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https://issues.apache.org/jira/browse/HIVE-14160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15367377#comment-15367377
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ASF GitHub Bot commented on HIVE-14160:
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GitHub user zhongdeyin opened a pull request:
https://github.com/apache/hive/pull/85
[HIVE-14160]Optimized group by within distinct data skew proplem
Jira issue: https://issues.apache.org/jira/browse/HIVE-14160
Modify GroupByOperator.endGroup() method, while keysCurrentGroup.size() is
greater than a threshold(hive.distinct.setsize.max), will new a HashSet instead
of clear set. Option hive.distinct.newset.max is the Maximum for getting new
hashset, beyond this threshold,will still execute hashset.clear(). This will
ensure task stability. User can set these two client parameters themselves.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/zhongdeyin/hive branch-1.1
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/hive/pull/85.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 #85
----
commit 390fb2e30d5043cd262ad73d3c1678a268c591e3
Author: zhongdeyin <zhong...@lenovo.com>
Date: 2016-07-08T07:38:14Z
Optimized group by within distinct data skew proplem
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> Reduce-task costs a long time to finish on the condition that the certain sql
> "select a,distinct(b) group by a" has been executed on the data which has
> skew distribution
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-14160
> URL: https://issues.apache.org/jira/browse/HIVE-14160
> Project: Hive
> Issue Type: Improvement
> Components: hpl/sql
> Affects Versions: 1.1.0
> Reporter: marymwu
>
> Reduce-task costs a long time to finish on the condition that the certain sql
> "select a,distinct(b) group by a" has been executed on the data which has
> skew distribution
> data scale: 64G
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