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From "Stas Levin (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (BEAM-2789) Watermarks can become unavailable for executors while it's updated with new values
Date Tue, 22 Aug 2017 12:32:00 GMT

     [ https://issues.apache.org/jira/browse/BEAM-2789?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Stas Levin updated BEAM-2789:
-----------------------------
    Summary: Watermarks can become unavailable for executors while it's updated with new values
 (was: Watermark can become unavailable for executors while it's updated with new values)

> Watermarks 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.
> To overcome this in tests, a workaround which assumes a single JVM setting is used. In
such a setting the watermark values are stored in a static member, accessible by both the
driver and the executors, bypassing the {{BlockManager#putSingle(...)}} {{BlockManager#removeBlock(...)}}
APIs.



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