Tom Lane wrote:
> Vlad Arkhipov <arhipov@dc.baikal.ru> writes:
> > In a BEFORE UPDATE trigger I need to know whether the row was previously
> > modified by this transaction. Is it safe to use xmin and txid_current()
> > for this purpose (xmin is 32-bit txid type but txid_current() returns
> > 64-bit bigint).
>
> > IF OLD.xmin = txid_current() THEN
>
> Comparing to txid_current() mod 2^32 would probably work,
I think we should be setting the initial epoch to something other than
zero. That way, some quick testing would have revealed this problem
immediately.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
