Matthias J. Sax created KAFKA-20893:
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Summary: KafkaStreams incorrectly reports task-offsets (ie state)
for non-existing (previously owned) in-memory stores to the task assignor
Key: KAFKA-20893
URL: https://issues.apache.org/jira/browse/KAFKA-20893
Project: Kafka
Issue Type: Bug
Components: streams
Affects Versions: 4.3.0
Reporter: Matthias J. Sax
Fix For: 4.4.0, 4.3.2
KIP-1035 replace the local state directory .checkpoint files with persistent
state store internal offset tracking, plus an in-memory offsets cache inside
StateDirectory. However, the cache is incorrectly populated with in-memory
store offsets, while it should only contain persistent store offsets.
After a task (with an in-memory) store is closed (and the in-memory state is
gone), these offset are still in the in-memory cache, and might get reported to
the task-assignor during a rebalance, which the task assignor would interpret
as "existing local state", even if there is none. This may leads to incorrect
task placement decisions.
The bug can only hit if a task has both an in-memory store and persisted store,
so by itself it should hit not too frequently, as most app either have all
in-memory or all persistent (even if `suppress()` which is only available
in-memory elevate the problem).
However, with the recent changes via KIP-1071 (not release yet), this bug will
be elevated and thus it should be fixed before AK 4.4 gets released, by
ensuring that in-memory offsets are never added to the cache in the first place.
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