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From jianqiao <...@git.apache.org>
Subject [GitHub] incubator-quickstep pull request #171: QUICKSTEP-68 Reorder intermediate rel...
Date Sun, 29 Jan 2017 20:02:39 GMT
GitHub user jianqiao opened a pull request:

    https://github.com/apache/incubator-quickstep/pull/171

    QUICKSTEP-68 Reorder intermediate relations'  attributes to improve copy performance.

    Currently, all the intermediate relations (i.e. temporary relations created during query
execution) have `SPLIT_ROW_STORE` layouts. One existing optimization that improves copy performance
for `SPLIT_ROW_STORE` layout is that, if two (or more) attributes are consecutive in both
the source relation and the destination relation, then we can memory-copy the attributes'
byte stream with just one `std::memcpy` call.
    
    This PR is a complementary improvement that it adjusts the ordering of the attributes
in the physical plan to maximize the opportunity of copying consecutive attributes – i.e.
to minimize the number of `std::memcpy` calls.
    
    This PR uses a simple greedy algorithm to reorder the attributes, which works well with
SSB/TPCH workloads. The algorithm may be further improved later.
    
    The feature can be turned on/off (default is **on**) with the `-reorder_columns` flag.

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

    $ git pull https://github.com/apache/incubator-quickstep reorder-attrs

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

    https://github.com/apache/incubator-quickstep/pull/171.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 #171
    
----
commit 2c1c0905b18e7ecd018a3a05b9db03fdf987720b
Author: Jianqiao Zhu <jianqiao@cs.wisc.edu>
Date:   2017-01-13T00:41:17Z

    Reorder output attribute order to improve copy performance.

----


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