Using extensions with PGD v5.6
PGD and other PostgreSQL extensions
PGD is implemented as a PostgreSQL extension (see Supported Postgres database servers), taking advantage of PostgreSQL's expandability and flexibility to modify low level system behavior to provide multi-master replication.
In principle other extensions - both those provided by community PostgreSQL and EPAS, as well as third-party extensions, can be used together with PGD, however the distributed nature of PGD means selection and installation of extensions should be carefully considered and planned.
Extensions providing logical decoding
Extensions providing logical decoding, such as wal2json, may in theory work with PGD, but there is no support for failover, meaning any WAL stream being read from such an extension may be interrupted.
Extensions providing replication and/or HA functionality
Any extension extending PostgreSQL with functionality related to replication and/or HA/failover is unlikely to work well with PGD, and may even be detrimental to the health of the PGD cluster, so should be avoided.
Supported extensions
This section lists extensions which are explicitly supported by PGD.
EDB Advanced Server Table Access methods
The EDB Advanced Storage Pack provides a selection of table access methods (TAMs) implemented as extensions of which the following are certified for use with PGD:
For more details, see Table access methods.
pgaudit
PGD has been modified to ensure compatibility with the pgaudit extension. See Postgres settings for configuration information.
Installing extensions
PostgreSQL extensions provide SQL objects such as functions and datatypes, and optionally also one or more shared libraries, which must be loaded into the PostgreSQL backend before the extension can be installed and used.
Warning
The relevant extension packages must be available on all nodes in the cluster, otherwise extension installation may fail and impact cluster stability.
If PGD is deployed using Trusted Postgres Architect, extensions should be configured via that. For more details see Adding Postgres extensions.
The following sections are relevant for manually configured PGD installations.
Configuring "shared_preload_libraries"
If an extension provides a shared library, this library must be included in the shared_preload_libraries configuration parameter before the extension itself is installed.
shared_preload_libraries consists of a comma-separated list of extension names.
It must include the bdr extension.
The order in which other extensions are specified is generally unimportant, however if using the pgaudit extension, pgaudit must appear in the list before bdr.
shared_preload_libraries should be configured on all nodes in the cluster before installing the extension with CREATE EXTENSION.
Note that it requires a PostgreSQL restart to activate the new configuration.
See also Postgres settings.
Installing the extension
The extension itself is installed with the CREATE EXTENSION command.
This only needs to be carried out on 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 e.g. disabling DDL replication before executing CREATE EXTENSION.
Do not use a command such as bdr.replicate_ddl_command() to execute CREATE EXTENSION.