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From "Richard Ding (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-627) PERFORMANCE: multi-query optimization
Date Mon, 23 Mar 2009 20:13:50 GMT

     [ https://issues.apache.org/jira/browse/PIG-627?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Richard Ding updated PIG-627:
-----------------------------

    Attachment: multiquery-phase2_0323.patch

Thanks for reviewing the patch.

In MultiQueryOptimizer:

    * what about mr not being map only and with mr splittee? - is this not handled for now?

    _Yeah. There are two cases where splittees will not be merged into splitter: (1) splitter
is not map only and splittee has reducer, and (2) splittee has multiple roots (loads)_

    * Is the single mapper case and the single map-reduce case when the script has an explicit
store 'file' and load 'file' - if  this is so, then in mergeOnlyMapperSplittee() and mergeOnlyMapReduceSplittee(),
the store is removed - shouldn't the store remain?

    _Explicit store/load combination in a script is transformed into an implicit split, hence
the store remains_

    * There is common code in mergeOnlyMapperSplittee() and meregOnlyMapReduceSplittee() which
should be moved to a function to reduce the code duplication.

    _Fixed_

Just want to confirm that the multi query optimization is only for map reduce mode - since
the optimizer is being called in  MapReduceLauncher

   _Yes_

In POForEach when there is POStatus.STATUS_ERR, it is returned to the caller. I noticed that
in POSplit, it causes an exception - I think it should return the error whhic would later
be caught in the map() or reduce() - a test to make sure errors do get caught and cause failures
would be good.

   _Fixed_

spawnChildWalker() of ReverseDependencyOrderWalker should return an instance of ReverseDependencyWalker.

   _Fixed_



> PERFORMANCE: multi-query optimization
> -------------------------------------
>
>                 Key: PIG-627
>                 URL: https://issues.apache.org/jira/browse/PIG-627
>             Project: Pig
>          Issue Type: Improvement
>    Affects Versions: 1.0.0
>            Reporter: Olga Natkovich
>         Attachments: file_cmds-0305.patch, multi-store-0303.patch, multi-store-0304.patch,
multiquery-phase2_0313.patch, multiquery-phase2_0323.patch, multiquery_0223.patch, multiquery_0224.patch,
multiquery_0306.patch, multiquery_explain_fix.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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