Re: COUNT(*) and index-only scans

Greg Stark wrote:
> On Mon, Oct 10, 2011 at 9:17 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > My intention was to allow it to consider any covering index. ?You're
> > thinking about the cost estimate, which is really entirely different.
> >
> 
> Is there any reason to consider more than one? I would have expected
> the narrowest one to be the best choice. There's something to be said
> for using the same index consistently but we already have that problem
> and make no attempt to do that. And partial indexes might be better
> but then we would already be considering them if their constraints are
> satisfied.

Actually, I think the smallest non-partial one on disk might be the best
--- that is very easy to find out.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +