postgresql #0

Supports: trusty


PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness. It is fully ACID compliant, has full support for foreign keys, joins, views, triggers, and stored procedures (in multiple languages). It includes most SQL:2008 data types, including INTEGER, NUMERIC, BOOLEAN, CHAR, VARCHAR, DATE, INTERVAL, and TIMESTAMP. It also supports storage of binary large objects, including pictures, sounds, or video. It has native programming interfaces for C/C++, Java, .Net, Perl, Python, Ruby, Tcl, ODBC, among others, and exceptional documentation (


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PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness. It is fully ACID compliant, has full support for foreign keys, joins, views, triggers, and stored procedures (in multiple languages). It includes most SQL:2008 data types, including INTEGER, NUMERIC, BOOLEAN, CHAR, VARCHAR, DATE, INTERVAL, and TIMESTAMP. It also supports storage of binary large objects, including pictures, sounds, or video. It has native programming interfaces for C/C++, Java, .Net, Perl, Python, Ruby, Tcl, ODBC, among others, and exceptional documentation.

An enterprise class database, PostgreSQL boasts sophisticated features such as Multi-Version Concurrency Control (MVCC), point in time recovery, tablespaces, asynchronous replication, nested transactions (savepoints), online/hot backups, a sophisticated query planner/optimizer, and write ahead logging for fault tolerance. It supports international character sets, multibyte character encodings, Unicode, and it is locale-aware for sorting, case-sensitivity, and formatting. It is highly scalable both in the sheer quantity of data it can manage and in the number of concurrent users it can accommodate. There are active PostgreSQL systems in production environments that manage in excess of 4 terabytes of data.


This charm supports several deployment models:

  • A single service containing one unit. This provides a 'standalone' environment.

  • A service containing multiple units. One unit will be a 'master', and every other unit is a 'hot standby'. The charm sets up and maintains replication for you, using standard PostgreSQL streaming replication.

To setup a single 'standalone' service::

juju deploy postgresql pg-a

Scale Out Usage

To replicate this 'standalone' database to a 'hot standby', turning the existing unit into a 'master'::

juju add-unit pg-a

To deploy a new service containing a 'master' and two 'hot standbys'::

juju deploy -n 2 postgresql pg-b
[ ... wait until units are stable ... ]
juju add-unit pg-b

You can remove units as normal. If the master unit is removed, failover occurs and the most up to date 'hot standby' is promoted to 'master'. The 'db-relation-changed' and 'db-admin-relation-changed' hooks are fired, letting clients adjust::

juju remove-unit pg-b/0

To setup a client using a PostgreSQL database, in this case a vanilla Django installation listening on port 8080::

juju deploy postgresql
juju deploy python-django
juju deploy gunicorn
juju add-relation python-django postgresql:db
juju add-relation python-django gunicorn
juju expose python-django

Known Limitations and Issues

⚠ Due to current limitations with juju, you cannot reliably create a service initially containing more than 2 units (eg. juju deploy -n 3 postgresql). Instead, you must first create a service with 2 units. Once the environment is stable and all the hooks have finished running, you may add more units.

⚠ Do not attempt to relate client charms to a PostgreSQL service containing multiple units unless you know the charm supports a replicated service.

⚠ To host multiple units on a single server, you must use an lxc container.

Interacting with the Postgresql Service

At a minimum, you just need to join a the db relation, and a user and database will be created for you. For more complex environments, you can provide the database name allowing multiple services to share the same database. A client may also wish to defer its setup until the unit name is listed in allowed-units, to avoid attempting to connect to a database before it has been authorized.

The db-admin relation may be used similarly to the db relation. The automatically generated user for db-admin relations is a PostgreSQL superuser.

During db-relation-joined

the client service provides:

  • database: Optional. The name of the database to use. The postgresql service will create it if necessary. If your charm sets this, then it must wait until a matching database value is presented on the PostgreSQL side of the relation (ie. relation-get database returns the value you set).
  • roles: Optional. A comma separated list of database roles to grant the database user. Typically these roles will have been granted permissions to access the tables and other database objects. Do not grant permissions directly to juju generated database users, as the charm may revoke them.

During db-relation-changed

the postgresql service provides:

  • host: the host to contact.
  • database: a regular database.
  • port: the port PostgreSQL is listening on.
  • user: a regular user authorized to read the database.
  • password: the password for user.
  • state: 'standalone', 'master' or 'hot standby'.
  • allowed-units: space separated list of allowed clients (unit name). You should check this to determine if you can connect to the database yet.

During db-admin-relation-changed

the postgresql service provides:

  • host: the host to contact
  • port: the port PostgreSQL is listening on
  • user: a created super user
  • password: the password for user
  • state: 'standalone', 'master' or 'hot standby'
  • allowed-units: space separated list of allowed clients (unit name). You should check this to determine if you can connect to the database yet.

During syslog-relation-changed

the postgresql service provides:

  • programname: the syslog 'programname' identifying this unit's PostgreSQL logs.
  • log_line_prefix: the log_line_prefix setting for the PostgreSQL service.

For replicated database support

A PostgreSQL service may contain multiple units (a single master, and optionally one or more hot standbys). The client charm can tell which unit in a relation is the master and which are hot standbys by inspecting the 'state' property on the relation, and it needs to be aware of how many units are in the relation by using the 'relation-list' hook tool.

If there is a single PostgreSQL unit related, the state will be 'standalone'. All database connections of course go to this unit.

If there is more than one PostgreSQL unit related, the client charm must only use units with state set to 'master' or 'hot standby'. The unit with 'master' state can accept read and write connections. The units with 'hot standby' state can accept read-only connections, and any attempted writes will fail. Units with any other state must not be used and should be ignored ('standalone' units are new units joining the service that are not yet setup, and 'failover' state will occur when the master unit is being shutdown and a new master is being elected).

The client charm needs to watch for state changes in its relation-changed hook. New units may be added to a single unit service, and the client charm must stop using existing 'standalone' unit and wait for 'master' and 'hot standby' units to appear. Units may be removed, possibly causing a 'hot standby' unit to be promoted to a master, or even having the service revert to a single 'standalone' unit.

Example client hooks


import sys
from charmhelpers.core.hookenv import (
    Hooks, config, relation_set, relation_get,
    local_unit, related_units, remote_unit)

hooks = Hooks()
hook = hooks.hook

def db_relation_joined():
    relation_set('database', config('database'))  # Explicit database name
    relation_set('roles', 'reporting,standard')  # DB roles required

def db_relation_changed():

def db_relation_departed():
    # Note we currently have to explicitly filter the dying unit
    # from our list of database units due to LP Bug #1192433
        unit for unit in related_units() if unit != remote_unit())

def db_relation_broken():

def db_changed(active_db_units):
    # Rather than try to merge in just this particular database
    # connection that triggered the hook into our existing connections,
    # it is easier to iterate over all active related databases and
    # reset the entire list of connections.
    conn_str_tmpl = "dbname={dbname} user={user} host={host} port={port}"
    master_conn_str = None
    slave_conn_strs = []
    for db_unit in active_db_units:
        if relation_get('database', db_unit) != config('database'):
            continue  # Not yet acknowledged requested database name.

        allowed_units = relation_get('allowed-units') or ''  # May be None
        if local_unit() not in allowed_units.split():
            continue  # Not yet authorized.

        conn_str = conn_str_tmpl.format(**relation_get(unit=db_unit)
        remote_state = relation_get('state', db_unit)

        if remote_state == 'standalone' and len(active_db_units) == 1:
            master_conn_str = conn_str
        elif relation_state == 'master':
            master_conn_str = conn_str
        elif relation_state == 'hot standby':

    update_my_db_config(master=master_conn_str, slaves=slave_conn_strs)

if __name__ == '__main__':

Upgrade-charm hook notes

The PostgreSQL charm has deprecated volume-map and volume-ephemeral-storage configuration options in favor of using the storage subordinate charm for general external storage management. If the installation being upgraded is using these deprecated options, there are a couple of manual steps necessary to finish migration and continue using the current external volumes. Even though all data will remain intact, and PostgreSQL service will continue running, the upgrade-charm hook will intentionally fail and exit 1 as well to raise awareness of the manual procedure which will also be documented in the juju logs on the PostgreSQL units.

The following steps must be additionally performed to continue using external volume maps for the PostgreSQL units once juju upgrade-charm is run from the command line: 1. cat > storage.cfg <<EOF storage: provider:block-storage-broker root: /srv/data volume_map: "{postgresql/0: your-vol-id, postgresql/1: your-2nd-vol-id}" EOF 2. juju deploy --config storage.cfg storage 3. juju deploy block-storage-broker 4. juju add-relation block-storage-broker storage 5. juju resolved --retry postgresql/0 # for each postgresql unit running 6. juju add-relation postgresql storage

Contact Information



(string) A comma-separated list of IP Addresses (or single IP) admin tools like pgAdmin3 will connect from, this is most useful for developers running juju in local mode who need to connect tools like pgAdmin to a postgres. The IP addresses added here will be included in the pg_hba.conf file allowing ip connections to all databases on the server from the given using md5 password encryption.
(int) An advisory lock key used internally by the charm. You do not need to change it unless it happens to conflict with an advisory lock key being used by your applications.
(string) Command used to archive WAL files when archive_mode is set and wal_level > minimal.
(boolean) Enable archiving of WAL files using the command specified by archive_command. If archive_mode is enabled and archive_command not set, then archiving is deferred until archive_command is set and the WAL files will accumulate.
(boolean) Autovacuum should almost always be running. If you want to turn this off, you are probably following out of date documentation.
(float) Fraction of table size before analyze
(int) min number of row updates before analyze
(string) Default vacuum cost delay for autovacuum, in milliseconds; -1 means use vacuum_cost_delay
(float) Fraction of table size before vacuum
(string) Directory to place backups in
(int) Number of recent backups to retain.
(string) Cron-formatted schedule for database backups.
13 4 * * *
(int) in logfile segments, min 1, 16MB each. Ignored unless 'performance_tuning' is set to 'manual'.
(string) Maximum time between automatic WAL checkpoints. range '30s-1h'. If left empty, the default postgresql value will be used.
(string) Name of the cluster we want to install the DBs into
(string) The command to run whenever config has changed. Accepted values are "reload" or "restart" - any other value will mean neither is executed after a config change (which may be desired, if you're running a production server and would rather handle these out of band). Note that postgresql will still need to be reloaded whenever authentication and access details are updated, so disabling either doesn't mean PostgreSQL will never be reloaded.
(string) Path to a dumpfile to load into DB when service is initiated.
(string) Effective cache size is an estimate of how much memory is available for disk caching within the database. (50% to 75% of system memory). This string should be of the format '###MB'. Ignored unless 'performance_tuning' is set to 'manual'.
(string) Default encoding used to store text in this service. Can only be set when deploying the first unit of a service.
(string) Extra packages to install on the postgresql service units.
(string) DEPRECATED & IGNORED. Use install_sources and install_keys.
(string) A comma separated extra pg_hba.conf auth rules. This will be written to the pg_hba.conf file, one line per rule. Note that this should not be needed as db relations already create those rules the right way. Only use this if you really need too (e.g. on a development environment)
(boolean) Turns forced synchronization on/off. If fsync is turned off, database failures are likely to involve database corruption and require recreating the unit
(boolean) Recover from partial page writes.
(boolean) Hot standby or warm standby. When True, queries can be run against the database when in recovery or standby mode (ie. replicated). Overridden by juju when master/slave relations are used.
(boolean) Hot standby feedback, informing a master about in progress transactions on a streaming hot standby and allowing the master to defer cleanup and avoid query cancelations on the hot standby.
(string) List of signing keys for install_sources package sources, per charmhelpers standard. YAML format.
(string) List of extra package sources, per charm-helpers standard. YAML format.
(int) Total amount of shared memory available, in bytes.
(int) The maximum size, in bytes, of a shared memory segment.
(string) IP to listen on
(int) Port to listen on. Default is automatically assigned.
(string) Locale of service, defining language, default collation order, and default formatting of numbers, currency, dates & times. Can only be set when deploying the first unit of a service.
(int) -1 disables, 0 logs all actions and their durations, > 0 logs only actions running at least this number of milliseconds.
(boolean) Log checkpoints
(boolean) Log connections
(boolean) Log disconnections
(string) special values: %a = application name %u = user name %d = database name %r = remote host and port %h = remote host %p = process ID %t = timestamp without milliseconds %m = timestamp with milliseconds %i = command tag %e = SQL state %c = session ID %l = session line number %s = session start timestamp %v = virtual transaction ID %x = transaction ID (0 if none) %q = stop here in non-session processes %% = '%' e.g. '<%u%%%d> '
%t [%p]: [%l-1] db=%d,user=%u
(boolean) log lock waits >= deadlock_timeout
(int) -1 is disabled, 0 logs all statements and their durations, > 0 logs only statements running at least this number of milliseconds
(string) Log timezone
(string) Maintenance working memory. Ignored unless 'performance_tuning' is set to 'manual'.
(int) Maximum number of connections to allow to the PG database
(int) Maximum number of hot standbys that can connect using streaming replication. Set this to the expected maximum number of hot standby units to avoid unnecessary blocking and database restarts. Overridden by juju if necessary.
(string) Used by the nrpe-external-master subordinate charm. A string that will be prepended to instance name to set the host name in nagios. So for instance the hostname would be something like: juju-postgresql-0 If you're running multiple environments with the same services in them this allows you to differentiate between them.
(string) EXPERIMENTAL. OpenStack Swift authentication URL.
(string) EXPERIMENTAL. OpenStack Swift password.
(string) EXPERIMENTAL. OpenStack Swift tenant name.
(string) EXPERIMENTAL. OpenStack Swift username.
(string) The status of service-affecting packages will be set to this value in the dpkg database. Useful valid values are "install" and "hold".
(string) Possible values here are "manual", "DW" (data warehouse), "OLTP" (online transaction processing), "Web" (web application), "Desktop" or "Mixed". When this is set to a value other than "manual", the charm invokes the pgtune tool to tune a number of performance parameters based on the specified load type. pgtune gathers information about the node on which you are deployed and tries to make intelligent guesses about what tuning parameters to set based on available RAM and CPU under the assumption that it's the only significant service running on this node.
(boolean) Enable the PostgreSQL Global Development Group APT repository ( This package source provides official PostgreSQL packages for Ubuntu LTS releases beyond those provided by the main Ubuntu archive.
(float) Random page cost
(int) Value of wal_keep_segments used when this service is replicated. This setting only exists to provide a sane default when replication is requested (so it doesn't fail) and nobody bothered to change the wal_keep_segments setting.
(string) Comma separated list of schema names for the default SQL search path.
(string) The amount of memory the database server uses for shared memory buffers. This string should be of the format '###MB'. Ignored unless 'performance_tuning' is set to 'manual'.
(string) Whether PostgreSQL should talk SSL
(boolean) Standard conforming strings
(boolean) EXPERIMENTAL. Enable streaming replication. Normally, streaming replication is always used, and any log shipping configured is used as a fallback. Turning this off without configuring log shipping is an error.
(int) EXPERIMENTAL. Number of recent base backups to retain. You need enough space in Swift for this many backups plus one more, as an old backup will only be removed after a new one has been successfully made to replace it.
(string) EXPERIMENTAL. Cron-formatted schedule for SwiftWAL database backups.
(string) EXPERIMENTAL. Swift container prefix for SwiftWAL to use. Must be set if any SwiftWAL features are enabled.
(boolean) EXPERIMENTAL. Archive WAL files into Swift. If swiftwal_backup_schedule is set, this allows point-in-time recovery and WAL files are removed automatically with old backups. If swiftwal_backup_schedule is not set then WAL files are never removed. Enabling this option will override the archive_mode and archive_command settings.
(boolean) Immediate fsync after commit.
(string) The maximum number of temporary buffers used by each database session.
(string) Version of PostgreSQL that we want to install. Supported versions are "9.1", "9.2", "9.3". The default version for the deployed Ubuntu release is used when the version is not specified.
(string) min 32kB, -1 sets based on shared_buffers (change requires restart). Ignored unless 'performance_tuning' is set to 'manual'.
(int) Number of old WAL files to keep, providing a larger buffer for streaming hot standbys to catch up from when lagged. Each WAL file is 16MB in size. The WAL files are the buffer of how far a hot standby can lag behind the master, and replication fails if this buffer is overrun. When this service is replicated, the larger value of wal_keep_segments and replicated_wal_keep_segments is used.
(string) 'minimal', 'archive' or 'hot_standby'. Defines how much information is written to the WAL. Set to 'minimal' for stand alone databases and 'hot_standby' for replicated setups. Overridden by juju when replication s used.
(string) Working Memory. Ignored unless 'performance_tuning' is set to 'manual'.