4 PostgreSQL is designed to be easily extensible. For this reason,
5 extensions loaded into the database can function just like features
6 that are built in. The contrib/ directory shipped with the source code
7 contains several extensions, which are described in Appendix F. Other
8 extensions are developed independently, like PostGIS. Even PostgreSQL
9 replication solutions can be developed externally. For example, Slony-I
10 is a popular primary/standby replication solution that is developed
11 independently from the core project.