Re: Improving count(*)

> -----Original Message-----
> From: pgsql-hackers-owner(at)postgresql(dot)org [mailto:pgsql-hackers-
> owner(at)postgresql(dot)org] On Behalf Of Tom Lane
> Sent: Thursday, November 17, 2005 4:17 PM
> To: Simon Riggs
> Cc: Kevin Grittner; pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Improving count(*)
>
> Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> > From here, another proposal. We have a GUC called
count_uses_estimate
> > that is set to off by default. If set to true, then a count(*) will
use
> > the planner logic to estimate number of rows in the table and return
> > that as the answer, rather than actually count the row.
>
> Ugh. Why not just provide a function to retrieve the planner
estimate,
> but *not* call it count(*)? It would fit nicely with the
contrib/dbsize
> stuff (or I should say, the stuff formerly in dbsize...)

An estimate of the number of rows would be nice to have.
A function called cardinality_estimate() or something of that nature
seems more natural than count(*)