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From "amit hadke (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-4147) Union All operator runs in a single fragment
Date Tue, 01 Dec 2015 03:20:10 GMT
amit hadke created DRILL-4147:
---------------------------------

             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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