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https://issues.apache.org/jira/browse/DRILL-4147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15036014#comment-15036014
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ASF GitHub Bot commented on DRILL-4147:
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GitHub user hsuanyi opened a pull request:
https://github.com/apache/drill/pull/288
DRILL-4147: Change UnionPrel's DrillDistributionTrait to be ANY to al…
…low Union-All to be done in parallel
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/hsuanyi/incubator-drill DRILL-4147
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/drill/pull/288.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #288
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commit 9f31a4c04c2cb219237519070b35d5fae3010908
Author: Hsuan-Yi Chu <[email protected]>
Date: 2015-12-02T00:46:51Z
DRILL-4147: Change UnionPrel's DrillDistributionTrait to be ANY to allow
Union-All to be done in parallel
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> 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
> Assignee: Sean Hsuan-Yi Chu
>
> 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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