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From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: Richard Guo <guofenglinux@gmail.com>, nikhil raj <nikhilraj474@gmail.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Significant Execution Time Difference Between PG13.14 and PG16.4 for Query on information_schema Tables.
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Wed, 28 Aug 2024 11:03:08 +1200"
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David Rowley <dgrowleyml@gmail.com> writes:
> 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.

That seems like a pretty fishy way to do it.  Are you saying that
Memoize is never applicable if there aren't outer joins in the
query?  Without OJs there probably won't be any PHVs.

			regards, tom lane