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https://issues.apache.org/jira/browse/HIVE-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13611419#comment-13611419
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Gopal V commented on HIVE-4103:
-------------------------------
I'm following some commonly repeated wisdom here
http://stackoverflow.com/questions/2414105/why-is-it-a-bad-practice-to-call-system-gc/2414120#2414120
THe corner cases merely require -Xmx to be upped, but this slows down the
queries by 8-10%.
> Remove System.gc() call from the map-join local-task loop
> ---------------------------------------------------------
>
> Key: HIVE-4103
> URL: https://issues.apache.org/jira/browse/HIVE-4103
> Project: Hive
> Issue Type: Bug
> Reporter: Gopal V
> Assignee: Gopal V
> Priority: Minor
> Attachments: HIVE-4103.patch
>
>
> Hive's HashMapWrapper calls System.gc() twice within the
> HashMapWrapper::isAbort() which produces a significant slow-down during the
> loop.
> {code}
> 2013-03-01 04:54:28 The gc calls took 677 ms
> 2013-03-01 04:54:28 Processing rows: 200000 Hashtable size:
> 199999 Memory usage: 62955432 rate: 0.033
> 2013-03-01 04:54:31 The gc calls took 956 ms
> 2013-03-01 04:54:31 Processing rows: 300000 Hashtable size:
> 299999 Memory usage: 90826656 rate: 0.048
> 2013-03-01 04:54:33 The gc calls took 967 ms
> 2013-03-01 04:54:33 Processing rows: 384160 Hashtable size:
> 384160 Memory usage: 114412712 rate: 0.06
> {code}
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