From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-bugs@lists.postgresql.org
Cc: Hung Nguyen <hungnq1989@gmail.com>, pgsql-bugs@lists.postgresql.org,
 "rjuju123@gmail.com" <rjuju123@gmail.com>,
 Ronan Dunklau <ronan.dunklau@aiven.io>
Subject: Re: index cost estimation
Date: Wed, 06 Jul 2022 17:42:28 +0200
Message-ID: <3439542.iIbC2pHGDl@aivenronan>
Organization: aiven
In-Reply-To: <2187702.iZASKD2KPV@aivenronan>
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Le mercredi 6 juillet 2022, 16:52:09 CEST Ronan Dunklau a =E9crit :
> Le mercredi 6 juillet 2022, 16:41:29 CEST Tom Lane a =E9crit :
> > Hm, so it'd seem this probably could happen when comparing *any*
> > non-btree index to a btree index, because I don't think we are
> > particularly careful with CPU cost estimation for any of the
> > other index types.  If we do something about this, we probably
> > have to look at all of them.
>=20
> For gist and sp-gist, a descent cost is taken into account, by estimating=
=20
the
> tree height so that particular effect is mitigated. Whether the cpu cost
> estimation is sensible regarding to btree is another topic, but at least =
the
> index cost doesn't vanish when inside a loop.
>=20
> Hash, brin and bloom are quite different, so maybe another examination wo=
uld=20
be
> required but probably outside the scope of this bug report.

Here is a patch tentatively addressing the problem. I'm not sure what I'm=20
doing with the number of searched entries is right though.


=2D-=20
Ronan Dunklau
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