4.1. Prerequisites for configuration

hot_standby must always be set to on, as repmgr needs to be able to connect to each server it manages.

Note that hot_standby defaults to on from PostgreSQL 10 and later; in PostgreSQL 9.6 and earlier, the default was off.

PostgreSQL documentation: hot_standby.

wal_level must be one of replica or logical (PostgreSQL 9.5 and earlier: one of hot_standby or logical).

PostgreSQL documentation: wal_level.

max_wal_senders must be set to a value of 2 or greater. In general you will need one WAL sender for each standby which will attach to the PostgreSQL instance; additionally repmgr will require two free WAL senders in order to clone further standbys.

max_wal_senders should be set to an appropriate value on all PostgreSQL instances in the replication cluster which may potentially become a primary server or (in cascading replication) the upstream server of a standby.

PostgreSQL documentation: max_wal_senders.

If you are intending to use replication slots, max_replication_slots must be set to a non-zero value.

max_replication_slots should be set to an appropriate value on all PostgreSQL instances in the replication cluster which may potentially become a primary server or (in cascading replication) the upstream server of a standby.

PostgreSQL documentation: max_replication_slots.

If you are intending to use pg_rewind, and the cluster was not initialised using data checksums, you may want to consider enabling wal_log_hints.

For more details see Using pg_rewind.

PostgreSQL documentation: wal_log_hints.

We suggest setting archive_mode to on (and archive_command to /bin/true; see below) even if you are currently not planning to use WAL file archiving.

This will make it simpler to set up WAL file archiving if it is ever required, as changes to archive_mode require a full PostgreSQL server restart, while archive_command changes can be applied via a normal configuration reload.

However, repmgr itself does not require WAL file archiving.

PostgreSQL documentation: archive_mode.

If you have set archive_mode to on but are not currently planning to use WAL file archiving, set archive_command to a command which does nothing but returns true, such as /bin/true. See above for details.

PostgreSQL documentation: archive_command.

Normally there is no need to set wal_keep_segments (default: 0), as it is not a reliable way of ensuring that all required WAL segments are available to standbys. Replication slots and/or an archiving solution such as Barman are recommended to ensure standbys have a reliable source of WAL segments at all times.

The only reason ever to set wal_keep_segments is you have you have configured pg_basebackup_options in repmgr.conf to include the setting --wal-method=fetch (PostgreSQL 9.6 and earlier: --xlog-method=fetch) and you have not set restore_command in repmgr.conf to fetch WAL files from a reliable source such as Barman, in which case you'll need to set wal_keep_segments to a sufficiently high number to ensure that all WAL files required by the standby are retained. However we do not recommend managing replication in this way.

PostgreSQL documentation: wal_keep_segments.