C.1. General

C.1.1. What's the difference between the repmgr versions?

repmgr 4 is a complete rewrite of the existing repmgr code base and implements repmgr as a PostgreSQL extension. It supports all PostgreSQL versions from 9.3 (although some repmgr features are not available for PostgreSQL 9.3 and 9.4).

repmgr 3.x builds on the improved replication facilities added in PostgreSQL 9.3, as well as improved automated failover support via repmgrd, and is not compatible with PostgreSQL 9.2 and earlier. We recommend upgrading to repmgr 4, as the repmgr 3.x series will no longer be actively maintained.

repmgr 2.x supports PostgreSQL 9.0 ~ 9.3. While it is compatible with PostgreSQL 9.3, we recommend using repmgr 4.x. repmgr 2.x is no longer maintained.

C.1.2. What's the advantage of using replication slots?

Replication slots, introduced in PostgreSQL 9.4, ensure that the primary server will retain WAL files until they have been consumed by all standby servers. This means standby servers should never fail due to not being able to retrieve required WAL files from the primary.

However this does mean that if a standby is no longer connected to the primary, the presence of the replication slot will cause WAL files to be retained indefinitely, and eventually lead to disk space exhaustion.

Tip: 2ndQuadrant's recommended configuration is to configure Barman as a fallback source of WAL files, rather than maintain replication slots for each standby. See also: Using Barman as a WAL file source.

C.1.3. How many replication slots should I define in max_replication_slots?

Normally at least same number as the number of standbys which will connect to the node. Note that changes to max_replication_slots require a server restart to take effect, and as there is no particular penalty for unused replication slots, setting a higher figure will make adding new nodes easier.

C.1.4. Does repmgr support hash indexes?

Before PostgreSQL 10, hash indexes were not WAL logged and are therefore not suitable for use in streaming replication in PostgreSQL 9.6 and earlier. See the PostgreSQL documentation for details.

From PostgreSQL 10, this restriction has been lifted and hash indexes can be used in a streaming replication cluster.

C.1.5. Can repmgr assist with upgrading a PostgreSQL cluster?

For minor version upgrades, e.g. from 9.6.7 to 9.6.8, a common approach is to upgrade a standby to the latest version, perform a switchover promoting it to a primary, then upgrade the former primary.

For major version upgrades (e.g. from PostgreSQL 9.6 to PostgreSQL 10), the traditional approach is to "reseed" a cluster by upgrading a single node with pg_upgrade and recloning standbys from this.

To minimize downtime during major upgrades, for more recent PostgreSQL versions (PostgreSQL 9.4 and later), pglogical can be used to set up a parallel cluster using the newer PostgreSQL version, which can be kept in sync with the existing production cluster until the new cluster is ready to be put into production.

C.1.6. What does this error mean: ERROR: could not access file "$libdir/repmgr"?

It means the repmgr extension code is not installed in the PostgreSQL application directory. This typically happens when using PostgreSQL packages provided by a third-party vendor, which often have different filesystem layouts.

Either use PostgreSQL packages provided by the community or 2ndQuadrant; if this is not possible, contact your vendor for assistance.

C.1.7. How can I obtain old versions of repmgr packages?

See appendix Installing old package versions for details.

C.1.8. Is repmgr required for streaming replication?

No.

repmgr (together with repmgrd) assists with managing replication. It does not actually perform replication, which is part of the core PostgreSQL functionality.

C.1.9. Will replication stop working if repmgr is uninstalled?

No. See preceding question.