amit hadke created DRILL-4147:
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Summary: Union All operator runs in a single fragment
Key: DRILL-4147
URL: https://issues.apache.org/jira/browse/DRILL-4147
Project: Apache Drill
Issue Type: Bug
Reporter: amit hadke
A User noticed that running select from a single directory is much faster than
union all on two directories.
(https://drill.apache.org/blog/2014/12/09/running-sql-queries-on-amazon-s3/#comment-2349732267)
It seems like UNION ALL operator doesn't parallelize sub scans (its using
SINGLETON for distribution type). Everything is ran in single fragment.
We may have to use SubsetTransformer in UnionAllPrule.
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