Grokbase Groups Pig dev November 2007
FAQ
setting parallel from grunt via set command
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Key: PIG-16
URL: https://issues.apache.org/jira/browse/PIG-16
Project: Pig
Issue Type: Improvement
Components: grunt
Reporter: Olga Natkovich
Priority: Minor


I'd like to propose a different model which uses the grunt "set" option and/or a command line option which sets reduce
parallelism to the be true and automatic.

set reduce_parallelism TRUE
set reduce_parallelism FALSE [Default - BTW, why is this the default?]

This way I won't have to update my script every single time I try playing with -D"hod=-m N", parallelism for reduce
statements will default, appropriately, to 2*(N-1).

Alternatively, could I just specify PARALLEL with no value or PARALLEL DEFAULT; And any time I needed to force reduce
to be single job, I could write PARALLEL 1.

Basically, this whole thing tripped me up for a long time and I just haven't understood if there is a really good
reason to not make parallelism.

I guess it might be if you have aggregation functions that do not parallelize.

If this is the case, then it seems to me that this should be detectable automagically based on whether the function is
a vanilla EvalFunction or if it is an AlgebraicFunction.


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