hadoop-mapreduce-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5211) Reducer intermediate files can collide during merge
Date Wed, 08 May 2013 23:29:16 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652508#comment-13652508

Arun C Murthy commented on MAPREDUCE-5211:

+1 for the branch-0.23 patch.

Looks like this existed forever in trunk and got accidentally fixed by MAPREDUCE-2264 which
introduced CompressAwarePath which extends Path i.e. with a correct impl of toString - hence
the bug in MapOutput.toString got fixed accidentally.

However, the fix in trunk is truly accidental, and we'll get paths which have the suffix ".merge"
for each level of merge etc. repeated.

So, we should apply a similar fix to trunk too.

> Reducer intermediate files can collide during merge
> ---------------------------------------------------
>                 Key: MAPREDUCE-5211
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5211
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 0.23.7
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>            Priority: Critical
>         Attachments: MAPREDUCE-5211.branch-0.23.patch
> The OnDiskMerger.merge method constructs an output path that is not unique to a reduce
attempt, and as a result can result in a file collision with other reducers from the same
app that are running on the same node.  In addition the name of the output file is based on
MapOutput.toString which may not be unique in light of multi-pass merges on disk since the
mapId will be null and the basename ends up as "MapOutput(null, DISK)"

This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira

View raw message