Re: count(*) slow on large tables - Mailing list pgsql-performance

From Tomasz Myrta
Subject Re: count(*) slow on large tables
Date
Msg-id 3F7C7E4A.9080803@klaster.net
Whole thread Raw
In response to count(*) slow on large tables  (Dror Matalon <dror@zapatec.com>)
List pgsql-performance
> Hi,
>
> I have a somewhat large table, 3 million rows, 1 Gig on disk,  and growing. Doing a
> count(*) takes around 40 seconds.
>
> Looks like the count(*) fetches the table from disk and goes through it.
> Made me wonder, why the optimizer doesn't just choose the smallest index
> which in my case is around 60 Megs and goes through it, which it could
> do in a fraction of the time.
>
> Dror

Just like other aggregate functions, count(*) won't use indexes when
counting whole table.

Regards,
Tomasz Myrta


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