arnabnandy7 opened a new pull request, #22864:
URL: https://github.com/apache/kafka/pull/22864
Fixes KAFKA-20731.
`DefaultStateUpdater` could call the non-idempotent
`ChangelogReader#transitToUpdateStandby` method while the changelog reader was
already in `STANDBY_UPDATING`. This could happen after all updating standby
tasks were paused or removed because the empty-task state did not transition
the reader back to `ACTIVE_RESTORING`. Adding or resuming a standby task
afterward attempted the standby transition again, throwing an
`IllegalStateException` and terminating the state updater thread.
This change centralizes changelog reader state transitions in
`DefaultStateUpdater` and enforces the following invariants:
- When there are no updating tasks, the reader is in `ACTIVE_RESTORING`.
- When only standby tasks are updating, the reader transitions to
`STANDBY_UPDATING` only if it is currently restoring active tasks.
- The existing non-idempotent contract and defensive exception in
`StoreChangelogReader#transitToUpdateStandby` remain unchanged.
The transition helper is invoked after task additions, resumptions, pauses,
removals, failures, and active restoration completion so that the reader state
remains consistent with the updating task set.
The `DefaultStateUpdaterTest` changelog reader mock now models the actual
reader state transitions. This allows the standby pause/resume regression test
to fail if `transitToUpdateStandby` is invoked twice without an intervening
transition back to active restoration.
Testing:
```
gradle streams:test \
--tests
org.apache.kafka.streams.processor.internals.DefaultStateUpdaterTest \
--no-daemon \
--console=plain
```
All 87 `DefaultStateUpdaterTest` tests passed. The test execution also
completed `checkstyleMain`, `checkstyleTest`, and `spotbugsMain` successfully.
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