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From "Pradeep Kamath (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-744) PERFORMANCE: Bag creation can be more efficiently handled in order by
Date Wed, 01 Apr 2009 20:39:13 GMT
PERFORMANCE: Bag creation can be more efficiently handled in order by
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                 Key: PIG-744
                 URL: https://issues.apache.org/jira/browse/PIG-744
             Project: Pig
          Issue Type: Improvement
    Affects Versions: 0.2.0
            Reporter: Pradeep Kamath
             Fix For: 0.3.0


Currently order by results in multiple map reduce jobs (2 or 3 depending on the script) of
which the last one does the actual ordering. In this last map reduce job, we create a bag
of values (each value being the entire tuple that is getting sorted) for each sort key(s)
using POPackage in the reduce phase. Then we turn around and flatten the bag in the foreach
following the package. So there is really no need for the bag. But to be generic and use the
existing operators, we can be more efficient by tagging the POPackage to create bags which
are backed by the Hadoop iterator itself. This way we do not create a bag by making a copy
of each tuple from the hadoop iterator. This should help both performance and scalability
by making better use of memory.

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