Replication

Master-slave replication

The master serves reads and writes. Writes are replicated to other slaves through a replication mechanism (WAL?). Slaves can replicate to eaech other. If the master goes offline, the server can continue to operate in a read-only mode. Otherwise, the slaves can promote each other to leadership.

Master-master replication

Both masters serve reads and writes and coordinate with each other. If either master goes down, the system can continue to operate with reads and writes functionally.

Pros

• Can serve reads and writes

Cons

• You’ll need a load balancer or you’ll need to make changes to your application logic to determine where to write.
• Most master-master systems are either loosely consistent (violating ACID) or have increased write latency due to synchronization.
• Conflict resolution comes more into play as more write nodes are added and as latency increases.