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https://issues.apache.org/jira/browse/DRILL-4147?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15402513#comment-15402513
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ASF GitHub Bot commented on DRILL-4147:
---------------------------------------
Github user sudheeshkatkam commented on a diff in the pull request:
https://github.com/apache/drill/pull/555#discussion_r73022403
--- Diff: exec/java-exec/src/test/java/org/apache/drill/TestUnionAll.java
---
@@ -32,6 +34,9 @@
public class TestUnionAll extends BaseTestQuery{
private static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(TestUnionAll.class);
+ private static final String sliceTargetSmall = "alter session set
`planner.slice_target` = 1";
+ private static final String sliceTargetDefault = "alter session set
`planner.slice_target` = " + ExecConstants.SLICE_TARGET_DEFAULT;
--- End diff --
```private static final String sliceTargetDefault = "RESET
`planner.slice_target`"; ```
> 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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