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https://issues.apache.org/jira/browse/HIVE-10600?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matt McCline resolved HIVE-10600.
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Resolution: Duplicate
HIVE-12369
> optimize group by for GC
> ------------------------
>
> Key: HIVE-10600
> URL: https://issues.apache.org/jira/browse/HIVE-10600
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Matt McCline
>
> Quoting [~gopalv]:
> {noformat}
> So, something like a sum() GROUP BY will create a few hundred thousand
> AbstractAggregationBuffer objects all of which will suddenly go out of
> scope when the map.aggr flushes it down to the sort buffer.
> That particular GC collection takes forever because the tiny buffers take
> a lot of time to walk over and then they leave the memory space
> fragmented, which requires a compaction pass (which btw, writes to a
> page-interleaved NUMA zone).
> And to make things worse, the pre-allocated sort buffers with absolutely
> zero data in them take up most of the tenured regions causing these chunks
> of memory to be visited more and more often as they are part of the Eden
> space.
> {noformat}
> We need flat data structures to be GC friendly.
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