Thread: Approximate count(*)
Folks, Please find enclosed a patch that shows how to get a quick approximation of count(*) on a table. Cheers, D -- David Fetter david@fetter.org http://fetter.org/ phone: +1 510 893 6100 mobile: +1 415 235 3778 Remember to vote!
David Fetter <david@fetter.org> writes:
> Please find enclosed a patch that shows how to get a quick
> approximation of count(*) on a table.
I'm not sure we should be encouraging people to look at reltuples...
for one thing, it's deliberately a moving average under 8.0.
regards, tom lane
On Thu, Mar 24, 2005 at 12:34:51PM -0500, Tom Lane wrote: > David Fetter <david@fetter.org> writes: > > Please find enclosed a patch that shows how to get a quick > > approximation of count(*) on a table. > > I'm not sure we should be encouraging people to look at reltuples... > for one thing, it's deliberately a moving average under 8.0. Should there be more caveats? Cheers, D -- David Fetter david@fetter.org http://fetter.org/ phone: +1 510 893 6100 mobile: +1 415 235 3778 Remember to vote!
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 David Fetter wrote: > Please find enclosed a patch that shows how to get a quick > approximation of count(*) on a table. You should mention that ANALYZE will also populate reltuples. To be real anal, you should say pg_catalog.pg_class too. :) Tom Lane asked: >> I'm not sure we should be encouraging people to look at reltuples... >> for one thing, it's deliberately a moving average under 8.0. > Should there be more caveats? Well, it already says "approximate", the value-laden word is "good". Perhaps if that went away... - -- Greg Sabino Mullane greg@turnstep.com PGP Key: 0x14964AC8 200503242126 http://biglumber.com/x/web?pk=2529DF6AB8F79407E94445B4BC9B906714964AC8 -----BEGIN PGP SIGNATURE----- iD8DBQFCQ3iivJuQZxSWSsgRAm+PAKCNJPUl7Xns0kLKvbDjOiuNN2g4agCfbmg+ hX8RHO4R2Ad2fQyCPl+Ha3I= =2Gal -----END PGP SIGNATURE-----
David, If Jim and I finish our work for 8.1, then you'll be able to do: SELECT approx_records FROM pg_sysviews.pg_tables WHERE schema_name = 'schema' AND table_name = 'table' But the same caveats will apply. -- Josh Berkus Aglio Database Solutions San Francisco
Josh, David-
Do you think it's worth adding a function that would do the select for
you? IE: tuplecount('schema', 'tablename')?
On Thu, Mar 24, 2005 at 07:19:00PM -0800, Josh Berkus wrote:
> David,
>
> If Jim and I finish our work for 8.1, then you'll be able to do:
>
> SELECT approx_records FROM pg_sysviews.pg_tables WHERE schema_name = 'schema'
> AND table_name = 'table'
>
> But the same caveats will apply.
>
> --
> Josh Berkus
> Aglio Database Solutions
> San Francisco
>
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--
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