Re: "xmin" system column

On Fri, Jan 27, 2006 at 11:18:23AM +0100, Christian Kratzer wrote:
> Hi,
>
> On Thu, 26 Jan 2006, Eric B. Ridge wrote:
> <snip/>
> ><long pause>
> >
> >hahaha, *blush*. I could just use "now()", right? pg8.1 docs say that
> >now()/CURRENT_TIMESTAMP "return the start time of the current transaction;
> >their values do not change during the transaction". I could use a
> >composite of (now(), GetTopTransctionId()) to assume batch uniqueness.
>
> Or use a touple of (now(), pg_backend_pid()) for this kind of stuff.
> pg_backend_pid() should sufficiently disambiguate now() to make obove
> touple unique.

That doesn't provide very good protection against the system clock
moving backwards though. I suspect you'd be better doing a tuple of
now() and a 2 byte sequence.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461