Re: How to check whether the row was modified by this transaction before? - Mailing list pgsql-hackers

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/
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