Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: David Rowley <dgrowleyml@gmail.com>, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>, Andy Fan <zhihui.fan1213@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2021-02-23T01:51:17Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> Except for the annoying issue that that we pervasively use Lists as
> expressions, I'd argue that we should actually cache "subtree
> volatility" in Expr nodes, similar to the way we use OpExpr.opfuncid
> etc. That'd allow us to make contain_volatile_functions() very cheap

... and completely break changing volatility with ALTER FUNCTION.
The case of OpExpr.opfuncid is okay only because we don't provide
a way to switch an operator's underlying function.  (See also
9f1255ac8.)

It'd certainly be desirable to reduce the number of duplicated
function property lookups in the planner, but I'm not convinced
that that is a good way to go about it.

			regards, tom lane

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.