There have been several instances where we will receive two login attempts at the exact same time and cause a constraint exception to occur.

I'm fairly confident that the constraint exception doesn't cause any adverse effects to other transactions, but it might be worth it to remove the constraint since IRL we seem to get login attempts that have the exact same date.

Here is the exception that is thrown:

org.springframework.dao.DataIntegrityViolationException: Could not execute JDBC batch update; nested exception is org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
   at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:
...
Caused by: java.sql.BatchUpdateException: Batch entry 0 insert into metrics.user_login (user_login_type_id, users_id, date_created) values (0, 3c1e0f7b-01f7-4a0f-9cb7-88250e609ea9, 2011-04-20 17:52:29.144000 -07:00:00) was aborted. Call getNextException to see the cause.