Horton

Re: A performance issue with Memoize

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>, David Rowley <dgrowleyml@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2023-10-25T06:45:59Z
Lists: pgsql-hackers 
On Fri, Oct 20, 2023 at 7:43 PM Pavel Stehule <pavel.stehule@gmail.com>
wrote:

> +1
>
> it would be great to fix this problem - I've seen this issue a few times.
>

Thanks for the input.  I guess this is not rare in the real world.  If
the subquery contains lateral reference to a Var that also appears in
the subquery's join clauses, we'd probably suffer from this issue.

Thanks
Richard

Commits

  1. Attempt to fix newly added Memoize regression test

  2. Compare varnullingrels too in assign_param_for_var().

  3. De-dupicate Memoize cache keys

  4. Improve NestLoopParam generation for lateral subqueries

  5. Avoid sharing PARAM_EXEC slots between different levels of NestLoop.