From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-bugs@lists.postgresql.org
Cc: Hung Nguyen <hungnq1989@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org, "rjuju123@gmail.com" <rjuju123@gmail.com>
Cc: 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> (raw)
In-Reply-To: <2187702.iZASKD2KPV@aivenronan>
References: <CABs3KGQnOkyQ42-zKQqiE7M0Ks9oWDSee=+Jx3-TGq=68xqWYw@mail.gmail.com>
<2194637.1657118489@sss.pgh.pa.us>
<2187702.iZASKD2KPV@aivenronan>
Le mercredi 6 juillet 2022, 16:52:09 CEST Ronan Dunklau a écrit :
> Le mercredi 6 juillet 2022, 16:41:29 CEST Tom Lane a écrit :
> > 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.
>
> For gist and sp-gist, a descent cost is taken into account, by estimating
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.
>
> Hash, brin and bloom are quite different, so maybe another examination would
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
doing with the number of searched entries is right though.
--
Ronan Dunklau
Attachments:
v1-0001-Fix-gin-costing.patch (text/x-patch, 0B) download
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Subject: Re: index cost estimation
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