From: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com> |
---|---|
To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
Cc: | 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: | 2021-10-20 18:33:15 |
Message-ID: | CAFBsxsEg0qdfx=LKM46=9ntZuYcLnvyOhkKKxq=WXc_Eh8vB3A@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Oct 20, 2021 at 2:23 PM Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
wrote:
>
> Couldn't we simply inspect the visibility map, use the index data only
> for fully visible/summarized ranges, and inspect the heap for the
> remaining pages? That'd still be a huge improvement for tables with most
> only a few pages modified recently, which is a pretty common case.
>
> I think the bigger issue is that people rarely do COUNT(*) on the whole
> table. There are usually other conditions and/or GROUP BY, and I'm not
> sure how would that work.
Right. My (possibly hazy) recollection is that people don't have quite as
high an expectation for queries with more complex predicates and/or
grouping. It would be interesting to see what the balance is.
--
John Naylor
EDB: http://www.enterprisedb.com
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