PostgreSQL Replication with Slony-I

"In this post, we look at another replication mechanism available for PostgreSQL, Slony-I. Slony-I is an asynchronous, master-slave replication system. With PGCluster, we had the ability to load balance connections to the PostgreSQL database, knowing that data that is modified in one server will be replicated across to the other server. Additionally, its synchronous nature gave us confidence that, in the event of a failure, all completed transactions will be accounted for. With Slony-I, we run into a very different type of replication. Slony-I is a master-slave system, designed to utilize one master database, and one or more slaves. Data is replicated in a one-way fashion, from the master to the slave(s). It does not include a built-in load balancing feature like PGCluster, and there is no automatic failover from a failed master to one of the slaves. Failover must be manually configured using a third-party utility, such as heartbeat. Slony-I's asynchronous nature means that, in the event of a database failure, there may be uncommitted transactions that have not been replicated across. Slony-I performs batching of transaction replication in order to improve performance. However, if the master fails prior to a batch of transactions being replicated, those transactions are lost."