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From Jun Rao <jun...@gmail.com>
Subject Re: Partition reassignment reversed
Date Thu, 04 Dec 2014 00:48:19 GMT
Not sure exactly what happened there. We did fix a few bugs in reassigning
partitions in 0.8.1.1. So, you probably want to upgrade to that one or the
upcoming 0.8.2 release.

Thanks,

Jun

On Tue, Dec 2, 2014 at 2:33 PM, Andrew Jorgensen <ajorgensen@twitter.com>
wrote:

> I am using kafka 0.8.
> Yes I did run —verify, but got some weird output from it I had never seen
> before that looked something like:
>
> Status of partition reassignment:
> ERROR: Assigned replicas (5,2) don't match the list of replicas for
> reassignment (5) for partition [topic-1,248]
> ERROR: Assigned replicas (7,3) don't match the list of replicas for
> reassignment (7) for partition [topic-2,228]
>
> There were a large number of these but it seems to just be for topic-1,
> and topic-2. In this case I was migrating around 4 or 5 topics. These two
> are also the ones that got reversed when I bounced all the processes
> yesterday.
>
> Here are some more logs that I found from that day that may help piece
> together what might have happened
>
> [2014-11-19 16:56:52,938] ERROR [KafkaApi-1] Error when processing fetch
> request for partition [topic-2,317] offset 408324093 from follower with
> correlation id 2458 (kafka.server.KafkaApis)
> kafka.common.OffsetOutOfRangeException: Request for offset 408324093 but
> we only have log segments in the range 409018400 to 425346400.
> at kafka.log.Log.read(Log.scala:380)
> at
> kafka.server.KafkaApis.kafka$server$KafkaApis$$readMessageSet(KafkaApis.scala:530)
> at
> kafka.server.KafkaApis$$anonfun$kafka$server$KafkaApis$$readMessageSets$1.apply(KafkaApis.scala:476)
> at
> kafka.server.KafkaApis$$anonfun$kafka$server$KafkaApis$$readMessageSets$1.apply(KafkaApis.scala:471)
> at
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
> at
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
> at scala.collection.immutable.HashMap$HashMap1.foreach(HashMap.scala:17[image:
> 8)]
> at
> scala.collection.immutable.HashMap$HashTrieMap.foreach(HashMap.scala:347)
> at
> scala.collection.immutable.HashMap$HashTrieMap.foreach(HashMap.scala:347)
> at scala.collection.TraversableLike$class.map(TraversableLike.scala:233)
> at scala.collection.immutable.HashMap.map(HashMap.scala:3[image: 8)]
> at
> kafka.server.KafkaApis.kafka$server$KafkaApis$$readMessageSets(KafkaApis.scala:471)
> at kafka.server.KafkaApis.handleFetchRequest(KafkaApis.scala:437)
> at kafka.server.KafkaApis.handle(KafkaApis.scala:186)
> at kafka.server.KafkaRequestHandler.run(KafkaRequestHandler.scala:42)
> at java.lang.Thread.run(Thread.java:724)
>
> -----
>
> [2014-11-19 16:24:37,959] ERROR Conditional update of path
> /brokers/topics/topic-2/partitions/248/state with data
> {"controller_epoch":15,"leader":2,"version":1,"leader_epoch":1,"isr":[2,5]}
> and expected version 1 failed due to
> org.apache.zookeeper.KeeperException$BadVersionException: KeeperErrorCode =
> BadVersion for /brokers/topics/topic-2/partitions/248/state
> (kafka.utils.ZkUtils$)
>
>
>
> --
> Andrew Jorgensen
> @ajorgensen
>
> On December 2, 2014 at 5:28:07 PM, Jun Rao (junrao@gmail.com) wrote:
>
> Did you run the --verify option (
> http://kafka.apache.org/documentation.html#basic_ops_restarting) to check
> if the reassignment process completes? Also, what version of Kafka are you
> using?
>
> Thanks,
>
> Jun
>
> On Mon, Dec 1, 2014 at 7:16 PM, Andrew Jorgensen <
> ajorgensen@twitter.com.invalid> wrote:
>
> > I unfortunately do not have any specific logs from these events but I
> will
> > try and describe the events as accurately as possible to give an idea
> of
> > the problem I saw.
> >
> > The odd behavior manifested itself when I bounced all of the kafka
> > processes on each of the servers in a 12 node cluster. A few weeks prior
> I
> > did a partition reassignment to add four new kafka brokers to the
> cluster.
> > This cluster has 4 topics on it each with 350 partitions each, a
> retention
> > policy of 6 hours, and a replication factor of 1. Originally I attempted
> to
> > run a migration on all of the topics and partitions adding the 4 new
> nodes
> > using the partition reassignment tool. This seemed to cause a lot of
> > network congestion and according to the logs some of the nodes were
> having
> > trouble talking to each other. The network congestion lasted for the
> > duration of the migration and began to get better toward the end. After
> the
> > migration I confirmed that data was being stored and served from the new
> > brokers. Today I bounced each of the kafka processes on each of the
> brokers
> > to pick up a change made to the log4j properties. After bouncing one
> > processes I started seeing some strange errors on the four newer broker
> > nodes that looked like:
> >
> > kafka.common.NotAssignedReplicaException: Leader 10 failed to record
> > follower 7's position 0 for partition [topic-1,185] since the replica 7
> is
> > not recognized to be one of the assigned replicas 10 for partition
> > [topic-2,185]
> >
> > and on the older kafka brokers the errors looked like:
> >
> > [2014-12-01 17:06:04,268] ERROR [ReplicaFetcherThread-0-12], Error for
> > partition [topic-1,175] to broker 12:class kafka.common.UnknownException
> > (kafka.server.ReplicaFetcherThread)
> >
> > I proceeded to bounce the rest of the kafka processes and after bouncing
> > the rest the errors seemed to stop. It wasn’t until a few hours later I
> > noticed that the amount of data stored on the 4 new kafka brokers had
> > dropped off significantly. When I ran a describe for the topics in the
> > errors it was clear that the assigned partitions had been reverted to a
> > state prior to the original migration to add the 4 new brokers. I am
> unsure
> > of why bouncing the kafka process would cause the state in zookeeper to
> get
> > overwritten given that it had seemed to have been working for the last
> few
> > weeks until the process was restarted. My hunch is that the controller
> > keeps some state about the world pre-reassignment and removes that state
> > after it detects that the reassignment happened successfully. In this
> case
> > the network congestion on each of the brokers caused the controller not
> to
> > get notified when all the reassignments were completed and thus kept the
> > pre-assignement state around. When the process was bounced it read from
> > zookeeper to get this state and reverted the existing scheme to the
> > pre-assignment state. Has this behavior been observed before? Does this
> > sound like a logical understanding of what happened in this case?
> >
> > --
> > Andrew Jorgensen
> > @ajorgensen
>
>

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