[PR] [Subscription] Fix WAL replay after leader failover [iotdb]

["Caideyipi (via GitHub)" <gi...@apache.org>]

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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Re: [PR] [Subscription] Fix WAL replay after leader failover [iotdb]

["jt2594838 (via GitHub)" <gi...@apache.org>]

jt2594838 merged PR #18474:
URL: https://github.com/apache/iotdb/pull/18474


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