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From "Mridul Muralidharan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-1530) PIG Logical Optimization: Push LOFilter above LOCogroup
Date Sun, 01 Aug 2010 15:28:15 GMT

    [ https://issues.apache.org/jira/browse/PIG-1530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12894388#action_12894388
] 

Mridul Muralidharan commented on PIG-1530:
------------------------------------------

Cant edit comments .. to add to previous comment : 
To clarify my prev comment, a general pattern would not stop just at co-group, but at most
(if not all) operators which dont modify the relevant fields.

>  PIG Logical Optimization: Push LOFilter above LOCogroup
> --------------------------------------------------------
>
>                 Key: PIG-1530
>                 URL: https://issues.apache.org/jira/browse/PIG-1530
>             Project: Pig
>          Issue Type: New Feature
>          Components: impl
>            Reporter: Swati Jain
>            Assignee: Swati Jain
>            Priority: Minor
>             Fix For: 0.8.0
>
>
> Consider the following:
> {noformat}
> A = load '<any file>' USING PigStorage(',') as (a1:int,a2:int,a3:int);
> B = load '<any file>' USING PigStorage(',') as (b1:int,b2:int,b3:int);
> G = COGROUP A by (a1,a2) , B by (b1,b2);
> D = Filter G by group.$0 + 5 > group.$1;
> explain D;
> {noformat}
> In the above example, LOFilter can be pushed above LOCogroup. Note there are some tricky
NULL issues to think about when the Cogroup is not of type INNER (Similar to issues that need
to be thought through when pushing LOFilter on the right side of a LeftOuterJoin).
> Also note that typically the LOFilter in user programs will be below a ForEach-Cogroup
pair. To make this really useful, we need to also implement LOFilter pushed across ForEach.


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