Re: Improving count(*)

Tom Lane wrote:
> Richard Huxton <dev(at)archonet(dot)com> writes:
> > 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.
>
> There is already code in the optimizer that does similar rewriting
> for min/max queries. However, that's a hard-wired transformation.
> I don't see any very simple way to provide a user-configurable
> equivalent.

I guess there must be a query-rewriting mechanism for implementing
materialized views. With that in place we may be able to implement this
other thing ... Is anybody working on materialized views?

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Alvaro Herrera http://www.CommandPrompt.com/
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