Re: Hybrid Hash/Nested Loop joins and caching results from subplans

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: Hybrid Hash/Nested Loop joins and caching results from subplans
Date: 2020-11-05 22:12:33
Message-ID: CAApHDvoj_sH1H3JVXgHuwnxf1FQbjRVOqqgxzOgJX13NiA9-cg@mail.gmail.com
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On Mon, 2 Nov 2020 at 20:43, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> On Tue, 20 Oct 2020 at 22:30, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> I did some further tests this time with some tuple deforming. Again,
> it does seem that v9 is slower than v8.
>
> Graphs attached
>
> Looking at profiles, I don't really see any obvious reason as to why
> this is. I'm very much inclined to just pursue the v8 patch (separate
> Result Cache node) and just drop the v9 idea altogether.

Nobody raised any objections, so I'll start taking a more serious look
at the v8 version (the patch with the separate Result Cache node).

One thing that I had planned to come back to about now is the name
"Result Cache". I admit to not thinking for too long on the best name
and always thought it was something to come back to later when there's
some actual code to debate a better name for. "Result Cache" was
always a bit of a placeholder name.

Some other names that I'd thought of were:

"MRU Hash"
"MRU Cache"
"Parameterized Tuple Cache" (bit long)
"Parameterized Cache"
"Parameterized MRU Cache"

I know Robert had shown some interest in using a different name. It
would be nice to settle on something most people are happy with soon.

David

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