Note: At present, this section is just taken from PostgreSQL documentation and is subject to revision for Postgres-XC.
This appendix contains information regarding the modules that can be found in the contrib directory of the PostgreSQL distribution. These include porting tools, analysis utilities, and plug-in features that are not part of the core PostgreSQL system, mainly because they address a limited audience or are too experimental to be part of the main source tree. This does not preclude their usefulness.
When building from the source distribution, these modules are not built automatically, unless you build the "world" target (see step 2). You can build and install all of them by running:
gmake gmake install
in the contrib directory of a configured source tree; or to build and install just one selected module, do the same in that module's subdirectory. Many of the modules have regression tests, which can be executed by running:
gmake installcheck
once you have a PostgreSQL server running. (Note that gmake check is not supported; you must have an operational database server to perform these tests, and you must have built and installed the module(s) to be tested.)
If you are using a pre-packaged version of PostgreSQL, these modules are typically made available as a separate subpackage, such as postgresql-contrib.
Many modules supply new user-defined functions, operators, or types. To make use of one of these modules, after you have installed the code you need to register the new SQL objects in the database system. In PostgreSQL 9.1 and later, this is done by executing a CREATE EXTENSION command. In a fresh database, you can simply do
CREATE EXTENSION module_name;
This command must be run by a database superuser. This registers the new SQL objects in the current database only, so you need to run this command in each database that you want the module's facilities to be available in. Alternatively, run it in database template1 so that the extension will be copied into subsequently-created databases by default.
Many modules allow you to install their objects in a schema of your choice. To do that, add SCHEMA schema_name to the CREATE EXTENSION command. By default, the objects will be placed in your current creation target schema, typically public.
If your database was brought forward by dump and reload from a pre-9.1 version of PostgreSQL, and you had been using the pre-9.1 version of the module in it, you should instead do
CREATE EXTENSION module_name FROM unpackaged;
This will update the pre-9.1 objects of the module into a proper extension object. Future updates to the module will be managed by ALTER EXTENSION. For more information about extension updates, see Section 34.15.