GitHub user jianqiao reopened 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 â 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
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commit 62b1742ef29bc8dea19d08fac6e0e04f45dc3f8a
Author: Jianqiao Zhu <[email protected]>
Date: 2017-01-13T00:41:17Z
Reorder output attribute order to improve copy performance.
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