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https://issues.apache.org/jira/browse/DRILL-4147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15402584#comment-15402584
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ASF GitHub Bot commented on DRILL-4147:
---------------------------------------
Github user jinfengni commented on a diff in the pull request:
https://github.com/apache/drill/pull/555#discussion_r73028431
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/UnionAllPrule.java
---
@@ -61,7 +61,8 @@ public void onMatch(RelOptRuleCall call) {
convertedInputList.add(convertedInput);
}
- traits =
call.getPlanner().emptyTraitSet().plus(Prel.DRILL_PHYSICAL).plus(DrillDistributionTrait.SINGLETON);
+ // distribution trait is set to ANY to allow Union-All to inherit
the distribution of its child
+ traits =
call.getPlanner().emptyTraitSet().plus(Prel.DRILL_PHYSICAL).plus(DrillDistributionTrait.ANY);
--- End diff --
Will it work by setting "ANY" in case inputs of union-all has different
distribution trait?
Let's say LHS has Hash-distribution(col1), RHS has Hash-distribution(co1,
col2), or Random distribution. What will union-all's distribution trait? Will
it use LHS, or RHS ?
> 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: Aman Sinha
>
> 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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