Caideyipi opened a new pull request, #18474:
URL: https://github.com/apache/iotdb/pull/18474
## Description
### Problem
After an IoTConsensus leader failover, the new leader can replay WAL entries
replicated from the former leader. These entries carry valid writer progress
but keep `searchIndex = -1` because they do not have a local search index.
Replay-start lookup treated an uncovered follower entry before the first
locally indexed entry as non-replayable and returned `LOCATE_MISS`. This
surfaced as subscription error 1904 when one DataNode went down in a replicated
cluster.
### Fix
- Use only non-negative local search indexes to choose the local replay
cursor.
- Keep replicated follower entries visible to `ProgressWALIterator`; writer
progress continues to deduplicate already committed entries.
- Preserve the recovery writer progress when the WAL contains only uncovered
follower entries.
- Add regression coverage for follower entries before a local lower bound
and for the follower-only boundary.
No client change is required for this case. With another provider available,
the existing consumer poll path marks the failed provider unavailable and
continues failover; an application may temporarily receive an empty poll
result, but it does not need a special retry for error 1904.
### Validation
- `mvn spotless:apply -pl iotdb-core/datanode`
- `mvn test -pl iotdb-core/datanode
"-Dtest=ConsensusPrefetchingQueueTest,ProgressWALIteratorTest,ConsensusPrefetchingQueueWalBackpressureTest"`
- 40 tests run, 0 failures, 0 errors, 1 existing conditional skip
- `mvn checkstyle:check -pl iotdb-core/datanode`
- `git diff --check`
<hr>
This PR has:
- [x] been self-reviewed.
- [x] added comments explaining the intent of the non-obvious replay
behavior.
- [x] added or updated unit tests to cover the changed code paths.
<hr>
##### Key changed/added classes
- `ConsensusPrefetchingQueue`
- `ConsensusPrefetchingQueueTest`
- `ProgressWALIteratorTest`
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