Horton

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

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: David Rowley <dgrowleyml@gmail.com>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2020-07-08T16:53:56Z
Lists: pgsql-hackers 
Hi,

On 2020-05-20 23:44:27 +1200, David Rowley wrote:
> I've attached a patch which implements this.  The new node type is
> called "Result Cache".  I'm not particularly wedded to keeping that
> name, but if I change it, I only want to do it once. I've got a few
> other names I mind, but I don't feel strongly or confident enough in
> them to go and do the renaming.

I'm not convinced it's a good idea to introduce a separate executor node
for this. There's a fair bit of overhead in them, and they will only be
below certain types of nodes afaict. It seems like it'd be better to
pull the required calls into the nodes that do parametrized scans of
subsidiary nodes. Have you considered that?

Greetings,

Andres Freund

Commits

  1. Add Result Cache executor node (take 2)

  2. Add Result Cache executor node

  3. Allow estimate_num_groups() to pass back further details about the estimation

  4. Allow users of simplehash.h to perform direct deletions

  5. Cache if PathTarget and RestrictInfos contain volatile functions

  6. Fix pull_varnos' miscomputation of relids set for a PlaceHolderVar.