When serializability comes without cost

It is usually expected that performance is reduced by using stricter concurrency control, which reduces the risk of anomalies that can lead to data corruption. For example, the weak isolation level Read Committed allows anomalies that are prevented by two-phase locking (abbreviated 2PL), and because 2PL holds locks for longer than RC, it has lower throughput. We show that sometimes, guaranteed correctness can be obtained along with better throughput than RC, by use of the multiversion snapshot isolation mechanism along with modifications to application programs as proposed by Fekete et al. We investigate the conditions under which this effect occurs.