Re: preserving forensic information when we freeze

On Mon, Dec 23, 2013 at 1:57 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> Well, all of the fundamental changes (combocids, the initial multixact
> introduction) have been quite some time ago. I think backward compat has
> a much higher value these days (I also don't see much point in looking
> at cmin/cmax for anything but diagnostic purposes). I don't think any of
> the usecases I've seen would be broken by either fk-locks (multixacts
> have been there before, doesn't matter much that they now contain
> updates) nor by forensic freezing. The latter because they really only
> checked that xmin/xmax were the same, and we hopefully haven't broken
> that...
>
> But part of my point really was the usability, not only the
> performance. Requiring LATERAL queries to be usable sensibly causes a
> "Meh" from my side ;)

I simply can't imagine that we're going to want to add a system column
every time we change something, or even enough of them to cover all of
the things we've already got. We'd need at least infomask, infomask2,
and hoff, and maybe some functions for peeking through mxacts to find
the updater and locker XIDs and lock modes. With a couple of
functions we can do all that and not look back.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company