| From: | "Mark Lewis" <mark(dot)lewis(at)mir3(dot)com> |
|---|---|
| To: | "Craig James" <craig_james(at)emolecules(dot)com> |
| Cc: | <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: count * performance issue |
| Date: | 2008-03-06 16:16:31 |
| Message-ID: | 1204820047.9048.902.camel@archimedes |
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| Thread: | |
| Lists: | pgsql-performance |
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?
>
> 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
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