GitHub user jianqiao opened a pull request:
https://github.com/apache/incubator-quickstep/pull/106
Improve StarSchemaSimpleCostModel to provide better group cardinality
estimation for aggregations.
This PR revises `StarSchemaSimpleCostModel` to provide better group
cardinality estimation for aggregations. This information will be used by a
subsequent PR from Harshad to decide when to use _partitioned hash tables_.
The estimation relies on the _number of distinct values_ statistic of each
group-by attribute, which can be gathered by running `\analyze` command on the
corresponding table.
This PR does not affect the query plans for SSB queries. It changes some of
the TPC-H query plans (and a subsequent `LIPFilter` PR will bring more changes
to TPC-H query plans).
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/apache/incubator-quickstep
estimate-num-distinct-values
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-quickstep/pull/106.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #106
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commit ad1f8c406954778d332f02b680e08e0118727436
Author: Jianqiao Zhu <[email protected]>
Date: 2016-10-04T04:58:30Z
Improve StarSchemaSimpleCostModel to provide closer estimation of number of
groups for hash aggregation.
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