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https://issues.apache.org/jira/browse/HIVE-19578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16478651#comment-16478651
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Prasanth Jayachandran commented on HIVE-19578:
----------------------------------------------
Ran a quick benchmark with following scenarios
{code:java}
testHLLAddHive - Current Hive implementation that uses TreeMap for HLL Sparse
Register
testHLLAddInt2ByteSortedMap - TreeMap replaced with Int2ByteSortedMap for HLL
Sparse Regsiter
testHLLAddInt2ByteSortedMapPlusOpt - Int2ByteSortedMap + branch optimizations
in HLL add() inner loop{code}
{code:java}
Benchmark Mode Cnt Score Error Units
HyperLogLogAdd.testHLLAddInt2ByteSortedMapPlusOpt avgt 10 12.773 ± 0.382 ns/op
HyperLogLogAdd.testHLLAddInt2ByteSortedMap avgt 10 25.675 ± 0.439 ns/op
HyperLogLogAdd.testHLLAddHive avgt 10 37.559 ± 0.488
ns/op{code}
> HLL merges tempList on every add
> --------------------------------
>
> Key: HIVE-19578
> URL: https://issues.apache.org/jira/browse/HIVE-19578
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Prasanth Jayachandran
> Priority: Major
> Attachments: Screen Shot 2018-05-16 at 15.29.12 .png
>
>
> See comments on HIVE-18866; this has significant perf overhead after the
> even bigger overhead from hashing is removed. !Screen Shot 2018-05-16 at
> 15.29.12 .png!
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