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https://issues.apache.org/jira/browse/MAPREDUCE-4946?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Siddharth Seth updated MAPREDUCE-4946:
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Resolution: Fixed
Fix Version/s: 0.23.7
2.0.3-alpha
Hadoop Flags: Reviewed
Status: Resolved (was: Patch Available)
Committed to trunk, branch-2 and branch-0.23. Thanks Jason
> Type conversion of map completion events leads to performance problems with
> large jobs
> --------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4946
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4946
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mr-am
> Affects Versions: 2.0.2-alpha, 0.23.5
> Reporter: Jason Lowe
> Assignee: Jason Lowe
> Priority: Critical
> Fix For: 2.0.3-alpha, 0.23.7
>
> Attachments: MAPREDUCE-4946-branch-0.23.patch, MAPREDUCE-4946.patch
>
>
> We've seen issues with large jobs (e.g.: 13,000 maps and 3,500 reduces) where
> reducers fail to connect back to the AM after being launched due to
> connection timeout. Looking at stack traces of the AM during this time we
> see a lot of IPC servers stuck waiting for a lock to get the application ID
> while type converting the map completion events. What's odd is that normally
> getting the application ID should be very cheap, but in this case we're
> type-converting thousands of map completion events for *each* reducer
> connecting. That means we end up type-converting the map completion events
> over 45 million times during the lifetime of the example job (13,000 * 3,500).
> We either need to make the type conversion much cheaper (i.e.: lockless or at
> least read-write locked) or, even better, store the completion events in a
> form that does not require type conversion when serving them up to reducers.
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