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From "Daniel Dai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PIG-483) PERFORMANCE: different strategies for large and small order bys
Date Mon, 04 Apr 2011 17:38:05 GMT

    [ https://issues.apache.org/jira/browse/PIG-483?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13015511#comment-13015511

Daniel Dai commented on PIG-483:

Here the focus is one single reduce not the size of data. Currently when doing sorting, Pig
will sample the data in the first map-reduce job, then doing the sort in the second. However,
If we detects order by only use one reduce, sampling is not necessary.

> PERFORMANCE: different strategies for large and small order bys
> ---------------------------------------------------------------
>                 Key: PIG-483
>                 URL: https://issues.apache.org/jira/browse/PIG-483
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 0.2.0
>            Reporter: Olga Natkovich
>              Labels: gsoc2011
> Currently pig always does a multi-pass order by where it first determines a distribution
for the keys and then orders in a second pass.  This avoids the necessity of having a single
reducer.  However, in cases where the data is small enough to fit into a single reducer, this
is inefficient.  For small data sets it would be good to realize the small size of the set
and do the order by in a single pass with a single reducer.
> This is a candidate project for Google summer of code 2011. More information about the
program can be found at http://wiki.apache.org/pig/GSoc2011

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