neo4j/neo4j — pull request #1212 by jakewins (2013-09-20 14:17:02+00:00)
Title: Constraint creation in HA clusters.

o To protect from race conditions between constraints coming online on master long before they are enforced on slaves,
master now rejects transactions that were started before a constraint was brought online.

o This initial implementation does not verify if these started-before transactions fail the new constraint, it simply
fails all. The reasoning here is that the window for this is a few milliesconds to a second, and it will only occur
when an admin has manually brought a constraint online. As such, it felt uneccessary to duplicate the constraint
validation code.