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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Igor ALBUQUERQUE SILVA <i.albuquerque-silva@kayrros.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Geometric types row estimation
Date: Wed, 30 Nov 2022 12:18:41 -0500
Message-ID: <1358779.1669828721@sss.pgh.pa.us> (raw)
In-Reply-To: <CADArKzXZnFixqw-GRkpwOasYzJRQOE7qH-6XgocG_njvM7EMmA@mail.gmail.com>
References: <CADArKzXZnFixqw-GRkpwOasYzJRQOE7qH-6XgocG_njvM7EMmA@mail.gmail.com>

Igor ALBUQUERQUE SILVA <i.albuquerque-silva@kayrros.com> writes:
> I'm having a problem regarding the point type/gist indexes. Here's a
> minimal reproduction of it:
> ...
> What I was expecting is the first query to estimate 4 rows and the second
> to estimate 1, like what I get If I try the same thing using integers.

Unfortunately, the selectivity estimation functions for PG's geometric
types are mostly just stubs.  The estimation function for point <@ box
in particular is contsel [1]:

/*
 *	contsel -- How likely is a box to contain (be contained by) a given box?
 *
 * This is a tighter constraint than "overlap", so produce a smaller
 * estimate than areasel does.
 */
Datum
contsel(PG_FUNCTION_ARGS)
{
	PG_RETURN_FLOAT8(0.001);
}

It's been like that (excepting notational changes) since Berkeley days,
because nobody has bothered to make it better.

In general, PG's built-in geometric types have never gotten much
beyond their origins as an academic proof-of-concept.  I think people
who are doing serious work that requires such operations mostly use
PostGIS, and I'd suggest looking into that.

Or, if you feel like doing a lot of work to make these estimators
better, have at it.

			regards, tom lane

[1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob_plain;f=src/backend/utils/adt/geo_selfunc...





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