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From "Richard Ding (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (PIG-627) PERFORMANCE: multi-query optimization
Date Sat, 07 Mar 2009 02:01:00 GMT

    [ https://issues.apache.org/jira/browse/PIG-627?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679797#action_12679797
] 

rding edited comment on PIG-627 at 3/6/09 5:59 PM:
----------------------------------------------------------

This patch contains the enhanced split operator to support multi-store queries. It instroduces
a new MROperPlan adjuster that merges single-load mapper-only MapReduceOper to its predecesor
based on the (implicit) split boundary. The goal is to reduce the total number of MR jobs
for a given multi-query task.

This patch is for the multi query branch

      was (Author: rding):
    This patch contains the enhanced split operator to support multi-store queries. It instroduces
a new MROperPlan adjuster that merges single-load mapper-only MapReduceOper to its predecesor
based on the (implicit) split boundary. The goal is to reduce the total number of MR jobs
for a given multi-query task.
  
> PERFORMANCE: multi-query optimization
> -------------------------------------
>
>                 Key: PIG-627
>                 URL: https://issues.apache.org/jira/browse/PIG-627
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: types_branch
>            Reporter: Olga Natkovich
>             Fix For: types_branch
>
>         Attachments: file_cmds-0305.patch, multi-store-0303.patch, multi-store-0304.patch,
multiquery_0223.patch, multiquery_0224.patch, multiquery_0306.patch
>
>
> Currently, if your Pig script contains multiple stores and some shared computation, Pig
will execute several independent queries. For instance:
> A = load 'data' as (a, b, c);
> B = filter A by a > 5;
> store B into 'output1';
> C = group B by b;
> store C into 'output2';
> This script will result in map-only job that generated output1 followed by a map-reduce
job that generated output2. As the resuld data is read, parsed and filetered twice which is
unnecessary and costly. 

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