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From: Nathan Bossart <[email protected]>
To: Corey Huinker <[email protected]>
Cc: Jeff Davis <[email protected]>
Cc: Robert Treat <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: jian he <[email protected]>
Cc: Bruce Momjian <[email protected]>
Cc: Matthias van de Meent <[email protected]>
Cc: Magnus Hagander <[email protected]>
Cc: Stephen Frost <[email protected]>
Cc: Ashutosh Bapat <[email protected]>
Cc: Peter Smith <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: [email protected]
Subject: Re: Statistics Import and Export
Date: Wed, 2 Apr 2025 21:38:18 -0500
Message-ID: <Z-30mug1X82YOn-0@nathan> (raw)
In-Reply-To: <CADkLM=d4U6hjoLGx2tRxLzSsEDYz7oj8PmmTYPKmnfPk5RLzKQ@mail.gmail.com>
References: <CADkLM=desCuf3dVHasADvdUVRmb-5gO0mhMO5u9nzgv6i7U86Q@mail.gmail.com>
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	<[email protected]>
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On Wed, Apr 02, 2025 at 10:34:58PM -0400, Corey Huinker wrote:
>>
>> > Also, why do we need the clause "WHERE s.tablename = ANY($2)"? Isn't
>> > that already implied by "JOIN unnest($1, $2) ... s.tablename =
>> > u.tablename"?
>>
>> Good question.  Corey, do you recall why this was needed?
>>
> 
> In my patch, that SQL statement came with the comment:
> 
> + /*
> + * The results must be in the order of relations supplied in the
> + * parameters to ensure that they are in sync with a walk of the TOC.
> + *
> + * The redundant (and incomplete) filter clause on s.tablename = ANY(...)
> + * is a way to lead the query into using the index
> + * pg_class_relname_nsp_index which in turn allows the planner to avoid an
> + * expensive full scan of pg_stats.
> + *
> + * We may need to adjust this query for versions that are not so easily
> + * led.
> + */

Thanks.  I included that in the latest patch set.

-- 
nathan





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