I have always had a special affection for PostgreSQL because it is the first RDBMS I used. At the time, it was a version of PostgreSQL 7.1.3. The new version of PostgreSQL offers some new large concepts which are oriented for high availability.
The Hot Stanby which allows you to run read-only queries while the server is in recovery or standby mode archive.
The streaming replication allows a standby server to stay up to date than is possible with log shipping in files. The standby connects to the primary, which sends the standby WAL records once they are generated, without waiting for a WAL file to get filled.