Re: tracking commit timestamps

On 2014-11-05 08:57:07 +0900, Michael Paquier wrote:
> On Tue, Nov 4, 2014 at 10:01 PM, Alvaro Herrera <alvherre@2ndquadrant.com>
> wrote:
> 
> > Michael Paquier wrote:
> >
> > > I'm still on a -1 for that. You mentioned that there is perhaps no reason
> > > to delay a decision on this matter, but IMO there is no reason to rush
> > > either in doing something we may regret. And I am not the only one on
> > this
> > > thread expressing concern about this extra data thingy.
> > >
> > > If this extra data field is going to be used to identify from which node
> > a
> > > commit comes from, then it is another feature than what is written on the
> > > subject of this thread. In this case let's discuss it in the thread
> > > dedicated to replication identifiers, or come up with an extra patch once
> > > the feature for commit timestamps is done.
> >
> > Introducing the extra data field in a later patch would mean an on-disk
> > representation change, i.e. pg_upgrade trouble.
> 
> Then why especially 4 bytes for the extra field? Why not 8 or 16?

It's sufficiently long that you can build infrastructure to storing more
transaction metadata data ontop. I could live making it 8 bytes, but I
don't see a clear advantage.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services