Re: [PERFORM] encouraging index-only scans

On Thu, Dec 13, 2012 at 09:40:40AM +0000, Simon Riggs wrote:
> On 13 December 2012 03:51, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> >> Yes, this does seem like a problem for upgrades from 9.2 to 9.3? We can
> >> have pg_dump --binary-upgrade set these, or have ANALYZE set it. I
> >> would prefer the later.
> >
> > ANALYZE does not set that value, and is not going to start doing so,
> > because it doesn't scan enough of the table to derive a trustworthy
> > value.
>
> ISTM that ANALYZE doesn't need to scan the table to do this. The
> vismap is now trustworthy and we can scan it separately on ANALYZE.
>
> More to the point, since we run ANALYZE more frequently than we run
> VACUUM, the value stored by the last VACUUM could be very stale.

Wouldn't inserts affect the relallvisible ratio, but not cause a vacuum?
Seems we should be having analyze update this independent of pg_upgrade
needing it. Also, why is this in pg_class?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +