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https://issues.apache.org/jira/browse/KAFKA-19996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18101082#comment-18101082
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Yunseop Eom commented on KAFKA-19996:
-------------------------------------
PR opened: https://github.com/apache/kafka/pull/23024
Prevented premature ISR expansion under min ISR by requiring the follower to
satisfy the existing caught-up check, while preserving leader-epoch expansion
when the partition is not under min ISR. Added regression coverage for a
follower that reaches the HWM but remains behind the leader LEO.
Validation: PartitionTest (87 tests) passed and static checks passed. Full
:core:check ran 3,383 tests with unrelated timing-sensitive failures in
DynamicConnectionQuotaTest and SocketServerTest; the changed-path test passed
and the former passed in isolation.
Status: PR open and awaiting review.
> The conflicts between ExpandIsr and ShrinkIsr
> ---------------------------------------------
>
> Key: KAFKA-19996
> URL: https://issues.apache.org/jira/browse/KAFKA-19996
> Project: Kafka
> Issue Type: Bug
> Reporter: Calvin Liu
> Priority: Major
>
> Thanks to [~mjd95] to report the following issue.
> In the Partition.scala, the condition for the ISR expand and shrink does not
> match, which can cause a follower flapping in and out of ISR when:
> # The partition is under min-isr which means the HWM can't advance.
> # The replication is slow.
> # The follower is far behind the LEO, but it is at/above the HWM.
> Due to the "conflict" between the ISR expand and shrink:
> * Shrink ISR, attempted on a schedule, triggers if the follower's LEO has
> not recently caught up with the leader's LEO which takes the last caught up
> time into the consideration.
> {code:java}
> /**
> * Returns true when the replica is considered as "caught-up". A replica is
> * considered "caught-up" when its log end offset is equals to the log end
> * offset of the leader OR when its last caught up time minus the current
> * time is smaller than the max replica lag.
> */
> public boolean isCaughtUp(
> long leaderEndOffset,
> long currentTimeMs,
> long replicaMaxLagMs) {
> return leaderEndOffset == logEndOffset() || currentTimeMs -
> lastCaughtUpTimeMs <= replicaMaxLagMs;
> } {code}
>
> * Expand ISR, attempted on processing follower fetch, triggers if the
> follower's LEO caught up with the leader's HWM in this fetch which only
> consider whether the replica reaches the HWM.
> {code:java}
> private def isFollowerInSync(followerReplica: Replica): Boolean = {
> leaderLogIfLocal.exists { leaderLog =>
> val followerEndOffset = followerReplica.stateSnapshot.logEndOffset
> followerEndOffset >= leaderLog.highWatermark &&
> leaderEpochStartOffsetOpt.exists(followerEndOffset >= _)
> }
> } {code}
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