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

Note that hot_standby defaults to on from LightDB 21 and later.

LightDB documentation: hot_standby.

wal_level must be one of replica or logical.

LightDB 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 LightDB instance; additionally ltcluster will require two free WAL senders in order to clone further standbys.

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

LightDB 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 LightDB instances in the replication cluster which may potentially become a primary server or (in cascading replication) the upstream server of a standby.

LightDB documentation: max_replication_slots.

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

For more details see Using lt_rewind.

LightDB 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 LightDB server restart, while archive_command changes can be applied via a normal configuration reload.

However, ltcluster itself does not require WAL file archiving.

LightDB 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.

LightDB documentation: archive_command.

Normally there is no need to set wal_keep_segments (LightDB 21 and later: wal_keep_size; 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 are recommended to ensure standbys have a reliable source of WAL segments at all times.

The only reason ever to set wal_keep_segments / wal_keep_size is you have you have configured pg_basebackup_options in ltcluster.conf to include the setting --wal-method=fetch and you have not set restore_command in ltcluster.conf to fetch WAL files from a reliable source, 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 WAL retention in this way.

LightDB documentation: wal_keep_segments.