[jira] [Resolved] (MAPREDUCE-2047) reduce overhead of findSpeculativeTask

["Allen Wittenauer (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-2047?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Allen Wittenauer resolved MAPREDUCE-2047.
-----------------------------------------

    Resolution: Incomplete

Spec exec got a major overhaul since then. Closing this as stale.

> reduce overhead of findSpeculativeTask
> --------------------------------------
>
>                 Key: MAPREDUCE-2047
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2047
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobtracker
>         Environment: hadoop-20 with HADOOP-2141
>            Reporter: Joydeep Sen Sarma
>            Assignee: Joydeep Sen Sarma
>         Attachments: 2047.3.patch, mapreduce-2047.1.patch, mapreduce-2047.2.patch
>
>
> We are bottlenecked (in the JT) on the jobtracker lock and calls to findSpeculativeTask frequently show up as one of the top routines (by time) called holding this lock.
> this routine calls canBeSpeculated() and hasRunOnMachine() for each task in a candidate job. Both these routines are reasonably expensive when invoked repeatedly  for thousands of tasks. The top candidates for speculation from a job only need to be refreshed periodically (and not once every heartbeat) - and we can can avoid most of these invocations this way.



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