Stanislav Kozlovski created KAFKA-10301:
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Summary: RemoteReplicasMap can be empty in certain race conditions
Key: KAFKA-10301
URL: https://issues.apache.org/jira/browse/KAFKA-10301
Project: Kafka
Issue Type: Bug
Reporter: Stanislav Kozlovski
Assignee: Stanislav Kozlovski
In Partition#updateAssignmentAndIsr, we would previously update the
`partition#remoteReplicasMap` by adding the new replicas to the map and then
removing the old ones
([source]([https://github.com/apache/kafka/blob/7f9187fe399f3f6b041ca302bede2b3e780491e7/core/src/main/scala/kafka/cluster/Partition.scala#L657)]
During a recent refactoring, we changed it to first clear the map and then add
all the replicas to it
([source]([https://github.com/apache/kafka/blob/2.6/core/src/main/scala/kafka/cluster/Partition.scala#L663]))
While this is done in a write lock (`inWriteLock(leaderIsrUpdateLock)`), not
all callers that access the map structure use a lock. Some examples:
- Partition#updateFollowerFetchState
- DelayedDeleteRecords#tryComplete
- Partition#getReplicaOrException - called in `checkEnoughReplicasReachOffset`
without a lock, which itself is called by DelayedProduce. I think this can fail
a `ReplicaManager#appendRecords` call.
While we want to polish the code to ensure these sort of race conditions become
harder (or impossible) to introduce, it sounds safest to revert to the previous
behavior given the timelines regarding the 2.6 release. Jira X tracks that.
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