From: Alvaro Herrera <alvherre@commandprompt.com>
To: Craig James <craig_james@emolecules.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: LIKE search and performance
Date: Thu, 24 May 2007 17:46:54 -0400
Message-ID: <20070524214654.GR4320@alvh.no-ip.org> (raw)
In-Reply-To: <46560264.2020406@emolecules.com>
References: <009501c79d4c$445428f0$0b00a8c0@mpsro.dom>
<88daf38c0705230905u1a981102k691b47bd36011a80@mail.gmail.com>
<4655DE75.4080506@mansionfamily.plus.com>
<4655E64B.5050503@hagander.net>
<4655FB8A.1040707@mansionfamily.plus.com>
<1180040560.31471.262.camel@archimedes>
<46560264.2020406@emolecules.com>
Craig James wrote:
> Mark Lewis wrote:
>
> >PG could scan the index looking for matches first and only load the
> >actual rows if it found a match, but that could only be a possible win
> >if there were very few matches, because the difference in cost between a
> >full index scan and a sequential scan would need to be greater than the
> >cost of randomly fetching all of the matching data rows from the table
> >to look up the visibility information.
>
> Just out of curiosity: Does Postgress store a duplicate of the data in the
> index, even for long strings? I thought indexes only had to store the
> string up to the point where there was no ambiguity, for example, if I have
> "missing", "mississippi" and "misty", the index only needs "missin",
> "missis" and "mist" in the actual index.
What would happen when you inserted a new tuple with just "miss"? You
would need to expand all the other tuples in the index.
--
Alvaro Herrera http://www.flickr.com/photos/alvherre/
"Puedes vivir solo una vez, pero si lo haces bien, una vez es suficiente"
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To: pgsql-performance@postgresql.org
Cc: alvherre@commandprompt.com, craig_james@emolecules.com
Subject: Re: LIKE search and performance
In-Reply-To: <20070524214654.GR4320@alvh.no-ip.org>
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