Re: Improving count(*)

Simon Riggs wrote:
> One of the major complaints is always "Select count(*) is slow".

Although there seem to have been plenty of ideas on this they all seem
to just provide a solution for the "whole table" case. It might be that
the solution provides other benefits, but for this one case it does seem
like a lot of work.

Might it be possible to apply rule-style rewriting to a clause of an
ordinary select query? That is, is it prohibitively expensive to get PG
to recognise
SELECT count(*) FROM big_table
and replace it with
SELECT sum(summary_count) FROM my_materialised_view

This should allow you to have where-clauses and apply to a range of
cases. What I fear is that checking to see if the rule applies will cost
too much on all those queries where it doesn't apply.

--
Richard Huxton
Archonet Ltd