Re: An idle thought

Jeff Davis wrote:
> On Tue, 2010-03-16 at 15:29 +0000, Greg Stark wrote:
> > I'm picturing storing a bit in the visibility map indicating that *no*
> > records are visible in a given page.
> 
> I've been thinking for a while that we could store the visibility
> information in a structure separate from the heap -- sort of like the
> visibility map, but per-tuple and authoritative rather than a per-page
> hint.
> 
> There are all kinds of challenges there, but it might be worth thinking
> about. Visibility information is highly compressible, and requires
> constant maintenance (updates, deletes, freezing, etc.). It also might
> make it possible to move to 64-bit xids, if we wanted to.

I don't think we want to move to 64-bit xids becasue we would still need
to do vacuum freeze to trim the clog.  In fact we do vacuum freeze much
more frequently than required for 32-bit xids for this very reason.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do