On Thu, Jan 19, 2012 at 9:49 AM, Scott Marlowe <scott.marlowe@xxxxxxxxx> wrote: > On Thu, Jan 19, 2012 at 7:54 AM, Florian Weimer <fweimer@xxxxxx> wrote: >> * Gnanakumar: >> >>>> Just create a unique index on EMAIL column and handle error if it comes >>> >>> Thanks for your suggestion. Of course, I do understand that this could be >>> enforced/imposed at the database-level at any time. But I'm trying to find >>> out whether this could be solved at the application layer itself. Any >>> thoughts/ideas? >> >> If you use serializable transactions in PostgreSQL 9.1, you can >> implement such constraints in the application without additional >> locking. However, with concurrent writes and without an index, the rate >> of detected serialization violations and resulting transactions aborts >> will be high. > > No, you sadly can't. PostgreSQL doesn't yet support proper predicate > locking to allow the application to be sure that the OP's original > statement, and ones like it, don't have a race condition. A unique > index is the only way to be sure. Wait, did 9.1 implement proper predicate locking to allow this? If so I apologize for being out of the loop on the new versions. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
