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From "David Ciemiewicz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-777) Code refactoring: Create optimization out of store/load post processing code
Date Tue, 28 Apr 2009 14:42:30 GMT

    [ https://issues.apache.org/jira/browse/PIG-777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12703659#action_12703659

David Ciemiewicz commented on PIG-777:

This seems like it could be useful but I don't understand the full issue as a user.

I often want to compute intermediate summaries, store them, and then continue computation.

{code}A = load ...
store D into ...
E = group D by ...
store H into ...{code}

The problem I encountered in earlier versions of Pig was that to PREVENT two executions of
A thru D, I had to introduce a load step before E:

{code}A = load ...
store D into ...
D = load ...
E = group D by ...
store H into ...{code}

It's great that you will be introducing code that possibly eliminates D = load in the execution.

However, is anything being done so that I don't need to introduce D = load in the first place?

> Code refactoring: Create optimization out of store/load post processing code
> ----------------------------------------------------------------------------
>                 Key: PIG-777
>                 URL: https://issues.apache.org/jira/browse/PIG-777
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Gunther Hagleitner
> The postProcessing method in the pig server checks whether a logical graph contains stores
to and loads from the same location. If so, it will either connect the store and load, or
optimize by throwing out the load and connecting the store predecessor with the successor
of the load.
> Ideally the introduction of the store and load connection should happen in the query
compiler, while the optimization should then happen in an separate optimizer step as part
of the optimizer framework.

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