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From "David Bowen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1105) Reducers don't make "progress" while iterating through values
Date Mon, 02 Apr 2007 16:10:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12486058

David Bowen commented on HADOOP-1105:

I don't think it is useful to use volatile in these two cases:

  private volatile Progress taskProgress = new Progress();  
  private volatile Counters counters = new Counters(); 

These would be useful if one thread was assigning to  the variables taskProgress and counters,
and another reading them.  What we have instead is one thread calling updater methods on the
objects, and another calling getters.

I think the threading issues need to be handled in the objects themselves.  Counters already
aims to be thread-safe.  If you don't want to put synchroniztion in Progress, you might want
to make its status, progress and currentPhase fields volatile.

> Reducers don't make "progress" while iterating through values
> -------------------------------------------------------------
>                 Key: HADOOP-1105
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1105
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.12.0
>            Reporter: Owen O'Malley
>         Assigned To: Owen O'Malley
>             Fix For: 0.12.3
>         Attachments: 1105.patch, 1105.patch
> Reduces make progress when they go to a new key, but not when they read the next value,
which could cause reduces to time out when they have a lot of values for the same key.

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