# FAQ (Frequently Asked Questions)

## General

### What's the difference between the repmgr versions?

&repmgr; 4 is a complete rewrite of the previous &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; 5 is fundamentally the same code base as &repmgr; 4, but provides support for the revised replication configuration mechanism in PostgreSQL 12.

Support for PostgreSQL 9.3 is no longer available from &repmgr; 5.2.

&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 We recommend upgrading to &repmgr; 4, as the &repmgr; 3.x series is no longer maintained.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 While it is compatible with PostgreSQL 9.3, we recommend using repmgr 4.x. &repmgr; 2.x is no longer maintained.

See also &repmgr; compatibility matrix and Should I upgrade &repmgr;?.

### 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.

Our 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.

### 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.

### 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.

### 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 from 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.

### 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 EnterpriseDB; if this is not possible, contact your vendor for assistance.

### How can I obtain old versions of &repmgr; packages?

See appendix packages-old-versions for details.

### 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.

### Will replication stop working if &repmgr; is uninstalled?

No. See preceding question.

### Does it matter if different &repmgr; versions are present in the replication cluster?

Yes. If different "major" &repmgr; versions (e.g. 3.3.x and 4.1.x) are present, &repmgr; (in particular &repmgrd;) may not run, or run properly, or in the worst case (if different &repmgrd; versions are running and there are differences in the failover implementation) break your replication cluster.

If different "minor" &repmgr; versions (e.g. 4.1.1 and 4.1.6) are installed, &repmgr; will function, but we strongly recommend always running the same version to ensure there are no unexpected surprises, e.g. a newer version behaving slightly differently to the older version.

See also Should I upgrade &repmgr;?.

### Should I upgrade &repmgr;?

Yes.

We don't release new versions for fun, you know. Upgrading may require a little effort, but running an older &repmgr; version with bugs which have since been fixed may end up costing you more effort. The same applies to PostgreSQL itself.

### Why do I need to specify the data directory location in repmgr.conf?

In some circumstances &repmgr; may need to access a PostgreSQL data directory while the PostgreSQL server is not running, e.g. to confirm it shut down cleanly during a switchover.

Additionally, this provides support when using &repmgr; on PostgreSQL 9.6 and earlier, where the `repmgr` user is not a superuser; in that case the `repmgr` user will not be able to access the `data_directory` configuration setting, access to which is restricted to superusers.

In PostgreSQL 10 and later, non-superusers can be added to the default role `pg_read_all_settings` (or the meta-role `pg_monitor`) which will enable them to read this setting.

### Are &repmgr; packages compatible with `$third_party_vendor`'s packages?

&repmgr; packages provided by EnterpriseDB are compatible with the community-provided PostgreSQL packages and specified software provided by EnterpriseDB.

A number of other vendors provide their own versions of PostgreSQL packages, often with different package naming schemes and/or file locations.

We cannot guarantee that &repmgr; packages will be compatible with these packages. It may be possible to override package dependencies (e.g. `rpm --nodeps` for CentOS-based systems or `dpkg --force-depends` for Debian-based systems).

## `repmgr`

### Can I register an existing PostgreSQL server with repmgr?

Yes, any existing PostgreSQL server which is part of the same replication cluster can be registered with &repmgr;. There's no requirement for a standby to have been cloned using &repmgr;.

### Can I use a standby not cloned by &repmgr; as a &repmgr; node?

For a standby which has been manually cloned or recovered from an external backup manager such as Barman, the command `repmgr standby clone --replication-conf-only` can be used to create the correct replication configuration file for use with &repmgr; (and will create a replication slot if required). Once this has been done, register the node as usual.

### What does &repmgr; write in the replication configuration, and what options can be set there?

See section Customising replication configuration.

### How can a failed primary be re-added as a standby?

This is a two-stage process. First, the failed primary's data directory must be re-synced with the current primary; secondly the failed primary needs to be re-registered as a standby.

It's possible to use `pg_rewind` to re-synchronise the existing data directory, which will usually be much faster than re-cloning the server. However `pg_rewind` can only be used if PostgreSQL either has `wal_log_hints` enabled, or data checksums were enabled when the cluster was initialized.

Note that `pg_rewind` is available as part of the core PostgreSQL distribution from PostgreSQL 9.5, and as a third-party utility for PostgreSQL 9.3 and 9.4.

&repmgr; provides the command `repmgr node rejoin` which can optionally execute `pg_rewind`; see the repmgr-node-rejoin documentation for details, in particular the section repmgr-node-rejoin-pg-rewind.

If `pg_rewind` cannot be used, then the data directory will need to be re-cloned from scratch.

### Is there an easy way to check my primary server is correctly configured for use with &repmgr;?

Execute `repmgr standby clone` with the `--dry-run` option; this will report any configuration problems which need to be rectified.

### When cloning a standby, how can I get &repmgr; to copy `postgresql.conf` and `pg_hba.conf` from the PostgreSQL configuration directory in `/etc`?

Use the command line option `--copy-external-config-files`. For more details see repmgr-standby-clone-config-file-copying.

### Do I need to include `shared_preload_libraries = 'repmgr'` in `postgresql.conf` if I'm not using &repmgrd;?

No, the `repmgr` shared library is only needed when running &repmgrd;. If you later decide to run &repmgrd;, you just need to add `shared_preload_libraries = 'repmgr'` and restart PostgreSQL.

### I've provided replication permission for the `repmgr` user in `pg_hba.conf` but `repmgr`/&repmgrd; complains it can't connect to the server... Why?

`repmgr` and &repmgrd; need to be able to connect to the repmgr database with a normal connection to query metadata. The `replication` connection permission is for PostgreSQL's streaming replication (and doesn't necessarily need to be the `repmgr` user).

### When cloning a standby, why do I need to provide the connection parameters for the primary server on the command line, not in the configuration file?

Cloning a standby is a one-time action; the role of the server being cloned from could change, so fixing it in the configuration file would create confusion. If &repmgr; needs to establish a connection to the primary server, it can retrieve this from the `repmgr.nodes` table on the local node, and if necessary scan the replication cluster until it locates the active primary.

### When cloning a standby, how do I ensure the WAL files are placed in a custom directory?

Provide the option `--waldir` (`--xlogdir` in PostgreSQL 9.6 and earlier) with the absolute path to the WAL directory in `pg_basebackup_options`. For more details see cloning-advanced-pg-basebackup-options.

In &repmgr; 5.2 and later, this setting will also be honoured when cloning from Barman.

### Why is there no foreign key on the `node_id` column in the `repmgr.events` table?

Under some circumstances event notifications can be generated for servers which have not yet been registered; it's also useful to retain a record of events which includes servers removed from the replication cluster which no longer have an entry in the `repmgr.nodes` table.

### Why are some values in `recovery.conf` (PostgreSQL 11 and earlier) surrounded by pairs of single quotes?

This is to ensure that user-supplied values which are written as parameter values in `recovery.conf` are escaped correctly and do not cause errors when the file is parsed.

The escaping is performed by an internal PostgreSQL routine, which leaves strings consisting of digits and alphabetical characters only as-is, but wraps everything else in pairs of single quotes, even if the string does not contain any characters which need escaping.

### How can I exclude &repmgr; metadata from pg_dump output?

Beginning with &repmgr; 5.2, the metadata tables associated with the &repmgr; extension (`repmgr.nodes`, `repmgr.events` and `repmgr.monitoring_history`) have been marked as dumpable as they contain configuration and user-generated data.

To exclude these from pg_dump output, add the flag `--exclude-schema=repmgr`.

To exclude individual &repmgr; metadata tables from pg_dump output, add the flag e.g. `--exclude-table=repmgr.monitoring_history`. This flag can be provided multiple times to exclude individual tables,

## &repmgrd;

### How can I prevent a node from ever being promoted to primary?

In `repmgr.conf`, set its priority to a value of `0`; apply the changed setting with `repmgr standby register --force`.

Additionally, if `failover` is set to `manual`, the node will never be considered as a promotion candidate.

### Does &repmgrd; support delayed standbys?

&repmgrd; can monitor delayed standbys - those set up with `recovery_min_apply_delay` set to a non-zero value in the replication configuration. However &repmgrd; does not currently consider this setting, and therefore may not be able to properly evaluate the node as a promotion candidate.

We recommend that delayed standbys are explicitly excluded from promotion by setting `priority` to `0` in `repmgr.conf`.

Note that after registering a delayed standby, &repmgrd; will only start once the metadata added in the primary node has been replicated.

### How can I get &repmgrd; to rotate its logfile?

Configure your system's `logrotate` service to do this; see repmgrd-log-rotation.

### I've recloned a failed primary as a standby, but &repmgrd; refuses to start?

Check you registered the standby after recloning. If unregistered, the standby cannot be considered as a promotion candidate even if `failover` is set to `automatic`, which is probably not what you want. &repmgrd; will start if `failover` is set to `manual` so the node's replication status can still be monitored, if desired.

### &repmgrd; ignores pg_bindir when executing `promote_command` or `follow_command`

`promote_command` or `follow_command` can be user-defined scripts, so &repmgr; will not apply `pg_bindir` even if executing &repmgr;. Always provide the full path; see repmgrd-automatic-failover-configuration for more details.

### &repmgrd; aborts startup with the error "`upstream node must be running before repmgrd can start`"

&repmgrd; does this to avoid starting up on a replication cluster which is not in a healthy state. If the upstream is unavailable, &repmgrd; may initiate a failover immediately after starting up, which could have unintended side-effects, particularly if &repmgrd; is not running on other nodes.

In particular, it's possible that the node's local copy of the `repmgr.nodes` copy is out-of-date, which may lead to incorrect failover behaviour.

The onus is therefore on the administrator to manually set the cluster to a stable, healthy state before starting &repmgrd;.