[PR] [Subscription] Keep WAL iterator across bounded gap rounds [iotdb]

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

Caideyipi opened a new pull request, #18783:
URL: https://github.com/apache/iotdb/pull/18783

   ## Summary
   - Keep the subscription WAL iterator across bounded pending-gap replay rounds. Reopening it on every round forces `hasNext()` to scan the retained WAL prefix again before reaching the current cursor.
   - Advance the iterator's local lower bound with the existing writer-progress coverage guard. Seek, memory-blocked replay, and WAL visibility-gap recovery retain their explicit reset paths.
   - Extend the bounded-gap regression case to assert that five WAL entries are consumed over three rounds with one iterator creation and five reads.
   
   ## Evidence
   In the 28502 run, the subscription entry queue overflowed and the consumers received 5,365 of 5,500 expected table rows before their 120-second idle timeout. The independent follow-up CPU sample spent 27.02% of inclusive samples in `fillGapFromWAL` and 25.49% in `ProgressWALIterator.hasNext`. This change targets repeated scan work; the 135-row tail is not proven permanently lost.
   
   ## Safety
   - The WAL retention bound remains `min(committed, replay)`; no deletion rule changes.
   - `advanceTo` can skip an entire WAL file only when all writer progress in that file is covered. Uncovered follower entries remain available for sequential replay.
   
   ## Verification
   - `git diff --check origin/master...HEAD` passed.
   - Java formatting was applied with `mvn spotless:apply -pl iotdb-core/datanode` before the commit was ported to this branch.
   - Local tests were not run, as requested.
   


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Re: [PR] [Subscription] Keep WAL iterator across bounded gap rounds [iotdb]

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

Caideyipi closed pull request #18783: [Subscription] Keep WAL iterator across bounded gap rounds
URL: https://github.com/apache/iotdb/pull/18783


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