Data consistency in distributed operations such as replication adds additional wrinkles to the “normal” database issues of ACID properties (atomicity, consistency, isolation, and durability) and transaction isolation levels. There are two main types of replicated data consistency:
In the context of replication, transactional consistency means that, after replication, data at any participating site is the same data that would have resulted had all transactions been performed at only a single site. That is, the act of replicating the data does not in itself expose situations where data is changed in ways that would not occur, were replication used.
In the context of replication, data convergence means that all sites end up with the same data values, but not necessarily the ones that would have resulted had all the work been done at only one site.