Use POMergeJoin for Left Outer Join when join using 'merge'
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Key: PIG-1590
URL: https://issues.apache.org/jira/browse/PIG-1590
Project: Pig
Issue Type: Improvement
Components: impl
Affects Versions: 0.8.0
Reporter: Ashutosh Chauhan
Priority: Minor
C = join A by $0 left, B by $0 using 'merge';
will result in map-side sort merge join. Internally, it will translate to use
POMergeCogroup + ForEachFlatten. POMergeCogroup places quite a few restrictions
on its loaders (A and B in this case) which is cumbersome. Currently, only
Zebra is known to satisfy all those requirements. It will be better to use
POMergeJoin in this case, since it has far fewer requirements on its loader.
Importantly, it works with PigStorage. Plus, POMergeJoin will be faster then
POMergeCogroup + FE-Flatten.
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