From: Jim C. Nasby <jnasby@pervasive.com>
To: Theo Kramer <theo@flame.co.za>
Cc: pgsql-performance@postgresql.org
Subject: Re: Indexes with descending date columns
Date: Fri, 31 Mar 2006 09:55:54 -0600
Message-ID: <20060331155554.GO49405@pervasive.com> (raw)
In-Reply-To: <1143629550.2985.29.camel@theo-laptop.int.coza.net.za>
References: <200603170625.k2H6PJ926955@pillette.com>
<1143112188.2810.27.camel@theo-laptop.int.coza.net.za>
<20060324102138.GR90527@pervasive.com>
<1143629550.2985.29.camel@theo-laptop.int.coza.net.za>
On Wed, Mar 29, 2006 at 12:52:31PM +0200, Theo Kramer wrote:
> On Fri, 2006-03-24 at 12:21, Jim C. Nasby wrote:
> > On Thu, Mar 23, 2006 at 01:09:49PM +0200, Theo Kramer wrote:
> > > ii If no to i, is it feasible to extend PostgreSQL to allow traversing
> > > an index in column descending and column ascending order - assuming
> > > an order by on more than one column with column order not
> > > in the same direction and indexes existing? ... if that makes sense.
> >
> > Yes.
> >
> > stats=# explain select * from email_contrib order by project_id desc, id desc, date desc limit 10;
> > QUERY PLAN
> > ------------------------------------------------------------------------------------------------------------------------
> > Limit (cost=0.00..31.76 rows=10 width=24)
> > -> Index Scan Backward using email_contrib_pkey on email_contrib (cost=0.00..427716532.18 rows=134656656 width=24)
> > (2 rows)
>
> Not quite what I mean - redo the above as follows and then see what
> explain returns
>
> explain select * from email_contrib order by project_id, id, date desc
> limit 10;
Ahh. There's a hack to do that by defining a new opclass that reverses <
and >, and then doing ORDER BY project_id, id, date USING new_opclass.
I think there's a TODO about this, but I'm not sure...
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, theo@flame.co.za
Subject: Re: Indexes with descending date columns
In-Reply-To: <20060331155554.GO49405@pervasive.com>
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