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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-951) Reset parallelism to 1 for indexing job in MergeJoin
Date Thu, 17 Sep 2009 17:43:57 GMT

    [ https://issues.apache.org/jira/browse/PIG-951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12756654#action_12756654

Alan Gates commented on PIG-951:

I'll be reviewing this patch.

> Reset parallelism to 1 for indexing job in MergeJoin
> ----------------------------------------------------
>                 Key: PIG-951
>                 URL: https://issues.apache.org/jira/browse/PIG-951
>             Project: Pig
>          Issue Type: Bug
>          Components: impl
>            Reporter: Ashutosh Chauhan
>            Assignee: Ashutosh Chauhan
>         Attachments: pig-951.patch
> After sampling one tuple from every block, one reducer is used to sort the index entries
in reduce phase to produce sorted index to be used in actual join job. Thus, parallelism of
index job should be explictly set to 1. Currently, its not.
> Currently, this is a non-issue, since we don't allow any blocking operators in pipeline
before merge-join. However, later when we do allow blocking operators, then parallelism of
indexing job will be that of preceding blocking operator. Even then, job will complete successfully
because all tuple will go to only one reducer, because we are grouping on only one key "all".
However, it will waste cluster resources by starting all the extra reducers which get no data
and thus do nothing.

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