From: | Noah Misch <noah(at)leadboat(dot)com> |
---|---|
To: | Gurjeet Singh <gurjeet(at)singh(dot)im> |
Cc: | PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Using Index-only scans to speed up count(*) |
Date: | 2014-06-07 15:04:10 |
Message-ID: | 20140607150410.GA509883@tornado.leadboat.com |
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Lists: | pgsql-hackers |
On Sat, Jun 07, 2014 at 08:35:27AM -0400, Gurjeet Singh wrote:
> While reading [1] in context of Postgres Hibernator, I see that
> Mitsuru mentioned one of the ways other RDBMS allows count(*) to be
> driven by an index.
>
> > 'select /*+ INDEX(emp emp_pk) */ count(*) from emp;' to load index blocks
>
> I am not sure if Postgres planner already allows this,
It does:
create table t (c, junk) as select *, repeat('a', 100)
from generate_series(1,10000);
alter table t add primary key (c);
vacuum t;
analyze t;
explain select count(*) from t;
--
Noah Misch
EnterpriseDB http://www.enterprisedb.com
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