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https://issues.apache.org/jira/browse/QUICKSTEP-28?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15507716#comment-15507716
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ASF GitHub Bot commented on QUICKSTEP-28:
-----------------------------------------

Github user asfgit closed the pull request at:

    https://github.com/apache/incubator-quickstep/pull/90


> Make multiple aggregations work on a common hash table
> ------------------------------------------------------
>
>                 Key: QUICKSTEP-28
>                 URL: https://issues.apache.org/jira/browse/QUICKSTEP-28
>             Project: Apache Quickstep
>          Issue Type: Improvement
>          Components: Expressions, Storage
>            Reporter: Rathijit Sen
>              Labels: performance
>
> Currently each aggregation operation uses a separate hash table. This has the 
> following disadvantages:
> * Multiple probes happen for the same key, once per hash table.
> * Space for keys is duplicated across hash tables.
> * Mutexes are acquired once per aggregation operation for each value.
> A more efficient design is to have a common hash table where the hash table 
> payload for each key is partitioned among multiple aggregation handles. 
> Changes are needed both to the aggregate and merge operations.
> Preliminary experiments suggest up to 3x speedup for TPC-H Q1 that has 8 
> aggregation operations.



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