From: Andrea Arcangeli <andrea@cpushare.com>
To: Jim C. Nasby <jnasby@pervasive.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: NOT LIKE much faster than LIKE?
Date: Wed, 11 Jan 2006 21:39:47 +0100
Message-ID: <20060111203947.GL15897@opteron.random> (raw)
In-Reply-To: <20060111184032.GS3902@pervasive.com>
References: <20060110014447.GB18474@opteron.random>
<20060111184032.GS3902@pervasive.com>
On Wed, Jan 11, 2006 at 12:40:32PM -0600, Jim C. Nasby wrote:
> On Tue, Jan 10, 2006 at 02:44:47AM +0100, Andrea Arcangeli wrote:
> > "cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
> > "preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference
>
> One thing you could do is change the like to:
>
> WHERE position(' PREEMPT ' in kernel_version) != 0
That alone fixed it, with this I don't even need the index (yet). Thanks
a lot.
> And then create a functional index on that:
>
> 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.
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To: pgsql-performance@postgresql.org
Cc: andrea@cpushare.com, jnasby@pervasive.com
Subject: Re: NOT LIKE much faster than LIKE?
In-Reply-To: <20060111203947.GL15897@opteron.random>
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