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From "Thejas M Nair (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-420) Limit on nothing functionality
Date Thu, 19 Nov 2009 14:47:39 GMT

    [ https://issues.apache.org/jira/browse/PIG-420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780011#action_12780011
] 

Thejas M Nair commented on PIG-420:
-----------------------------------

The idea proposed by Rekha seems to be better alternative for 'limit on nothing' . It would
be good to have something similar to C++ preprocessor macros . This way the "if debug" decisions
can be done at compile time, and there will not be any performance impact.

Pig could have some syntax to denote debug only sections of the pig script , something like
-
{code}
a = load 'file';
b = #IFDEF DEBUG { limit a, 100; } #ELSE { a; /*assuming we start supporting the syntax "b=a;"
*/}
c = filter b by $0 = 1;
#IFDEF DEBUG { store c into 'debug_file' ; }

{code}

> Limit on nothing functionality
> ------------------------------
>
>                 Key: PIG-420
>                 URL: https://issues.apache.org/jira/browse/PIG-420
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Anand Murugappan
>
> Pig 2.0 implements the limit feature but as a standalone statement. 
> Limit is very useful in debug mode where we could run queries on smaller amount of data
(faster and on fewer nodes) to iron out issues but in the production mode we would like to
run through all the data. It would be good to have a easy "switch" between debug and prod
mode using the limit statement without having to change the underlying code templates. Given
that LIMIT is a separate standalone statement it gets hard to parametrize the code. 
> For instance a query template might look like, 
> A = LOAD '...';
> B = LIMIT A $N;
> C = FOREACH B .... 
> In debug mode, we would like to set the variable $N to 100 but in prod mode we would
like to set it to a 'special value' that would not apply LIMIT and letting us run it on all
the data. 

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