While transactions typically specify their read and write operations on logical data items, a replicated database has to execute them over the physical data copies. When transactions run concurrently in the system, their executions may interfere. The replicated database system has to isolate these transactions. The strongest, and most well-known correctness criterion for replicated databases is 1-copy-serializability. A concurrent execution of transactions in a replicated database is 1-copy-serializable if it is “equivalent” to a serial execution of these transactions over a single logical copy of the database.