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https://issues.apache.org/jira/browse/KAFKA-9307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16997882#comment-16997882
]
Dhruvil Shah commented on KAFKA-9307:
-------------------------------------
Exception during step 6 that led to partial completion of become-follower
transition:
{code:java}
2019-12-12 03:11:56,320] ERROR [Transaction State Manager 3]: The metadata
cache for txn partition 41 has already exist with epoch 111 and 6 entries while
trying to add to it; this should not happen
(kafka.coordinator.transaction.TransactionStateManager) [2019-12-12
03:11:56,320] ERROR Uncaught exception in scheduled task
'load-txns-for-partition-__transaction_state-41' (kafka.utils.KafkaScheduler)
java.lang.IllegalStateException: The metadata cache for txn partition 41 has
already exist with epoch 111 and 6 entries while trying to add to it; this
should not happen at
kafka.coordinator.transaction.TransactionStateManager.addLoadedTransactionsToCache(TransactionStateManager.scala:369)
at
kafka.coordinator.transaction.TransactionStateManager$$anonfun$kafka$coordinator$transaction$TransactionStateManager$$loadTransactions$1$1.apply$mcV$sp(TransactionStateManager.scala:394)
at
kafka.coordinator.transaction.TransactionStateManager$$anonfun$kafka$coordinator$transaction$TransactionStateManager$$loadTransactions$1$1.apply(TransactionStateManager.scala:393)
at
kafka.coordinator.transaction.TransactionStateManager$$anonfun$kafka$coordinator$transaction$TransactionStateManager$$loadTransactions$1$1.apply(TransactionStateManager.scala:393)
at kafka.utils.CoreUtils$.inLock(CoreUtils.scala:251) at
kafka.utils.CoreUtils$.inWriteLock(CoreUtils.scala:259) at
kafka.coordinator.transaction.TransactionStateManager.kafka$coordinator$transaction$TransactionStateManager$$loadTransactions$1(TransactionStateManager.scala:392)
at
kafka.coordinator.transaction.TransactionStateManager$$anonfun$loadTransactionsForTxnTopicPartition$2.apply$mcV$sp(TransactionStateManager.scala:426)
at
kafka.utils.KafkaScheduler$$anonfun$1.apply$mcV$sp(KafkaScheduler.scala:114) at
kafka.utils.CoreUtils$$anon$1.run(CoreUtils.scala:63) at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at
java.util.concurrent.FutureTask.run(FutureTask.java:266) at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java)
at java.lang.Thread.run(Thread.java:748)
{code}
> Transaction coordinator could be left in unknown state after ZK session
> timeout
> -------------------------------------------------------------------------------
>
> Key: KAFKA-9307
> URL: https://issues.apache.org/jira/browse/KAFKA-9307
> Project: Kafka
> Issue Type: Bug
> Components: core
> Reporter: Dhruvil Shah
> Assignee: Dhruvil Shah
> Priority: Major
>
> We observed a case where the transaction coordinator could not load
> transaction state from __transaction-state topic partition. Clients would
> continue seeing COORDINATOR_LOAD_IN_PROGRESS exceptions until the broker
> hosting the coordinator is restarted.
> This is the sequence of events that leads to the issue:
> # The broker is the leader of one (or more) transaction state topic
> partitions.
> # The broker loses its ZK session due to a network issue.
> # Broker reestablishes session with ZK, though there are still transient
> network issues.
> # Broker is made follower of the transaction state topic partition it was
> leading earlier.
> # During the become-follower transition, the broker loses its ZK session
> again.
> # The become-follower transition for this broker fails in-between, leaving
> us in a partial leader / partial follower state for the transaction topic.
> This meant that we could not unload the transaction metadata. However, the
> broker successfully caches the leader epoch of associated with the
> LeaderAndIsrRequest.
> # Later, when the ZK session is finally established successfully, the broker
> ignores the become-follower transition as the leader epoch was same as the
> one it had cached. This prevented the transaction metadata from being
> unloaded.
> # Because this partition was a partial follower, we had setup replica
> fetchers. The partition continued to fetch from the leader until it was made
> part of the ISR.
> # Once it was part of the ISR, preferred leader election kicked in and
> elected this broker as the leader.
> # When processing the become-leader transition, the operation failed as we
> already had transaction metadata loaded at a previous epoch.
> # This meant that this partition was left in the "loading" state and we thus
> returned COORDINATOR_LOAD_IN_PROGRESS errors.
> # Broker restart fixed this partial in-memory state and we were able to
> resume processing for transactions.
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