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From "Matei Zaharia (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4664) Parallelize job initialization
Date Fri, 27 Feb 2009 18:33:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4664?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12677450#action_12677450
] 

Matei Zaharia commented on HADOOP-4664:
---------------------------------------

No, go ahead and take it forward. Please note though that in my tests it didn't help much
without something like HADOOP-4372 as well.

> Parallelize job initialization
> ------------------------------
>
>                 Key: HADOOP-4664
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4664
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Matei Zaharia
>            Assignee: Matei Zaharia
>            Priority: Blocker
>             Fix For: 0.20.0
>
>         Attachments: parallel-job-init-v1.patch
>
>
> The job init thread currently initializes one job at a time. However, this is a lengthy
and partly IO-bound process because all of the job's block locations need to be resolved through
the namenode and a map of them needs to be built. It can take tens of seconds. As a result,
the cluster sometimes initializes jobs too slowly for full utilization to be achieved, if
there are many small jobs queued up. It would be better to have a pool of threads that initialize
multiple jobs in parallel. One thing to be careful of, however, is not causing deadlocks or
holding locks for too long in these threads.

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