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From "Ari Rabkin (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3961) resource estimation works badly in some cases
Date Fri, 15 Aug 2008 21:59:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12623033#action_12623033
] 

Ari Rabkin commented on HADOOP-3961:
------------------------------------

Issue is a blocker, because in the case where maps have negligible output, but there's only
one reduce (e.g., sort validator), the reduce sometimes never gets placed.  

> resource estimation works badly in some cases
> ---------------------------------------------
>
>                 Key: HADOOP-3961
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3961
>             Project: Hadoop Core
>          Issue Type: Bug
>            Reporter: Ari Rabkin
>            Assignee: Ari Rabkin
>            Priority: Blocker
>
> The disk space estimation introduced in HADOOP-657 performs badly under some circumstances.
 In particular, if maps have very small output, the initial estimate of output size equals
input size throws everything off.
> Fix is to use a smaller initial estimate, and to update it appropriately.

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