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Re: "select max/count(id)" not using index

From: Tomasz Myrta <jasiek(at)klaster(dot)net>
To: Ryszard Lach <siaco(at)autograf(dot)pl>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: "select max/count(id)" not using index
Date: 2003-12-22 11:03:45
Message-ID: 3FE6CF91.6070300@klaster.net (view raw or flat)
Thread:
Lists: pgsql-performance
Dnia 2003-12-22 11:39, Użytkownik Ryszard Lach napisał:

> Hi.
> 
> I have a table with 24k records and btree index on column 'id'. Is this
> normal, that 'select max(id)' or 'select count(id)' causes a sequential
> scan? It takes over 24 seconds (on a pretty fast machine):
'select count(id)'
Yes, this is normal. Because of MVCC all rows must be checked and 
Postgres doesn't cache count(*) like Mysql.

'select max(id)'
This is also normal, but try to change this query into:
select id from some_table order by id desc limit 1;

What is your Postgresql version?

Regards,
Tomasz Myrta


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