Re: 16-bit page checksums for 9.2

On Mon, Feb 06, 2012 at 08:51:34AM +0100, Heikki Linnakangas wrote:
> >I wonder if we should just dedicate 3 page header bits, call that the
> >page version number, and set this new version number to 1, and assume
> >all previous versions were zero, and have them look in the old page
> >version location if the new version number is zero.  I am basically
> >thinking of how we can plan ahead to move the version number to a new
> >location and have a defined way of finding the page version number using
> >old and new schemes.
> 
> Three bits seems short-sighted, but yeah, something like 6-8 bits
> should be enough. On the whole, though. I think we should bite the
> bullet and invent a way to extend the page header at upgrade.

I just emailed a possible layout that allows for future page version
number expansion.  

I don't think there is any magic bullet that will allow for page header
extension by pg_upgrade.  If it is going to be done, it would have to
happen in the backend while the system is running.  Anything that
requires pg_upgrade to do lots of reads or writes basically makes
pg_upgrade useless.

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