set log end offset on partition [%s,%d]'s local replica %d".format(topic, partitionId, brokerId))
+    } else {
+      logEndOffsetMetadata = newLogEndOffset
+      logEndOffsetUpdateTimeMsValue.set(time.milliseconds)
+      trace("Setting log end offset for replica %d for partition [%s,%d] to [%s]"
+        .format(brokerId, topic, partitionId, logEndOffsetMetadata))
+    }
   }
 
-  def highWatermark = {
+  def logEndOffset =
     if (isLocal)
-      highWatermarkValue.get()
+      log.get.logEndOffsetMetadata
     else
-      throw new KafkaException("Unable to get highwatermark for replica %d partition [%s,%d] since it's not local"
-              .format(brokerId, topic, partitionId))
+      logEndOffsetMetadata
+
+  def logEndOffsetUpdateTimeMs = logEndOffsetUpdateTimeMsValue.get()
+
+  def highWatermark_=(newHighWatermark: LogOffsetMetadata) {
+    if (isLocal) {
+      highWatermarkMetadata = newHighWatermark
+      trace("Setting high watermark for replica %d partition [%s,%d] on broker %d to [%s]"
+        .format(brokerId, topic, partitionId, brokerId, newHighWatermark))
+    } else {
+      throw new KafkaException("Should not set high watermark on partition [%s,%d]'s non-local replica %d".format(topic, partitionId, brokerId))
+    }
+  }
+
+  def highWatermark = highWatermarkMetadata
+
+  def convertHWToLocalOffsetMetadata() = {
+    if (isLocal) {
+      highWatermarkMetadata = log.get.convertToOffsetMetadata(highWatermarkMetadata.messageOffset)
+      if (highWatermarkMetadata == LogOffsetMetadata.UnknownOffsetMetadata)
+        highWatermarkMetadata = log.get.logEndOffsetMetadata
+    } else {
+      throw new KafkaException("Should not construct complete high watermark on partition [%s,%d]'s non-local replica %d".format(topic, partitionId, brokerId))
+    }
   }
 
   override def equals(that: Any): Boolean = {
diff --git a/core/src/main/scala/kafka/consumer/ConsumerFetcherThread.scala b/core/src/main/scala/kafka/consumer/ConsumerFetcherThread.scala
index f8c1b4e..57b51c3 100644
--- a/core/src/main/scala/kafka/consumer/ConsumerFetcherThread.scala
+++ b/core/src/main/scala/kafka/consumer/ConsumerFetcherThread.scala
@@ -20,7 +20,7 @@ package kafka.consumer
 import kafka.cluster.Broker
 import kafka.server.AbstractFetcherThread
 import kafka.message.ByteBufferMessageSet
-import kafka.api.{Request, OffsetRequest, FetchResponsePartitionData}
+import kafka.api.{Request, OffsetRequest, PartitionData}
 import kafka.common.TopicAndPartition
 
 
@@ -41,7 +41,7 @@ class ConsumerFetcherThread(name: String,
                                       isInterruptible = true) {
 
   // process fetched data
-  def processPartitionData(topicAndPartition: TopicAndPartition, fetchOffset: Long, partitionData: FetchResponsePartitionData) {
+  def processPartitionData(topicAndPartition: TopicAndPartition, fetchOffset: Long, partitionData: PartitionData) {
     val pti = partitionMap(topicAndPartition)
     if (pti.getFetchOffset != fetchOffset)
       throw new RuntimeException("Offset doesn't match for partition [%s,%d] pti offset: %d fetch offset: %d"
diff --git a/core/src/main/scala/kafka/consumer/SimpleConsumer.scala b/core/src/main/scala/kafka/consumer/SimpleConsumer.scala
index 0e64632..8db9203 100644
--- a/core/src/main/scala/kafka/consumer/SimpleConsumer.scala
+++ b/core/src/main/scala/kafka/consumer/SimpleConsumer.scala
@@ -71,7 +71,7 @@ class SimpleConsumer(val host: String,
         response = blockingChannel.receive()
       } catch {
         case e : Throwable =>
-          info("Reconnect due to socket error: %s".format(e.getMessage))
+          info("Reconnect due to socket error: %s".format(e.toString))
           // retry once
           try {
             reconnect()
diff --git a/core/src/main/scala/kafka/log/Log.scala b/core/src/main/scala/kafka/log/Log.scala
index b7bc5ff..87e2595 100644
--- a/core/src/main/scala/kafka/log/Log.scala
+++ b/core/src/main/scala/kafka/log/Log.scala
@@ -21,7 +21,7 @@ import kafka.utils._
 import kafka.message._
 import kafka.common._
 import kafka.metrics.KafkaMetricsGroup
-import kafka.server.BrokerTopicStats
+import kafka.server.{LogOffsetMetadata, FetchDataInfo, BrokerTopicStats}
 
 import java.io.{IOException, File}
 import java.util.concurrent.{ConcurrentNavigableMap, ConcurrentSkipListMap}
@@ -51,11 +51,11 @@ import com.yammer.metrics.core.Gauge
 class Log(val dir: File,
           @volatile var config: LogConfig,
           @volatile var recoveryPoint: Long = 0L,
-          val scheduler: Scheduler,
+          scheduler: Scheduler,
           time: Time = SystemTime) extends Logging with KafkaMetricsGroup {
 
   import kafka.log.Log._
-  
+
   /* A lock that guards all modifications to the log */
   private val lock = new Object
 
@@ -67,7 +67,7 @@ class Log(val dir: File,
   loadSegments()
   
   /* Calculate the offset of the next message */
-  private val nextOffset: AtomicLong = new AtomicLong(activeSegment.nextOffset())
+  @volatile var nextOffsetMetadata = new LogOffsetMetadata(activeSegment.nextOffset(), activeSegment.baseOffset, activeSegment.size.toInt)
 
   val topicAndPartition: TopicAndPartition = Log.parseTopicPartitionName(name)
 
@@ -167,6 +167,10 @@ class Log(val dir: File,
     for (s <- logSegments)
       s.index.sanityCheck()
   }
+
+  private def updateLogEndOffset(messageOffset: Long) {
+    nextOffsetMetadata = new LogOffsetMetadata(messageOffset, activeSegment.baseOffset, activeSegment.size.toInt)
+  }
   
   private def recoverLog() {
     // if we have the clean shutdown marker, skip recovery
@@ -246,14 +250,14 @@ class Log(val dir: File,
     try {
       // they are valid, insert them in the log
       lock synchronized {
-        appendInfo.firstOffset = nextOffset.get
+        appendInfo.firstOffset = nextOffsetMetadata.messageOffset
 
         // maybe roll the log if this segment is full
         val segment = maybeRoll()
 
         if(assignOffsets) {
           // assign offsets to the message set
-          val offset = new AtomicLong(nextOffset.get)
+          val offset = new AtomicLong(nextOffsetMetadata.messageOffset)
           try {
             validMessages = validMessages.assignOffsets(offset, appendInfo.codec)
           } catch {
@@ -262,7 +266,7 @@ class Log(val dir: File,
           appendInfo.lastOffset = offset.get - 1
         } else {
           // we are taking the offsets we are given
-          if(!appendInfo.offsetsMonotonic || appendInfo.firstOffset < nextOffset.get)
+          if(!appendInfo.offsetsMonotonic || appendInfo.firstOffset < nextOffsetMetadata.messageOffset)
             throw new IllegalArgumentException("Out of order offsets found in " + messages)
         }
 
@@ -282,10 +286,10 @@ class Log(val dir: File,
         segment.append(appendInfo.firstOffset, validMessages)
 
         // increment the log end offset
-        nextOffset.set(appendInfo.lastOffset + 1)
+        updateLogEndOffset(appendInfo.lastOffset + 1)
 
         trace("Appended message set to log %s with first offset: %d, next offset: %d, and messages: %s"
-                .format(this.name, appendInfo.firstOffset, nextOffset.get(), validMessages))
+                .format(this.name, appendInfo.firstOffset, nextOffsetMetadata.messageOffset, validMessages))
 
         if(unflushedMessages >= config.flushInterval)
           flush()
@@ -307,7 +311,7 @@ class Log(val dir: File,
    * @param offsetsMonotonic Are the offsets in this message set monotonically increasing
    */
   case class LogAppendInfo(var firstOffset: Long, var lastOffset: Long, codec: CompressionCodec, shallowCount: Int, validBytes: Int, offsetsMonotonic: Boolean)
-  
+
   /**
    * Validate the following:
    * <ol>
@@ -392,15 +396,15 @@ class Log(val dir: File,
    * @param maxOffset -The offset to read up to, exclusive. (i.e. the first offset NOT included in the resulting message set).
    * 
    * @throws OffsetOutOfRangeException If startOffset is beyond the log end offset or before the base offset of the first segment.
-   * @return The messages read
+   * @return The fetch data information including offset metadata and messages read
    */
-  def read(startOffset: Long, maxLength: Int, maxOffset: Option[Long] = None): MessageSet = {
+  def read(startOffset: Long, maxLength: Int, maxOffset: Option[Long] = None): FetchDataInfo = {
     trace("Reading %d bytes from offset %d in log %s of length %d bytes".format(maxLength, startOffset, name, size))
 
     // check if the offset is valid and in range
-    val next = nextOffset.get
+    val next = nextOffsetMetadata.messageOffset
     if(startOffset == next)
-      return MessageSet.Empty
+      return FetchDataInfo(nextOffsetMetadata, MessageSet.Empty)
     
     var entry = segments.floorEntry(startOffset)
       
@@ -412,15 +416,26 @@ class Log(val dir: File,
     // but if that segment doesn't contain any messages with an offset greater than that
     // continue to read from successive segments until we get some messages or we reach the end of the log
     while(entry != null) {
-      val messages = entry.getValue.read(startOffset, maxOffset, maxLength)
-      if(messages == null)
+      val fetchInfo = entry.getValue.read(startOffset, maxOffset, maxLength)
+      if(fetchInfo == null) {
         entry = segments.higherEntry(entry.getKey)
-      else
-        return messages
+      } else {
+        return fetchInfo
+      }
     }
     
-    // okay we are beyond the end of the last segment but less than the log end offset
-    MessageSet.Empty
+    // okay we are beyond the end of the last segment with no data fetched although the start offset is in range,
+    // this can happen when all messages with offset larger than start offsets have been deleted.
+    // In this case, we will return the empty set with log end offset metadata
+    FetchDataInfo(nextOffsetMetadata, MessageSet.Empty)
+  }
+
+  /**
+   * Given a message offset, find its log metadata
+   */
+  def convertToOffsetMetadata(offset: Long): LogOffsetMetadata = {
+    val fetchDataInfo = read(offset, 1)
+    fetchDataInfo.fetchOffset
   }
 
   /**
@@ -433,7 +448,7 @@ class Log(val dir: File,
     // find any segments that match the user-supplied predicate UNLESS it is the final segment 
     // and it is empty (since we would just end up re-creating it
     val lastSegment = activeSegment
-    var deletable = logSegments.takeWhile(s => predicate(s) && (s.baseOffset != lastSegment.baseOffset || s.size > 0))
+    val deletable = logSegments.takeWhile(s => predicate(s) && (s.baseOffset != lastSegment.baseOffset || s.size > 0))
     val numToDelete = deletable.size
     if(numToDelete > 0) {
       lock synchronized {
@@ -458,9 +473,14 @@ class Log(val dir: File,
   def logStartOffset: Long = logSegments.head.baseOffset
 
   /**
+   * The offset metadata of the next message that will be appended to the log
+   */
+  def logEndOffsetMetadata: LogOffsetMetadata = nextOffsetMetadata
+
+  /**
    *  The offset of the next message that will be appended to the log
    */
-  def logEndOffset: Long = nextOffset.get
+  def logEndOffset: Long = nextOffsetMetadata.messageOffset
 
   /**
    * Roll the log over to a new empty log segment if necessary
@@ -582,7 +602,7 @@ class Log(val dir: File,
         val deletable = logSegments.filter(segment => segment.baseOffset > targetOffset)
         deletable.foreach(deleteSegment(_))
         activeSegment.truncateTo(targetOffset)
-        this.nextOffset.set(targetOffset)
+        updateLogEndOffset(targetOffset)
         this.recoveryPoint = math.min(targetOffset, this.recoveryPoint)
       }
     }
@@ -602,7 +622,7 @@ class Log(val dir: File,
                                 indexIntervalBytes = config.indexInterval, 
                                 maxIndexSize = config.maxIndexSize,
                                 time = time))
-      this.nextOffset.set(newOffset)
+      updateLogEndOffset(newOffset)
       this.recoveryPoint = math.min(newOffset, this.recoveryPoint)
     }
   }
diff --git a/core/src/main/scala/kafka/log/LogCleaner.scala b/core/src/main/scala/kafka/log/LogCleaner.scala
index afbeffc..c20de4a 100644
--- a/core/src/main/scala/kafka/log/LogCleaner.scala
+++ b/core/src/main/scala/kafka/log/LogCleaner.scala
@@ -17,20 +17,22 @@
 
 package kafka.log
 
+import kafka.common._
+import kafka.message._
+import kafka.utils._
+import kafka.metrics.KafkaMetricsGroup
+
 import scala.collection._
 import scala.math
 import java.nio._
 import java.util.Date
 import java.io.File
-import kafka.common._
-import kafka.message._
-import kafka.utils._
-import kafka.metrics.KafkaMetricsGroup
-import com.yammer.metrics.core.Gauge
 import java.lang.IllegalStateException
 import java.util.concurrent.CountDownLatch
 import java.util.concurrent.TimeUnit
 
+import com.yammer.metrics.core.Gauge
+
 /**
  * The cleaner is responsible for removing obsolete records from logs which have the dedupe retention strategy.
  * A message with key K and offset O is obsolete if there exists a message with key K and offset O' such that O < O'.
@@ -325,7 +327,6 @@ private[log] class Cleaner(val id: Int,
    * @param log The log being cleaned
    * @param segments The group of segments being cleaned
    * @param map The offset map to use for cleaning segments
-   * @param expectedTruncateCount A count used to check if the log is being truncated and rewritten under our feet
    * @param deleteHorizonMs The time to retain delete tombstones
    */
   private[log] def cleanSegments(log: Log,
diff --git a/core/src/main/scala/kafka/log/LogSegment.scala b/core/src/main/scala/kafka/log/LogSegment.scala
index 0d6926e..8d42404 100644
--- a/core/src/main/scala/kafka/log/LogSegment.scala
+++ b/core/src/main/scala/kafka/log/LogSegment.scala
@@ -14,15 +14,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
- package kafka.log
+package kafka.log
 
-import scala.math._
-import java.io.File
 import kafka.message._
 import kafka.common._
 import kafka.utils._
+import kafka.server.{LogOffsetMetadata, FetchDataInfo}
 
-/**
+import scala.math._
+import java.io.File
+
+
+ /**
  * A segment of the log. Each segment has two components: a log and an index. The log is a FileMessageSet containing
  * the actual messages. The index is an OffsetIndex that maps from logical offsets to physical file positions. Each 
  * segment has a base offset which is an offset <= the least offset of any message in this segment and > any offset in
@@ -86,7 +89,7 @@ class LogSegment(val log: FileMessageSet,
    * Find the physical file position for the first message with offset >= the requested offset.
    * 
    * The lowerBound argument is an optimization that can be used if we already know a valid starting position
-   * in the file higher than the greast-lower-bound from the index.
+   * in the file higher than the greatest-lower-bound from the index.
    * 
    * @param offset The offset we want to translate
    * @param startingFilePosition A lower bound on the file position from which to begin the search. This is purely an optimization and
@@ -99,7 +102,7 @@ class LogSegment(val log: FileMessageSet,
     val mapping = index.lookup(offset)
     log.searchFor(offset, max(mapping.position, startingFilePosition))
   }
-  
+
   /**
    * Read a message set from this segment beginning with the first offset >= startOffset. The message set will include
    * no more than maxSize bytes and will end before maxOffset if a maxOffset is specified.
@@ -108,22 +111,26 @@ class LogSegment(val log: FileMessageSet,
    * @param maxSize The maximum number of bytes to include in the message set we read
    * @param maxOffset An optional maximum offset for the message set we read
    * 
-   * @return The message set read or null if the startOffset is larger than the largest offset in this log.
+   * @return The fetched data information or null if the startOffset is larger than the largest offset in this log
    */
   @threadsafe
-  def read(startOffset: Long, maxOffset: Option[Long], maxSize: Int): MessageSet = {
+  def read(startOffset: Long, maxOffset: Option[Long], maxSize: Int): FetchDataInfo = {
     if(maxSize < 0)
       throw new IllegalArgumentException("Invalid max size for log read (%d)".format(maxSize))
-    if(maxSize == 0)
-      return MessageSet.Empty
-    
+
     val logSize = log.sizeInBytes // this may change, need to save a consistent copy
     val startPosition = translateOffset(startOffset)
-    
+
     // if the start position is already off the end of the log, return null
     if(startPosition == null)
       return null
-    
+
+    val offsetMetadata = new LogOffsetMetadata(startOffset, this.baseOffset, startPosition.position)
+
+    // if the size is zero, still return a log segment but with zero size
+    if(maxSize == 0)
+      return FetchDataInfo(offsetMetadata, MessageSet.Empty)
+
     // calculate the length of the message set to read based on whether or not they gave us a maxOffset
     val length = 
       maxOffset match {
@@ -143,7 +150,7 @@ class LogSegment(val log: FileMessageSet,
           min(endPosition - startPosition.position, maxSize) 
         }
       }
-    log.read(startPosition.position, length)
+    FetchDataInfo(offsetMetadata, log.read(startPosition.position, length))
   }
   
   /**
@@ -222,7 +229,7 @@ class LogSegment(val log: FileMessageSet,
     if(ms == null) {
       baseOffset
     } else {
-      ms.lastOption match {
+      ms.messageSet.lastOption match {
         case None => baseOffset
         case Some(last) => last.nextOffset
       }
diff --git a/core/src/main/scala/kafka/server/AbstractFetcherThread.scala b/core/src/main/scala/kafka/server/AbstractFetcherThread.scala
index 3b15254..5859ba8 100644
--- a/core/src/main/scala/kafka/server/AbstractFetcherThread.scala
+++ b/core/src/main/scala/kafka/server/AbstractFetcherThread.scala
@@ -18,21 +18,22 @@
 package kafka.server
 
 import kafka.cluster.Broker
-import collection.mutable
-import scala.collection.Set
-import scala.collection.Map
-import kafka.message.{InvalidMessageException, ByteBufferMessageSet, MessageAndOffset}
-import kafka.metrics.KafkaMetricsGroup
-import com.yammer.metrics.core.Gauge
 import kafka.utils.{Pool, ShutdownableThread}
 import kafka.consumer.{PartitionTopicInfo, SimpleConsumer}
-import kafka.api.{FetchRequest, FetchResponse, FetchResponsePartitionData, FetchRequestBuilder}
+import kafka.api.{FetchRequest, FetchResponse, PartitionData, FetchRequestBuilder}
 import kafka.common.{KafkaException, ClientIdAndBroker, TopicAndPartition, ErrorMapping}
 import kafka.utils.Utils.inLock
+import kafka.message.{InvalidMessageException, ByteBufferMessageSet, MessageAndOffset}
+import kafka.metrics.KafkaMetricsGroup
+
+import scala.collection.mutable
+import scala.collection.Set
+import scala.collection.Map
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.locks.ReentrantLock
 import java.util.concurrent.atomic.AtomicLong
 
+import com.yammer.metrics.core.Gauge
 
 /**
  *  Abstract class for fetching data from multiple partitions from the same broker.
@@ -59,7 +60,7 @@ abstract class AbstractFetcherThread(name: String, clientId: String, sourceBroke
 
   // process fetched data
   def processPartitionData(topicAndPartition: TopicAndPartition, fetchOffset: Long,
-                           partitionData: FetchResponsePartitionData)
+                           partitionData: PartitionData)
 
   // handle a partition whose offset is out of range and return a new fetch offset
   def handleOffsetOutOfRange(topicAndPartition: TopicAndPartition): Long
@@ -92,12 +93,12 @@ abstract class AbstractFetcherThread(name: String, clientId: String, sourceBroke
     val partitionsWithError = new mutable.HashSet[TopicAndPartition]
     var response: FetchResponse = null
     try {
-      trace("issuing to broker %d of fetch request %s".format(sourceBroker.id, fetchRequest))
+      trace("Issuing to broker %d of fetch request %s".format(sourceBroker.id, fetchRequest))
       response = simpleConsumer.fetch(fetchRequest)
     } catch {
       case t: Throwable =>
         if (isRunning.get) {
-          warn("Error in fetch %s. Possible cause: %s".format(fetchRequest, t.getMessage))
+          warn("Error in fetch %s. Possible cause: %s".format(fetchRequest, t.toString))
           partitionMapLock synchronized {
             partitionsWithError ++= partitionMap.keys
           }
diff --git a/core/src/main/scala/kafka/server/DelayedFetch.scala b/core/src/main/scala/kafka/server/DelayedFetch.scala
new file mode 100644
index 0000000..bb56336
--- /dev/null
+++ b/core/src/main/scala/kafka/server/DelayedFetch.scala
@@ -0,0 +1,90 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.network.RequestChannel
+import kafka.api.{FetchResponse, FetchRequest}
+import kafka.common.{UnknownTopicOrPartitionException, NotLeaderForPartitionException, TopicAndPartition}
+
+import scala.collection.immutable.Map
+import scala.collection.Seq
+
+/**
+ * A delayed fetch request, which is satisfied (or more
+ * accurately, unblocked) -- if:
+ * Case A: This broker is no longer the leader for some partitions it tries to fetch
+ *   - should return whatever data is available for the rest partitions.
+ * Case B: This broker is does not know of some partitions it tries to fetch
+ *   - should return whatever data is available for the rest partitions.
+ * Case C: The fetch offset locates not on the last segment of the log
+ *   - should return all the data on that segment.
+ * Case D: The accumulated bytes from all the fetching partitions exceeds the minimum bytes
+ *   - should return whatever data is available.
+ */
+
+class DelayedFetch(override val keys: Seq[TopicPartitionRequestKey],
+                   override val request: RequestChannel.Request,
+                   override val delayMs: Long,
+                   val fetch: FetchRequest,
+                   private val partitionFetchOffsets: Map[TopicAndPartition, LogOffsetMetadata])
+  extends DelayedRequest(keys, request, delayMs) {
+
+  def isSatisfied(replicaManager: ReplicaManager) : Boolean = {
+    var accumulatedSize = 0
+    val fromFollower = fetch.isFromFollower
+    partitionFetchOffsets.foreach {
+      case (topicAndPartition, fetchOffset) =>
+        try {
+          if (fetchOffset != LogOffsetMetadata.UnknownOffsetMetadata) {
+            val replica = replicaManager.getLeaderReplicaIfLocal(topicAndPartition.topic, topicAndPartition.partition)
+            val endOffset =
+              if (fromFollower)
+                replica.logEndOffset
+              else
+                replica.highWatermark
+
+            if (endOffset.offsetOnOlderSegment(fetchOffset)) {
+              // Case C, this can happen when the new follower replica fetching on a truncated leader
+              debug("Satisfying fetch request %s since it is fetching later segments of partition %s.".format(fetch, topicAndPartition))
+            } else if (fetchOffset.offsetOnOlderSegment(endOffset)) {
+              // Case C, this can happen when the folloer replica is lagging too much
+              debug("Satisfying fetch request %s immediately since it is fetching older segments.".format(fetch))
+              return true
+            } else if (fetchOffset.precedes(endOffset)) {
+              accumulatedSize += endOffset.positionDiff(fetchOffset)
+            }
+          }
+        } catch {
+          case utpe: UnknownTopicOrPartitionException => // Case A
+            debug("Broker no longer know of %s, satisfy %s immediately".format(topicAndPartition, fetch))
+            return true
+          case nle: NotLeaderForPartitionException =>  // Case B
+            debug("Broker is no longer the leader of %s, satisfy %s immediately".format(topicAndPartition, fetch))
+            return true
+        }
+    }
+
+    // Case D
+    accumulatedSize >= fetch.minBytes
+  }
+
+  def respond(replicaManager: ReplicaManager): FetchResponse = {
+    val topicData = replicaManager.readMessageSets(fetch)
+    FetchResponse(fetch.correlationId, topicData.mapValues(_.data))
+  }
+}
\ No newline at end of file
diff --git a/core/src/main/scala/kafka/server/DelayedProduce.scala b/core/src/main/scala/kafka/server/DelayedProduce.scala
new file mode 100644
index 0000000..9481508
--- /dev/null
+++ b/core/src/main/scala/kafka/server/DelayedProduce.scala
@@ -0,0 +1,115 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.api._
+import kafka.common.ErrorMapping
+import kafka.common.TopicAndPartition
+import kafka.utils.Logging
+import kafka.network.RequestChannel
+
+import scala.Some
+import scala.collection.immutable.Map
+import scala.collection.Seq
+
+/** A delayed produce request, which is satisfied (or more
+  * accurately, unblocked) -- if for every partition it produce to:
+  * Case A: This broker is not the leader: unblock - should return error.
+  * Case B: This broker is the leader:
+  *   B.1 - If there was a localError (when writing to the local log): unblock - should return error
+  *   B.2 - else, at least requiredAcks replicas should be caught up to this request.
+  */
+
+class DelayedProduce(override val keys: Seq[TopicPartitionRequestKey],
+                     override val request: RequestChannel.Request,
+                     override val delayMs: Long,
+                     val produce: ProducerRequest,
+                     val partitionStatus: Map[TopicAndPartition, DelayedProduceResponseStatus],
+                     val offsetCommitRequestOpt: Option[OffsetCommitRequest] = None)
+  extends DelayedRequest(keys, request, delayMs) with Logging {
+
+  // first update the acks pending variable according to the error code
+  partitionStatus foreach { case (topicAndPartition, delayedStatus) =>
+    if (delayedStatus.responseStatus.error == ErrorMapping.NoError) {
+      // Timeout error state will be cleared when required acks are received
+      delayedStatus.acksPending = true
+      delayedStatus.responseStatus.error = ErrorMapping.RequestTimedOutCode
+    } else {
+      delayedStatus.acksPending = false
+    }
+
+    trace("Initial partition status for %s is %s".format(topicAndPartition, delayedStatus))
+  }
+
+  def respond(offsetManager: OffsetManager): RequestOrResponse = {
+    val responseStatus = partitionStatus.mapValues(status => status.responseStatus)
+
+    val errorCode = responseStatus.find { case (_, status) =>
+      status.error != ErrorMapping.NoError
+    }.map(_._2.error).getOrElse(ErrorMapping.NoError)
+
+    if (errorCode == ErrorMapping.NoError) {
+      offsetCommitRequestOpt.foreach(ocr => offsetManager.putOffsets(ocr.groupId, ocr.requestInfo) )
+    }
+
+    val response = offsetCommitRequestOpt.map(_.responseFor(errorCode, offsetManager.config.maxMetadataSize))
+      .getOrElse(ProducerResponse(produce.correlationId, responseStatus))
+
+    response
+  }
+
+  def isSatisfied(replicaManager: ReplicaManager) = {
+    // check for each partition if it still has pending acks
+    partitionStatus.foreach { case (topicAndPartition, fetchPartitionStatus) =>
+      trace("Checking producer request satisfaction for %s, acksPending = %b"
+        .format(topicAndPartition, fetchPartitionStatus.acksPending))
+      // skip those partitions that have already been satisfied
+      if (fetchPartitionStatus.acksPending) {
+        val partitionOpt = replicaManager.getPartition(topicAndPartition.topic, topicAndPartition.partition)
+        val (hasEnough, errorCode) = partitionOpt match {
+          case Some(partition) =>
+            partition.checkEnoughReplicasReachOffset(
+              fetchPartitionStatus.requiredOffset,
+              produce.requiredAcks)
+          case None =>
+            (false, ErrorMapping.UnknownTopicOrPartitionCode)
+        }
+        if (errorCode != ErrorMapping.NoError) {
+          fetchPartitionStatus.acksPending = false
+          fetchPartitionStatus.responseStatus.error = errorCode
+        } else if (hasEnough) {
+          fetchPartitionStatus.acksPending = false
+          fetchPartitionStatus.responseStatus.error = ErrorMapping.NoError
+        }
+      }
+    }
+
+    // unblocked if there are no partitions with pending acks
+    val satisfied = ! partitionStatus.exists(p => p._2.acksPending)
+    satisfied
+  }
+}
+
+case class DelayedProduceResponseStatus(val requiredOffset: Long,
+                                        val responseStatus: ProducerResponseStatus) {
+  @volatile var acksPending = false
+
+  override def toString =
+    "acksPending:%b, error: %d, startOffset: %d, requiredOffset: %d".format(
+      acksPending, responseStatus.error, responseStatus.offset, requiredOffset)
+}
diff --git a/core/src/main/scala/kafka/server/DelayedRequestKey.scala b/core/src/main/scala/kafka/server/DelayedRequestKey.scala
new file mode 100644
index 0000000..628ef59
--- /dev/null
+++ b/core/src/main/scala/kafka/server/DelayedRequestKey.scala
@@ -0,0 +1,38 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.common.TopicAndPartition
+
+/**
+ * Keys used for delayed request metrics recording
+ */
+trait DelayedRequestKey {
+  def keyLabel: String
+}
+
+object DelayedRequestKey {
+  val globalLabel = "All"
+}
+
+case class TopicPartitionRequestKey(topic: String, partition: Int) extends DelayedRequestKey {
+
+  def this(topicAndPartition: TopicAndPartition) = this(topicAndPartition.topic, topicAndPartition.partition)
+
+  override def keyLabel = "%s-%d".format(topic, partition)
+}
diff --git a/core/src/main/scala/kafka/server/FetchDataInfo.scala b/core/src/main/scala/kafka/server/FetchDataInfo.scala
new file mode 100644
index 0000000..26f278f
--- /dev/null
+++ b/core/src/main/scala/kafka/server/FetchDataInfo.scala
@@ -0,0 +1,22 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.message.MessageSet
+
+case class FetchDataInfo(fetchOffset: LogOffsetMetadata, messageSet: MessageSet)
diff --git a/core/src/main/scala/kafka/server/FetchRequestPurgatory.scala b/core/src/main/scala/kafka/server/FetchRequestPurgatory.scala
new file mode 100644
index 0000000..ed13188
--- /dev/null
+++ b/core/src/main/scala/kafka/server/FetchRequestPurgatory.scala
@@ -0,0 +1,69 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.metrics.KafkaMetricsGroup
+import kafka.network.RequestChannel
+import kafka.api.FetchResponseSend
+
+import java.util.concurrent.TimeUnit
+
+/**
+ * The purgatory holding delayed fetch requests
+ */
+class FetchRequestPurgatory(replicaManager: ReplicaManager, requestChannel: RequestChannel)
+  extends RequestPurgatory[DelayedFetch](replicaManager.config.brokerId, replicaManager.config.fetchPurgatoryPurgeIntervalRequests) {
+  this.logIdent = "[FetchRequestPurgatory-%d] ".format(replicaManager.config.brokerId)
+
+  private class DelayedFetchRequestMetrics(forFollower: Boolean) extends KafkaMetricsGroup {
+    private val metricPrefix = if (forFollower) "Follower" else "Consumer"
+
+    val expiredRequestMeter = newMeter(metricPrefix + "ExpiresPerSecond", "requests", TimeUnit.SECONDS)
+  }
+
+  private val aggregateFollowerFetchRequestMetrics = new DelayedFetchRequestMetrics(forFollower = true)
+  private val aggregateNonFollowerFetchRequestMetrics = new DelayedFetchRequestMetrics(forFollower = false)
+
+  private def recordDelayedFetchExpired(forFollower: Boolean) {
+    val metrics = if (forFollower) aggregateFollowerFetchRequestMetrics
+    else aggregateNonFollowerFetchRequestMetrics
+
+    metrics.expiredRequestMeter.mark()
+  }
+
+  /**
+   * Check if a specified delayed fetch request is satisfied
+   */
+  def checkSatisfied(delayedFetch: DelayedFetch): Boolean = delayedFetch.isSatisfied(replicaManager)
+
+  /**
+   * When a delayed fetch request expires just answer it with whatever data is present
+   */
+  def expire(delayedFetch: DelayedFetch) {
+    debug("Expiring fetch request %s.".format(delayedFetch.fetch))
+    val fromFollower = delayedFetch.fetch.isFromFollower
+    recordDelayedFetchExpired(fromFollower)
+    respond(delayedFetch)
+  }
+
+  // TODO: purgatory should not be responsible for sending back the responses
+  def respond(delayedFetch: DelayedFetch) {
+    val response = delayedFetch.respond(replicaManager)
+    requestChannel.sendResponse(new RequestChannel.Response(delayedFetch.request, new FetchResponseSend(response)))
+  }
+}
\ No newline at end of file
diff --git a/core/src/main/scala/kafka/server/KafkaApis.scala b/core/src/main/scala/kafka/server/KafkaApis.scala
index fd5f12e..bb94673 100644
--- a/core/src/main/scala/kafka/server/KafkaApis.scala
+++ b/core/src/main/scala/kafka/server/KafkaApis.scala
@@ -23,13 +23,10 @@ import kafka.log._
 import kafka.message._
 import kafka.network._
 import kafka.admin.AdminUtils
-import kafka.metrics.KafkaMetricsGroup
 import kafka.network.RequestChannel.Response
 import kafka.controller.KafkaController
-import kafka.utils.{Pool, SystemTime, Logging}
+import kafka.utils.{SystemTime, Logging}
 
-import java.util.concurrent.TimeUnit
-import java.util.concurrent.atomic._
 import scala.collection._
 
 import org.I0Itec.zkclient.ZkClient
@@ -45,11 +42,10 @@ class KafkaApis(val requestChannel: RequestChannel,
                 val config: KafkaConfig,
                 val controller: KafkaController) extends Logging {
 
-  private val producerRequestPurgatory =
-    new ProducerRequestPurgatory(replicaManager.config.producerPurgatoryPurgeIntervalRequests)
-  private val fetchRequestPurgatory =
-    new FetchRequestPurgatory(requestChannel, replicaManager.config.fetchPurgatoryPurgeIntervalRequests)
-  private val delayedRequestMetrics = new DelayedRequestMetrics
+  val producerRequestPurgatory = new ProducerRequestPurgatory(replicaManager, offsetManager, requestChannel)
+  val fetchRequestPurgatory = new FetchRequestPurgatory(replicaManager, requestChannel)
+  // TODO: the following line will be removed in 0.9
+  replicaManager.initWithRequestPurgatory(producerRequestPurgatory, fetchRequestPurgatory)
   var metadataCache = new MetadataCache
   this.logIdent = "[KafkaApi-%d] ".format(brokerId)
 
@@ -127,22 +123,6 @@ class KafkaApis(val requestChannel: RequestChannel,
     requestChannel.sendResponse(new Response(request, new BoundedByteBufferSend(controlledShutdownResponse)))
   }
 
-  /**
-   * Check if a partitionData from a produce request can unblock any
-   * DelayedFetch requests.
-   */
-  def maybeUnblockDelayedFetchRequests(topic: String, partition: Int, messageSizeInBytes: Int) {
-    val satisfied =  fetchRequestPurgatory.update(RequestKey(topic, partition), messageSizeInBytes)
-    trace("Producer request to (%s-%d) unblocked %d fetch requests.".format(topic, partition, satisfied.size))
-
-    // send any newly unblocked responses
-    for(fetchReq <- satisfied) {
-      val topicData = readMessageSets(fetchReq.fetch)
-      val response = FetchResponse(fetchReq.fetch.correlationId, topicData)
-      requestChannel.sendResponse(new RequestChannel.Response(fetchReq.request, new FetchResponseSend(response)))
-    }
-  }
-
   private def producerRequestFromOffsetCommit(offsetCommitRequest: OffsetCommitRequest) = {
     val msgs = offsetCommitRequest.filterLargeMetadata(config.offsetMetadataMaxSize).map {
       case (topicAndPartition, offset) =>
@@ -171,27 +151,21 @@ class KafkaApis(val requestChannel: RequestChannel,
    * Handle a produce request or offset commit request (which is really a specialized producer request)
    */
   def handleProducerOrOffsetCommitRequest(request: RequestChannel.Request) {
-
-    val (produceRequest, offsetCommitRequestOpt) = if (request.requestId == RequestKeys.OffsetCommitKey) {
-      val offsetCommitRequest = request.requestObj.asInstanceOf[OffsetCommitRequest]
-      (producerRequestFromOffsetCommit(offsetCommitRequest), Some(offsetCommitRequest))
-    }
-    else {
-      (request.requestObj.asInstanceOf[ProducerRequest], None)
-    }
+    val (produceRequest, offsetCommitRequestOpt) =
+      if (request.requestId == RequestKeys.OffsetCommitKey) {
+        val offsetCommitRequest = request.requestObj.asInstanceOf[OffsetCommitRequest]
+        (producerRequestFromOffsetCommit(offsetCommitRequest), Some(offsetCommitRequest))
+      } else {
+        (request.requestObj.asInstanceOf[ProducerRequest], None)
+      }
 
     val sTime = SystemTime.milliseconds
     val localProduceResults = appendToLocalLog(produceRequest)
     debug("Produce to local log in %d ms".format(SystemTime.milliseconds - sTime))
+
     val firstErrorCode = localProduceResults.find(_.errorCode != ErrorMapping.NoError).map(_.errorCode).getOrElse(ErrorMapping.NoError)
 
     val numPartitionsInError = localProduceResults.count(_.error.isDefined)
-    produceRequest.data.foreach(partitionAndData =>
-      maybeUnblockDelayedFetchRequests(partitionAndData._1.topic, partitionAndData._1.partition, partitionAndData._2.sizeInBytes))
-
-    val allPartitionHaveReplicationFactorOne =
-      !produceRequest.data.keySet.exists(
-        m => replicaManager.getReplicationFactorForPartition(m.topic, m.partition) != 1)
     if(produceRequest.requiredAcks == 0) {
       // no operation needed if producer request.required.acks = 0; however, if there is any exception in handling the request, since
       // no response is expected by the producer the handler will send a close connection response to the socket server
@@ -214,7 +188,6 @@ class KafkaApis(val requestChannel: RequestChannel,
       }
     } else if (produceRequest.requiredAcks == 1 ||
         produceRequest.numPartitions <= 0 ||
-        allPartitionHaveReplicationFactorOne ||
         numPartitionsInError == produceRequest.numPartitions) {
 
       if (firstErrorCode == ErrorMapping.NoError) {
@@ -229,46 +202,27 @@ class KafkaApis(val requestChannel: RequestChannel,
     } else {
       // create a list of (topic, partition) pairs to use as keys for this delayed request
       val producerRequestKeys = produceRequest.data.keys.map(
-        topicAndPartition => new RequestKey(topicAndPartition)).toSeq
+        topicAndPartition => new TopicPartitionRequestKey(topicAndPartition)).toSeq
       val statuses = localProduceResults.map(r =>
         r.key -> DelayedProduceResponseStatus(r.end + 1, ProducerResponseStatus(r.errorCode, r.start))).toMap
       val delayedRequest =  new DelayedProduce(
         producerRequestKeys,
         request,
-        statuses,
-        produceRequest,
         produceRequest.ackTimeoutMs.toLong,
+        produceRequest,
+        statuses,
         offsetCommitRequestOpt)
 
-      producerRequestPurgatory.watch(delayedRequest)
-
-      /*
-       * Replica fetch requests may have arrived (and potentially satisfied)
-       * delayedProduce requests while they were being added to the purgatory.
-       * Here, we explicitly check if any of them can be satisfied.
-       */
-      var satisfiedProduceRequests = new mutable.ArrayBuffer[DelayedProduce]
-      producerRequestKeys.foreach(key =>
-        satisfiedProduceRequests ++=
-          producerRequestPurgatory.update(key, key))
-      debug(satisfiedProduceRequests.size +
-        " producer requests unblocked during produce to local log.")
-      satisfiedProduceRequests.foreach(_.respond())
-
-      // we do not need the data anymore
-      produceRequest.emptyData()
+      // add the produce request for watch if it's not satisfied, otherwise send the response back
+      val satisfiedByMe = producerRequestPurgatory.checkAndMaybeWatch(delayedRequest)
+      if (satisfiedByMe)
+        producerRequestPurgatory.respond(delayedRequest)
     }
-  }
-
-  case class DelayedProduceResponseStatus(requiredOffset: Long,
-                                          status: ProducerResponseStatus) {
-    var acksPending = false
 
-    override def toString =
-      "acksPending:%b, error: %d, startOffset: %d, requiredOffset: %d".format(
-        acksPending, status.error, status.offset, requiredOffset)
+    // we do not need the data anymore
+    produceRequest.emptyData()
   }
-  
+
   case class ProduceResult(key: TopicAndPartition, start: Long, end: Long, error: Option[Throwable] = None) {
     def this(key: TopicAndPartition, throwable: Throwable) = 
       this(key, -1L, -1L, Some(throwable))
@@ -288,13 +242,12 @@ class KafkaApis(val requestChannel: RequestChannel,
     partitionAndData.map {case (topicAndPartition, messages) =>
       try {
         val partitionOpt = replicaManager.getPartition(topicAndPartition.topic, topicAndPartition.partition)
-        val info =
-          partitionOpt match {
-            case Some(partition) => partition.appendMessagesToLeader(messages.asInstanceOf[ByteBufferMessageSet])
-            case None => throw new UnknownTopicOrPartitionException("Partition %s doesn't exist on %d"
-              .format(topicAndPartition, brokerId))
-
-          }
+        val info = partitionOpt match {
+          case Some(partition) =>
+            partition.appendMessagesToLeader(messages.asInstanceOf[ByteBufferMessageSet])
+          case None => throw new UnknownTopicOrPartitionException("Partition %s doesn't exist on %d"
+            .format(topicAndPartition, brokerId))
+        }
 
         val numAppendedMessages = if (info.firstOffset == -1L || info.lastOffset == -1L) 0 else (info.lastOffset - info.firstOffset + 1)
 
@@ -338,121 +291,58 @@ class KafkaApis(val requestChannel: RequestChannel,
    */
   def handleFetchRequest(request: RequestChannel.Request) {
     val fetchRequest = request.requestObj.asInstanceOf[FetchRequest]
-    if(fetchRequest.isFromFollower) {
-      maybeUpdatePartitionHw(fetchRequest)
-      // after updating HW, some delayed produce requests may be unblocked
-      var satisfiedProduceRequests = new mutable.ArrayBuffer[DelayedProduce]
-      fetchRequest.requestInfo.foreach {
-        case (topicAndPartition, _) =>
-          val key = new RequestKey(topicAndPartition)
-          satisfiedProduceRequests ++= producerRequestPurgatory.update(key, key)
-      }
-      debug("Replica %d fetch unblocked %d producer requests."
-        .format(fetchRequest.replicaId, satisfiedProduceRequests.size))
-      satisfiedProduceRequests.foreach(_.respond())
-    }
-
-    val dataRead = readMessageSets(fetchRequest)
-    val bytesReadable = dataRead.values.map(_.messages.sizeInBytes).sum
+    val dataRead = replicaManager.readMessageSets(fetchRequest)
+
+    // if the fetch request comes from the follower,
+    // update its corresponding log end offset
+    if(fetchRequest.isFromFollower)
+      recordFollowerLogEndOffsets(fetchRequest.replicaId, dataRead.mapValues(_.offset))
+
+    // check if this fetch request can be satisfied right away
+    val bytesReadable = dataRead.values.map(_.data.messages.sizeInBytes).sum
+    val errorReadingData = dataRead.values.foldLeft(false)((errorIncurred, dataAndOffset) =>
+      errorIncurred || (dataAndOffset.data.error != ErrorMapping.NoError))
+    // send the data immediately if 1) fetch request does not want to wait
+    //                              2) fetch request does not require any data
+    //                              3) has enough data to respond
+    //                              4) some error happens while reading data
     if(fetchRequest.maxWait <= 0 ||
+       fetchRequest.numPartitions <= 0 ||
        bytesReadable >= fetchRequest.minBytes ||
-       fetchRequest.numPartitions <= 0) {
+       errorReadingData) {
       debug("Returning fetch response %s for fetch request with correlation id %d to client %s"
-        .format(dataRead.values.map(_.error).mkString(","), fetchRequest.correlationId, fetchRequest.clientId))
-      val response = new FetchResponse(fetchRequest.correlationId, dataRead)
+        .format(dataRead.values.map(_.data.error).mkString(","), fetchRequest.correlationId, fetchRequest.clientId))
+      val response = new FetchResponse(fetchRequest.correlationId, dataRead.mapValues(_.data))
       requestChannel.sendResponse(new RequestChannel.Response(request, new FetchResponseSend(response)))
     } else {
       debug("Putting fetch request with correlation id %d from client %s into purgatory".format(fetchRequest.correlationId,
         fetchRequest.clientId))
       // create a list of (topic, partition) pairs to use as keys for this delayed request
-      val delayedFetchKeys = fetchRequest.requestInfo.keys.toSeq.map(new RequestKey(_))
-      val delayedFetch = new DelayedFetch(delayedFetchKeys, request, fetchRequest, fetchRequest.maxWait, bytesReadable)
-      fetchRequestPurgatory.watch(delayedFetch)
+      val delayedFetchKeys = fetchRequest.requestInfo.keys.toSeq.map(new TopicPartitionRequestKey(_))
+      val delayedFetch = new DelayedFetch(delayedFetchKeys, request, fetchRequest.maxWait, fetchRequest,
+        dataRead.mapValues(_.offset))
+
+      // add the fetch request for watch if it's not satisfied, otherwise send the response back
+      val satisfiedByMe = fetchRequestPurgatory.checkAndMaybeWatch(delayedFetch)
+      if (satisfiedByMe)
+        fetchRequestPurgatory.respond(delayedFetch)
     }
   }
 
-  private def maybeUpdatePartitionHw(fetchRequest: FetchRequest) {
-    debug("Maybe update partition HW due to fetch request: %s ".format(fetchRequest))
-    fetchRequest.requestInfo.foreach(info => {
-      val (topic, partition, offset) = (info._1.topic, info._1.partition, info._2.offset)
-      replicaManager.recordFollowerPosition(topic, partition, fetchRequest.replicaId, offset)
-    })
-  }
+  private def recordFollowerLogEndOffsets(replicaId: Int, offsets: Map[TopicAndPartition, LogOffsetMetadata]) {
+    debug("Record follower log end offsets: %s ".format(offsets))
+    offsets.foreach {
+      case (topicAndPartition, offset) =>
+        replicaManager.updateReplicaLEOAndPartitionHW(topicAndPartition.topic,
+          topicAndPartition.partition, replicaId, offset)
 
-  /**
-   * Read from all the offset details given and return a map of
-   * (topic, partition) -> PartitionData
-   */
-  private def readMessageSets(fetchRequest: FetchRequest) = {
-    val isFetchFromFollower = fetchRequest.isFromFollower
-    fetchRequest.requestInfo.map
-    {
-      case (TopicAndPartition(topic, partition), PartitionFetchInfo(offset, fetchSize)) =>
-        val partitionData =
-          try {
-            val (messages, highWatermark) = readMessageSet(topic, partition, offset, fetchSize, fetchRequest.replicaId)
-            BrokerTopicStats.getBrokerTopicStats(topic).bytesOutRate.mark(messages.sizeInBytes)
-            BrokerTopicStats.getBrokerAllTopicsStats.bytesOutRate.mark(messages.sizeInBytes)
-            if (!isFetchFromFollower) {
-              new FetchResponsePartitionData(ErrorMapping.NoError, highWatermark, messages)
-            } else {
-              debug("Leader %d for partition [%s,%d] received fetch request from follower %d"
-                            .format(brokerId, topic, partition, fetchRequest.replicaId))
-              new FetchResponsePartitionData(ErrorMapping.NoError, highWatermark, messages)
-            }
-          } catch {
-            // NOTE: Failed fetch requests is not incremented for UnknownTopicOrPartitionException and NotLeaderForPartitionException
-            // since failed fetch requests metric is supposed to indicate failure of a broker in handling a fetch request
-            // for a partition it is the leader for
-            case utpe: UnknownTopicOrPartitionException =>
-              warn("Fetch request with correlation id %d from client %s on partition [%s,%d] failed due to %s".format(
-                   fetchRequest.correlationId, fetchRequest.clientId, topic, partition, utpe.getMessage))
-              new FetchResponsePartitionData(ErrorMapping.codeFor(utpe.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty)
-            case nle: NotLeaderForPartitionException =>
-              warn("Fetch request with correlation id %d from client %s on partition [%s,%d] failed due to %s".format(
-                fetchRequest.correlationId, fetchRequest.clientId, topic, partition, nle.getMessage))
-              new FetchResponsePartitionData(ErrorMapping.codeFor(nle.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty)
-            case t: Throwable =>
-              BrokerTopicStats.getBrokerTopicStats(topic).failedFetchRequestRate.mark()
-              BrokerTopicStats.getBrokerAllTopicsStats.failedFetchRequestRate.mark()
-              error("Error when processing fetch request for partition [%s,%d] offset %d from %s with correlation id %d. Possible cause: %s"
-                    .format(topic, partition, offset, if (isFetchFromFollower) "follower" else "consumer", fetchRequest.correlationId, t.getMessage))
-              new FetchResponsePartitionData(ErrorMapping.codeFor(t.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty)
-          }
-        (TopicAndPartition(topic, partition), partitionData)
+        // for producer requests with ack > 1, we need to check
+        // if they can be unblocked after some follower's log end offsets have moved
+        replicaManager.unblockDelayedProduceRequests(new TopicPartitionRequestKey(topicAndPartition))
     }
   }
 
   /**
-   * Read from a single topic/partition at the given offset upto maxSize bytes
-   */
-  private def readMessageSet(topic: String, 
-                             partition: Int, 
-                             offset: Long,
-                             maxSize: Int, 
-                             fromReplicaId: Int): (MessageSet, Long) = {
-    // check if the current broker is the leader for the partitions
-    val localReplica = if(fromReplicaId == Request.DebuggingConsumerId)
-      replicaManager.getReplicaOrException(topic, partition)
-    else
-      replicaManager.getLeaderReplicaIfLocal(topic, partition)
-    trace("Fetching log segment for topic, partition, offset, size = " + (topic, partition, offset, maxSize))
-    val maxOffsetOpt = 
-      if (Request.isValidBrokerId(fromReplicaId))
-        None
-      else
-        Some(localReplica.highWatermark)
-    val messages = localReplica.log match {
-      case Some(log) =>
-        log.read(offset, maxSize, maxOffsetOpt)
-      case None =>
-        error("Leader for partition [%s,%d] on broker %d does not have a local log".format(topic, partition, brokerId))
-        MessageSet.Empty
-    }
-    (messages, localReplica.highWatermark)
-  }
-
-  /**
    * Service the offset request API 
    */
   def handleOffsetRequest(request: RequestChannel.Request) {
@@ -473,7 +363,7 @@ class KafkaApis(val requestChannel: RequestChannel,
           if (!offsetRequest.isFromOrdinaryClient) {
             allOffsets
           } else {
-            val hw = localReplica.highWatermark
+            val hw = localReplica.highWatermark.messageOffset
             if (allOffsets.exists(_ > hw))
               hw +: allOffsets.dropWhile(_ > hw)
             else 
@@ -643,209 +533,5 @@ class KafkaApis(val requestChannel: RequestChannel,
     producerRequestPurgatory.shutdown()
     debug("Shut down complete.")
   }
-
-  private [kafka] trait MetricKey {
-    def keyLabel: String
-  }
-  private [kafka] object MetricKey {
-    val globalLabel = "All"
-  }
-
-  private [kafka] case class RequestKey(topic: String, partition: Int)
-          extends MetricKey {
-
-    def this(topicAndPartition: TopicAndPartition) = this(topicAndPartition.topic, topicAndPartition.partition)
-
-    def topicAndPartition = TopicAndPartition(topic, partition)
-
-    override def keyLabel = "%s-%d".format(topic, partition)
-  }
-
-  /**
-   * A delayed fetch request
-   */
-  class DelayedFetch(keys: Seq[RequestKey], request: RequestChannel.Request, val fetch: FetchRequest, delayMs: Long, initialSize: Long)
-    extends DelayedRequest(keys, request, delayMs) {
-    val bytesAccumulated = new AtomicLong(initialSize)
-  }
-
-  /**
-   * A holding pen for fetch requests waiting to be satisfied
-   */
-  class FetchRequestPurgatory(requestChannel: RequestChannel, purgeInterval: Int)
-          extends RequestPurgatory[DelayedFetch, Int](brokerId, purgeInterval) {
-    this.logIdent = "[FetchRequestPurgatory-%d] ".format(brokerId)
-
-    /**
-     * A fetch request is satisfied when it has accumulated enough data to meet the min_bytes field
-     */
-    def checkSatisfied(messageSizeInBytes: Int, delayedFetch: DelayedFetch): Boolean = {
-      val accumulatedSize = delayedFetch.bytesAccumulated.addAndGet(messageSizeInBytes)
-      accumulatedSize >= delayedFetch.fetch.minBytes
-    }
-
-    /**
-     * When a request expires just answer it with whatever data is present
-     */
-    def expire(delayed: DelayedFetch) {
-      debug("Expiring fetch request %s.".format(delayed.fetch))
-      try {
-        val topicData = readMessageSets(delayed.fetch)
-        val response = FetchResponse(delayed.fetch.correlationId, topicData)
-        val fromFollower = delayed.fetch.isFromFollower
-        delayedRequestMetrics.recordDelayedFetchExpired(fromFollower)
-        requestChannel.sendResponse(new RequestChannel.Response(delayed.request, new FetchResponseSend(response)))
-      }
-      catch {
-        case e1: LeaderNotAvailableException =>
-          debug("Leader changed before fetch request %s expired.".format(delayed.fetch))
-        case e2: UnknownTopicOrPartitionException =>
-          debug("Replica went offline before fetch request %s expired.".format(delayed.fetch))
-      }
-    }
-  }
-
-  class DelayedProduce(keys: Seq[RequestKey],
-                       request: RequestChannel.Request,
-                       val partitionStatus: immutable.Map[TopicAndPartition, DelayedProduceResponseStatus],
-                       produce: ProducerRequest,
-                       delayMs: Long,
-                       offsetCommitRequestOpt: Option[OffsetCommitRequest] = None)
-          extends DelayedRequest(keys, request, delayMs) with Logging {
-
-    // first update the acks pending variable according to the error code
-    partitionStatus foreach { case (topicAndPartition, delayedStatus) =>
-      if (delayedStatus.status.error == ErrorMapping.NoError) {
-        // Timeout error state will be cleared when requiredAcks are received
-        delayedStatus.acksPending = true
-        delayedStatus.status.error = ErrorMapping.RequestTimedOutCode
-      } else {
-        delayedStatus.acksPending = false
-      }
-
-      trace("Initial partition status for %s is %s".format(topicAndPartition, delayedStatus))
-    }
-
-    def respond() {
-      val responseStatus = partitionStatus.map { case (topicAndPartition, delayedStatus) =>
-        topicAndPartition -> delayedStatus.status
-      }
-
-      val errorCode = responseStatus.find { case (_, status) =>
-        status.error != ErrorMapping.NoError
-      }.map(_._2.error).getOrElse(ErrorMapping.NoError)
-
-      if (errorCode == ErrorMapping.NoError) {
-        offsetCommitRequestOpt.foreach(ocr => offsetManager.putOffsets(ocr.groupId, ocr.requestInfo) )
-      }
-
-      val response = offsetCommitRequestOpt.map(_.responseFor(errorCode, config.offsetMetadataMaxSize))
-                                           .getOrElse(ProducerResponse(produce.correlationId, responseStatus))
-
-      requestChannel.sendResponse(new RequestChannel.Response(
-        request, new BoundedByteBufferSend(response)))
-    }
-
-    /**
-     * Returns true if this delayed produce request is satisfied (or more
-     * accurately, unblocked) -- this is the case if for every partition:
-     * Case A: This broker is not the leader: unblock - should return error.
-     * Case B: This broker is the leader:
-     *   B.1 - If there was a localError (when writing to the local log): unblock - should return error
-     *   B.2 - else, at least requiredAcks replicas should be caught up to this request.
-     *
-     * As partitions become acknowledged, we may be able to unblock
-     * DelayedFetchRequests that are pending on those partitions.
-     */
-    def isSatisfied(followerFetchRequestKey: RequestKey) = {
-      val topic = followerFetchRequestKey.topic
-      val partitionId = followerFetchRequestKey.partition
-      val fetchPartitionStatus = partitionStatus(TopicAndPartition(topic, partitionId))
-      trace("Checking producer request satisfaction for %s-%d, acksPending = %b"
-        .format(topic, partitionId, fetchPartitionStatus.acksPending))
-      if (fetchPartitionStatus.acksPending) {
-        val partitionOpt = replicaManager.getPartition(topic, partitionId)
-        val (hasEnough, errorCode) = partitionOpt match {
-          case Some(partition) =>
-            partition.checkEnoughReplicasReachOffset(fetchPartitionStatus.requiredOffset, produce.requiredAcks)
-          case None =>
-            (false, ErrorMapping.UnknownTopicOrPartitionCode)
-        }
-        if (errorCode != ErrorMapping.NoError) {
-          fetchPartitionStatus. acksPending = false
-          fetchPartitionStatus.status.error = errorCode
-        } else if (hasEnough) {
-          fetchPartitionStatus.acksPending = false
-          fetchPartitionStatus.status.error = ErrorMapping.NoError
-        }
-        if (!fetchPartitionStatus.acksPending) {
-          val messageSizeInBytes = produce.topicPartitionMessageSizeMap(followerFetchRequestKey.topicAndPartition)
-          maybeUnblockDelayedFetchRequests(topic, partitionId, messageSizeInBytes)
-        }
-      }
-
-      // unblocked if there are no partitions with pending acks
-      val satisfied = ! partitionStatus.exists(p => p._2.acksPending)
-      trace("Producer request satisfaction for %s-%d = %b".format(topic, partitionId, satisfied))
-      satisfied
-    }
-  }
-
-  /**
-   * A holding pen for produce requests waiting to be satisfied.
-   */
-  private [kafka] class ProducerRequestPurgatory(purgeInterval: Int)
-          extends RequestPurgatory[DelayedProduce, RequestKey](brokerId, purgeInterval) {
-    this.logIdent = "[ProducerRequestPurgatory-%d] ".format(brokerId)
-
-    protected def checkSatisfied(followerFetchRequestKey: RequestKey,
-                                 delayedProduce: DelayedProduce) =
-      delayedProduce.isSatisfied(followerFetchRequestKey)
-
-    /**
-     * Handle an expired delayed request
-     */
-    protected def expire(delayedProduce: DelayedProduce) {
-      for ((topicPartition, responseStatus) <- delayedProduce.partitionStatus if responseStatus.acksPending)
-        delayedRequestMetrics.recordDelayedProducerKeyExpired(RequestKey(topicPartition.topic, topicPartition.partition))
-
-      delayedProduce.respond()
-    }
-  }
-
-  private class DelayedRequestMetrics {
-    private class DelayedProducerRequestMetrics(keyLabel: String = MetricKey.globalLabel) extends KafkaMetricsGroup {
-      val expiredRequestMeter = newMeter(keyLabel + "ExpiresPerSecond", "requests", TimeUnit.SECONDS)
-    }
-
-
-    private class DelayedFetchRequestMetrics(forFollower: Boolean) extends KafkaMetricsGroup {
-      private val metricPrefix = if (forFollower) "Follower" else "Consumer"
-
-      val expiredRequestMeter = newMeter(metricPrefix + "ExpiresPerSecond", "requests", TimeUnit.SECONDS)
-    }
-
-    private val producerRequestMetricsForKey = {
-      val valueFactory = (k: MetricKey) => new DelayedProducerRequestMetrics(k.keyLabel + "-")
-      new Pool[MetricKey, DelayedProducerRequestMetrics](Some(valueFactory))
-    }
-
-    private val aggregateProduceRequestMetrics = new DelayedProducerRequestMetrics
-
-    private val aggregateFollowerFetchRequestMetrics = new DelayedFetchRequestMetrics(forFollower = true)
-    private val aggregateNonFollowerFetchRequestMetrics = new DelayedFetchRequestMetrics(forFollower = false)
-
-    def recordDelayedProducerKeyExpired(key: MetricKey) {
-      val keyMetrics = producerRequestMetricsForKey.getAndMaybePut(key)
-      List(keyMetrics, aggregateProduceRequestMetrics).foreach(_.expiredRequestMeter.mark())
-    }
-
-    def recordDelayedFetchExpired(forFollower: Boolean) {
-      val metrics = if (forFollower) aggregateFollowerFetchRequestMetrics
-        else aggregateNonFollowerFetchRequestMetrics
-      
-      metrics.expiredRequestMeter.mark()
-    }
-  }
 }
 
diff --git a/core/src/main/scala/kafka/server/LogOffsetMetadata.scala b/core/src/main/scala/kafka/server/LogOffsetMetadata.scala
new file mode 100644
index 0000000..be5afed
--- /dev/null
+++ b/core/src/main/scala/kafka/server/LogOffsetMetadata.scala
@@ -0,0 +1,87 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import org.apache.kafka.common.KafkaException
+
+object LogOffsetMetadata {
+  val UnknownOffsetMetadata = new LogOffsetMetadata(-1, 0, 0)
+  val UnknownSegBaseOffset = -1L
+  val UnknownFilePosition = -1
+
+  class OffsetOrdering extends Ordering[LogOffsetMetadata] {
+    override def compare(x: LogOffsetMetadata , y: LogOffsetMetadata ): Int = {
+      return x.messageDiff(y).toInt
+    }
+  }
+
+}
+
+/*
+ * A log offset structure, including:
+ *  1. the message offset
+ *  2. the base message offset of the located segment
+ *  3. the physical position on the located segment
+ */
+case class LogOffsetMetadata(messageOffset: Long,
+                             segmentBaseOffset: Long = LogOffsetMetadata.UnknownSegBaseOffset,
+                             relativePositionInSegment: Int = LogOffsetMetadata.UnknownFilePosition) {
+
+  // check if this offset is already on an older segment compared with the given offset
+  def offsetOnOlderSegment(that: LogOffsetMetadata): Boolean = {
+    if (messageOffsetOnly())
+      throw new KafkaException("%s cannot compare its segment info with %s since it only has message offset info".format(this, that))
+
+    this.segmentBaseOffset < that.segmentBaseOffset
+  }
+
+  // check if this offset is on the same segment with the given offset
+  def offsetOnSameSegment(that: LogOffsetMetadata): Boolean = {
+    if (messageOffsetOnly())
+      throw new KafkaException("%s cannot compare its segment info with %s since it only has message offset info".format(this, that))
+
+    this.segmentBaseOffset == that.segmentBaseOffset
+  }
+
+  // check if this offset is before the given offset
+  def precedes(that: LogOffsetMetadata): Boolean = this.messageOffset < that.messageOffset
+
+  // compute the number of messages between this offset to the given offset
+  def messageDiff(that: LogOffsetMetadata): Long = {
+    this.messageOffset - that.messageOffset
+  }
+
+  // compute the number of bytes between this offset to the given offset
+  // if they are on the same segment and this offset precedes the given offset
+  def positionDiff(that: LogOffsetMetadata): Int = {
+    if(!offsetOnSameSegment(that))
+      throw new KafkaException("%s cannot compare its segment position with %s since they are not on the same segment".format(this, that))
+    if(messageOffsetOnly())
+      throw new KafkaException("%s cannot compare its segment position with %s since it only has message offset info".format(this, that))
+
+    this.relativePositionInSegment - that.relativePositionInSegment
+  }
+
+  // decide if the offset metadata only contains message offset info
+  def messageOffsetOnly(): Boolean = {
+    segmentBaseOffset == LogOffsetMetadata.UnknownSegBaseOffset && relativePositionInSegment == LogOffsetMetadata.UnknownFilePosition
+  }
+
+  override def toString = messageOffset.toString + " [" + segmentBaseOffset + " : " + relativePositionInSegment + "]"
+
+}
diff --git a/core/src/main/scala/kafka/server/OffsetManager.scala b/core/src/main/scala/kafka/server/OffsetManager.scala
index 0e22897..43eb2a3 100644
--- a/core/src/main/scala/kafka/server/OffsetManager.scala
+++ b/core/src/main/scala/kafka/server/OffsetManager.scala
@@ -17,26 +17,29 @@
 
 package kafka.server
 
+import org.apache.kafka.common.protocol.types.{Struct, Schema, Field}
+import org.apache.kafka.common.protocol.types.Type.STRING
+import org.apache.kafka.common.protocol.types.Type.INT32
+import org.apache.kafka.common.protocol.types.Type.INT64
+
 import kafka.utils._
 import kafka.common._
-import java.nio.ByteBuffer
-import java.util.Properties
 import kafka.log.{FileMessageSet, LogConfig}
-import org.I0Itec.zkclient.ZkClient
-import scala.collection._
 import kafka.message._
-import java.util.concurrent.TimeUnit
 import kafka.metrics.KafkaMetricsGroup
-import com.yammer.metrics.core.Gauge
-import scala.Some
 import kafka.common.TopicAndPartition
 import kafka.tools.MessageFormatter
+
+import scala.Some
+import scala.collection._
 import java.io.PrintStream
-import org.apache.kafka.common.protocol.types.{Struct, Schema, Field}
-import org.apache.kafka.common.protocol.types.Type.STRING
-import org.apache.kafka.common.protocol.types.Type.INT32
-import org.apache.kafka.common.protocol.types.Type.INT64
 import java.util.concurrent.atomic.AtomicBoolean
+import java.nio.ByteBuffer
+import java.util.Properties
+import java.util.concurrent.TimeUnit
+
+import com.yammer.metrics.core.Gauge
+import org.I0Itec.zkclient.ZkClient
 
 
 /**
@@ -271,7 +274,7 @@ class OffsetManager(val config: OffsetManagerConfig,
             // loop breaks if leader changes at any time during the load, since getHighWatermark is -1
             while (currOffset < getHighWatermark(offsetsPartition) && !shuttingDown.get()) {
               buffer.clear()
-              val messages = log.read(currOffset, config.loadBufferSize).asInstanceOf[FileMessageSet]
+              val messages = log.read(currOffset, config.loadBufferSize).messageSet.asInstanceOf[FileMessageSet]
               messages.readInto(buffer, 0)
               val messageSet = new ByteBufferMessageSet(buffer)
               messageSet.foreach { msgAndOffset =>
@@ -312,7 +315,7 @@ class OffsetManager(val config: OffsetManagerConfig,
     val partitionOpt = replicaManager.getPartition(OffsetManager.OffsetsTopicName, partitionId)
 
     val hw = partitionOpt.map { partition =>
-      partition.leaderReplicaIfLocal().map(_.highWatermark).getOrElse(-1L)
+      partition.leaderReplicaIfLocal().map(_.highWatermark.messageOffset).getOrElse(-1L)
     }.getOrElse(-1L)
 
     hw
diff --git a/core/src/main/scala/kafka/server/ProducerRequestPurgatory.scala b/core/src/main/scala/kafka/server/ProducerRequestPurgatory.scala
new file mode 100644
index 0000000..d4a7d4a
--- /dev/null
+++ b/core/src/main/scala/kafka/server/ProducerRequestPurgatory.scala
@@ -0,0 +1,69 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kafka.server
+
+import kafka.metrics.KafkaMetricsGroup
+import kafka.utils.Pool
+import kafka.network.{BoundedByteBufferSend, RequestChannel}
+
+import java.util.concurrent.TimeUnit
+
+/**
+ * The purgatory holding delayed producer requests
+ */
+class ProducerRequestPurgatory(replicaManager: ReplicaManager, offsetManager: OffsetManager, requestChannel: RequestChannel)
+  extends RequestPurgatory[DelayedProduce](replicaManager.config.brokerId, replicaManager.config.producerPurgatoryPurgeIntervalRequests) {
+  this.logIdent = "[ProducerRequestPurgatory-%d] ".format(replicaManager.config.brokerId)
+
+  private class DelayedProducerRequestMetrics(keyLabel: String = DelayedRequestKey.globalLabel) extends KafkaMetricsGroup {
+    val expiredRequestMeter = newMeter(keyLabel + "ExpiresPerSecond", "requests", TimeUnit.SECONDS)
+  }
+
+  private val producerRequestMetricsForKey = {
+    val valueFactory = (k: DelayedRequestKey) => new DelayedProducerRequestMetrics(k.keyLabel + "-")
+    new Pool[DelayedRequestKey, DelayedProducerRequestMetrics](Some(valueFactory))
+  }
+
+  private val aggregateProduceRequestMetrics = new DelayedProducerRequestMetrics
+
+  private def recordDelayedProducerKeyExpired(key: DelayedRequestKey) {
+    val keyMetrics = producerRequestMetricsForKey.getAndMaybePut(key)
+    List(keyMetrics, aggregateProduceRequestMetrics).foreach(_.expiredRequestMeter.mark())
+  }
+
+  /**
+   * Check if a specified delayed fetch request is satisfied
+   */
+  def checkSatisfied(delayedProduce: DelayedProduce) = delayedProduce.isSatisfied(replicaManager)
+
+  /**
+   * When a delayed produce request expires answer it with possible time out error codes
+   */
+  def expire(delayedProduce: DelayedProduce) {
+    debug("Expiring produce request %s.".format(delayedProduce.produce))
+    for ((topicPartition, responseStatus) <- delayedProduce.partitionStatus if responseStatus.acksPending)
+      recordDelayedProducerKeyExpired(new TopicPartitionRequestKey(topicPartition))
+    respond(delayedProduce)
+  }
+
+  // TODO: purgatory should not be responsible for sending back the responses
+  def respond(delayedProduce: DelayedProduce) {
+    val response = delayedProduce.respond(offsetManager)
+    requestChannel.sendResponse(new RequestChannel.Response(delayedProduce.request, new BoundedByteBufferSend(response)))
+  }
+}
diff --git a/core/src/main/scala/kafka/server/ReplicaFetcherThread.scala b/core/src/main/scala/kafka/server/ReplicaFetcherThread.scala
index 75ae1e1..0d3da19 100644
--- a/core/src/main/scala/kafka/server/ReplicaFetcherThread.scala
+++ b/core/src/main/scala/kafka/server/ReplicaFetcherThread.scala
@@ -21,7 +21,7 @@ import kafka.admin.AdminUtils
 import kafka.cluster.Broker
 import kafka.log.LogConfig
 import kafka.message.ByteBufferMessageSet
-import kafka.api.{OffsetRequest, FetchResponsePartitionData}
+import kafka.api.{OffsetRequest, PartitionData}
 import kafka.common.{KafkaStorageException, TopicAndPartition}
 
 class ReplicaFetcherThread(name:String,
@@ -40,23 +40,26 @@ class ReplicaFetcherThread(name:String,
                                 isInterruptible = false) {
 
   // process fetched data
-  def processPartitionData(topicAndPartition: TopicAndPartition, fetchOffset: Long, partitionData: FetchResponsePartitionData) {
+  def processPartitionData(topicAndPartition: TopicAndPartition, fetchOffset: Long, partitionData: PartitionData) {
     try {
       val topic = topicAndPartition.topic
       val partitionId = topicAndPartition.partition
       val replica = replicaMgr.getReplica(topic, partitionId).get
       val messageSet = partitionData.messages.asInstanceOf[ByteBufferMessageSet]
 
-      if (fetchOffset != replica.logEndOffset)
-        throw new RuntimeException("Offset mismatch: fetched offset = %d, log end offset = %d.".format(fetchOffset, replica.logEndOffset))
+      if (fetchOffset != replica.logEndOffset.messageOffset)
+        throw new RuntimeException("Offset mismatch: fetched offset = %d, log end offset = %d.".format(fetchOffset, replica.logEndOffset.messageOffset))
       trace("Follower %d has replica log end offset %d for partition %s. Received %d messages and leader hw %d"
-            .format(replica.brokerId, replica.logEndOffset, topicAndPartition, messageSet.sizeInBytes, partitionData.hw))
+            .format(replica.brokerId, replica.logEndOffset.messageOffset, topicAndPartition, messageSet.sizeInBytes, partitionData.hw))
       replica.log.get.append(messageSet, assignOffsets = false)
       trace("Follower %d has replica log end offset %d after appending %d bytes of messages for partition %s"
-            .format(replica.brokerId, replica.logEndOffset, messageSet.sizeInBytes, topicAndPartition))
-      val followerHighWatermark = replica.logEndOffset.min(partitionData.hw)
-      replica.highWatermark = followerHighWatermark
-      trace("Follower %d set replica highwatermark for partition [%s,%d] to %d"
+            .format(replica.brokerId, replica.logEndOffset.messageOffset, messageSet.sizeInBytes, topicAndPartition))
+      val followerHighWatermark = replica.logEndOffset.messageOffset.min(partitionData.hw)
+      // for the follower replica, we do not need to keep
+      // its segment base offset the physical position,
+      // these values will be computed upon making the leader
+      replica.highWatermark = new LogOffsetMetadata(followerHighWatermark)
+      trace("Follower %d set replica high watermark for partition [%s,%d] to %s"
             .format(replica.brokerId, topic, partitionId, followerHighWatermark))
     } catch {
       case e: KafkaStorageException =>
@@ -82,7 +85,7 @@ class ReplicaFetcherThread(name:String,
      * There is a potential for a mismatch between the logs of the two replicas here. We don't fix this mismatch as of now.
      */
     val leaderEndOffset = simpleConsumer.earliestOrLatestOffset(topicAndPartition, OffsetRequest.LatestTime, brokerConfig.brokerId)
-    if (leaderEndOffset < replica.logEndOffset) {
+    if (leaderEndOffset < replica.logEndOffset.messageOffset) {
       // Prior to truncating the follower's log, ensure that doing so is not disallowed by the configuration for unclean leader election.
       // This situation could only happen if the unclean election configuration for a topic changes while a replica is down. Otherwise,
       // we should never encounter this situation since a non-ISR leader cannot be elected if disallowed by the broker configuration.
@@ -91,13 +94,13 @@ class ReplicaFetcherThread(name:String,
         // Log a fatal error and shutdown the broker to ensure that data loss does not unexpectedly occur.
         fatal("Halting because log truncation is not allowed for topic %s,".format(topicAndPartition.topic) +
           " Current leader %d's latest offset %d is less than replica %d's latest offset %d"
-          .format(sourceBroker.id, leaderEndOffset, brokerConfig.brokerId, replica.logEndOffset))
+          .format(sourceBroker.id, leaderEndOffset, brokerConfig.brokerId, replica.logEndOffset.messageOffset))
         Runtime.getRuntime.halt(1)
       }
 
       replicaMgr.logManager.truncateTo(Map(topicAndPartition -> leaderEndOffset))
       warn("Replica %d for partition %s reset its fetch offset from %d to current leader %d's latest offset %d"
-        .format(brokerConfig.brokerId, topicAndPartition, replica.logEndOffset, sourceBroker.id, leaderEndOffset))
+        .format(brokerConfig.brokerId, topicAndPartition, replica.logEndOffset.messageOffset, sourceBroker.id, leaderEndOffset))
       leaderEndOffset
     } else {
       /**
@@ -109,7 +112,7 @@ class ReplicaFetcherThread(name:String,
       val leaderStartOffset = simpleConsumer.earliestOrLatestOffset(topicAndPartition, OffsetRequest.EarliestTime, brokerConfig.brokerId)
       replicaMgr.logManager.truncateFullyAndStartAt(topicAndPartition, leaderStartOffset)
       warn("Replica %d for partition %s reset its fetch offset from %d to current leader %d's start offset %d"
-        .format(brokerConfig.brokerId, topicAndPartition, replica.logEndOffset, sourceBroker.id, leaderStartOffset))
+        .format(brokerConfig.brokerId, topicAndPartition, replica.logEndOffset.messageOffset, sourceBroker.id, leaderStartOffset))
       leaderStartOffset
     }
   }
diff --git a/core/src/main/scala/kafka/server/ReplicaManager.scala b/core/src/main/scala/kafka/server/ReplicaManager.scala
index 897783c..2715945 100644
--- a/core/src/main/scala/kafka/server/ReplicaManager.scala
+++ b/core/src/main/scala/kafka/server/ReplicaManager.scala
@@ -16,29 +16,39 @@
  */
 package kafka.server
 
-import collection._
-import mutable.HashMap
-import kafka.cluster.{Broker, Partition, Replica}
+import kafka.api._
+import kafka.common._
 import kafka.utils._
+import kafka.cluster.{Broker, Partition, Replica}
 import kafka.log.LogManager
 import kafka.metrics.KafkaMetricsGroup
-import kafka.common._
-import kafka.api.{UpdateMetadataRequest, StopReplicaRequest, PartitionStateInfo, LeaderAndIsrRequest}
 import kafka.controller.KafkaController
-import org.I0Itec.zkclient.ZkClient
-import com.yammer.metrics.core.Gauge
+import kafka.common.TopicAndPartition
+import kafka.message.MessageSet
+
 import java.util.concurrent.atomic.AtomicBoolean
 import java.io.{IOException, File}
 import java.util.concurrent.TimeUnit
+import scala.Predef._
+import scala.collection._
+import scala.collection.mutable.HashMap
+import scala.collection.Map
+import scala.collection.Set
+import scala.Some
+
+import org.I0Itec.zkclient.ZkClient
+import com.yammer.metrics.core.Gauge
 
 object ReplicaManager {
-  val UnknownLogEndOffset = -1L
   val HighWatermarkFilename = "replication-offset-checkpoint"
 }
 
-class ReplicaManager(val config: KafkaConfig,
-                     time: Time,
-                     val zkClient: ZkClient,
+case class PartitionDataAndOffset(data: PartitionData, offset: LogOffsetMetadata)
+
+
+class ReplicaManager(val config: KafkaConfig, 
+                     time: Time, 
+                     val zkClient: ZkClient, 
                      scheduler: Scheduler,
                      val logManager: LogManager,
                      val isShuttingDown: AtomicBoolean ) extends Logging with KafkaMetricsGroup {
@@ -54,6 +64,9 @@ class ReplicaManager(val config: KafkaConfig,
   this.logIdent = "[Replica Manager on Broker " + localBrokerId + "]: "
   val stateChangeLogger = KafkaController.stateChangeLogger
 
+  var producerRequestPurgatory: ProducerRequestPurgatory = null
+  var fetchRequestPurgatory: FetchRequestPurgatory = null
+
   newGauge(
     "LeaderCount",
     new Gauge[Int] {
@@ -87,17 +100,37 @@ class ReplicaManager(val config: KafkaConfig,
   }
 
   /**
-   * This function is only used in two places: in Partition.updateISR() and KafkaApis.handleProducerRequest().
-   * In the former case, the partition should have been created, in the latter case, return -1 will put the request into purgatory
+   * Initialize the replica manager with the request purgatory
+   *
+   * TODO: will be removed in 0.9 where we refactor server structure
    */
-  def getReplicationFactorForPartition(topic: String, partitionId: Int) = {
-    val partitionOpt = getPartition(topic, partitionId)
-    partitionOpt match {
-      case Some(partition) =>
-        partition.replicationFactor
-      case None =>
-        -1
-    }
+
+  def initWithRequestPurgatory(producerRequestPurgatory: ProducerRequestPurgatory, fetchRequestPurgatory: FetchRequestPurgatory) {
+    this.producerRequestPurgatory = producerRequestPurgatory
+    this.fetchRequestPurgatory = fetchRequestPurgatory
+  }
+
+  /**
+   * Unblock some delayed produce requests with the request key
+   */
+  def unblockDelayedProduceRequests(key: DelayedRequestKey) {
+    val satisfied = producerRequestPurgatory.update(key)
+    debug("Request key %s unblocked %d producer requests."
+      .format(key.keyLabel, satisfied.size))
+
+    // send any newly unblocked responses
+    satisfied.foreach(producerRequestPurgatory.respond(_))
+  }
+
+  /**
+   * Unblock some delayed fetch requests with the request key
+   */
+  def unblockDelayedFetchRequests(key: DelayedRequestKey) {
+    val satisfied = fetchRequestPurgatory.update(key)
+    debug("Request key %s unblocked %d fetch requests.".format(key.keyLabel, satisfied.size))
+
+    // send any newly unblocked responses
+    satisfied.foreach(fetchRequestPurgatory.respond(_))
   }
 
   def startup() {
@@ -155,10 +188,10 @@ class ReplicaManager(val config: KafkaConfig,
     }
   }
 
-  def getOrCreatePartition(topic: String, partitionId: Int, replicationFactor: Int): Partition = {
+  def getOrCreatePartition(topic: String, partitionId: Int): Partition = {
     var partition = allPartitions.get((topic, partitionId))
     if (partition == null) {
-      allPartitions.putIfNotExists((topic, partitionId), new Partition(topic, partitionId, replicationFactor, time, this))
+      allPartitions.putIfNotExists((topic, partitionId), new Partition(topic, partitionId, time, this))
       partition = allPartitions.get((topic, partitionId))
     }
     partition
@@ -203,6 +236,77 @@ class ReplicaManager(val config: KafkaConfig,
     }
   }
 
+  /**
+   * Read from all the offset details given and return a map of
+   * (topic, partition) -> PartitionData
+   */
+  def readMessageSets(fetchRequest: FetchRequest) = {
+    val isFetchFromFollower = fetchRequest.isFromFollower
+    fetchRequest.requestInfo.map
+    {
+      case (TopicAndPartition(topic, partition), PartitionFetchInfo(offset, fetchSize)) =>
+        val partitionDataAndOffsetInfo =
+          try {
+            val (fetchInfo, highWatermark) = readMessageSet(topic, partition, offset, fetchSize, fetchRequest.replicaId)
+            BrokerTopicStats.getBrokerTopicStats(topic).bytesOutRate.mark(fetchInfo.messageSet.sizeInBytes)
+            BrokerTopicStats.getBrokerAllTopicsStats.bytesOutRate.mark(fetchInfo.messageSet.sizeInBytes)
+            if (isFetchFromFollower) {
+              debug("Partition [%s,%d] received fetch request from follower %d"
+                .format(topic, partition, fetchRequest.replicaId))
+            }
+            new PartitionDataAndOffset(new PartitionData(ErrorMapping.NoError, highWatermark, fetchInfo.messageSet), fetchInfo.fetchOffset)
+          } catch {
+            // NOTE: Failed fetch requests is not incremented for UnknownTopicOrPartitionException and NotLeaderForPartitionException
+            // since failed fetch requests metric is supposed to indicate failure of a broker in handling a fetch request
+            // for a partition it is the leader for
+            case utpe: UnknownTopicOrPartitionException =>
+              warn("Fetch request with correlation id %d from client %s on partition [%s,%d] failed due to %s".format(
+                fetchRequest.correlationId, fetchRequest.clientId, topic, partition, utpe.getMessage))
+              new PartitionDataAndOffset(new PartitionData(ErrorMapping.codeFor(utpe.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty), LogOffsetMetadata.UnknownOffsetMetadata)
+            case nle: NotLeaderForPartitionException =>
+              warn("Fetch request with correlation id %d from client %s on partition [%s,%d] failed due to %s".format(
+                fetchRequest.correlationId, fetchRequest.clientId, topic, partition, nle.getMessage))
+              new PartitionDataAndOffset(new PartitionData(ErrorMapping.codeFor(nle.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty), LogOffsetMetadata.UnknownOffsetMetadata)
+            case t: Throwable =>
+              BrokerTopicStats.getBrokerTopicStats(topic).failedFetchRequestRate.mark()
+              BrokerTopicStats.getBrokerAllTopicsStats.failedFetchRequestRate.mark()
+              error("Error when processing fetch request for partition [%s,%d] offset %d from %s with correlation id %d. Possible cause: %s"
+                .format(topic, partition, offset, if (isFetchFromFollower) "follower" else "consumer", fetchRequest.correlationId, t.getMessage))
+              new PartitionDataAndOffset(new PartitionData(ErrorMapping.codeFor(t.getClass.asInstanceOf[Class[Throwable]]), -1L, MessageSet.Empty), LogOffsetMetadata.UnknownOffsetMetadata)
+          }
+        (TopicAndPartition(topic, partition), partitionDataAndOffsetInfo)
+    }
+  }
+
+  /**
+   * Read from a single topic/partition at the given offset upto maxSize bytes
+   */
+  private def readMessageSet(topic: String,
+                             partition: Int,
+                             offset: Long,
+                             maxSize: Int,
+                             fromReplicaId: Int): (FetchDataInfo, Long) = {
+    // check if the current broker is the leader for the partitions
+    val localReplica = if(fromReplicaId == Request.DebuggingConsumerId)
+      getReplicaOrException(topic, partition)
+    else
+      getLeaderReplicaIfLocal(topic, partition)
+    trace("Fetching log segment for topic, partition, offset, size = " + (topic, partition, offset, maxSize))
+    val maxOffsetOpt =
+      if (Request.isValidBrokerId(fromReplicaId))
+        None
+      else
+        Some(localReplica.highWatermark.messageOffset)
+    val fetchInfo = localReplica.log match {
+      case Some(log) =>
+        log.read(offset, maxSize, maxOffsetOpt)
+      case None =>
+        error("Leader for partition [%s,%d] does not have a local log".format(topic, partition))
+        FetchDataInfo(LogOffsetMetadata.UnknownOffsetMetadata, MessageSet.Empty)
+    }
+    (fetchInfo, localReplica.highWatermark.messageOffset)
+  }
+
   def maybeUpdateMetadataCache(updateMetadataRequest: UpdateMetadataRequest, metadataCache: MetadataCache) {
     replicaStateChangeLock synchronized {
       if(updateMetadataRequest.controllerEpoch < controllerEpoch) {
@@ -243,7 +347,7 @@ class ReplicaManager(val config: KafkaConfig,
         // First check partition's leader epoch
         val partitionState = new HashMap[Partition, PartitionStateInfo]()
         leaderAndISRRequest.partitionStateInfos.foreach{ case ((topic, partitionId), partitionStateInfo) =>
-          val partition = getOrCreatePartition(topic, partitionId, partitionStateInfo.replicationFactor)
+          val partition = getOrCreatePartition(topic, partitionId)
           val partitionLeaderEpoch = partition.getLeaderEpoch()
           // If the leader epoch is valid record the epoch of the controller that made the leadership decision.
           // This is useful while updating the isr to maintain the decision maker controller's epoch in the zookeeper path
@@ -403,7 +507,7 @@ class ReplicaManager(val config: KafkaConfig,
           .format(localBrokerId, controllerId, epoch, correlationId, TopicAndPartition(partition.topic, partition.partitionId)))
       }
 
-      logManager.truncateTo(partitionsToMakeFollower.map(partition => (new TopicAndPartition(partition), partition.getOrCreateReplica().highWatermark)).toMap)
+      logManager.truncateTo(partitionsToMakeFollower.map(partition => (new TopicAndPartition(partition), partition.getOrCreateReplica().highWatermark.messageOffset)).toMap)
 
       partitionsToMakeFollower.foreach { partition =>
         stateChangeLogger.trace(("Broker %d truncated logs and checkpointed recovery boundaries for partition [%s,%d] as part of " +
@@ -421,7 +525,9 @@ class ReplicaManager(val config: KafkaConfig,
       else {
         // we do not need to check if the leader exists again since this has been done at the beginning of this process
         val partitionsToMakeFollowerWithLeaderAndOffset = partitionsToMakeFollower.map(partition =>
-          new TopicAndPartition(partition) -> BrokerAndInitialOffset(leaders.find(_.id == partition.leaderReplicaIdOpt.get).get, partition.getReplica().get.logEndOffset)).toMap
+          new TopicAndPartition(partition) -> BrokerAndInitialOffset(
+            leaders.find(_.id == partition.leaderReplicaIdOpt.get).get,
+            partition.getReplica().get.logEndOffset.messageOffset)).toMap
         replicaFetcherManager.addFetcherForPartitions(partitionsToMakeFollowerWithLeaderAndOffset)
 
         partitionsToMakeFollower.foreach { partition =>
@@ -451,12 +557,23 @@ class ReplicaManager(val config: KafkaConfig,
     allPartitions.values.foreach(partition => partition.maybeShrinkIsr(config.replicaLagTimeMaxMs, config.replicaLagMaxMessages))
   }
 
-  def recordFollowerPosition(topic: String, partitionId: Int, replicaId: Int, offset: Long) = {
-    val partitionOpt = getPartition(topic, partitionId)
-    if(partitionOpt.isDefined) {
-      partitionOpt.get.updateLeaderHWAndMaybeExpandIsr(replicaId, offset)
-    } else {
-      warn("While recording the follower position, the partition [%s,%d] hasn't been created, skip updating leader HW".format(topic, partitionId))
+  def updateReplicaLEOAndPartitionHW(topic: String, partitionId: Int, replicaId: Int, offset: LogOffsetMetadata) = {
+    getPartition(topic, partitionId) match {
+      case Some(partition) =>
+        val replicaOpt = partition.getReplica(replicaId)
+        if(!replicaOpt.isDefined) {
+          throw new NotAssignedReplicaException(("Leader %d failed to record follower %d's position %d since the replica" +
+            " is not recognized to be one of the assigned replicas %s for partition [%s,%d]").format(localBrokerId, replicaId,
+            offset.messageOffset, partition.assignedReplicas().map(_.brokerId).mkString(","), topic, partitionId))
+        }
+        val replica = replicaOpt.get
+        replica.logEndOffset = offset
+
+        // check if we need to update HW and expand Isr
+        partition.updateLeaderHWAndMaybeExpandIsr(replicaId)
+        debug("Recorded follower %d position %d for partition [%s,%d].".format(replicaId, offset.messageOffset, topic, partitionId))
+      case None =>
+        warn("While recording the follower position, the partition [%s,%d] hasn't been created, skip updating leader HW".format(topic, partitionId))
     }
   }
 
@@ -470,7 +587,7 @@ class ReplicaManager(val config: KafkaConfig,
     val replicas = allPartitions.values.map(_.getReplica(config.brokerId)).collect{case Some(replica) => replica}
     val replicasByDir = replicas.filter(_.log.isDefined).groupBy(_.log.get.dir.getParentFile.getAbsolutePath)
     for((dir, reps) <- replicasByDir) {
-      val hwms = reps.map(r => (new TopicAndPartition(r) -> r.highWatermark)).toMap
+      val hwms = reps.map(r => (new TopicAndPartition(r) -> r.highWatermark.messageOffset)).toMap
       try {
         highWatermarkCheckpoints(dir).write(hwms)
       } catch {
diff --git a/core/src/main/scala/kafka/server/RequestPurgatory.scala b/core/src/main/scala/kafka/server/RequestPurgatory.scala
index 3d0ff1e..ce06d2c 100644
--- a/core/src/main/scala/kafka/server/RequestPurgatory.scala
+++ b/core/src/main/scala/kafka/server/RequestPurgatory.scala
@@ -17,13 +17,15 @@
 
 package kafka.server
 
-import scala.collection._
-import java.util.concurrent._
-import java.util.concurrent.atomic._
 import kafka.network._
 import kafka.utils._
 import kafka.metrics.KafkaMetricsGroup
+
 import java.util
+import java.util.concurrent._
+import java.util.concurrent.atomic._
+import scala.collection._
+
 import com.yammer.metrics.core.Gauge
 
 
@@ -45,8 +47,10 @@ class DelayedRequest(val keys: Seq[Any], val request: RequestChannel.Request, de
  *
  * For us the key is generally a (topic, partition) pair.
  * By calling 
- *   watch(delayedRequest) 
- * we will add triggers for each of the given keys. It is up to the user to then call
+ *   val isSatisfiedByMe = checkAndMaybeWatch(delayedRequest)
+ * we will check if a request is satisfied already, and if not add the request for watch on all its keys.
+ *
+ * It is up to the user to then call
  *   val satisfied = update(key, request) 
  * when a request relevant to the given key occurs. This triggers bookeeping logic and returns back any requests satisfied by this
  * new request.
@@ -61,18 +65,23 @@ class DelayedRequest(val keys: Seq[Any], val request: RequestChannel.Request, de
  * this function handles delayed requests that have hit their time limit without being satisfied.
  *
  */
-abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purgeInterval: Int = 1000)
+abstract class RequestPurgatory[T <: DelayedRequest](brokerId: Int = 0, purgeInterval: Int = 1000)
         extends Logging with KafkaMetricsGroup {
 
   /* a list of requests watching each key */
   private val watchersForKey = new Pool[Any, Watchers](Some((key: Any) => new Watchers))
 
-  private val requestCounter = new AtomicInteger(0)
+  /* the number of requests being watched, duplicates added on different watchers are also counted */
+  private val watched = new AtomicInteger(0)
+
+  /* background thread expiring requests that have been waiting too long */
+  private val expiredRequestReaper = new ExpiredRequestReaper
+  private val expirationThread = Utils.newThread(name="request-expiration-task", runnable=expiredRequestReaper, daemon=false)
 
   newGauge(
     "PurgatorySize",
     new Gauge[Int] {
-      def value = watchersForKey.values.map(_.numRequests).sum + expiredRequestReaper.numRequests
+      def value = watched.get() + expiredRequestReaper.numRequests
     }
   )
 
@@ -83,41 +92,50 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
     }
   )
 
-  /* background thread expiring requests that have been waiting too long */
-  private val expiredRequestReaper = new ExpiredRequestReaper
-  private val expirationThread = Utils.newThread(name="request-expiration-task", runnable=expiredRequestReaper, daemon=false)
   expirationThread.start()
 
   /**
-   * Add a new delayed request watching the contained keys
+   * Try to add the request for watch on all keys. Return true iff the request is
+   * satisfied and the satisfaction is done by the caller.
+   *
+   * Requests can be watched on only a few of the keys if it is found satisfied when
+   * trying to add it to each one of the keys. In this case the request is still treated as satisfied
+   * and hence no longer watched. Those already added elements will be later purged by the expire reaper.
    */
-  def watch(delayedRequest: T) {
-    requestCounter.getAndIncrement()
-
+  def checkAndMaybeWatch(delayedRequest: T): Boolean = {
     for(key <- delayedRequest.keys) {
-      var lst = watchersFor(key)
-      lst.add(delayedRequest)
+      val lst = watchersFor(key)
+      if(!lst.checkAndMaybeAdd(delayedRequest)) {
+        if(delayedRequest.satisfied.compareAndSet(false, true))
+          return true
+        else
+          return false
+      }
     }
+
+    // if it is indeed watched, add to the expire queue also
     expiredRequestReaper.enqueue(delayedRequest)
+
+    false
   }
 
   /**
    * Update any watchers and return a list of newly satisfied requests.
    */
-  def update(key: Any, request: R): Seq[T] = {
+  def update(key: Any): Seq[T] = {
     val w = watchersForKey.get(key)
     if(w == null)
       Seq.empty
     else
-      w.collectSatisfiedRequests(request)
+      w.collectSatisfiedRequests()
   }
 
   private def watchersFor(key: Any) = watchersForKey.getAndMaybePut(key)
   
   /**
-   * Check if this request satisfied this delayed request
+   * Check if this delayed request is already satisfied
    */
-  protected def checkSatisfied(request: R, delayed: T): Boolean
+  protected def checkSatisfied(request: T): Boolean
 
   /**
    * Handle an expired delayed request
@@ -125,7 +143,7 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
   protected def expire(delayed: T)
 
   /**
-   * Shutdown the expirey thread
+   * Shutdown the expire reaper thread
    */
   def shutdown() {
     expiredRequestReaper.shutdown()
@@ -136,17 +154,26 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
    * bookkeeping logic.
    */
   private class Watchers {
+    private val requests = new util.ArrayList[T]
 
-    private val requests = new util.LinkedList[T]
-
-    def numRequests = requests.size
-
-    def add(t: T) {
+    // potentially add the element to watch if it is not satisfied yet
+    def checkAndMaybeAdd(t: T): Boolean = {
       synchronized {
+        // if it is already satisfied, do not add to the watch list
+        if (t.satisfied.get)
+          return false
+        // synchronize on the delayed request to avoid any race condition
+        // with expire and update threads on client-side.
+        if(t synchronized checkSatisfied(t)) {
+          return false
+        }
         requests.add(t)
+        watched.getAndIncrement()
+        return true
       }
     }
 
+    // traverse the list and purge satisfied elements
     def purgeSatisfied(): Int = {
       synchronized {
         val iter = requests.iterator()
@@ -155,6 +182,7 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
           val curr = iter.next
           if(curr.satisfied.get()) {
             iter.remove()
+            watched.getAndDecrement()
             purged += 1
           }
         }
@@ -162,7 +190,8 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
       }
     }
 
-    def collectSatisfiedRequests(request: R): Seq[T] = {
+    // traverse the list and try to satisfy watched elements
+    def collectSatisfiedRequests(): Seq[T] = {
       val response = new mutable.ArrayBuffer[T]
       synchronized {
         val iter = requests.iterator()
@@ -174,9 +203,10 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
           } else {
             // synchronize on curr to avoid any race condition with expire
             // on client-side.
-            val satisfied = curr synchronized checkSatisfied(request, curr)
+            val satisfied = curr synchronized checkSatisfied(curr)
             if(satisfied) {
               iter.remove()
+              watched.getAndDecrement()
               val updated = curr.satisfied.compareAndSet(false, true)
               if(updated == true) {
                 response += curr
@@ -215,13 +245,12 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
               expire(curr)
             }
           }
-          if (requestCounter.get >= purgeInterval) { // see if we need to force a full purge
+          if (watched.get + numRequests >= purgeInterval) { // see if we need to force a full purge
             debug("Beginning purgatory purge")
-            requestCounter.set(0)
             val purged = purgeSatisfied()
             debug("Purged %d requests from delay queue.".format(purged))
             val numPurgedFromWatchers = watchersForKey.values.map(_.purgeSatisfied()).sum
-            debug("Purged %d (watcher) requests.".format(numPurgedFromWatchers))
+            debug("Purged %d requests from watch lists.".format(numPurgedFromWatchers))
           }
         } catch {
           case e: Exception =>
@@ -266,10 +295,12 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
     }
 
     /**
-     * Delete all expired events from the delay queue
+     * Delete all satisfied events from the delay queue and the watcher lists
      */
     private def purgeSatisfied(): Int = {
       var purged = 0
+
+      // purge the delayed queue
       val iter = delayed.iterator()
       while(iter.hasNext) {
         val curr = iter.next()
@@ -278,6 +309,7 @@ abstract class RequestPurgatory[T <: DelayedRequest, R](brokerId: Int = 0, purge
           purged += 1
         }
       }
+
       purged
     }
   }
diff --git a/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala b/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
index af47836..0353295 100644
--- a/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
+++ b/core/src/main/scala/kafka/tools/ReplicaVerificationTool.scala
@@ -199,7 +199,7 @@ private class ReplicaBuffer(expectedReplicasPerTopicAndPartition: Map[TopicAndPa
                             initialOffsetTime: Long,
                             reportInterval: Long) extends Logging {
   private val fetchOffsetMap = new Pool[TopicAndPartition, Long]
-  private val messageSetCache = new Pool[TopicAndPartition, Pool[Int, FetchResponsePartitionData]]
+  private val messageSetCache = new Pool[TopicAndPartition, Pool[Int, PartitionData]]
   private val fetcherBarrier = new AtomicReference(new CountDownLatch(expectedNumFetchers))
   private val verificationBarrier = new AtomicReference(new CountDownLatch(1))
   @volatile private var lastReportTime = SystemTime.milliseconds
@@ -222,7 +222,7 @@ private class ReplicaBuffer(expectedReplicasPerTopicAndPartition: Map[TopicAndPa
 
   private def initialize() {
     for (topicAndPartition <- expectedReplicasPerTopicAndPartition.keySet)
-      messageSetCache.put(topicAndPartition, new Pool[Int, FetchResponsePartitionData])
+      messageSetCache.put(topicAndPartition, new Pool[Int, PartitionData])
     setInitialOffsets()
   }
 
@@ -248,7 +248,7 @@ private class ReplicaBuffer(expectedReplicasPerTopicAndPartition: Map[TopicAndPa
     }
   }
 
-  def addFetchedData(topicAndPartition: TopicAndPartition, replicaId: Int, partitionData: FetchResponsePartitionData) {
+  def addFetchedData(topicAndPartition: TopicAndPartition, replicaId: Int, partitionData: PartitionData) {
     messageSetCache.get(topicAndPartition).put(replicaId, partitionData)
   }
 
@@ -372,7 +372,7 @@ private class ReplicaFetcher(name: String, sourceBroker: Broker, topicAndPartiti
       }
     } else {
       for (topicAndPartition <- topicAndPartitions)
-        replicaBuffer.addFetchedData(topicAndPartition, sourceBroker.id, new FetchResponsePartitionData(messages = MessageSet.Empty))
+        replicaBuffer.addFetchedData(topicAndPartition, sourceBroker.id, new PartitionData(messages = MessageSet.Empty))
     }
 
     fetcherBarrier.countDown()
diff --git a/core/src/main/scala/kafka/tools/TestEndToEndLatency.scala b/core/src/main/scala/kafka/tools/TestEndToEndLatency.scala
index 5f8f6bc..6c6c8e7 100644
--- a/core/src/main/scala/kafka/tools/TestEndToEndLatency.scala
+++ b/core/src/main/scala/kafka/tools/TestEndToEndLatency.scala
@@ -17,15 +17,17 @@
 
 package kafka.tools
 
+import org.apache.kafka.clients.producer.{ProducerConfig, ProducerRecord, KafkaProducer}
+
+import kafka.consumer._
+
 import java.util.Properties
 import java.util.Arrays
-import kafka.consumer._
-import org.apache.kafka.clients.producer.{ProducerConfig, ProducerRecord, KafkaProducer}
 
 object TestEndToEndLatency {
   def main(args: Array[String]) {
-    if (args.length != 4) {
-      System.err.println("USAGE: java " + getClass().getName + " broker_list zookeeper_connect topic num_messages")
+    if (args.length != 6) {
+      System.err.println("USAGE: java " + getClass().getName + " broker_list zookeeper_connect topic num_messages consumer_fetch_max_wait producer_acks")
       System.exit(1)
     }
 
@@ -33,31 +35,37 @@ object TestEndToEndLatency {
     val zkConnect = args(1)
     val topic = args(2)
     val numMessages = args(3).toInt
+    val consumerFetchMaxWait = args(4).toInt
+    val producerAcks = args(5).toInt
 
     val consumerProps = new Properties()
     consumerProps.put("group.id", topic)
     consumerProps.put("auto.commit.enable", "false")
     consumerProps.put("auto.offset.reset", "largest")
     consumerProps.put("zookeeper.connect", zkConnect)
-    consumerProps.put("fetch.wait.max.ms", "1")
+    consumerProps.put("fetch.wait.max.ms", consumerFetchMaxWait.toString)
     consumerProps.put("socket.timeout.ms", 1201000.toString)
 
     val config = new ConsumerConfig(consumerProps)
     val connector = Consumer.create(config)
-    var stream = connector.createMessageStreams(Map(topic -> 1)).get(topic).head.head
+    val stream = connector.createMessageStreams(Map(topic -> 1)).get(topic).head.head
     val iter = stream.iterator
 
     val producerProps = new Properties()
     producerProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, brokerList)
     producerProps.put(ProducerConfig.LINGER_MS_CONFIG, "0")
     producerProps.put(ProducerConfig.BLOCK_ON_BUFFER_FULL_CONFIG, "true")
+    producerProps.put(ProducerConfig.ACKS_CONFIG, producerAcks.toString)
     val producer = new KafkaProducer(producerProps)
 
+    // make sure the consumer fetcher has started before sending data
+    Thread.sleep(5000)
+
     val message = "hello there beautiful".getBytes
     var totalTime = 0.0
     val latencies = new Array[Long](numMessages)
     for (i <- 0 until numMessages) {
-      var begin = System.nanoTime
+      val begin = System.nanoTime
       producer.send(new ProducerRecord(topic, message))
       val received = iter.next
       val elapsed = System.nanoTime - begin
diff --git a/core/src/test/scala/other/kafka/StressTestLog.scala b/core/src/test/scala/other/kafka/StressTestLog.scala
index 8fcd068..e19b8b2 100644
--- a/core/src/test/scala/other/kafka/StressTestLog.scala
+++ b/core/src/test/scala/other/kafka/StressTestLog.scala
@@ -91,7 +91,7 @@ object StressTestLog {
     @volatile var offset = 0
     override def work() {
       try {
-        log.read(offset, 1024, Some(offset+1)) match {
+        log.read(offset, 1024, Some(offset+1)).messageSet match {
           case read: FileMessageSet if read.sizeInBytes > 0 => {
             val first = read.head
             require(first.offset == offset, "We should either read nothing or the message we asked for.")
diff --git a/core/src/test/scala/unit/kafka/api/RequestResponseSerializationTest.scala b/core/src/test/scala/unit/kafka/api/RequestResponseSerializationTest.scala
index cd16ced..4bb243c 100644
--- a/core/src/test/scala/unit/kafka/api/RequestResponseSerializationTest.scala
+++ b/core/src/test/scala/unit/kafka/api/RequestResponseSerializationTest.scala
@@ -40,10 +40,10 @@ object SerializationTestUtils {
   private val isr1 = List(0, 1, 2)
   private val leader2 = 0
   private val isr2 = List(0, 2, 3)
-  private val partitionDataFetchResponse0 = new FetchResponsePartitionData(messages = new ByteBufferMessageSet(new Message("first message".getBytes)))
-  private val partitionDataFetchResponse1 = new FetchResponsePartitionData(messages = new ByteBufferMessageSet(new Message("second message".getBytes)))
-  private val partitionDataFetchResponse2 = new FetchResponsePartitionData(messages = new ByteBufferMessageSet(new Message("third message".getBytes)))
-  private val partitionDataFetchResponse3 = new FetchResponsePartitionData(messages = new ByteBufferMessageSet(new Message("fourth message".getBytes)))
+  private val partitionDataFetchResponse0 = new PartitionData(messages = new ByteBufferMessageSet(new Message("first message".getBytes)))
+  private val partitionDataFetchResponse1 = new PartitionData(messages = new ByteBufferMessageSet(new Message("second message".getBytes)))
+  private val partitionDataFetchResponse2 = new PartitionData(messages = new ByteBufferMessageSet(new Message("third message".getBytes)))
+  private val partitionDataFetchResponse3 = new PartitionData(messages = new ByteBufferMessageSet(new Message("fourth message".getBytes)))
   private val partitionDataFetchResponseMap = Map((0, partitionDataFetchResponse0), (1, partitionDataFetchResponse1), (2, partitionDataFetchResponse2), (3, partitionDataFetchResponse3))
 
   private val topicDataFetchResponse = {
diff --git a/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala b/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
index 9f04bd3..a5386a0 100644
--- a/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
+++ b/core/src/test/scala/unit/kafka/integration/PrimitiveApiTest.scala
@@ -74,7 +74,7 @@ class PrimitiveApiTest extends JUnit3Suite with ProducerConsumerTestHarness with
 
     val replica = servers.head.replicaManager.getReplica(topic, 0).get
     assertTrue("HighWatermark should equal logEndOffset with just 1 replica",
-               replica.logEndOffset > 0 && replica.logEndOffset == replica.highWatermark)
+               replica.logEndOffset.messageOffset > 0 && replica.logEndOffset.equals(replica.highWatermark))
 
     val request = new FetchRequestBuilder()
       .clientId("test-client")
@@ -248,13 +248,13 @@ class PrimitiveApiTest extends JUnit3Suite with ProducerConsumerTestHarness with
                             "Published messages should be in the log")
 
     val replicaId = servers.head.config.brokerId
-    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test1", 0, replicaId).get.highWatermark == 2 },
+    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test1", 0, replicaId).get.highWatermark.messageOffset == 2 },
                             "High watermark should equal to log end offset")
-    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test2", 0, replicaId).get.highWatermark == 2 },
+    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test2", 0, replicaId).get.highWatermark.messageOffset == 2 },
                             "High watermark should equal to log end offset")
-    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test3", 0, replicaId).get.highWatermark == 2 },
+    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test3", 0, replicaId).get.highWatermark.messageOffset == 2 },
                             "High watermark should equal to log end offset")
-    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test4", 0, replicaId).get.highWatermark == 2 },
+    TestUtils.waitUntilTrue(() => { servers.head.replicaManager.getReplica("test4", 0, replicaId).get.highWatermark.messageOffset == 2 },
                             "High watermark should equal to log end offset")
 
     // test if the consumer received the messages in the correct order when producer has enabled request pipelining
diff --git a/core/src/test/scala/unit/kafka/log/LogManagerTest.scala b/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
index 7d4c70c..59bd8a9 100644
--- a/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogManagerTest.scala
@@ -94,7 +94,7 @@ class LogManagerTest extends JUnit3Suite {
     assertEquals("Now there should only be only one segment in the index.", 1, log.numberOfSegments)
     time.sleep(log.config.fileDeleteDelayMs + 1)
     assertEquals("Files should have been deleted", log.numberOfSegments * 2, log.dir.list.length)
-    assertEquals("Should get empty fetch off new log.", 0, log.read(offset+1, 1024).sizeInBytes)
+    assertEquals("Should get empty fetch off new log.", 0, log.read(offset+1, 1024).messageSet.sizeInBytes)
 
     try {
       log.read(0, 1024)
@@ -137,7 +137,7 @@ class LogManagerTest extends JUnit3Suite {
     assertEquals("Now there should be exactly 6 segments", 6, log.numberOfSegments)
     time.sleep(log.config.fileDeleteDelayMs + 1)
     assertEquals("Files should have been deleted", log.numberOfSegments * 2, log.dir.list.length)
-    assertEquals("Should get empty fetch off new log.", 0, log.read(offset + 1, 1024).sizeInBytes)
+    assertEquals("Should get empty fetch off new log.", 0, log.read(offset + 1, 1024).messageSet.sizeInBytes)
     try {
       log.read(0, 1024)
       fail("Should get exception from fetching earlier.")
diff --git a/core/src/test/scala/unit/kafka/log/LogSegmentTest.scala b/core/src/test/scala/unit/kafka/log/LogSegmentTest.scala
index 6b76037..7b97e6a 100644
--- a/core/src/test/scala/unit/kafka/log/LogSegmentTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogSegmentTest.scala
@@ -78,7 +78,7 @@ class LogSegmentTest extends JUnit3Suite {
     val seg = createSegment(40)
     val ms = messages(50, "hello", "there", "little", "bee")
     seg.append(50, ms)
-    val read = seg.read(startOffset = 41, maxSize = 300, maxOffset = None)
+    val read = seg.read(startOffset = 41, maxSize = 300, maxOffset = None).messageSet
     assertEquals(ms.toList, read.toList)
   }
   
@@ -94,7 +94,7 @@ class LogSegmentTest extends JUnit3Suite {
     seg.append(baseOffset, ms)
     def validate(offset: Long) = 
       assertEquals(ms.filter(_.offset == offset).toList, 
-                   seg.read(startOffset = offset, maxSize = 1024, maxOffset = Some(offset+1)).toList)
+                   seg.read(startOffset = offset, maxSize = 1024, maxOffset = Some(offset+1)).messageSet.toList)
     validate(50)
     validate(51)
     validate(52)
@@ -109,7 +109,7 @@ class LogSegmentTest extends JUnit3Suite {
     val ms = messages(50, "hello", "there")
     seg.append(50, ms)
     val read = seg.read(startOffset = 52, maxSize = 200, maxOffset = None)
-    assertNull("Read beyond the last offset in the segment should give null", null)
+    assertNull("Read beyond the last offset in the segment should give null", read)
   }
   
   /**
@@ -124,7 +124,7 @@ class LogSegmentTest extends JUnit3Suite {
     val ms2 = messages(60, "alpha", "beta")
     seg.append(60, ms2)
     val read = seg.read(startOffset = 55, maxSize = 200, maxOffset = None)
-    assertEquals(ms2.toList, read.toList)
+    assertEquals(ms2.toList, read.messageSet.toList)
   }
   
   /**
@@ -142,12 +142,12 @@ class LogSegmentTest extends JUnit3Suite {
       seg.append(offset+1, ms2)
       // check that we can read back both messages
       val read = seg.read(offset, None, 10000)
-      assertEquals(List(ms1.head, ms2.head), read.toList)
+      assertEquals(List(ms1.head, ms2.head), read.messageSet.toList)
       // now truncate off the last message
       seg.truncateTo(offset + 1)
       val read2 = seg.read(offset, None, 10000)
-      assertEquals(1, read2.size)
-      assertEquals(ms1.head, read2.head)
+      assertEquals(1, read2.messageSet.size)
+      assertEquals(ms1.head, read2.messageSet.head)
       offset += 1
     }
   }
@@ -204,7 +204,7 @@ class LogSegmentTest extends JUnit3Suite {
     TestUtils.writeNonsenseToFile(indexFile, 5, indexFile.length.toInt)
     seg.recover(64*1024)
     for(i <- 0 until 100)
-      assertEquals(i, seg.read(i, Some(i+1), 1024).head.offset)
+      assertEquals(i, seg.read(i, Some(i+1), 1024).messageSet.head.offset)
   }
   
   /**
diff --git a/core/src/test/scala/unit/kafka/log/LogTest.scala b/core/src/test/scala/unit/kafka/log/LogTest.scala
index 1da1393..577d102 100644
--- a/core/src/test/scala/unit/kafka/log/LogTest.scala
+++ b/core/src/test/scala/unit/kafka/log/LogTest.scala
@@ -131,11 +131,11 @@ class LogTest extends JUnitSuite {
     for(i <- 0 until messages.length)
       log.append(new ByteBufferMessageSet(NoCompressionCodec, messages = messages(i)))
     for(i <- 0 until messages.length) {
-      val read = log.read(i, 100, Some(i+1)).head
+      val read = log.read(i, 100, Some(i+1)).messageSet.head
       assertEquals("Offset read should match order appended.", i, read.offset)
       assertEquals("Message should match appended.", messages(i), read.message)
     }
-    assertEquals("Reading beyond the last message returns nothing.", 0, log.read(messages.length, 100, None).size)
+    assertEquals("Reading beyond the last message returns nothing.", 0, log.read(messages.length, 100, None).messageSet.size)
   }
   
   /**
@@ -153,7 +153,7 @@ class LogTest extends JUnitSuite {
       log.append(new ByteBufferMessageSet(NoCompressionCodec, new AtomicLong(messageIds(i)), messages = messages(i)), assignOffsets = false)
     for(i <- 50 until messageIds.max) {
       val idx = messageIds.indexWhere(_ >= i)
-      val read = log.read(i, 100, None).head
+      val read = log.read(i, 100, None).messageSet.head
       assertEquals("Offset read should match message id.", messageIds(idx), read.offset)
       assertEquals("Message should match appended.", messages(idx), read.message)
     }
@@ -176,7 +176,7 @@ class LogTest extends JUnitSuite {
     // now manually truncate off all but one message from the first segment to create a gap in the messages
     log.logSegments.head.truncateTo(1)
     
-    assertEquals("A read should now return the last message in the log", log.logEndOffset-1, log.read(1, 200, None).head.offset)
+    assertEquals("A read should now return the last message in the log", log.logEndOffset-1, log.read(1, 200, None).messageSet.head.offset)
   }
   
   /**
@@ -188,7 +188,7 @@ class LogTest extends JUnitSuite {
   def testReadOutOfRange() {
     createEmptyLogs(logDir, 1024)
     val log = new Log(logDir, logConfig.copy(segmentSize = 1024), recoveryPoint = 0L, time.scheduler, time = time)
-    assertEquals("Reading just beyond end of log should produce 0 byte read.", 0, log.read(1024, 1000).sizeInBytes)
+    assertEquals("Reading just beyond end of log should produce 0 byte read.", 0, log.read(1024, 1000).messageSet.sizeInBytes)
     try {
       log.read(0, 1024)
       fail("Expected exception on invalid read.")
@@ -219,12 +219,12 @@ class LogTest extends JUnitSuite {
     /* do successive reads to ensure all our messages are there */
     var offset = 0L
     for(i <- 0 until numMessages) {
-      val messages = log.read(offset, 1024*1024)
+      val messages = log.read(offset, 1024*1024).messageSet
       assertEquals("Offsets not equal", offset, messages.head.offset)
       assertEquals("Messages not equal at offset " + offset, messageSets(i).head.message, messages.head.message)
       offset = messages.head.offset + 1
     }
-    val lastRead = log.read(startOffset = numMessages, maxLength = 1024*1024, maxOffset = Some(numMessages + 1))
+    val lastRead = log.read(startOffset = numMessages, maxLength = 1024*1024, maxOffset = Some(numMessages + 1)).messageSet
     assertEquals("Should be no more messages", 0, lastRead.size)
     
     // check that rolling the log forced a flushed the log--the flush is asyn so retry in case of failure
@@ -245,7 +245,7 @@ class LogTest extends JUnitSuite {
     log.append(new ByteBufferMessageSet(DefaultCompressionCodec, new Message("hello".getBytes), new Message("there".getBytes)))
     log.append(new ByteBufferMessageSet(DefaultCompressionCodec, new Message("alpha".getBytes), new Message("beta".getBytes)))
     
-    def read(offset: Int) = ByteBufferMessageSet.decompress(log.read(offset, 4096).head.message)
+    def read(offset: Int) = ByteBufferMessageSet.decompress(log.read(offset, 4096).messageSet.head.message)
     
     /* we should always get the first message in the compressed set when reading any offset in the set */
     assertEquals("Read at offset 0 should produce 0", 0, read(0).head.offset)
@@ -363,7 +363,7 @@ class LogTest extends JUnitSuite {
     log = new Log(logDir, config, recoveryPoint = 0L, time.scheduler, time)    
     assertEquals("Should have %d messages when log is reopened".format(numMessages), numMessages, log.logEndOffset)
     for(i <- 0 until numMessages)
-      assertEquals(i, log.read(i, 100, None).head.offset)
+      assertEquals(i, log.read(i, 100, None).messageSet.head.offset)
     log.close()
   }
 
@@ -575,15 +575,15 @@ class LogTest extends JUnitSuite {
   
   @Test
   def testAppendMessageWithNullPayload() {
-    var log = new Log(logDir,
+    val log = new Log(logDir,
                       LogConfig(),
                       recoveryPoint = 0L,
                       time.scheduler,
                       time)
     log.append(new ByteBufferMessageSet(new Message(bytes = null)))
-    val ms = log.read(0, 4096, None)
-    assertEquals(0, ms.head.offset)
-    assertTrue("Message payload should be null.", ms.head.message.isNull)
+    val messageSet = log.read(0, 4096, None).messageSet
+    assertEquals(0, messageSet.head.offset)
+    assertTrue("Message payload should be null.", messageSet.head.message.isNull)
   }
   
   @Test
diff --git a/core/src/test/scala/unit/kafka/message/BaseMessageSetTestCases.scala b/core/src/test/scala/unit/kafka/message/BaseMessageSetTestCases.scala
index 6db245c..dd8847f 100644
--- a/core/src/test/scala/unit/kafka/message/BaseMessageSetTestCases.scala
+++ b/core/src/test/scala/unit/kafka/message/BaseMessageSetTestCases.scala
@@ -31,7 +31,7 @@ trait BaseMessageSetTestCases extends JUnitSuite {
   def createMessageSet(messages: Seq[Message]): MessageSet
 
   @Test
-  def testWrittenEqualsRead {
+  def testWrittenEqualsRead() {
     val messageSet = createMessageSet(messages)
     checkEquals(messages.iterator, messageSet.map(m => m.message).iterator)
   }
diff --git a/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala b/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
index e532c28..03a424d 100644
--- a/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
+++ b/core/src/test/scala/unit/kafka/server/HighwatermarkPersistenceTest.scala
@@ -58,7 +58,7 @@ class HighwatermarkPersistenceTest extends JUnit3Suite {
     replicaManager.checkpointHighWatermarks()
     var fooPartition0Hw = hwmFor(replicaManager, topic, 0)
     assertEquals(0L, fooPartition0Hw)
-    val partition0 = replicaManager.getOrCreatePartition(topic, 0, 1)
+    val partition0 = replicaManager.getOrCreatePartition(topic, 0)
     // create leader and follower replicas
     val log0 = logManagers(0).createLog(TopicAndPartition(topic, 0), LogConfig())
     val leaderReplicaPartition0 = new Replica(configs.head.brokerId, partition0, SystemTime, 0, Some(log0))
@@ -67,18 +67,12 @@ class HighwatermarkPersistenceTest extends JUnit3Suite {
     partition0.addReplicaIfNotExists(followerReplicaPartition0)
     replicaManager.checkpointHighWatermarks()
     fooPartition0Hw = hwmFor(replicaManager, topic, 0)
-    assertEquals(leaderReplicaPartition0.highWatermark, fooPartition0Hw)
-    try {
-      followerReplicaPartition0.highWatermark
-      fail("Should fail with KafkaException")
-    }catch {
-      case e: KafkaException => // this is ok
-    }
-    // set the highwatermark for local replica
-    partition0.getReplica().get.highWatermark = 5L
+    assertEquals(leaderReplicaPartition0.highWatermark.messageOffset, fooPartition0Hw)
+    // set the high watermark for local replica
+    partition0.getReplica().get.highWatermark = new LogOffsetMetadata(5L)
     replicaManager.checkpointHighWatermarks()
     fooPartition0Hw = hwmFor(replicaManager, topic, 0)
-    assertEquals(leaderReplicaPartition0.highWatermark, fooPartition0Hw)
+    assertEquals(leaderReplicaPartition0.highWatermark.messageOffset, fooPartition0Hw)
     EasyMock.verify(zkClient)
   }
 
@@ -97,7 +91,7 @@ class HighwatermarkPersistenceTest extends JUnit3Suite {
     replicaManager.checkpointHighWatermarks()
     var topic1Partition0Hw = hwmFor(replicaManager, topic1, 0)
     assertEquals(0L, topic1Partition0Hw)
-    val topic1Partition0 = replicaManager.getOrCreatePartition(topic1, 0, 1)
+    val topic1Partition0 = replicaManager.getOrCreatePartition(topic1, 0)
     // create leader log
     val topic1Log0 = logManagers(0).createLog(TopicAndPartition(topic1, 0), LogConfig())
     // create a local replica for topic1
@@ -105,15 +99,15 @@ class HighwatermarkPersistenceTest extends JUnit3Suite {
     topic1Partition0.addReplicaIfNotExists(leaderReplicaTopic1Partition0)
     replicaManager.checkpointHighWatermarks()
     topic1Partition0Hw = hwmFor(replicaManager, topic1, 0)
-    assertEquals(leaderReplicaTopic1Partition0.highWatermark, topic1Partition0Hw)
-    // set the highwatermark for local replica
-    topic1Partition0.getReplica().get.highWatermark = 5L
+    assertEquals(leaderReplicaTopic1Partition0.highWatermark.messageOffset, topic1Partition0Hw)
+    // set the high watermark for local replica
+    topic1Partition0.getReplica().get.highWatermark = new LogOffsetMetadata(5L)
     replicaManager.checkpointHighWatermarks()
     topic1Partition0Hw = hwmFor(replicaManager, topic1, 0)
-    assertEquals(5L, leaderReplicaTopic1Partition0.highWatermark)
+    assertEquals(5L, leaderReplicaTopic1Partition0.highWatermark.messageOffset)
     assertEquals(5L, topic1Partition0Hw)
     // add another partition and set highwatermark
-    val topic2Partition0 = replicaManager.getOrCreatePartition(topic2, 0, 1)
+    val topic2Partition0 = replicaManager.getOrCreatePartition(topic2, 0)
     // create leader log
     val topic2Log0 = logManagers(0).createLog(TopicAndPartition(topic2, 0), LogConfig())
     // create a local replica for topic2
@@ -121,13 +115,13 @@ class HighwatermarkPersistenceTest extends JUnit3Suite {
     topic2Partition0.addReplicaIfNotExists(leaderReplicaTopic2Partition0)
     replicaManager.checkpointHighWatermarks()
     var topic2Partition0Hw = hwmFor(replicaManager, topic2, 0)
-    assertEquals(leaderReplicaTopic2Partition0.highWatermark, topic2Partition0Hw)
+    assertEquals(leaderReplicaTopic2Partition0.highWatermark.messageOffset, topic2Partition0Hw)
     // set the highwatermark for local replica
-    topic2Partition0.getReplica().get.highWatermark = 15L
-    assertEquals(15L, leaderReplicaTopic2Partition0.highWatermark)
+    topic2Partition0.getReplica().get.highWatermark = new LogOffsetMetadata(15L)
+    assertEquals(15L, leaderReplicaTopic2Partition0.highWatermark.messageOffset)
     // change the highwatermark for topic1
-    topic1Partition0.getReplica().get.highWatermark = 10L
-    assertEquals(10L, leaderReplicaTopic1Partition0.highWatermark)
+    topic1Partition0.getReplica().get.highWatermark = new LogOffsetMetadata(10L)
+    assertEquals(10L, leaderReplicaTopic1Partition0.highWatermark.messageOffset)
     replicaManager.checkpointHighWatermarks()
     // verify checkpointed hw for topic 2
     topic2Partition0Hw = hwmFor(replicaManager, topic2, 0)
diff --git a/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala b/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
index 2cd3a3f..cd302aa 100644
--- a/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
+++ b/core/src/test/scala/unit/kafka/server/ISRExpirationTest.scala
@@ -46,7 +46,7 @@ class IsrExpirationTest extends JUnit3Suite {
     val leaderReplica = partition0.getReplica(configs.head.brokerId).get
 
     // let the follower catch up to 10
-    (partition0.assignedReplicas() - leaderReplica).foreach(r => r.logEndOffset = 10)
+    (partition0.assignedReplicas() - leaderReplica).foreach(r => r.logEndOffset = new LogOffsetMetadata(10L))
     var partition0OSR = partition0.getOutOfSyncReplicas(leaderReplica, configs.head.replicaLagTimeMaxMs, configs.head.replicaLagMaxMessages)
     assertEquals("No replica should be out of sync", Set.empty[Int], partition0OSR.map(_.brokerId))
 
@@ -69,7 +69,7 @@ class IsrExpirationTest extends JUnit3Suite {
     assertEquals("All replicas should be in ISR", configs.map(_.brokerId).toSet, partition0.inSyncReplicas.map(_.brokerId))
     val leaderReplica = partition0.getReplica(configs.head.brokerId).get
     // set remote replicas leo to something low, like 4
-    (partition0.assignedReplicas() - leaderReplica).foreach(r => r.logEndOffset = 4L)
+    (partition0.assignedReplicas() - leaderReplica).foreach(r => r.logEndOffset = new LogOffsetMetadata(4L))
 
     // now follower (broker id 1) has caught up to only 4, while the leader is at 15. Since the gap it larger than
     // replicaMaxLagBytes, the follower is out of sync.
@@ -83,7 +83,7 @@ class IsrExpirationTest extends JUnit3Suite {
                                                localLog: Log): Partition = {
     val leaderId=config.brokerId
     val replicaManager = new ReplicaManager(config, time, null, null, null, new AtomicBoolean(false))
-    val partition = replicaManager.getOrCreatePartition(topic, partitionId, 1)
+    val partition = replicaManager.getOrCreatePartition(topic, partitionId)
     val leaderReplica = new Replica(leaderId, partition, time, 0, Some(localLog))
 
     val allReplicas = getFollowerReplicas(partition, leaderId, time) :+ leaderReplica
@@ -97,7 +97,7 @@ class IsrExpirationTest extends JUnit3Suite {
 
   private def getLogWithLogEndOffset(logEndOffset: Long, expectedCalls: Int): Log = {
     val log1 = EasyMock.createMock(classOf[kafka.log.Log])
-    EasyMock.expect(log1.logEndOffset).andReturn(logEndOffset).times(expectedCalls)
+    EasyMock.expect(log1.logEndOffsetMetadata).andReturn(new LogOffsetMetadata(logEndOffset)).times(expectedCalls)
     EasyMock.replay(log1)
 
     log1
diff --git a/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala b/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
index 0ec120a..d5d351c 100644
--- a/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
+++ b/core/src/test/scala/unit/kafka/server/LogRecoveryTest.scala
@@ -85,7 +85,7 @@ class LogRecoveryTest extends JUnit3Suite with ZooKeeperTestHarness {
 
     // give some time for the follower 1 to record leader HW
     TestUtils.waitUntilTrue(() =>
-      server2.replicaManager.getReplica(topic, 0).get.highWatermark == numMessages,
+      server2.replicaManager.getReplica(topic, 0).get.highWatermark.messageOffset == numMessages,
       "Failed to update high watermark for follower after timeout")
 
     servers.foreach(server => server.replicaManager.checkpointHighWatermarks())
@@ -134,7 +134,7 @@ class LogRecoveryTest extends JUnit3Suite with ZooKeeperTestHarness {
 
     // give some time for follower 1 to record leader HW of 60
     TestUtils.waitUntilTrue(() =>
-      server2.replicaManager.getReplica(topic, 0).get.highWatermark == hw,
+      server2.replicaManager.getReplica(topic, 0).get.highWatermark.messageOffset == hw,
       "Failed to update high watermark for follower after timeout")
     // shutdown the servers to allow the hw to be checkpointed
     servers.foreach(server => server.shutdown())
@@ -147,7 +147,7 @@ class LogRecoveryTest extends JUnit3Suite with ZooKeeperTestHarness {
     val hw = 20L
     // give some time for follower 1 to record leader HW of 600
     TestUtils.waitUntilTrue(() =>
-      server2.replicaManager.getReplica(topic, 0).get.highWatermark == hw,
+      server2.replicaManager.getReplica(topic, 0).get.highWatermark.messageOffset == hw,
       "Failed to update high watermark for follower after timeout")
     // shutdown the servers to allow the hw to be checkpointed
     servers.foreach(server => server.shutdown())
@@ -165,7 +165,7 @@ class LogRecoveryTest extends JUnit3Suite with ZooKeeperTestHarness {
 
     // allow some time for the follower to get the leader HW
     TestUtils.waitUntilTrue(() =>
-      server2.replicaManager.getReplica(topic, 0).get.highWatermark == hw,
+      server2.replicaManager.getReplica(topic, 0).get.highWatermark.messageOffset == hw,
       "Failed to update high watermark for follower after timeout")
     // kill the server hosting the preferred replica
     server1.shutdown()
@@ -191,7 +191,7 @@ class LogRecoveryTest extends JUnit3Suite with ZooKeeperTestHarness {
 
     // allow some time for the follower to get the leader HW
     TestUtils.waitUntilTrue(() =>
-      server1.replicaManager.getReplica(topic, 0).get.highWatermark == hw,
+      server1.replicaManager.getReplica(topic, 0).get.highWatermark.messageOffset == hw,
       "Failed to update high watermark for follower after timeout")
     // shutdown the servers to allow the hw to be checkpointed
     servers.foreach(server => server.shutdown())
diff --git a/core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala b/core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala
index 9abf219..a9c4ddc 100644
--- a/core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala
+++ b/core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala
@@ -39,7 +39,7 @@ class ReplicaManagerTest extends JUnit3Suite {
     val mockLogMgr = TestUtils.createLogManager(config.logDirs.map(new File(_)).toArray)
     val time: MockTime = new MockTime()
     val rm = new ReplicaManager(config, time, zkClient, new MockScheduler(time), mockLogMgr, new AtomicBoolean(false))
-    val partition = rm.getOrCreatePartition(topic, 1, 1)
+    val partition = rm.getOrCreatePartition(topic, 1)
     partition.getOrCreateReplica(1)
     rm.checkpointHighWatermarks()
   }
@@ -53,7 +53,7 @@ class ReplicaManagerTest extends JUnit3Suite {
     val mockLogMgr = TestUtils.createLogManager(config.logDirs.map(new File(_)).toArray)
     val time: MockTime = new MockTime()
     val rm = new ReplicaManager(config, time, zkClient, new MockScheduler(time), mockLogMgr, new AtomicBoolean(false))
-    val partition = rm.getOrCreatePartition(topic, 1, 1)
+    val partition = rm.getOrCreatePartition(topic, 1)
     partition.getOrCreateReplica(1)
     rm.checkpointHighWatermarks()
   }
diff --git a/core/src/test/scala/unit/kafka/server/RequestPurgatoryTest.scala b/core/src/test/scala/unit/kafka/server/RequestPurgatoryTest.scala
index 4f61f84..168712d 100644
--- a/core/src/test/scala/unit/kafka/server/RequestPurgatoryTest.scala
+++ b/core/src/test/scala/unit/kafka/server/RequestPurgatoryTest.scala
@@ -46,17 +46,17 @@ class RequestPurgatoryTest extends JUnit3Suite {
   def testRequestSatisfaction() {
     val r1 = new DelayedRequest(Array("test1"), null, 100000L)
     val r2 = new DelayedRequest(Array("test2"), null, 100000L)
-    assertEquals("With no waiting requests, nothing should be satisfied", 0, purgatory.update("test1", producerRequest1).size)
-    purgatory.watch(r1)
-    assertEquals("Still nothing satisfied", 0, purgatory.update("test1", producerRequest1).size)
-    purgatory.watch(r2)
-    assertEquals("Still nothing satisfied", 0, purgatory.update("test2", producerRequest2).size)
+    assertEquals("With no waiting requests, nothing should be satisfied", 0, purgatory.update("test1").size)
+    assertFalse("r1 not satisfied and hence watched", purgatory.checkAndMaybeWatch(r1))
+    assertEquals("Still nothing satisfied", 0, purgatory.update("test1").size)
+    assertFalse("r2 not satisfied and hence watched", purgatory.checkAndMaybeWatch(r2))
+    assertEquals("Still nothing satisfied", 0, purgatory.update("test2").size)
     purgatory.satisfied += r1
-    assertEquals("r1 satisfied", mutable.ArrayBuffer(r1), purgatory.update("test1", producerRequest1))
-    assertEquals("Nothing satisfied", 0, purgatory.update("test1", producerRequest2).size)
+    assertEquals("r1 satisfied", mutable.ArrayBuffer(r1), purgatory.update("test1"))
+    assertEquals("Nothing satisfied", 0, purgatory.update("test1").size)
     purgatory.satisfied += r2
-    assertEquals("r2 satisfied", mutable.ArrayBuffer(r2), purgatory.update("test2", producerRequest2))
-    assertEquals("Nothing satisfied", 0, purgatory.update("test2", producerRequest2).size)
+    assertEquals("r2 satisfied", mutable.ArrayBuffer(r2), purgatory.update("test2"))
+    assertEquals("Nothing satisfied", 0, purgatory.update("test2").size)
   }
 
   @Test
@@ -65,8 +65,8 @@ class RequestPurgatoryTest extends JUnit3Suite {
     val r1 = new DelayedRequest(Array("test1"), null, expiration)
     val r2 = new DelayedRequest(Array("test1"), null, 200000L)
     val start = System.currentTimeMillis
-    purgatory.watch(r1)
-    purgatory.watch(r2)
+    assertFalse("r1 not satisfied and hence watched", purgatory.checkAndMaybeWatch(r1))
+    assertFalse("r2 not satisfied and hence watched", purgatory.checkAndMaybeWatch(r2))
     purgatory.awaitExpiration(r1)
     val elapsed = System.currentTimeMillis - start
     assertTrue("r1 expired", purgatory.expired.contains(r1))
@@ -74,7 +74,7 @@ class RequestPurgatoryTest extends JUnit3Suite {
     assertTrue("Time for expiration %d should at least %d".format(elapsed, expiration), elapsed >= expiration)
   }
   
-  class MockRequestPurgatory extends RequestPurgatory[DelayedRequest, ProducerRequest] {
+  class MockRequestPurgatory extends RequestPurgatory[DelayedRequest] {
     val satisfied = mutable.Set[DelayedRequest]()
     val expired = mutable.Set[DelayedRequest]()
     def awaitExpiration(delayed: DelayedRequest) = {
@@ -82,7 +82,7 @@ class RequestPurgatoryTest extends JUnit3Suite {
         delayed.wait()
       }
     }
-    def checkSatisfied(request: ProducerRequest, delayed: DelayedRequest): Boolean = satisfied.contains(delayed)
+    def checkSatisfied(delayed: DelayedRequest): Boolean = satisfied.contains(delayed)
     def expire(delayed: DelayedRequest) {
       expired += delayed
       delayed synchronized {
diff --git a/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala b/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
index b1c4ce9..f98af71 100644
--- a/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
+++ b/core/src/test/scala/unit/kafka/server/SimpleFetchTest.scala
@@ -16,17 +16,19 @@
  */
 package kafka.server
 
+import kafka.api._
 import kafka.cluster.{Partition, Replica}
+import kafka.common.{ErrorMapping, TopicAndPartition}
 import kafka.log.Log
 import kafka.message.{ByteBufferMessageSet, Message}
 import kafka.network.RequestChannel
 import kafka.utils.{ZkUtils, Time, TestUtils, MockTime}
+
+import scala.Some
+
 import org.easymock.EasyMock
 import org.I0Itec.zkclient.ZkClient
 import org.scalatest.junit.JUnit3Suite
-import kafka.api._
-import scala.Some
-import kafka.common.TopicAndPartition
 
 class SimpleFetchTest extends JUnit3Suite {
 
@@ -45,13 +47,13 @@ class SimpleFetchTest extends JUnit3Suite {
    * with a HW matching the leader's ("5") and LEO of "15", meaning it's not in-sync
    * but is still in ISR (hasn't yet expired from ISR).
    *
-   * When a normal consumer fetches data, it only should only see data upto the HW of the leader,
+   * When a normal consumer fetches data, it should only see data up to the HW of the leader,
    * in this case up an offset of "5".
    */
   def testNonReplicaSeesHwWhenFetching() {
     /* setup */
     val time = new MockTime
-    val leo = 20
+    val leo = 20L
     val hw = 5
     val fetchSize = 100
     val messages = new Message("test-message".getBytes())
@@ -64,7 +66,11 @@ class SimpleFetchTest extends JUnit3Suite {
     val log = EasyMock.createMock(classOf[kafka.log.Log])
     EasyMock.expect(log.logEndOffset).andReturn(leo).anyTimes()
     EasyMock.expect(log)
-    EasyMock.expect(log.read(0, fetchSize, Some(hw))).andReturn(new ByteBufferMessageSet(messages))
+    EasyMock.expect(log.read(0, fetchSize, Some(hw))).andReturn(
+      new FetchDataInfo(
+        new LogOffsetMetadata(0L, 0L, leo.toInt),
+        new ByteBufferMessageSet(messages)
+      )).anyTimes()
     EasyMock.replay(log)
 
     val logManager = EasyMock.createMock(classOf[kafka.log.LogManager])
@@ -76,14 +82,26 @@ class SimpleFetchTest extends JUnit3Suite {
     EasyMock.expect(replicaManager.logManager).andReturn(logManager)
     EasyMock.expect(replicaManager.replicaFetcherManager).andReturn(EasyMock.createMock(classOf[ReplicaFetcherManager]))
     EasyMock.expect(replicaManager.zkClient).andReturn(zkClient)
+    EasyMock.expect(replicaManager.readMessageSets(EasyMock.anyObject())).andReturn({
+      val fetchInfo = log.read(0, fetchSize, Some(hw))
+      val partitionData = new PartitionData(ErrorMapping.NoError, hw.toLong, fetchInfo.messageSet)
+      Map(TopicAndPartition(topic, partitionId) -> new PartitionDataAndOffset(partitionData, fetchInfo.fetchOffset))
+    }).anyTimes()
     EasyMock.replay(replicaManager)
 
     val partition = getPartitionWithAllReplicasInISR(topic, partitionId, time, configs.head.brokerId, log, hw, replicaManager)
-    partition.getReplica(configs(1).brokerId).get.logEndOffset = leo - 5L
+    partition.getReplica(configs(1).brokerId).get.logEndOffset = new LogOffsetMetadata(leo - 5L, 0L, leo.toInt - 5)
 
     EasyMock.reset(replicaManager)
     EasyMock.expect(replicaManager.config).andReturn(configs.head).anyTimes()
     EasyMock.expect(replicaManager.getLeaderReplicaIfLocal(topic, partitionId)).andReturn(partition.leaderReplicaIfLocal().get).anyTimes()
+    EasyMock.expect(replicaManager.initWithRequestPurgatory(EasyMock.anyObject(), EasyMock.anyObject()))
+    EasyMock.expect(replicaManager.readMessageSets(EasyMock.anyObject())).andReturn({
+      val fetchInfo = log.read(0, fetchSize, Some(hw))
+      val partitionData = new PartitionData(ErrorMapping.NoError, hw.toLong, fetchInfo.messageSet)
+      Map(TopicAndPartition(topic, partitionId) -> new PartitionDataAndOffset(partitionData, fetchInfo.fetchOffset))
+    }).anyTimes()
+
     EasyMock.replay(replicaManager)
 
     val offsetManager = EasyMock.createMock(classOf[kafka.server.OffsetManager])
@@ -138,7 +156,11 @@ class SimpleFetchTest extends JUnit3Suite {
 
     val log = EasyMock.createMock(classOf[kafka.log.Log])
     EasyMock.expect(log.logEndOffset).andReturn(leo).anyTimes()
-    EasyMock.expect(log.read(followerLEO, Integer.MAX_VALUE, None)).andReturn(new ByteBufferMessageSet(messages))
+    EasyMock.expect(log.read(followerLEO, Integer.MAX_VALUE, None)).andReturn(
+      new FetchDataInfo(
+        new LogOffsetMetadata(followerLEO, 0L, followerLEO),
+        new ByteBufferMessageSet(messages)
+      )).anyTimes()
     EasyMock.replay(log)
 
     val logManager = EasyMock.createMock(classOf[kafka.log.LogManager])
@@ -150,16 +172,28 @@ class SimpleFetchTest extends JUnit3Suite {
     EasyMock.expect(replicaManager.logManager).andReturn(logManager)
     EasyMock.expect(replicaManager.replicaFetcherManager).andReturn(EasyMock.createMock(classOf[ReplicaFetcherManager]))
     EasyMock.expect(replicaManager.zkClient).andReturn(zkClient)
+    EasyMock.expect(replicaManager.readMessageSets(EasyMock.anyObject())).andReturn({
+      val fetchInfo = log.read(followerLEO, Integer.MAX_VALUE, None)
+      val partitionData = new PartitionData(ErrorMapping.NoError, hw.toLong, fetchInfo.messageSet)
+      Map(TopicAndPartition(topic, partitionId) -> new PartitionDataAndOffset(partitionData, fetchInfo.fetchOffset))
+    }).anyTimes()
     EasyMock.replay(replicaManager)
 
     val partition = getPartitionWithAllReplicasInISR(topic, partitionId, time, configs.head.brokerId, log, hw, replicaManager)
-    partition.getReplica(followerReplicaId).get.logEndOffset = followerLEO.asInstanceOf[Long]
+    partition.getReplica(followerReplicaId).get.logEndOffset = new LogOffsetMetadata(followerLEO.asInstanceOf[Long], 0L, followerLEO)
 
     EasyMock.reset(replicaManager)
     EasyMock.expect(replicaManager.config).andReturn(configs.head).anyTimes()
-    EasyMock.expect(replicaManager.recordFollowerPosition(topic, partitionId, followerReplicaId, followerLEO))
+    EasyMock.expect(replicaManager.updateReplicaLEOAndPartitionHW(topic, partitionId, followerReplicaId, new LogOffsetMetadata(followerLEO.asInstanceOf[Long], 0L, followerLEO)))
     EasyMock.expect(replicaManager.getReplica(topic, partitionId, followerReplicaId)).andReturn(partition.inSyncReplicas.find(_.brokerId == configs(1).brokerId))
     EasyMock.expect(replicaManager.getLeaderReplicaIfLocal(topic, partitionId)).andReturn(partition.leaderReplicaIfLocal().get).anyTimes()
+    EasyMock.expect(replicaManager.initWithRequestPurgatory(EasyMock.anyObject(), EasyMock.anyObject()))
+    EasyMock.expect(replicaManager.readMessageSets(EasyMock.anyObject())).andReturn({
+      val fetchInfo = log.read(followerLEO, Integer.MAX_VALUE, None)
+      val partitionData = new PartitionData(ErrorMapping.NoError, hw.toLong, fetchInfo.messageSet)
+      Map(TopicAndPartition(topic, partitionId) -> new PartitionDataAndOffset(partitionData, fetchInfo.fetchOffset))
+    }).anyTimes()
+    EasyMock.expect(replicaManager.unblockDelayedProduceRequests(EasyMock.anyObject())).anyTimes()
     EasyMock.replay(replicaManager)
 
     val offsetManager = EasyMock.createMock(classOf[kafka.server.OffsetManager])
@@ -195,7 +229,7 @@ class SimpleFetchTest extends JUnit3Suite {
 
   private def getPartitionWithAllReplicasInISR(topic: String, partitionId: Int, time: Time, leaderId: Int,
                                                localLog: Log, leaderHW: Long, replicaManager: ReplicaManager): Partition = {
-    val partition = new Partition(topic, partitionId, 2, time, replicaManager)
+    val partition = new Partition(topic, partitionId, time, replicaManager)
     val leaderReplica = new Replica(leaderId, partition, time, 0, Some(localLog))
 
     val allReplicas = getFollowerReplicas(partition, leaderId, time) :+ leaderReplica
@@ -204,7 +238,7 @@ class SimpleFetchTest extends JUnit3Suite {
     partition.inSyncReplicas = allReplicas.toSet
     // set the leader and its hw and the hw update time
     partition.leaderReplicaIdOpt = Some(leaderId)
-    leaderReplica.highWatermark = leaderHW
+    leaderReplica.highWatermark = new LogOffsetMetadata(leaderHW)
     partition
   }