| From: | Thom Brown <thom(at)linux(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: COUNT(*) and index-only scans |
| Date: | 2011-10-10 17:34:02 |
| Message-ID: | CAA-aLv6-bWVgxLkxQKgwOFrV+CmxWtKwtFzpOOhM_fx6BWsqaQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 10 October 2011 18:23, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> I talked to Robert Haas and he said that index-only scans do not
> optimize COUNT(*). Is this something we can do for PG 9.2? Is anyone
> working on this?
Yes it does, provided that there is an appropriate WHERE clause. But
yes, I think we definitely want this if it's relatively easy. In
addition to this, it's not always easy to get it to use an index-only
scan even if it's going to significantly faster. I'm assuming some
supporting planner work needs to be added too.
--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935
EnterpriseDB UK: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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