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From: David Rowley <dgrowleyml@gmail.com>
Date: Wed, 28 Aug 2024 11:03:08 +1200
Message-ID: <CAApHDvp1mue1a5fdfsa2z2mAS6v2d9+kxMzxH7GhAiC0Z7o8Mw@mail.gmail.com>
Subject: Re: Significant Execution Time Difference Between PG13.14 and PG16.4
 for Query on information_schema Tables.
To: Tom Lane <tgl@sss.pgh.pa.us>, Richard Guo <guofenglinux@gmail.com>
Cc: nikhil raj <nikhilraj474@gmail.com>, pgsql-hackers@lists.postgresql.org
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On Wed, 28 Aug 2024 at 09:52, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The other problem with this is that it breaks one test case in
> memoize.sql: a query that formerly generated a memoize plan
> now does not use memoize.  I am not sure why not --- does that
> mean anything to you?

The reason it works in master is that get_memoize_path() calls
extract_lateral_vars_from_PHVs() and finds PlaceHolderVars to use as
the Memoize keys. With your patch PlannerInfo.placeholder_list is
empty.

The commit that made this work is 069d0ff02. Richard might be able to
explain better. I don't quite understand why RelOptInfo.lateral_vars
don't contain these in the first place.

David