On Tue, 21 Oct 2025 at 10:57, Marco Boeringa <marco@boeringa.demon.nl> wrote:
> PostGIS functions can be very expensive, especially in the context of
> the fact that Polygon and Line geometries can vary vastly in size in
> terms of the number of vertices that constitute them, which has a
> profound impact on some PostGIS function calls, merely due to the
> enormous complexity of some shapes.
How expensive the function call is is irrelevant as there simply is no
function result caching going on and there's nothing wired up in any
released version of PostgreSQL which gives you this with the query
you've written.
You still seem to be under the illusion that the self-join is giving
you some sort of caching. If you remain content in not trusting me on
that, by all means, create a plpgsql function with a RAISE NOTICE and
try it out for yourself.
> But of course you're right that any change will need some thorough
> testing before assuming it will actually benefit the queries.
I don't recall talking about testing... (It may help if you quote
things you're replying to. This conversation will be quite hard to
follow with your top post replies.)
This whole conversation has drifted well off what the original report
was about, so I think it's better if you need more help on this to use
pgsql-performance@lists.postgresql.org
David
