From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: Alexander Korotkov <aekorotkov@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>, pgsql-hackers@lists.postgresql.org
Subject: Re: Fix gin index cost estimation
Date: Fri, 02 Dec 2022 11:19:11 +0100
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Le mardi 25 octobre 2022, 16:18:57 CET Tom Lane a =E9crit :
> Alexander Korotkov <aekorotkov@gmail.com> writes:
> > I think Tom's point was that it's wrong to add a separate entry-tree CPU
> > cost estimation to another estimation, which tries (very inadequately) =
to
> > estimate the whole scan cost. Instead, I propose writing better
> > estimations
> > for both entry-tree CPU cost and data-trees CPU cost and replacing
> > existing
> > CPU estimation altogether.
>=20
> Great idea, if someone is willing to do it ...
>=20
> 			regards, tom lane

Hello,

Sorry for the delay, but here is an updated patch which changes the costing=
 in=20
the following way:

=2D add a descent cost similar to the btree one is charged for the initial=
=20
entry-tree
=2D additionally, a charge is applied per page in both the entry tree and=20
posting trees / lists
=2D instead of charging the quals to each tuple, charge them per entry only=
=2E We=20
still charge cpu_index_tuple_cost per tuple though.

With those changes, no need to tweak the magic number formula estimating th=
e=20
number of pages. Maybe we can come up with something better for estimating=
=20
those later on ?

Best regards,

=2D-
Ronan Dunklau

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