Re: On duplicate ignore

On Thu, Jan 19, 2012 at 9:49 AM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Thu, Jan 19, 2012 at 7:54 AM, Florian Weimer <fweimer(at)bfk(dot)de> 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.