[jira] [Created] (PIG-4885) Turn off union optimizer if there is PARALLEL clause in union in Tez

["Rohini Palaniswamy (JIRA)" <ji...@apache.org>]

Rohini Palaniswamy created PIG-4885:
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             Summary: Turn off union optimizer if there is PARALLEL clause in union in Tez
                 Key: PIG-4885
                 URL: https://issues.apache.org/jira/browse/PIG-4885
             Project: Pig
          Issue Type: Improvement
            Reporter: Rohini Palaniswamy
            Assignee: Rohini Palaniswamy
             Fix For: 0.16.0


In mapreduce, if PARALLEL clause was specified on UNION it was ignored as it was a map operation and split size was used. In Tez, when union optimizer is turned off it is a reduce side operation and we should let user control parallelism instead of relying on just auto-parallelism. This is specifically useful when user needs to control the number of output files.

data = UNION A, B, C, D, E, F, G, H, I, J;
store data;

In the above case instead of manually controlling parallelism of A to J aliases to achieve desired parallelism the UNION clause can specify the desired parallelism using PARALLEL. i.e

data = UNION A, B, C, D, E, F, G, H, I, J PARALLEL 50;

This only works today if we set pig.tez.opt.union=false. We should automatically and selectively turn off union optimization for those unions that have PARALLEL clause.



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