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Posted to issues@quickstep.apache.org by "ASF GitHub Bot (JIRA)" <ji...@apache.org> on 2016/09/20 20:33:20 UTC
[jira] [Commented] (QUICKSTEP-28) Make multiple aggregations work
on a common hash table
[ https://issues.apache.org/jira/browse/QUICKSTEP-28?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15507716#comment-15507716 ]
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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