Prasanth Jayachandran commented on HIVE-19578:

Int2ByteSortedMap is in fastutil. This dependency is 18MB jar. I am not sure if 
it be worth it to bring such a big dependency as this jar also has to be 
bundled with hive-exec. We discussed this during the initial HLL implementation 
that this 3rd party dependency is big and replaced Int2ByteSortedMap with java 
TreeMap. If performance becomes a bigger concern we can consider bringing the 
jar, I think for now we can stick on to TreeMap and add just the optimizations. 


> 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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