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287 lines
11 KiB
ReStructuredText
========================
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repmgr: Quickstart guide
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========================
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repmgr is an open-source tool suite for mananaging replication and failover
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among multiple PostgreSQL server nodes. It enhances PostgreSQL's built-in
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hot-standby capabilities with a set of administration tools for monitoring
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replication, setting up standby servers and performing failover/switchover
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operations.
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This quickstart guide assumes you are familiar with PostgreSQL replication
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setup and Linux/UNIX system administration. For a more detailed tutorial
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covering setup on a variety of different systems, see the README.rst file.
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Conceptual Overview
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===================
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repmgr provides two binaries:
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- ``repmgr``: a command-line client to manage replication and repmgr configuration
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- ``repmgrd``: an optional daemon process which runs on standby nodes to monitor
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replication and node status
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Each PostgreSQL node requires a repmgr configuration file; additionally
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it must be "registered" using the repmgr command-line client. repmgr stores
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information about managed nodes in a custom schema on the node's current master
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database.
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Requirements
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============
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repmgr works with PostgreSQL 9.0 and later. All server nodes must be running the
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same PostgreSQL major version, and preferably should be running the same minor
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version.
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repmgr will work on any Linux or UNIX-like environment capable of running
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PostgreSQL. rsync must also be installed.
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Installation
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============
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repmgr must be installed on each PostgreSQL server node.
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* Packages
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- RPM packages for RedHat-based distributions are available from PGDG
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- Debian/Ubuntu provide .deb packages.
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It is also possible to build .deb packages directly from the repmgr source;
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see README.rst for further details.
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* Source installation
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- repmgr source code is hosted at github (https://github.com/2ndQuadrant/repmgr);
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tar.gz files can be downloaded from https://github.com/2ndQuadrant/repmgr/releases .
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repmgr can be built easily using PGXS:
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sudo make USE_PGXS=1 install
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Configuration
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-------------
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* Server configuration
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Password-less SSH logins must be enabled for the database system user (typically ``postgres``)
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between all server nodes to enable repmgr to copy required files.
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* PostgreSQL configuration
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The master PostgreSQL node needs to be configured for replication with the
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following settings::
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wal_level = 'hot_standby' # minimal, archive, hot_standby, or logical
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archive_mode = on # allows archiving to be done
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archive_command = 'cd .' # command to use to archive a logfile segment
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max_wal_senders = 10 # max number of walsender processes
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wal_keep_segments = 5000 # in logfile segments, 16MB each; 0 disables
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hot_standby = on # "on" allows queries during recovery
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Note that repmgr expects a default of 5000 wal_keep_segments, although this
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value can be overridden when executing the ``repmgr`` client.
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Additionally, repmgr requires a dedicated PostgreSQL superuser account
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and a database in which to store monitoring and replication data. The
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database can in principle be any database, including the default postgres
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one, however it's probably advisable to create a dedicated repmgr database.
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* repmgr configuration
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Each PostgreSQL node requires a repmgr configuration file containing
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identification and database connection information::
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cluster=test
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node=1
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node_name=node1
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conninfo='host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
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pg_bindir=/path/to/postgres/bin
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* ``cluster``: common name for the replication cluster; this must be the same on all nodes
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* ``node``: a unique, abitrary integer identifier
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* ``name``: a unique, human-readable name
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* ``conninfo``: a standard conninfo string enabling repmgr to connect to the
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control database; user and name must be the same on all nodes, while other
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parameters such as port may differ. The ``host`` parameter *must* be a hostname
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resolvable by all nodes on the cluster.
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* ``pg_bindir``: (optional) location of PostgreSQL binaries, if not in the default $PATH
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Note that the configuration file should not be stored inside the PostgreSQL
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data directory.
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Each node configuration needs to be registered with repmgr, either using the
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repmgr command line tool, or the repmgrd daemon; for details see below. Details
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about each node are inserted into the repmgr database (for details see below).
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Replication setup and monitoring
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================================
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For the purposes of this guide, we'll assume the database user will be
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``repmgr_usr`` and the database will be ``repmgr_db``, and that the following
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environment variables are set on each node:
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- $HOME: the PostgreSQL system user's home directory
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- $PGDATA: the PostgreSQL data directory
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Master setup
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------------
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1. Configure PostgreSQL
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- create user and database::
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CREATE ROLE repmgr_usr LOGIN SUPERUSER;
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CREATE DATABASE repmgr_db OWNER repmgr_usr;
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- configure postgresql.conf for replication (see above)
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- update pg_hba.conf::
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host repmgr_usr repmgr_db 192.168.1.0/24 trust
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host replication all 192.168.1.0/24 trust
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Restart the PostgreSQL server after making these changes.
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2. Create the repmgr configuration file::
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$ cat $HOME/repmgr/repmgr.conf
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cluster=test
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node=1
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node_name=node1
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conninfo='host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
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pg_bindir=/path/to/postgres/bin
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3. Register the master node with repmgr::
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$ repmgr -f $HOME/repmgr/repmgr.conf --verbose master register
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[2014-07-04 10:43:42] [INFO] repmgr mgr connecting to master database
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[2014-07-04 10:43:42] [INFO] repmgr connected to master, checking its state
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[2014-07-04 10:43:42] [INFO] master register: creating database objects inside the repmgr_test schema
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[2014-07-04 10:43:43] [NOTICE] Master node correctly registered for cluster test with id 1 (conninfo: host=localhost user=repmgr_usr dbname=repmgr_db)
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-d is the database defined in repmgr.conf file.
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Slave/standby setup
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-------------------
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1. Use repmgr to clone the master::
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$ repmgr -f $HOME/repmgr/repmgr.conf -D $PGDATA -d repmgr_db -U repmgr_usr -R postgres --verbose standby clone 192.168.1.2
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Opening configuration file: ./repmgr.conf
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[2014-07-04 10:49:00] [ERROR] Did not find the configuration file './repmgr.conf', continuing
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[2014-07-04 10:49:00] [INFO] repmgr connecting to master database
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[2014-07-04 10:49:00] [INFO] repmgr connected to master, checking its state
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[2014-07-04 10:49:00] [INFO] Successfully connected to primary. Current installation size is 1807 MB
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[2014-07-04 10:49:00] [NOTICE] Starting backup...
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[2014-07-04 10:49:00] [INFO] creating directory "/path/to/data/"...
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(...)
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[2014-07-04 10:53:19] [NOTICE] Finishing backup...
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NOTICE: pg_stop_backup complete, all required WAL segments have been archived
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[2014-07-04 10:53:21] [INFO] repmgr requires primary to keep WAL files 0000000100000000000000AD until at least 0000000100000000000000AD
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[2014-07-04 10:53:21] [NOTICE] repmgr standby clone complete
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[2014-07-04 10:53:21] [NOTICE] HINT: You can now start your postgresql server
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[2014-07-04 10:53:21] [NOTICE] for example : /etc/init.d/postgresql start
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-R is the database system user on the master node. At this point it does not matter
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if the ``repmgr.conf`` file is not found.
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This will clone the PostgreSQL database files from the master, and additionally
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create an appropriate ``recovery.conf`` file.
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2. Start the PostgreSQL server
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3. Create the repmgr configuration file::
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$ cat $HOME/repmgr/repmgr.conf
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cluster=test
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node=2
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node_name=node2
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conninfo='host=repmgr_node2 user=repmgr_usr dbname=repmgr_db'
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pg_bindir=/path/to/postgres/bin
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4. Register the master node with repmgr::
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$ repmgr -f $HOME/repmgr/repmgr.conf --verbose standby register
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Opening configuration file: /path/to/repmgr/repmgr.conf
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[2014-07-04 11:48:13] [INFO] repmgr connecting to standby database
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[2014-07-04 11:48:13] [INFO] repmgr connected to standby, checking its state
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[2014-07-04 11:48:13] [INFO] repmgr connecting to master database
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[2014-07-04 11:48:13] [INFO] finding node list for cluster 'test'
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[2014-07-04 11:48:13] [INFO] checking role of cluster node 'host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
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[2014-07-04 11:48:13] [INFO] repmgr connected to master, checking its state
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[2014-07-04 11:48:13] [INFO] repmgr registering the standby
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[2014-07-04 11:48:13] [INFO] repmgr registering the standby complete
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[2014-07-04 11:48:13] [NOTICE] Standby node correctly registered for cluster test with id 2 (conninfo: host=localhost user=repmgr_usr dbname=repmgr_db)
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Monitoring
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----------
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``repmgrd`` is a management and monitoring daemon which runs on standby nodes
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and which and can automate remote actions. It can be started simply with e.g.::
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repmgrd -f $HOME/repmgr/repmgr.conf --verbose > $HOME/repmgr/repmgr.log 2>&1
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or alternatively::
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repmgrd -f $HOME/repmgr/repmgr.conf --verbose --monitoring-history > $HOME/repmgr/repmgrd.log 2>&1
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which will track advance or lag of the replication in every standby in the
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``repl_monitor`` table.
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Example log output::
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[2014-07-04 11:55:17] [INFO] repmgrd Connecting to database 'host=localhost user=repmgr_usr dbname=repmgr_db'
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[2014-07-04 11:55:17] [INFO] repmgrd Connected to database, checking its state
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[2014-07-04 11:55:17] [INFO] repmgrd Connecting to primary for cluster 'test'
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[2014-07-04 11:55:17] [INFO] finding node list for cluster 'test'
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[2014-07-04 11:55:17] [INFO] checking role of cluster node 'host=repmgr_node1 user=repmgr_usr dbname=repmgr_db'
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[2014-07-04 11:55:17] [INFO] repmgrd Checking cluster configuration with schema 'repmgr_test'
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[2014-07-04 11:55:17] [INFO] repmgrd Checking node 2 in cluster 'test'
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[2014-07-04 11:55:17] [INFO] Reloading configuration file and updating repmgr tables
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[2014-07-04 11:55:17] [INFO] repmgrd Starting continuous standby node monitoring
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Failover
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--------
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To promote a standby to master, on the standby execute e.g.::
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repmgr -f $HOME/repmgr/repmgr.conf --verbose standby promote
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repmgr will attempt to connect to the current master to verify that it
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is not available (if it is, repmgr will not promote the standby).
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Other standby servers need to be told to follow the new master with::
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repmgr -f $HOME/repmgr/repmgr.conf --verbose standby follow
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See file ``autofailover_quick_setup.rst`` for information on how to set up
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automated failover.
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repmgr database schema
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======================
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repmgr creates a small schema for its own use in the database specified in
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each node's conninfo configuration parameter. This database can in principle
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be any database. The schema name is the global ``cluster`` name prefixed
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with ``repmgr_``, so for the example setup above the schema name is
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``repmgr_test``.
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The schema contains two tables:
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* ``repl_nodes``
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stores information about all registered servers in the cluster
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* ``repl_monitor``
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stores monitoring information about each node
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and one view, ``repl_status``, which summarizes the latest monitoring information
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for each node.
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