| From: | Mark Mielke <mark(at)mark(dot)mielke(dot)cc> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Visibility map thoughts |
| Date: | 2007-11-06 13:01:16 |
| Message-ID: | 4730659C.2060607@mark.mielke.cc |
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| Lists: | pgsql-hackers |
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.
Cheers,
mark
--
Mark Mielke <mark(at)mielke(dot)cc>
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