Thread: Re: [HACKERS] Much Ado About COUNT(*)
A cardinality estimate function might be nice. SELECT cardinality_estimate(table_name) If it is off by 25% then no big deal. It would be useful for the PostgreSQL query planner also, I imagine. -----Original Message----- From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Wes Sent: Friday, January 14, 2005 2:59 PM To: Postgres general mailing list Subject: Re: [GENERAL] [HACKERS] Much Ado About COUNT(*) On 1/14/05 12:47 PM, "Frank D. Engel, Jr." <fde101@fjrhome.net> wrote: > It's probably too messy to be worthwhile this > way, though. More trouble than it would be worth. It would be rather useful if there was a way to get a reasonably accurate count (better than analyze provides) in a very short period. When you've got a relatively wide table that has hundreds of millions to over a billion rows, and you need to report on how many rows in the table, that can take a long time. Wes ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings
On Fri, Jan 14, 2005 at 03:11:32PM -0800, Dann Corbit wrote: > A cardinality estimate function might be nice. > SELECT cardinality_estimate(table_name) > If it is off by 25% then no big deal. > It would be useful for the PostgreSQL query planner also, I imagine. If that's all you want, what about the row estimate from pg_class? It has the number of rows active at last vacuum... For really large tables I imagine it'd be easily close enough... Hope this helps, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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On 1/14/05 5:37 PM, "Martijn van Oosterhout" <kleptog@svana.org> wrote: > If that's all you want, what about the row estimate from pg_class? It > has the number of rows active at last vacuum... For really large tables > I imagine it'd be easily close enough... For showing the changes in a given day (or even week), that isn't accurate enough. Wes