On Sun, Feb 5, 2012 at 3:59 AM, Bruce Momjian <br...@momjian.us> wrote: > On Sat, Dec 24, 2011 at 03:56:58PM +0000, Simon Riggs wrote: >> > Also, as far as I can see this patch usurps the page version field, >> > which I find unacceptably short-sighted. Do you really think this is >> > the last page layout change we'll ever make? >> >> No, I don't. I hope and expect the next page layout change to >> reintroduce such a field. >> >> But since we're agreed now that upgrading is important, changing page >> format isn't likely to be happening until we get an online upgrade >> process. So future changes are much less likely. If they do happen, we >> have some flag bits spare that can be used to indicate later versions. >> It's not the prettiest thing in the world, but it's a small ugliness >> in return for an important feature. If there was a way without that, I >> would have chosen it. > > Have you considered the CRC might match a valuid page version number? > Is that safe?
In the proposed scheme there are two flag bits set on the page to indicate whether the field is used as a checksum rather than a version number. So its possible the checksum could look like a valid page version number, but we'd still be able to tell the difference. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
