Re: constant time count(*) ?

Hi Mark,

Mark Harrison wrote:
> We're looking into moving some data from mysql to postgresql, and
> notice that count(*) does not seem to be a constant-time function
> as it seems to be in mysql.
>
> planb=# explain select count(*) from assets;
>                            QUERY PLAN
> ----------------------------------------------------------------
>  Aggregate  (cost=22.50..22.50 rows=1 width=0)
>    ->  Seq Scan on assets  (cost=0.00..20.00 rows=1000 width=0)
> (2 rows)
>
> Is there a way to optimize count(*) such that it does not have
> to do a sequential scan?  We use this on some big tables and it
> is slowing down processing quite a lot.

How do you need an unqualified
select count(*) on a table so often
it is making a problem?

Regards
Tino