Table of Contents
old_snapshot_threshold
statecrosstab
and others)SYSTEM_ROWS
sampling method for TABLESAMPLE
SYSTEM_TIME
sampling method for TABLESAMPLE
This appendix and the next one contain information on the
optional components
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.
They are separate 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.
This appendix covers extensions and other server plug-in module
libraries found in
contrib
. Appendix G covers utility
programs.
When building from the source distribution, these optional components are not built automatically, unless you build the "world" target (see Step 2). You can build and install all of them by running:
make
make 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:
make check
before installation or
make installcheck
once you have a PostgreSQL server running.
If you are using a pre-packaged version of PostgreSQL,
these components are typically made available as a separate subpackage,
such as postgresql-contrib
.
Many components supply new user-defined functions, operators, or types, packaged as extensions. To make use of one of these extensions, after you have installed the code you need to register the new SQL objects in the database system. This is done by executing a CREATE EXTENSION command. In a fresh database, you can simply do
CREATE EXTENSION extension_name
;
This command registers the new SQL objects in the current database only,
so you need to run it in every database in which you want
the extension's facilities to be available. Alternatively, run it in
database template1
so that the extension will be copied into
subsequently-created databases by default.
For all extensions, the CREATE EXTENSION
command must be
run by a database superuser, unless the extension is
considered “trusted”. Trusted extensions can be run by any
user who has CREATE
privilege on the current
database. Extensions that are trusted are identified as such in the
sections that follow. Generally, trusted extensions are ones that cannot
provide access to outside-the-database functionality.
The following extensions are trusted in a default installation:
btree_gin | fuzzystrmatch | ltree | tcn |
btree_gist | hstore | pgcrypto | tsm_system_rows |
citext | intarray | pg_trgm | tsm_system_time |
cube | isn | seg | unaccent |
dict_int | lo | tablefunc | uuid-ossp |
Many extensions allow you to install their objects in a schema of your
choice. To do that, add SCHEMA
to the schema_name
CREATE EXTENSION
command. By default, the objects will be placed in your current creation
target schema, which in turn defaults to public
.
Note, however, that some of these components are not “extensions” in this sense, but are loaded into the server in some other way, for instance by way of shared_preload_libraries. See the documentation of each component for details.