Date: Tue, 11 Feb 2014 19:31:03 +0100
From: Andres Freund <andres@2ndquadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Jim Nasby <jim@nasby.net>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 Peter Geoghegan <peter@2ndquadrant.com>,
 Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [PERFORM] encouraging index-only scans
Message-ID: <20140211183103.GJ15246@awork2.anarazel.de>
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 <20140211155607.GB2289@momjian.us>
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On 2014-02-11 13:23:19 -0500, Bruce Momjian wrote:
> On Tue, Feb 11, 2014 at 06:54:10PM +0100, Andres Freund wrote:
> > On 2014-02-11 12:12:13 -0500, Bruce Momjian wrote:
> > > Yes, that pretty much sums it up.  We introduced index-only scans in 9.2
> > > (2012) but they still seem to be not usable for insert-only workloads
> > > two years later.  Based on current progress, it doesn't look like this
> > > will be corrected until 9.5 (2015).  I am kind of confused why this has
> > > not generated more urgency.
> > 
> > I think this largely FUD. They are hugely beneficial in some scenarios
> > and less so in others. Just like lots of other features we have.
> 
> I don't understand.  Index-only scans are known to have benefits --- if
> an insert-only workload can't use that, why is that acceptable?  What is
> fear-uncertainty-and-doubt about that?  Please explain.

Uh, for one, insert only workloads certainly aren't the majority of
usecases. Ergo there are plenty of cases where index only scans work out
of the box.
Also, they *do* work for insert only workloads, you just either have to
wait longer, or manually trigger VACUUMs. That's a far cry from not
being usable.

I am not saying it shouldn't be improved, I just don't see the point of
bringing it up while everyone is busy with the last CF and claiming it
is unusable and that stating that it is surprisising that nobody really
cares.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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