[jira] [Created] (BEAM-2789) Watermark can become unavailable for executors while it's updated with new values

["Stas Levin (JIRA)" <ji...@apache.org>]

Stas Levin created BEAM-2789:
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             Summary: Watermark can become unavailable for executors while it's updated with new values
                 Key: BEAM-2789
                 URL: https://issues.apache.org/jira/browse/BEAM-2789
             Project: Beam
          Issue Type: Bug
          Components: runner-spark
    Affects Versions: 2.0.0, 2.1.0
            Reporter: Stas Levin
            Assignee: Amit Sela


The watermark is updated by the driver like so:

{code:java}
blockManager.removeBlock(WATERMARKS_BLOCK_ID, true);
blockManager.putSingle(WATERMARKS_BLOCK_ID, newValues, StorageLevel.MEMORY_ONLY(), 
true);
{code}

However, these operations are neither synchronous nor atomic, so if an executor requests the watermark values before they are actually put but after they have been removed, it may get a {{null}} as a response, which will make it default to negative infinity as the watermark. This can result in an erroneous results.



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