Creating PGD nodes v5.6

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Depending on your selected deployment method, you may or may not have to create PGD nodes manually. For example, if you are using TPA or the EDB Postgres Distributed for Kubernetes, the nodes are created automatically. But if you are manually deploying PGD or creating your own deployment method, you need to know how to create and configure a PGD node.

It's just Postgres

A PGD node is just a Postgres instance with the BDR extension installed. The BDR extension enables bidirectional replication between nodes and is the foundation of PGD.

That means, in the most general terms, you can create a PGD node by installing Postgres and the BDR extension, and then configuring the node to connect to the other nodes in the PGD group. But there are some specifics to consider.

Which Postgres version?

PGD is built on top of Postgres, so the distribution and version of Postgres you use for your PGD nodes is important. The version of Postgres you use must be compatible with the version of PGD you are using. You can find the compatibility matrix in the release notes. Features and functionality in PGD may depend on the distribution of Postgres you are using. The EDB Postgres Advanced Server is the recommended distribution for PGD. PGD also supports EDB Postgres Extended Server and Community Postgres. You can find out what features are available in each distribution in the Planning section's Choosing a server page.

Installing Postgres

You must install your selected Postgres distribution on each node you are configuring. You can find installation instructions for each distribution in the EDB Postgres Advanced Server documentation, EDB Postgres Extended Server documentation, and the Postgres installation documentation. You can also refer to the PGD manual installation guide which covers the installation of Postgres.

Installing the BDR extension

The BDR extension is the key to PGD's distributed architecture. You need to install the BDR extension on each node in your PGD cluster. The BDR extension is available from the EDB Postgres Distributed repository. You need to add the postgres_distributed repository to your package management system on Linux and then install the edb-bdr package. You can find the repository configuration instructions in the PGD manual installation guide.

Once the repository is configured, you can install the BDR package with your package manager. The package name is edb-bdr5-<postgresversion> where <postgresversion> is the version of Postgres you are using. For example, if you are using Postgres 13, the package name is edb-bdr5-13.

Configuring the database for PGD

This process is specific to PGD and involves configuring the Postgres instance to work with the BDR extension and adjusting various settings to work with the PGD cluster. This process is also detailed in the PGD manual installation guide The steps are as follows:

  • Add the BDR extension $libdir/bdr at the start of the shared_preload_libraries setting in postgresql.conf.
  • Set the wal_level GUC variable to logical in postgresql.conf.
  • Turn on commit timestamp tracking by setting track_commit_timestamp to 'on' in postgresql.conf.
  • Increase the maximum worker processes to 16 or higher by setting max_worker_processes to '16' in postgresql.conf.

    The max_worker_processes value

    The max_worker_processes value is derived from the topology of the cluster, the number of peers, number of databases, and other factors. To calculate the needed value, see Postgres configuration/settings. The value of 16 was calculated for the size of cluster being deployed in this example. It must be increased for larger clusters.

  • Set a password on the EnterprisedDB/Postgres user.
  • Add rules to pg_hba.conf to allow nodes to connect to each other.
    • Ensure that these lines are present in pg_hba.conf:
    host all all all md5
host replication all all md5
  • Add a .pgpass file to allow nodes to authenticate each other.
    • Configure a user with sufficient privileges to log in to the other nodes.
    • See The Password File in the Postgres documentation for more on the .pgpass file.

Once these steps are complete, restart the Postgres instance to apply the changes.

Initializing a PGD node

Log into the database instance you have configured and set up the BDR extension. You can do this by running the CREATE EXTENSION bdr; command as super user in the database. This command creates the BDR extension.

You also need to create a database within Postgres to use as PGD's replicated database. You can do this with the CREATE DATABASE command. The created database should be the name of the database that other nodes in the PGD cluster replicate. The convention is to name the database bdrdb.

Next steps

The node is now configured and ready to be join a group, or start a group, in the PGD cluster.

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