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From "Ismael Juma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-5758) Reassigning a topic's partitions can adversely impact other topics
Date Tue, 22 Aug 2017 15:54:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-5758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16136980#comment-16136980

Ismael Juma commented on KAFKA-5758:


> Reassigning a topic's partitions can adversely impact other topics
> ------------------------------------------------------------------
>                 Key: KAFKA-5758
>                 URL: https://issues.apache.org/jira/browse/KAFKA-5758
>             Project: Kafka
>          Issue Type: Bug
>          Components: core
>    Affects Versions:
>            Reporter: David van Geest
>              Labels: reliability
>             Fix For: 1.0.0
> We've noticed that reassigning a topic's partitions seems to adversely impact other topics.
Specifically, followers for other topics fall out of the ISR.
> While I'm not 100% sure about why this happens, the scenario seems to be as follows:
> 1. Reassignment is manually triggered on topic-partition X-Y, and broker A (which used
to be a follower for X-Y) is no longer a follower.
> 2. Broker A makes `FetchRequest` including topic-partition X-Y to broker B, just after
the reassignment.
> 3. Broker B can fulfill the `FetchRequest`, but while trying to do so it tries to record
the position of "follower" A. This fails, because broker A is no longer a follower for X-Y
(see exception below).
> 4. The entire `FetchRequest` request fails, and broker A's other followed topics start
falling behind.
> 5. Depending on the length of the reassignment, this sequence repeats.
> In step 3, we see exceptions like:
> {noformat}
> Error when handling request Name: FetchRequest; Version: 3; CorrelationId: 46781859;
ClientId: ReplicaFetcherThread-0-1001; ReplicaId: 1006; MaxWait: 500 ms; MinBytes: 1 bytes;
MaxBytes:10485760 bytes; RequestInfo: 
> kafka.common.NotAssignedReplicaException: Leader 1001 failed to record follower 1006's
position -1 since the replica is not recognized to be one of the assigned replicas 1001,1004,1005
for partition [topic_being_reassigned,5].
> at kafka.cluster.Partition.updateReplicaLogReadResult(Partition.scala:249)
> 	at kafka.server.ReplicaManager$$anonfun$updateFollowerLogReadResults$2.apply(ReplicaManager.scala:923)
> 	at kafka.server.ReplicaManager$$anonfun$updateFollowerLogReadResults$2.apply(ReplicaManager.scala:920)
> 	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
> 	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
> 	at kafka.server.ReplicaManager.updateFollowerLogReadResults(ReplicaManager.scala:920)
> 	at kafka.server.ReplicaManager.fetchMessages(ReplicaManager.scala:481)
> 	at kafka.server.KafkaApis.handleFetchRequest(KafkaApis.scala:534)
> 	at kafka.server.KafkaApis.handle(KafkaApis.scala:79)
> 	at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:60)
> 	at java.lang.Thread.run(Thread.java:745)
> {noformat}
> Does my assessment make sense? If so, this behaviour seems problematic. A few changes
that might improve matters (assuming I'm on the right track):
> 1. `FetchRequest` should be able to return partial results
> 2. The broker fulfilling the `FetchRequest` could ignore the `NotAssignedReplicaException`,
and return results without recording the not-any-longer-follower position.
> This behaviour was experienced with, although looking at the changelogs and
the code in question, I don't see any reason why it would have changed in later versions.
> Am very interested to have some discussion on this. Thanks!

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