PGCluster 介绍
PGCluster是一个为Postgresql设计的多主机数据同步备份系统。从PGCluster的官方介绍来看，它最大的两个特点就是：多主机和同步备份。
1. Since a replication system is a synchronous replication, delay does not
occur with the data duplicate between the Cluster DBs.
2. Since a server is multi-master composition, two or more the Cluster DBs
can receive access from a user simultaneously.