[I] [server] Leader-only rebalance may finish before new leader acknowledges NotifyLeaderAndIsr [fluss]

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

swuferhong opened a new issue, #3555:
URL: https://github.com/apache/fluss/issues/3555

   ### Search before asking
   
   - [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.
   
   
   ### Description
   
   ### Problem
   
   For leader-only rebalance, the coordinator is expected to execute leader migrations sequentially: the next task should not start until the current target leader has applied `NotifyLeaderAndIsr`.
   
   However, the current completion check can finish a leader-only rebalance task too early. `NotifyLeaderAndIsr` is sent to multiple replicas, and the coordinator may complete the task after receiving a successful response from a replica that is not the new leader, as long as the ZooKeeper leader has already changed to the target leader.
   
   This means the rebalance task can be marked completed before the new leader has acknowledged the request. For KV tables, this is risky because the leader-side KV state may not be ready yet.
   
   ### Expected Behavior
   
   For leader-only rebalance, a task should only be completed when:
   
   - the `NotifyLeaderAndIsr` result for the bucket succeeded
   - the response comes from the target new leader
   - the current leader is the target new leader
   
   In other words, completion should require `result.succeeded()` and `responseServerId == newLeader`.
   
   ### Root Cause
   
   The leader-only rebalance completion path only checked whether the current leader matched the target leader. It did not consider which tablet server returned the `NotifyLeaderAndIsr` response, nor whether the bucket-level result succeeded.
   
   
   ### Willingness to contribute
   
   - [ ] I'm willing to submit a PR!


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Re: [I] [server] Leader-only rebalance may finish before new leader acknowledges NotifyLeaderAndIsr [fluss]

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

wuchong closed issue #3555: [server] Leader-only rebalance may finish before new leader acknowledges NotifyLeaderAndIsr
URL: https://github.com/apache/fluss/issues/3555


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