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
