Using extensions with PGD v5
PGD and other PostgreSQL extensions
PGD is implemented as a PostgreSQL extension (see Supported Postgres database servers). 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, 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 EDB Advanced Storage Pack provides a selection of table access methods (TAMs) implemented as extensions. The following TAMs are certified for use with PGD:
For more details, see Table access methods.
pgaudit
PGD was modified to ensure compatibility with the pgaudit extension. See 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, configure extensions using that tool. For details, see Adding Postgres extensions.
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 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. However if you're using the pgaudit extension, pgaudit must appear in the list before bdr.
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 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.