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From "Amareshwari Sri Ramadasu (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-2131) Speculative execution should be allowed for reducers only
Date Tue, 08 Jan 2008 09:31:34 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-2131?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Amareshwari Sri Ramadasu updated HADOOP-2131:
---------------------------------------------

    Status: Patch Available  (was: Open)

Submiting after deprecating mapred.speculative.execution

> Speculative execution should be allowed for reducers only
> ---------------------------------------------------------
>
>                 Key: HADOOP-2131
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2131
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>         Environment: Hadoop job, map fetches data from external systems
>            Reporter: Srikanth Kakani
>            Assignee: Amareshwari Sri Ramadasu
>            Priority: Critical
>             Fix For: 0.16.0
>
>         Attachments: patch-2131.txt, patch-2131.txt
>
>
> Consider hadoop jobs where maps fetch data from external systems, and emit the data.
The reducers in this are identity reducers. The data processed by these jobs is huge. There
could be slow nodes in this cluster and some of the reducers run twice as slow as their counterparts.
This could result in a long tail. Speculative execution would help greatly in such cases.
However given the current hadoop, we have to select speculative execution for both maps and
reducers. In this case hurting the map performance as they are fetching data from external
systems thereby overloading the external systems.
> Speculative execution only on reducers would be a great way to solve this problem.

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