What are the different approaches used for database synchronization and replication?
A. In database replication schemes, physical transactions on each node are recorded and played back on all the other nodes. This technique would only work if each node has a replica of the full-set data. There is also a stability issue with physical transaction based replications when the number of nodes goes up. Transactions on different replicas could conflict with each other. To handle this, normally cross system locking or complicated conflict resolution schemes are needed. In fact, they are used in eager replication and lazy replication respectively. Eager replication synchronously updates all replicas as part of one atomic transaction. This is also called synchronous replication or pessimistic replication as it incurs global locking and waiting. In contrast to eager replication, lazy replication allows updates of any replicas without locking others. The local transactions then propagate to other replicas in background. This scheme is also called asynchronous replication or optimi
