Index: lucene/contrib/misc/src/java/org/apache/lucene/store/DirectIOLinuxDirectory.java
===================================================================
--- lucene/contrib/misc/src/java/org/apache/lucene/store/DirectIOLinuxDirectory.java	(revision 1143438)
+++ lucene/contrib/misc/src/java/org/apache/lucene/store/DirectIOLinuxDirectory.java	(working copy)
@@ -27,6 +27,7 @@
 
 import org.apache.lucene.store.Directory; // javadoc
 import org.apache.lucene.store.NativeFSLockFactory; // javadoc
+import org.apache.lucene.store.IOContext.Context;
 
 /**
  * An {@link Directory} implementation that uses the
@@ -71,15 +72,19 @@
   @Override
   public IndexInput openInput(String name, IOContext context) throws IOException {
     ensureOpen();
-    //nocommit - use buffer based on IOContext
-    return new DirectIOLinuxIndexInput(new File(getDirectory(), name), forcedBufferSize == 0 ? BufferedIndexInput.BUFFER_SIZE : forcedBufferSize);
+    if (forcedBufferSize != 0) 
+      return new DirectIOLinuxIndexInput(new File(getDirectory(), name), forcedBufferSize, context);
+    
+    else if (context.context == Context.MERGE) 
+      return new DirectIOLinuxIndexInput(new File(getDirectory(), name), BufferedIndexInput.MERGE_BUFFER_SIZE, context);
+    
+    return new DirectIOLinuxIndexInput(new File(getDirectory(), name), BufferedIndexInput.BUFFER_SIZE, context);
   }
 
   @Override
-  public IndexOutput createOutput(String name,IOContext context) throws IOException {
+  public IndexOutput createOutput(String name, IOContext context) throws IOException {
     ensureOpen();
     ensureCanWrite(name);
-    //nocommit - use buffer based on IOContext
     return new DirectIOLinuxIndexOutput(new File(getDirectory(), name), forcedBufferSize == 0 ? BufferedIndexOutput.BUFFER_SIZE : forcedBufferSize);
   }
 
@@ -239,8 +244,14 @@
     private long filePos;
     private int bufferPos;
 
-    public DirectIOLinuxIndexInput(File path, int bufferSize) throws IOException {
-      FileDescriptor fd = NativePosixUtil.open_direct(path.toString(), true);
+    public DirectIOLinuxIndexInput(File path, int bufferSize, IOContext context) throws IOException {
+      FileDescriptor fd;
+      
+      if (context.context == Context.MERGE) 
+        fd = NativePosixUtil.open_direct(path.toString(), true);       
+      else
+        fd = NativePosixUtil.open_direct(path.toString(), true);
+      
       fis = new FileInputStream(fd);
       channel = fis.getChannel();
       this.bufferSize = bufferSize;
Index: lucene/contrib/misc/src/java/org/apache/lucene/store/WindowsDirectory.java
===================================================================
--- lucene/contrib/misc/src/java/org/apache/lucene/store/WindowsDirectory.java	(revision 1143438)
+++ lucene/contrib/misc/src/java/org/apache/lucene/store/WindowsDirectory.java	(working copy)
@@ -70,7 +70,6 @@
   @Override
   public IndexInput openInput(String name, IOContext context) throws IOException {
     ensureOpen();
-    //nocommit - use buffer based on IOContext
     return new WindowsIndexInput(new File(getDirectory(), name), DEFAULT_BUFFERSIZE);
   }
   
Index: lucene/src/java/org/apache/lucene/index/BufferedDeletesStream.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/BufferedDeletesStream.java	(revision 1143438)
+++ lucene/src/java/org/apache/lucene/index/BufferedDeletesStream.java	(working copy)
@@ -274,8 +274,7 @@
         if (coalescedDeletes != null) {
           // Lock order: IW -> BD -> RP
           assert readerPool.infoIsLive(info);
-          //nocommit is IOContext.DEFAULT the right thing to do here?
-          SegmentReader reader = readerPool.get(info, false, IOContext.DEFAULT);
+          SegmentReader reader = readerPool.get(info, false, IOContext.READ);
           int delCount = 0;
           final boolean segAllDeletes;
           try {
Index: lucene/src/java/org/apache/lucene/index/SegmentNorms.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/SegmentNorms.java	(revision 1143438)
+++ lucene/src/java/org/apache/lucene/index/SegmentNorms.java	(working copy)
@@ -220,7 +220,6 @@
     // NOTE: norms are re-written in regular directory, not cfs
     si.advanceNormGen(this.number);
     final String normFileName = si.getNormFileName(this.number);
-    //nocommit not sure if this is the correct information provided to FlushInfo
     IndexOutput out = owner.directory().createOutput(normFileName, new IOContext(new FlushInfo(si.docCount, 0)));
     boolean success = false;
     try {
Index: lucene/src/java/org/apache/lucene/index/codecs/DefaultSegmentInfosWriter.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/codecs/DefaultSegmentInfosWriter.java	(revision 1143438)
+++ lucene/src/java/org/apache/lucene/index/codecs/DefaultSegmentInfosWriter.java	(working copy)
@@ -23,6 +23,7 @@
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.store.ChecksumIndexOutput;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.FlushInfo;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexOutput;
 import org.apache.lucene.util.IOUtils;
@@ -57,8 +58,7 @@
   @Override
   public IndexOutput writeInfos(Directory dir, String segmentFileName, SegmentInfos infos, IOContext context)
           throws IOException {
-    //nocommit should this context always be flush?
-    IndexOutput out = createOutput(dir, segmentFileName, context);
+    IndexOutput out = createOutput(dir, segmentFileName, new IOContext(new FlushInfo(infos.size(), infos.totalDocCount())));
     boolean success = false;
     try {
       out.writeInt(FORMAT_CURRENT); // write FORMAT
Index: lucene/src/java/org/apache/lucene/store/BufferedIndexInput.java
===================================================================
--- lucene/src/java/org/apache/lucene/store/BufferedIndexInput.java	(revision 1143438)
+++ lucene/src/java/org/apache/lucene/store/BufferedIndexInput.java	(working copy)
@@ -24,6 +24,14 @@
 
   /** Default buffer size */
   public static final int BUFFER_SIZE = 1024;
+  
+  // The normal read buffer size defaults to 1024, but
+  // increasing this during merging seems to yield
+  // performance gains.  However we don't want to increase
+  // it too much because there are quite a few
+  // BufferedIndexInputs created during merging.  See
+  // LUCENE-888 for details.
+  public static final int MERGE_BUFFER_SIZE = 1024;
 
   private int bufferSize = BUFFER_SIZE;
   
@@ -43,7 +51,6 @@
   public BufferedIndexInput() {}
 
   /** Inits BufferedIndexInput with a specific bufferSize */
-  //nocommit To cleanup class variable bufferSize as the the default size is always used 
   public BufferedIndexInput(int bufferSize) {
     checkBufferSize(BufferedIndexInput.BUFFER_SIZE);
     this.bufferSize = bufferSize;
Index: lucene/src/java/org/apache/lucene/store/SimpleFSDirectory.java
===================================================================
--- lucene/src/java/org/apache/lucene/store/SimpleFSDirectory.java	(revision 1143438)
+++ lucene/src/java/org/apache/lucene/store/SimpleFSDirectory.java	(working copy)
@@ -21,7 +21,9 @@
 import java.io.IOException;
 import java.io.RandomAccessFile;
 
+import org.apache.lucene.store.IOContext.Context;
 
+
 /** A straightforward implementation of {@link FSDirectory}
  *  using java.io.RandomAccessFile.  However, this class has
  *  poor concurrent performance (multiple threads will
@@ -87,8 +89,10 @@
     protected final int chunkSize;
     
     public SimpleFSIndexInput(File path, IOContext context, int chunkSize) throws IOException {
-      //nocommit Use IOContext to decide bufferSize instead of BufferedIndexInput.BUFFER_SIZE
       super(BufferedIndexInput.BUFFER_SIZE);
+      if (context.context == Context.MERGE) {
+        setBufferSize(MERGE_BUFFER_SIZE);
+      }
       file = new Descriptor(path, "r");
       this.chunkSize = chunkSize;
     }