| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Joe Conway <mail(at)joeconway(dot)com> |
| Cc: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [RFC] speed up count(*) |
| Date: | 2021-10-21 20:06:29 |
| Message-ID: | CA+TgmoYrwq7uTufUMhFC6+f9hwUaSvxQ1gTa=NAxpAcoah7_Kw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Oct 21, 2021 at 9:09 AM Joe Conway <mail(at)joeconway(dot)com> wrote:
> I think you are exactly correct. People seem to understand that with a
> predicate it is harder, but they expect
>
> select count(*) from foo;
>
> to be nearly instantaneous, and they don't really need it to be exact.
> The stock answer for that has been to do
>
> select reltuples from pg_class
> where relname = 'foo';
>
> But that is unsatisfying because the problem is often with some
> benchmark or another that cannot be changed.
I would also expect it to almost always give the wrong answer.
--
Robert Haas
EDB: http://www.enterprisedb.com
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