Haruki Okada created KAFKA-15046:
------------------------------------
Summary: Produce performance issue under high disk load
Key: KAFKA-15046
URL: https://issues.apache.org/jira/browse/KAFKA-15046
Project: Kafka
Issue Type: Improvement
Affects Versions: 3.3.2
Reporter: Haruki Okada
Attachments: image-2023-06-01-12-46-30-058.png,
image-2023-06-01-12-52-40-959.png, image-2023-06-01-12-54-04-211.png,
image-2023-06-01-12-56-19-108.png
* Phenomenon:
** !image-2023-06-01-12-46-30-058.png|width=259,height=236!
** Producer response time 99%ile got quite bad when we performed replica
reassignment on the cluster
*** RequestQueue scope was significant
** Also request-time throttling happens almost all the time. This caused
producers to delay sending messages at the incidental time.
** At the incidental time, the disk I/O latency was higher than usual due to
the high load for replica reassignment.
*** !image-2023-06-01-12-56-19-108.png|width=255,height=128!
* Analysis:
** The request-handler utilization was much higher than usual.
*** !image-2023-06-01-12-52-40-959.png|width=278,height=113!
** Also, thread time utilization was much higher than usual on almost all users
*** !image-2023-06-01-12-54-04-211.png|width=276,height=110!
** 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.
***
{code:java}
"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([email protected]/Native Method)
at
sun.nio.ch.FileDispatcherImpl.force([email protected]/FileDispatcherImpl.java:82)
at
sun.nio.ch.FileChannelImpl.force([email protected]/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([email protected]/Thread.java:829) {code}
** Also there were bunch of logs that writing producer snapshots took hundreds
of milliseconds.
***
{code:java}
...
[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)
... {code}
* 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 hundreds of partition leaders with high
load, 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 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
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