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