| From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
|---|---|
| To: | Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Corey Huinker <corey(dot)huinker(at)gmail(dot)com> |
| Cc: | Ashwin Agrawal <aagrawal(at)pivotal(dot)io>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Jeff Davis <pgsql(at)j-davis(dot)com> |
| Subject: | Re: Extracting only the columns needed for a query |
| Date: | 2020-01-31 17:52:09 |
| Message-ID: | CAAKRu_YHAqXdGrF2NiN68XQXw6_RBHZCPCaQcsY4qzWwuU5QZg@mail.gmail.com |
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| Lists: | pgsql-hackers |
I'm bumping this to the next commitfest because I haven't had a chance
to address the questions posed by Dmitry. I'm sure I'll get to it in
the next few weeks.
> I believe it would be beneficial to add this potential API extension
patch into
> the thread (as an example of an interface defining how scanCols could be
used)
> and review them together.
As for including some code that uses the scanCols, after discussing
off-list with a few folks, there are three options I would like to
pursue for doing this.
One option I will pursue is using the scanCols to inform the columns
needed to be spilled for memory-bounded hashagg (mentioned by Jeff
here [1]).
The second is potentially using the scanCols in the context of FDW.
Corey, would you happen to have any specific examples handy of when
this might be useful?
The third is exercising it with a test only but providing an example
of how a table AM API user like Zedstore uses the columns during
planning.
[1]
https://www.postgresql.org/message-id/e5566f7def33a9e9fdff337cca32d07155d7b635.camel%40j-davis.com
--
Melanie Plageman
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