| From: | "Marko Kreen" <markokr(at)gmail(dot)com> |
|---|---|
| To: | "Mark Mielke" <mark(at)mark(dot)mielke(dot)cc> |
| Cc: | "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Visibility map thoughts |
| Date: | 2007-11-06 13:17:05 |
| Message-ID: | e51f66da0711060517p229164a7uf59140d1d5d90645@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 11/6/07, Mark Mielke <mark(at)mark(dot)mielke(dot)cc> wrote:
> Simon Riggs wrote:
> > On Mon, 2007-11-05 at 09:52 +0000, Heikki Linnakangas wrote:
> > I'm racking my brain trying to think of a query that will benefit from
> > index-only scans without specifically creating covered indexes. Apart
> > from count(*) queries and RI lookups. I can't see RI lookups being much
> > cheaper with this technique, do you see something there
> I'm not sure what RI lookup is. Sorry. :-)
>
> My list would be:
> - EXISTS / NOT EXISTS
> - COUNT(*)
> - Tables that are heavily updated - any case where the index entry often
> maps to a non-visible tuple.
>
> Beyond that, yeah, I cannot think of other benefits.
Joins?
--
marko
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