Using extensions with PGD
=========================

PGD and other PostgreSQL extensions
-----------------------------------

PGD is implemented as a PostgreSQL extension (see 
`Supported Postgres database servers <https://www.enterprisedb.com/docs/pgd/latest/overview/compatibility/>`_  ). It
takes advantage of PostgreSQL’s expandability and flexibility to modify
low-level system behavior to provide multi-master replication.

In principle, extensions provided by community PostgreSQL, EDB Postgres
Advanced Server, and third-party extensions can be used with PGD.
However, the distributed nature of PGD means that you need to carefully
consider and plan the extensions you select and install.

Extensions providing logical decoding
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Extensions providing logical decoding, such as `wal2json <https://github.com/eulerto/wal2json>`_  , may in
theory work with PGD. However, there’s no support for failover, meaning
any WAL stream being read from such an extension can be interrupted.

Extensions providing replication or HA functionality
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Any extension extending PostgreSQL with functionality related to
replication or HA/failover is unlikely to work well with PGD and may
even be detrimental to the health of the PGD cluster. We recommend
avoiding these.

Supported extensions
--------------------

These extensions are explicitly supported by PGD.

EDB Advanced Storage table access methods
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The :ref:`EDB Advanced Storage Pack <Using extensions with PGD>`  provides a selection of table access methods (TAMs)
implemented as extensions. The following TAMs are certified for use with
PGD:

- :ref:`Autocluster <Using extensions with PGD>`  

- :ref:`Refdata <Using extensions with PGD>`  

For more details, see :ref:`Use of table access methods (TAMs) in PGD <Use of table access methods (TAMs) in PGD>`  .

pgaudit
^^^^^^^

PGD was modified to ensure compatibility with the `pgaudit <https://www.pgaudit.org/>`_ 
extension. See :ref:`Postgres settings <Postgres settings>`  for configuration information.

Installing extensions
---------------------

PostgreSQL extensions provide SQL objects, such as functions, datatypes,
and, optionally, one or more shared libraries. These must be loaded into
the PostgreSQL backend before you can install and use the extension.

..  Warning::
   The relevant extension packages must be available on all nodes in the cluster. Otherwise extension installation can fail and impact cluster stability.

If PGD is deployed using `Trusted Postgres Architect <https://www.enterprisedb.com/docs/tpa/latest/>`_  , configure extensions using that
tool. For details, see `Adding Postgres extensions <https://www.enterprisedb.com/docs/tpa/latest/reference/postgres_extension_configuration>`_  .

The following is relevant for manually configured PGD installations.

Configuring shared_preload_libraries
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If an extension provides a shared library, include this library in the
`shared_preload_libraries <https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES>`_  configuration parameter before installing the extension.

``shared_preload_libraries`` consists of a comma-separated list of
extension names. It must include ``bdr`` . The order in which you
specify other extensions generally doesn’t matter.

Configure ``shared_preload_libraries`` on all nodes in the cluster
before installing the extension with ``CREATE EXTENSION`` . You must
restart PostgreSQL to activate the new configuration.

See also :ref:`Postgres settings <Postgres settings>`  .

Installing the extension
^^^^^^^^^^^^^^^^^^^^^^^^

Install the extension using the ``CREATE EXTENSION`` command. You need
to do this on only one node in the cluster. PGD’s DDL replication will
ensure that it propagates to all other nodes.

..  Warning::
   Do not attempt to install extensions manually on each node by, for example, disabling DDL replication before executing `CREATE EXTENSION` .

Do not use a command such as ``bdr.replicate_ddl_command()`` to execute
``CREATE EXTENSION`` .