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  1. Kafka
  2. KAFKA-16105

Reassignment of tiered topics is failing due to RemoteStorageException




      When partition reassignment is happening for a tiered topic in most of the cases it's stuck with RemoteStorageException's on follower nodes saying that it can not construct remote log auxilary state:


      [2024-01-09 08:34:02,899] ERROR [ReplicaFetcher replicaId=7, leaderId=6, fetcherId=2] Error building remote log auxiliary state for test-24 (kafka.server.ReplicaFetcherThread)
                                               org.apache.kafka.server.log.remote.storage.RemoteStorageException: Couldn't build the state from remote store for partition: test-24, currentLeaderEpoch: 8, leaderLocalLogStartOffset: 209, leaderLogStartOffset: 0, epoch: 0 as the previous remote log segment metadata was not found
                                                       at kafka.server.ReplicaFetcherTierStateMachine.buildRemoteLogAuxState(ReplicaFetcherTierStateMachine.java:259)
                                                       at kafka.server.ReplicaFetcherTierStateMachine.start(ReplicaFetcherTierStateMachine.java:106)
                                                       at kafka.server.AbstractFetcherThread.handleOffsetsMovedToTieredStorage(AbstractFetcherThread.scala:762)
                                                       at kafka.server.AbstractFetcherThread.$anonfun$processFetchRequest$7(AbstractFetcherThread.scala:413)
                                                       at scala.Option.foreach(Option.scala:437)
                                                       at kafka.server.AbstractFetcherThread.$anonfun$processFetchRequest$6(AbstractFetcherThread.scala:332)
                                                       at kafka.server.AbstractFetcherThread.$anonfun$processFetchRequest$6$adapted(AbstractFetcherThread.scala:331)
                                                       at kafka.utils.Implicits$MapExtensionMethods$.$anonfun$forKeyValue$1(Implicits.scala:62)
                                                       at scala.collection.convert.JavaCollectionWrappers$JMapWrapperLike.foreachEntry(JavaCollectionWrappers.scala:407)
                                                       at scala.collection.convert.JavaCollectionWrappers$JMapWrapperLike.foreachEntry$(JavaCollectionWrappers.scala:403)
                                                       at scala.collection.convert.JavaCollectionWrappers$AbstractJMapWrapper.foreachEntry(JavaCollectionWrappers.scala:321)
                                                       at kafka.server.AbstractFetcherThread.processFetchRequest(AbstractFetcherThread.scala:331)
                                                       at kafka.server.AbstractFetcherThread.$anonfun$maybeFetch$3(AbstractFetcherThread.scala:130)
                                                       at kafka.server.AbstractFetcherThread.$anonfun$maybeFetch$3$adapted(AbstractFetcherThread.scala:129)
                                                       at scala.Option.foreach(Option.scala:437)
                                                       at kafka.server.AbstractFetcherThread.maybeFetch(AbstractFetcherThread.scala:129)
                                                       at kafka.server.AbstractFetcherThread.doWork(AbstractFetcherThread.scala:112)
                                                       at kafka.server.ReplicaFetcherThread.doWork(ReplicaFetcherThread.scala:98)
                                                       at org.apache.kafka.server.util.ShutdownableThread.run(ShutdownableThread.java:130)



      A cluster of 3 nodes with a single topic with 30 partitions. All partitions have tiered segments.
      Adding 3 more nodes to the cluster and making a reassignment to move all the data to new nodes.
      For most of the partitions reassignment is happening smoothly.
      For some of the partitions when a new node starts to get assignments it reads __remote_log_metadata topic and tries to initialize the metadata cache on records with COPY_SEGMENT_STARTED. If it's reading such a message for the partition before the partition was assigned to this specific node it ignores the message, so skips the cache initialization and marks the partition as assigned. So reassignment is stuck since COPY_SEGMENT_STARTED is never properly processed.

      Expected behavior:
      The partitions should not be marked as assigned before the cache is initialized to be able to re-read COPY_SEGMENT_STARTED message and initialize the cache.


      Some notes:
      This is most probably happening when there are messages in a single metadata partition and the order of the messages does not correspond to the order of assignment. So the follower reads the COPY_SEGMENT_STARTED message, sees that the user partition is not yet assigned to this node, skips the message, and marks the user partition as assigned. On the next iteration, it resets to beginning ONLY the metadata partitions for user partitions that were not yet assigned, the rest of the metadata partitions it reads from the offset it remembers from the previous step, and that for some reason does not help. So that skipped COPY_SEGMENT_STARTED seems to be never re-read, so the metadata cache is not initialized.

      One solution can be not to track the last read offset for the metadata partition but instead, always reset them to the beginning if reassignment has changed. This seems not to bring any harm since the messages that were processed before will be just skipped. And this seems to allow the reassignment to finish properly.

      Draft PR https://github.com/apache/kafka/pull/15165


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              anatolypopov Anatolii Popov
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