[PR] [client][fix] Deduplicate insertIfNotExists lookups with same key in same batch to prevent deadlock [fluss]

["Prajwal-banakar (via GitHub)" <gi...@apache.org>]

Prajwal-banakar opened a new pull request, #2907:
URL: https://github.com/apache/fluss/pull/2907

   
   
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   ### Purpose
   
   <!-- Linking this pull request to the issue -->
   Linked issue: close #2874
   
   <!-- What is the purpose of the change -->
   When `lookup.insert-if-not-exists=true` and `lookup.async=true`, multiple lookups for the same key can land in the same `LookupBatch` within a single drain cycle. The server acquires a row-level latch per key during insert — 
   two entries for the same key in one RPC batch cause a deadlock in the server-side handler, leaving `LookupQuery` futures never completed and hanging the `AsyncWaitOperator` indefinitely, resulting in a 60s timeout.
   
   This did not affect `async=false` because sync lookups execute sequentially via `.get()`, so the same key never appears twice in one drain cycle.
   
   ### Brief change log
   
   <!-- Please describe the changes made in this pull request and explain how they address the issue -->
   - In `LookupSender.sendLookupRequest`, when `insertIfNotExists=true`, duplicate lookups for the same key bytes within the same batch are detected using `ByteBuffer` key comparison. The duplicate's future is chained to the first lookup's future instead of being added to the RPC batch, ensuring  only one server-side entry is sent per unique key per drain cycle.
   ### Tests
   
   <!-- List UT and IT cases to verify this change -->
   - `Flink119TableSourceITCase#testLookupInsertIfNotExists` (existing test, previously flaky with `async=true`, now passes consistently with  `-Dsurefire.rerunFailingTestsCount=5`)
   ### API and Format
   
   <!-- Does this change affect API or storage format -->
   No API or storage format changes.
   ### Documentation
   
   <!-- Does this change introduce a new feature -->
   No new feature introduced. Bug fix only.


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Re: [PR] [client][fix] Deduplicate insertIfNotExists lookups with same key in same batch to prevent deadlock [fluss]

["Prajwal-banakar (via GitHub)" <gi...@apache.org>]

Prajwal-banakar commented on PR #2907:
URL: https://github.com/apache/fluss/pull/2907#issuecomment-4810711616

   @luoyuxia could you please help review this?


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