On Thu, Nov 08, 2012 at 11:47:37AM +0200, Marko Kreen wrote: > On Wed, Nov 7, 2012 at 10:21 AM, Andres Freund <andres@xxxxxxxxxxx> wrote: > > On Tue, Nov 06, 2012 at 02:55:40PM -0800, Mike Lewis wrote: > >> I am trying to make a trigger that updates a row once and only once per > >> transaction (even if this trigger gets fired multiple times). The general > >> idea is that for a user we have a version number. When we modify the > >> user's data, the version number is incremented then set on the object. We > >> only need to increment the version number once. > >> > >> I am thinking about doing something like: > >> > >> update user > >> set version=version+1 > >> where txid_current() != xmin and user_id = 352395; > >> > >> > >> So I guess my questions are: > >> > >> How dirty is this? > >> Will I run into issues? > > > > It won't work in the presenence of subtransactions and is a bit more > > complicated if you inserted the row in the same transaction. > > This can be solved by storing txid_current() into row > and using that in comparision instead xmin/xmax. If there is sufficient demand for this it should be easy enough to add a function that checks for stuff like this using the information already available in the backends memory. The hardest part seems to be to find a good name... It would basically only need to wrap TransactionIdIsCurrentTransactionId. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
