From: Anibal David Acosta <aa@devshock.com>
To: 'Craig James' <craig_james@emolecules.com>
To: pgsql-performance@postgresql.org
Subject: Re: how fast index works?
Date: Tue, 6 Sep 2011 16:28:12 -0400
Message-ID: <008b01cc6cd3$820581c0$86108540$@devshock.com> (raw)
In-Reply-To: <4E6671DE.40506@emolecules.com>
References: <001501cc6cc3$3649a3c0$a2dceb40$@devshock.com>
<4E6671DE.40506@emolecules.com>
Thanks!
De: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org] En nombre de Craig James
Enviado el: martes, 06 de septiembre de 2011 03:18 p.m.
Para: pgsql-performance@postgresql.org
Asunto: Re: [PERFORM] how fast index works?
On 9/6/11 11:31 AM, Anibal David Acosta wrote:
Hi everyone,
My question is, if I have a table with 500,000 rows, and a SELECT of one row
is returned in 10 milliseconds, if the table has 6,000,000 of rows and
everything is OK (statistics, vacuum etc)
can i suppose that elapsed time will be near to 10?
Theoretically the index is a B-tree with log(N) performance, so a larger
table could be slower. But in a real database, the entire subtree might
fall together in one spot on the disk, so retrieving a record from a 500,000
record database could take the same time as a 6,000,000 record database.
On the other hand, if you do a lot of updates and don't have your autovacuum
parameters set right, a 500,000 record index might get quite bloated and
slow as it digs through several disk blocks to find one record.
There is no simple answer to your question. In a well-maintained database,
6,000,000 records are not a problem.
Craig
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Subject: Re: how fast index works?
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