Re: count(*) performance improvement ideas

Tom Lane wrote:
> "Stephen Denne" <Stephen(dot)Denne(at)datamail(dot)co(dot)nz> writes:
> > From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> >> As for 2) and 3), can't you look into the pg_settings view?
>
> > pg_settings view doesn't contain custom variables created on the
> > fly,
>
> Really? [ pokes around ... ] Hm, you're right, because
> add_placeholder_variable() sets the GUC_NO_SHOW_ALL flag, and in this
> usage it'll never be cleared. I wonder if we should change that.
>
> The whole thing is a bit of an abuse of what the mechanism was
> intended for, and so I'm not sure we should rejigger GUC's behavior
> to make it more pleasant, but on the other hand if we're not ready to
> provide a better substitute ...

While I agree with that part, is there any actual *reason* why we
shouldn't have the custom variables included in pg_settings? ISTM that
it would be usable in cases that aren't an abuse as well...

//Magnus