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

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.16.0
• Hadoop Flags: Reviewed
• Assignee: Rohini Palaniswamy
• Reporter: Rohini Palaniswamy
• Created: 03/May/16 22:53
• Updated: 08/Jun/16 20:48
• Resolved: 23/May/16 22:38

Description

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.