[GitHub] Ngone51 commented on issue #23842: [SPARK-26927]Fix race condition may cause dynamic allocation not working

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Ngone51 commented on issue #23842: [SPARK-26927]Fix race condition may cause dynamic allocation not working
URL: https://github.com/apache/spark/pull/23842#issuecomment-468523250
 
 
   So, to make the solution more determined rather than basing on the assume `the late events for the executor will be correctly handled before the removal`, I have a new idea here:
   
   maintain `taskStartExecutorIds` and `removedExecutorIds` concurrently. 
   
   When we receive TaskSatrtEvent with executor id X, 
   
   * if X is in `removedExecutorIds`, indicating this TaskSatrtEvent is coming after ExecutorRemovedEvent, so we clear X in `removedExecutorIds`;
   
   * if X is not in `removedExecutorIds`, contrarily, we store X in `taskStartExecutorIds`.
   
   When we receive ExecutorRemovedEvent with executor id Y,
   
   * if Y is not in `taskStartExecutorIds`, indicating this ExecutorRemovedEvent is comming before TaskSatrtEvent, so we store Y in `removedExecutorIds`;
   
   * if Y is in `taskStartExecutorIds`, contrarily, we clear Y in `taskStartExecutorIds`;
   
   
   And the rest thing we need to care about is what if `taskStartExecutorIds` or `removedExecutorIds` is full ?
   Lets take `removedExecutorIds` for example. Hmmm, if we follow the solution above, I think it's extreamly impossible for `removedExecutorIds` to be full since we'll intermittently clear `removedExecutorIds`. But it may be still possible that `removedExecutorIds` to be full due to plenty of TaskStartEvents blocked for a long long time theoretically. If it really happens, I'd choose to fail the entire  ExecutorAllocationManager immediately.

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