Multiversion Concurrency Control (MVCC) for Replication Clients

Multiversion Concurrency Control (MVCC) is a Berkeley DB feature that offers repeatable reads, but with a different performance tradeoff than default Berkeley DB Transactional Data Store (TDS) behavior. MVCC makes extra copies of database pages when performing write operations. This is known as the copy-on-write protocol. These additional copies of database pages enable read operations to avoid locking while still remaining repeatable.

MVCC was originally implemented for replication masters and has been extended to replication clients. MVCC is desirable on replication clients because some applications are read-intensive on client sites and it is useful to optimize read operation performance on these sites.