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