| From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
|---|---|
| To: | Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
| Cc: | tgl(at)sss(dot)pgh(dot)pa(dot)us, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Identity projection |
| Date: | 2012-12-14 11:41:25 |
| Message-ID: | 50CB1065.6050900@iki.fi |
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| Thread: | |
| Lists: | pgsql-hackers |
On 12.11.2012 12:07, Kyotaro HORIGUCHI wrote:
> Hello, This is new version of identity projection patch.
>
> Reverted projectionInfo and ExecBuildProjectionInfo. Identity
> projection is recognized directly in ExecGroup, ExecResult, and
> ExecWindowAgg. nodeAgg is reverted because I couldn't make it
> sane..
>
> The following is the result of performance test posted before in
> order to show the source of the gain.
Hmm, this reminds me of the discussion on removing useless Limit nodes:
http://archives.postgresql.org/pgsql-performance/2012-12/msg00127.php.
The optimization on Group, WindowAgg and Agg nodes doesn't seem that
important, the cost of doing the aggregation/grouping is likely
overwhelming the projection cost, and usually you do projection in
grouping/aggregation anyway. But makes sense for Result.
For Result, I think you should aim to remove the useless Result node
from the plan altogether. And do the same for useless Limit nodes.
- Heikki
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