Re: [RFC] speed up count(*)

On 10/21/21 4:06 PM, Robert Haas wrote:
> 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.

That is a grossly overstated position. When I have looked, it is often
not that terribly far off. And for many use cases that I have heard of
at least, quite adequate.

Joe

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