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From "Marco Nicosia (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1336) turn on speculative execution by defaul
Date Sat, 15 Dec 2007 06:28:43 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1336?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Marco Nicosia updated HADOOP-1336:
----------------------------------


At the risk of stirring up closed issues, are we sure this is the correct choice? We've been
keeping speculative execution off on our clusters, and recently accidentally turned it on.
Drama ensued. The way I see it, there are two scenarios for users who don't know about speculative
execution. Either it's off by default, and it's no problem to anyone, or it's on by default,
and a subset are bewildered by Hadoop's "odd" behavior. This is a support burden.

The only reason to have it on by default (I think?) is to improve performance across the board.
But this is by far not the only solution to affect performance, so we are doing significant
user auditing regardless. If our less-efficient users can take advantage of speculative execution
for their jobs, they will. I think, since some knowledge of speculative execution is good
before enabling it, it's better used as part of the optimization process, rather than making
it a default of the framework.


> turn on speculative execution by defaul
> ---------------------------------------
>
>                 Key: HADOOP-1336
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1336
>             Project: Hadoop
>          Issue Type: Task
>          Components: mapred
>    Affects Versions: 0.12.3
>            Reporter: Owen O'Malley
>            Assignee: Owen O'Malley
>             Fix For: 0.14.0
>
>         Attachments: spec-exec.patch
>
>
> Now that speculative execution is working again, we should enable it by default.

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