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https://issues.apache.org/jira/browse/KAFKA-1382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13965456#comment-13965456
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Jun Rao commented on KAFKA-1382:
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Controller's update to isr will always succeed. It keeps re-reading the current
value in ZK and then does the conditional update. The leader's update to isr
has to fail if the previous update was made by the controller. Checking the
value itself will work for most cases, but may not cover 100%. It can happen
that the controller updated isr to the same value that the leader wants to
write. In this case, we still want to fail the update made by the leader.
> Update zkVersion on partition state update failures
> ---------------------------------------------------
>
> Key: KAFKA-1382
> URL: https://issues.apache.org/jira/browse/KAFKA-1382
> Project: Kafka
> Issue Type: Bug
> Reporter: Joel Koshy
>
> Our updateIsr code is currently:
> private def updateIsr(newIsr: Set[Replica]) {
> debug("Updated ISR for partition [%s,%d] to %s".format(topic,
> partitionId, newIsr.mkString(",")))
> val newLeaderAndIsr = new LeaderAndIsr(localBrokerId, leaderEpoch,
> newIsr.map(r => r.brokerId).toList, zkVersion)
> // use the epoch of the controller that made the leadership decision,
> instead of the current controller epoch
> val (updateSucceeded, newVersion) =
> ZkUtils.conditionalUpdatePersistentPath(zkClient,
> ZkUtils.getTopicPartitionLeaderAndIsrPath(topic, partitionId),
> ZkUtils.leaderAndIsrZkData(newLeaderAndIsr, controllerEpoch), zkVersion)
> if (updateSucceeded){
> inSyncReplicas = newIsr
> zkVersion = newVersion
> trace("ISR updated to [%s] and zkVersion updated to
> [%d]".format(newIsr.mkString(","), zkVersion))
> } else {
> info("Cached zkVersion [%d] not equal to that in zookeeper, skip
> updating ISR".format(zkVersion))
> }
> We encountered an interesting scenario recently when a large producer fully
> saturated the broker's NIC for over an hour. The large volume of data led to
> a number of ISR shrinks (and subsequent expands). The NIC saturation
> affected the zookeeper client heartbeats and led to a session timeout. The
> timeline was roughly as follows:
> - Attempt to expand ISR
> - Expansion written to zookeeper (confirmed in zookeeper transaction logs)
> - Session timeout after around 13 seconds (the configured timeout is 20
> seconds) so that lines up.
> - zkclient reconnects to zookeeper (with the same session ID) and retries
> the write - but uses the old zkVersion. This fails because the zkVersion
> has already been updated (above).
> - The ISR expand keeps failing after that and the only way to get out of it
> is to bounce the broker.
> In the above code, if the zkVersion is different we should probably update
> the cached version and even retry the expansion until it succeeds.
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