[KAFKA-15046] Produce performance issue under high disk load

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.3.2
• Fix Version/s: 3.7.0
• Component/s: core
• Labels: performance
• Assignee: Haruki Okada
• Reporter: Haruki Okada
• Created: 01/Jun/23 04:57
• Updated: 12/Apr/24 17:30
• Resolved: 29/Nov/23 17:44

Description

• Phenomenon:
  • 
  • Producer response time 99%ile got quite bad when we performed replica reassignment on the cluster
    • RequestQueue scope was significant
  • Also request-time throttling happened at the incidental time. This caused producers to delay sending messages in the mean time.
  • The disk I/O latency was higher than usual due to the high load for replica reassignment.
    • 
• Analysis:
  • The request-handler utilization was much higher than usual.
    • 
  • Also, thread time utilization was much higher than usual on almost all users
    • 
  • From taking jstack several times, for most of them, we found that a request-handler was doing fsync for flusing ProducerState and meanwhile other request-handlers were waiting Log#lock for appending messages.

• • • "data-plane-kafka-request-handler-14" #166 daemon prio=5 os_prio=0 cpu=51264789.27ms elapsed=599242.76s tid=0x00007efdaeba7770 nid=0x1e704 runnable  [0x00007ef9a12e2000]
         java.lang.Thread.State: RUNNABLE
              at sun.nio.ch.FileDispatcherImpl.force0(java.base@11.0.17/Native Method)
              at sun.nio.ch.FileDispatcherImpl.force(java.base@11.0.17/FileDispatcherImpl.java:82)
              at sun.nio.ch.FileChannelImpl.force(java.base@11.0.17/FileChannelImpl.java:461)
              at kafka.log.ProducerStateManager$.kafka$log$ProducerStateManager$$writeSnapshot(ProducerStateManager.scala:451)
              at kafka.log.ProducerStateManager.takeSnapshot(ProducerStateManager.scala:754)
              at kafka.log.UnifiedLog.roll(UnifiedLog.scala:1544)
              - locked <0x000000060d75d820> (a java.lang.Object)
              at kafka.log.UnifiedLog.maybeRoll(UnifiedLog.scala:1523)
              - locked <0x000000060d75d820> (a java.lang.Object)
              at kafka.log.UnifiedLog.append(UnifiedLog.scala:919)
              - locked <0x000000060d75d820> (a java.lang.Object)
              at kafka.log.UnifiedLog.appendAsLeader(UnifiedLog.scala:760)
              at kafka.cluster.Partition.$anonfun$appendRecordsToLeader$1(Partition.scala:1170)
              at kafka.cluster.Partition.appendRecordsToLeader(Partition.scala:1158)
              at kafka.server.ReplicaManager.$anonfun$appendToLocalLog$6(ReplicaManager.scala:956)
              at kafka.server.ReplicaManager$$Lambda$2379/0x0000000800b7c040.apply(Unknown Source)
              at scala.collection.StrictOptimizedMapOps.map(StrictOptimizedMapOps.scala:28)
              at scala.collection.StrictOptimizedMapOps.map$(StrictOptimizedMapOps.scala:27)
              at scala.collection.mutable.HashMap.map(HashMap.scala:35)
              at kafka.server.ReplicaManager.appendToLocalLog(ReplicaManager.scala:944)
              at kafka.server.ReplicaManager.appendRecords(ReplicaManager.scala:602)
              at kafka.server.KafkaApis.handleProduceRequest(KafkaApis.scala:666)
              at kafka.server.KafkaApis.handle(KafkaApis.scala:175)
              at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:75)
              at java.lang.Thread.run(java.base@11.0.17/Thread.java:829) 

• • Also there were bunch of logs that writing producer snapshots took hundreds of milliseconds.

    • ...
      [2023-05-01 11:08:36,689] INFO [ProducerStateManager partition=xxx-4] Wrote producer snapshot at offset 1748817854 with 8 producer ids in 809 ms. (kafka.log.ProducerStateManager)
      [2023-05-01 11:08:37,319] INFO [ProducerStateManager partition=yyy-34] Wrote producer snapshot at offset 247996937813 with 0 producer ids in 547 ms. (kafka.log.ProducerStateManager)
      [2023-05-01 11:08:38,887] INFO [ProducerStateManager partition=zzz-9] Wrote producer snapshot at offset 226222355404 with 0 producer ids in 576 ms. (kafka.log.ProducerStateManager)
      ... 

• From the analysis, we summarized the issue as below:

• • 1. Disk write latency got worse due to the replica reassignment
    • We already use replication quota, and lowering the quota further may not be acceptable for too long assignment duration
  • 2. ProducerStateManager#takeSnapshot started to take time due to fsync latency
    • This is done at every log segment roll.
    • In our case, the broker hosts high load partitions so log roll is occurring very frequently.
  • 3. During ProducerStateManager#takeSnapshot is doing fsync, all subsequent produce requests to the partition is blocked due to Log#lock
  • 4. During produce requests waiting the lock, they consume request handler threads time so it's accounted as thread-time utilization and caused throttling
• Suggestion:
  • We didn't see this phenomenon when we used Kafka 2.4.1.
    • ProducerState fsync was introduced in 2.8.0 by this: https://issues.apache.org/jira/browse/KAFKA-9892
  • The reason why ProducerState needs to be fsync is not well described in above ticket though, we think fsync is not really necessary here. Because:

• • • If ProducerState snapshot file was not written to the disk after power failure, it will be just rebuilt from logs.
    • Also, even if ProducerState snapshot was corrupted after power failure, it will be rebuilt from logs thanks to CRC

Issue Links

• fixes: KAFKA-9693 Kafka latency spikes caused by log segment flush on roll
• links to: GitHub Pull Request #14242