From: Jim C. Nasby <jnasby@pervasive.com>
To: Andrea Arcangeli <andrea@cpushare.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
Date: Wed, 11 Jan 2006 15:02:21 -0600
Message-ID: <20060111210221.GD63175@pervasive.com> (raw)
In-Reply-To: <20060111203947.GL15897@opteron.random>
References: <20060110014447.GB18474@opteron.random>
<20060111184032.GS3902@pervasive.com>
<20060111203947.GL15897@opteron.random>
On Wed, Jan 11, 2006 at 09:39:47PM +0100, Andrea Arcangeli wrote:
> > CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );
>
> The index only helps the above query with = 0 and not the one with != 0,
> but it seems not needed in practice.
Hrm. If you need indexing then, you'll probably have to do 2 indexes
with a WHERE clause...
CREATE INDEX ... WHERE position(...) = 0;
CREATE INDEX ... WHERE position(...) != 0;
I suspect this is because of a lack of stats for functional indexes.
--
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, andrea@cpushare.com
Subject: Re: NOT LIKE much faster than LIKE?
In-Reply-To: <20060111210221.GD63175@pervasive.com>
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