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Subject: Re: count * performance issue
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From: "Mark Lewis" <mark.lewis@mir3.com>
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On Thu, 2008-03-06 at 07:28 -0800, Craig James wrote:
...
> My question is: What do the other databases do that Postgres can't do, =
and why not?
>=20
> Count() on Oracle and MySQL is almost instantaneous, even for very =
large tables. So why can't Postgres do what they do?
...

I can vouch that Oracle can still take linear time to perform a
count(*), at least in some cases.

I have also seen count(*) fast in some cases too... my understanding is
that they maintain a list of "interested transactions" on a per-relation
basis.  Perhaps they do an optimization based on the index size if there
are no pending DML transactions?

-- Mark