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  1. Samza
  2. SAMZA-1384

Race condition with async commit affects checkpoint correctness

    Details

    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 0.13.1
    • Component/s: None
    • Labels:
      None

      Description

      tl;dr if any in-flight request updates the offsets between producer.flush() and offsetmanager.checkpoint() we could write a checkpoint for a message that did not yet go out over the wire and could subsequently fail.

      Consider two threads A and B. A is performing an async commit. B is an in-flight process(). The following sequence will cause data loss:
      A: TaskInstance.commit() begins
      A: producer.flush() is called // no new messages will go out in this batch

      B: producer.send() is called
      B: TaskCallback is invoked for the finished process()
      B: OffsetManager records the offset for the completed process()

      A: producer.flush() finishes
      A: checkpoint is written using the latest offsets from the OffsetManager. This INCLUDES the offset for the latest send, which has not yet gone out over the wire.
      A: TaskInstance.commit() finishes

      B: producer.send()->callback is invoked with an error. Send was unsuccessful, but has been checkpointed already.
      B: Exception is propagated and container fails
      Result: Container is restarted and starts from the last checkpoint.

      Note that this is only an issue when the commit() occurs concurrently with in-flight requests, so it doesn't affect the fully-synchronous mode or concurrent mode with synchronous commit().

      Proposed solution:
      Take a snapshot of the offsets in the OffsetManager at the beginning of commit(). Only checkpoint those offsets and nothing new that has been sent since the commit() started.

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              • Assignee:
                jmakes Jake Maes
                Reporter:
                jmakes Jake Maes
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                • Created:
                  Updated:
                  Resolved: