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From jianqiao <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #177: Reduce the number of group-by attribu...
Date Thu, 02 Feb 2017 20:25:14 GMT
GitHub user jianqiao opened a pull request:

    https://github.com/apache/incubator-quickstep/pull/177

    Reduce the number of group-by attributes by pulling tables up aggregation.

    This PR implements an optimization (physical plan transformation) that pulls a table up
an aggregation if many of that table's attributes serve as group-by attributes in the aggregation.
We do the optimization because it is relatively slow to aggregate with a large set of group-by
attributes, as well as to avoid copying the table's many attributes all the way up a chain
of operators.
    
    For example, let `R` be a relation with `PRIMARY KEY x` and attributes `y`, `z`. Let `S`
be a relation with `FOREIGN KEY u` refering to `R.x` and attribute `v`. Then the optimization
rule will transform the physical plan:
    
    ```
    Aggregate(
      [input relation]: HashJoin(
                          [probe relation]: S
                          [build relation]: R
                          [join expression]: S.u = R.x
                          [project attributes]: v, x, y, z
                        )
      [aggregate expression]: SUM(v) AS sum_v
      [group-by attributes]: x, y, z
    )
    ``` 
    into:
    ```
    HashJoin(
      [probe relation]: Aggregate(
                          [input relation]: S
                          [aggregate expression]: SUM(v) AS sum_v
                          [group-by attribute]: u
                        ) AS T
      [build relation]: R
      [join expression]: T.u = R.x
      [project attributes]: sum_v, x, y, z
    )
    ```
    
    This optimization improves the performance of TPC-H Q10 from ~13s to ~5.7s, with scale
factor 100 on a cloudlab machine.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/apache/incubator-quickstep reduce-group-by-attrs

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/incubator-quickstep/pull/177.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 #177
    
----
commit 83d1b592445eb27ad34d56ded14618b019bdd11d
Author: Jianqiao Zhu <jianqiao@cs.wisc.edu>
Date:   2017-01-30T00:36:14Z

    Reduce the number of group-by attributes by pulling tables up aggregations

----


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