Read Me
Backup and Recovery Manager for PostgreSQL Tutorial
Barman (backup and recovery manager) is an administration tool for
disaster recovery of PostgreSQL servers written in Python. Barman can
perform remote backups of multiple servers in business critical
environments, and helps DBAs during the recovery phase.
Barman's most wanted features include: backup catalogues, retention
policies, remote recovery, archiving and compression of WAL files and
of backups. Barman is written and maintained by PostgreSQL
professionals 2ndQuadrant.
__________________________________________________________________
Introduction
In a perfect world, there would be no need for a backup. However it is
important, especially in business environments, to be prepared for when
the "unexpected" happens. In a database scenario, the unexpected could
take any of the following forms:
* data corruption;
* system failure, including hardware failure;
* human error;
* natural disaster.
In such cases, any ICT manager or DBA should be able to repair the
incident and recover the database in the shortest possible time. We
normally refer to this discipline as Disaster recovery.
This guide assumes that you are familiar with theoretical disaster
recovery concepts, and you have a grasp of PostgreSQL fundamentals in
terms of physical backup and disaster recovery. If not, we encourage
you to read the PostgreSQL documentation or any of the recommended
books on PostgreSQL.
Professional training on this topic is another effective way of
learning these concepts. At any time of the year you can find many
courses available all over the world, delivered by PostgreSQL companies
such as 2ndQuadrant.
For now, you should be aware that any PostgreSQL physical/binary backup
(not to be confused with the logical backups produced by the pg_dump
utility) is composed of:
* a base backup;
* one or more WAL files (usually collected through continuous
archiving).
PostgreSQL offers the core primitives that allow DBAs to setup a really
robust Disaster Recovery environment. However, it becomes complicated
to manage multiple backups, from one or more PostgreSQL servers.
Restoring a given backup is another task that any PostgreSQL DBA would
love to see more automated and user friendly.
With these goals in mind, 2ndQuadrant started the development of Barman
for PostgreSQL. Barman is an acronym for "Backup and Recovery Manager".
Currently Barman works only on Linux and Unix operating systems.
__________________________________________________________________
Before you start
The first step is to decide the architecture of your backup. In a
simple scenario, you have one PostgreSQL instance (server) running on a
host. You want your data continuously backed up to another server,
called the backup server.
Barman allows you to launch PostgreSQL backups directly from the backup
server, using SSH connections. Furthermore, it allows you to centralise
your backups in case you have more than one PostgreSQL server to
manage.
During this guide, we will assume that:
* there is one PostgreSQL instance on a host (called pg for
simplicity)
* there is one backup server on another host (called backup)
* communication via SSH between the two servers is enabled
* the PostgreSQL server can be reached from the backup server as the
postgres operating system user (or another user with PostgreSQL
database superuser privileges, typically configured via ident
authentication)
It is important to note that, for disaster recovery, these two servers
must not share any physical resource except for the network. You can
use Barman in geographical redundancy scenarios for better disaster
recovery outcomes.
System requirements
* Linux/Unix
* Python 2.6 or 2.7
* Python modules:
+ argcomplete
+ argh >= 0.21.2
+ psycopg2
+ python-dateutil < 2.0 (since version 2.0 requires python3)
+ distribute (optional)
* PostgreSQL >= 8.3
* rsync >= 3.0.4
Important
The same major version of PostgreSQL should be installed on both
servers.
Tip
Users of RedHat Enterprise Linux, CentOS and Scientific Linux are
advised to install the Extra Packages Enterprise Linux (EPEL)
repository.
[Further information at [1]http://fedoraproject.org/wiki/EPEL]
Note
Version 1.2.3 of Barman has been refactored for Python 3 support.
Please consider it as experimental now and report any bug through the
ticketing system on SourceForge or mailing list.
__________________________________________________________________
Installation
On RedHat/CentOS using RPM packages
Barman can be installed on RHEL5 and RHEL6 Linux systems using RPM
packages.
Barman is available through the PostgreSQL Global Development Group RPM
repository with Yum. You need to follow the instructions for your
distribution (RedHat, CentOS, Fedora, etc.) and architecture that you
can find at [2]http://yum.postgresql.org/.
Then, as root simply type:
yum install barman
On Debian/Ubuntu using packages
Barman can be installed on Debian and Ubuntu Linux systems using
packages.
It is available in the official repository for Debian Sid (unstable)
and Ubuntu 14.04 (Trusty Tahr).
Note
You can install an up-to-date version of Barman on many Debian and
Ubuntu releases using the PostgreSQL Community APT repository at
[3]http://apt.postgresql.org/. Instructions can be found at
[4]https://wiki.postgresql.org/wiki/Apt.
Installing Barman is as simple as typing as root user:
apt-get install barman
From sources
Create a system user called barman on the backup server. As barman
user, download the sources and uncompress them.
For a system-wide installation, type:
barman@backup$ ./setup.py build
barman@backup# ./setup.py install # run this command with root privileges or s
udo
For a local installation, type:
barman@backup$ ./setup.py install --user
Important
The --user option works only with python-distribute
barman will be installed in your user directory (make sure that your
PATH environment variable is set properly).
__________________________________________________________________
Getting started
Prerequisites
SSH connection
Barman needs a bidirectional SSH connection between the barman user on
the backup server and the postgres user. SSH must be configured such
that there is no password prompt presented when connecting. on the pg
server. As the barman user on the backup server, generate an SSH key
with an empty password, and append the public key to the
authorized_keys file of the postgres user on the pg server.
The barman user on the backup server should then be able to perform the
following operation without typing a password:
barman@backup$ ssh postgres@pg
The procedure must be repeated with sides swapped in order to allow the
postgres user on the pg server to connect to the backup server as the
barman user without typing a password:
postgres@pg$ ssh barman@backup
For further information, refer to OpenSSH documentation.
PostgreSQL connection
You need to make sure that the backup server allows connection to the
PostgreSQL server on pg as superuser (postgres).
You can choose your favourite client authentication method among those
offered by PostgreSQL. More information can be found here:
[5]http://www.postgresql.org/docs/current/static/client-authentication.
html
barman@backup$ psql -c 'SELECT version()' -U postgres -h pg
Note
As of version 1.1.2, Barman honours the application_name connection
option for PostgreSQL servers 9.0 or higher.
Backup directory
Barman needs a main backup directory to store all the backups. Even
though you can define a separate folder for each server you want to
back up and for each type of resource (backup or WAL segments, for
instance), we suggest that you adhere to the default rules and stick
with the conventions that Barman chooses for you.
You will see that the configuration file (as explained below) defines a
barman_home variable, which is the directory where Barman will store
all your backups by default. We choose /var/lib/barman as home
directory for Barman:
barman@backup$ sudo mkdir /var/lib/barman
barman@backup$ sudo chown barman:barman /var/lib/barman
Important
We assume that you have enough space, and that you have already thought
about redundancy and safety of your disks.
Basic configuration
In the docs directory you will find a minimal configuration file. Use
it as a template, and copy it to /etc/barman.conf, or to
~/.barman.conf. In general, the former applies to all the users on the
backup server, while the latter applies only to the barman user; for
the purpose of this tutorial there is no difference in using one or the
other.
From version 1.2.1, you can use /etc/barman/barman.conf as default
system configuration file.
The configuration file follows the standard INI format, and is split
in:
* a section for general configuration (identified by the barman
label)
* a section for each PostgreSQL server to be backed up (identified by
the server label, e.g. main or pg)
[all and barman are reserved words and cannot be used as server
labels]
Global/server options
Every option in the configuration file has a scope:
* global
* server
* global/server
Global options can be present in the general section (identified by
barman). Server options can only be specified in a server section.
Some options can be defined at global level and overridden at server
level, allowing users to specify a generic behaviour and refine it for
one or more servers. For a list of all the available configurations and
their scope, please refer to [6]section 5 of the man page:
man 5 barman
Configuration files directory
As of version 1.1.2, you can now specify a directory for configuration
files similarly to other Linux applications, using the
configuration_files_directory option (empty by default). If the value
of configuration_files_directory is a directory, Barman will read all
the files with .conf extension that exist in that folder. For example,
if you set it to /etc/barman.d, you can specify your PostgreSQL servers
placing each section in a separate .conf file inside the /etc/barman.d
folder.
Otherwise, you can use Barman's standard way of specifying sections
within the main configuration file.
Example of configuration
; Barman, Backup and Recovery Manager for PostgreSQL
; http://www.pgbarman.org/ - http://www.2ndQuadrant.com/
;
; Main configuration file
[barman]
; Main directory
barman_home = /var/lib/barman
; System user
barman_user = barman
; Log location
log_file = /var/log/barman/barman.log
; Default compression level: possible values are None (default), bzip2, gzip o
r custom
;compression = gzip
; Incremental backup support: possible values are None (default), link or copy
;reuse_backup = link
; Pre/post backup hook scripts
;pre_backup_script = env | grep ^BARMAN
;post_backup_script = env | grep ^BARMAN
; Pre/post archive hook scripts
;pre_archive_script = env | grep ^BARMAN
;post_archive_script = env | grep ^BARMAN
; Directory of configuration files. Place your sections in separate files with
.conf extension
; For example place the 'main' server section in /etc/barman.d/main.conf
;configuration_files_directory = /etc/barman.d
; Minimum number of required backups (redundancy) - default 0
;minimum_redundancy = 0
; Global retention policy (REDUNDANCY or RECOVERY WINDOW) - default empty
;retention_policy =
; Global bandwidth limit in KBPS - default 0 (meaning no limit)
;bandwidth_limit = 4000
; Immediate checkpoint for backup command - default false
;immediate_checkpoint = false
; Enable network compression for data transfers - default false
;network_compression = false
; Identify the standard behavior for backup operations: possible values are
; exclusive_backup (default), concurrent_backup
;backup_options = exclusive_backup
; Number of retries of data copy during base backup after an error - default 0
;basebackup_retry_times = 0
; Number of seconds of wait after a failed copy, before retrying - default 30
;basebackup_retry_sleep = 30
; Time frame that must contain the latest backup date.
; If the latest backup is older than the time frame, barman check
; command will report an error to the user.
; If empty, the latest backup is always considered valid.
; Syntax for this option is: "i (DAYS | WEEKS | MONTHS)" where i is an
; integer > 0 which identifies the number of days | weeks | months of
; validity of the latest backup for this check. Also known as 'smelly backup'.
;last_backup_maximum_age =
;; ; 'main' PostgreSQL Server configuration
;; [main]
;; ; Human readable description
;; description = "Main PostgreSQL Database"
;;
;; ; SSH options
;; ssh_command = ssh postgres@pg
;;
;; ; PostgreSQL connection string
;; conninfo = host=pg user=postgres
;;
;; ; Minimum number of required backups (redundancy)
;; ; minimum_redundancy = 1
;;
;; ; Examples of retention policies
;;
;; ; Retention policy (disabled)
;; ; retention_policy =
;; ; Retention policy (based on redundancy)
;; ; retention_policy = REDUNDANCY 2
;; ; Retention policy (based on recovery window)
;; ; retention_policy = RECOVERY WINDOW OF 4 WEEKS
Initial checks
Once you have created your configuration file (or files), you can now
test Barman's configuration by executing:
barman@backup$ barman show-server main
barman@backup$ barman check main
Write down the incoming_wals_directory, as printed by the barman
show-server main command, because you will need it to setup continuous
WAL archiving.
Important
The barman check main command automatically creates all the directories
for the continuous backup of the main server.
Continuous WAL archiving
Edit the postgresql.conf file of the PostgreSQL instance on the pg
database and activate the archive mode:
wal_level = 'archive' # For PostgreSQL >= 9.0
archive_mode = on
archive_command = 'rsync -a %p barman@backup:INCOMING_WALS_DIRECTORY/%f'
Make sure you change the INCOMING_WALS_DIRECTORY placeholder with the
value returned by the barman show-server main command above.
In case you use Hot Standby, wal_level must be set to hot_standby.
Restart the PostgreSQL server.
In order to test that continuous archiving is on and properly working,
you need to check both the PostgreSQL server
[For more information, refer to the PostgreSQL documentation]
and the backup server (in particular, that the WAL files are collected
in the destination directory).
Listing the servers
The following command displays the list of all the available servers:
barman@backup$ barman list-server
Executing a full backup
To take a backup for the main server, issue the following command:
barman@backup$ barman backup main
As of version 1.1.0, you can serialise the backup of your managed
servers by using the all target for the server:
barman@backup$ barman backup all
This will iterate through your available servers and sequentially take
a backup for each of them.
Immediate Checkpoint
As of version 1.3.0, it is possible to use the immediate_checkpoint
configuration global/server option (set to false by default).
When issuing a backup, Barman normally waits for the checkpoint to
happen on the PostgreSQL server (depending on the configuration
settings for workload or time checkpoint control). This might take
longer for a backup to start.
By setting immediate_checkpoint to true, you can force the checkpoint
on the Postgres server to happen immediately and start your backup copy
process as soon as possible:
At any time, you can override the configuration option behaviour, by
issuing barman backup with any of these two options:
* --immediate-checkpoint, which forces an immediate checkpoint;
* --no-immediate-checkpoint, which forces to wait for the checkpoint
to happen.
Viewing the list of backups for a server
To list all the available backups for a given server, issue:
barman@backup$ barman list-backup main
the format of the output is as in:
main - 20120529T092136 - Wed May 30 15:20:25 2012 - Size: 5.0 TiB - WAL Size:
845.0 GiB (tablespaces: tb_name:/home/tblspace/name, tb_temp:/home/tblspace/temp
)
where 20120529T092136 is the ID of the backup and Wed May 30 15:20:25
2012 is the start time of the operation, Size is the size of the base
backup and WAL Size is the size of WAL files archived.
As of version 1.1.2, you can get a listing of the available backups for
all your servers, using the all target for the server:
barman@backup$ barman list-backup all
Restoring a whole server
To restore a whole server issue the following command:
barman@backup$ barman recover main 20110920T185953 /path/to/recover/directory
where 20110920T185953 is the ID of the backup to be restored. When this
command completes succesfully, /path/to/recover/directory contains a
complete data directory ready to be started as a PostgreSQL database
server.
Here is an example of a command that starts the server:
barman@backup$ pg_ctl -D /path/to/recover/directory start
Important
If you run this command as user barman, it will become the database
superuser.
You can retrieve a list of backup IDs for a specific server with:
barman@backup$ barman list-backup srvpgsql
Important
Barman does not currently keep track of symbolic links inside PGDATA
(except for tablespaces inside pg_tblspc). We encourage system
administrators to keep track of symbolic links and to add them to the
disaster recovery plans/procedures in case they need to be restored in
their original location.
Remote recovery
Barman is able to recover a backup on a remote server through the
--remote-ssh-command COMMAND option for the recover command.
If this option is specified, barman uses COMMAND to connect to a remote
host.
Note
The postgres user is normally used to recover on a remote host.
There are some limitations when using remote recovery. It is important
to be aware that:
* Barman needs at least 4GB of free space in the system temporary
directory (usually /tmp);
* the SSH connection between Barman and the remote host must use
public key exchange authentication method;
* the remote user must be able to create the required destination
directories for PGDATA and, where applicable, tablespaces;
* there must be enough free space on the remote server to contain the
base backup and the WAL files needed for recovery.
Relocating one or more tablespaces
Important
As of version 1.3.0, it is possible to relocate a tablespace both with
local and remote recovery.
Barman is able to automatically relocate one or more tablespaces using
the recover command with the --tablespace option. The option accepts a
pair of values as arguments using the NAME:DIRECTORY format:
* name/identifier of the tablespace (NAME);
* destination directory (DIRECTORY).
If the destination directory does not exists, Barman will try to create
it (assuming you have enough privileges).
Restoring to a given point in time
Barman employs PostgreSQL's Point-in-Time Recovery (PITR) by allowing
DBAs to specify a recovery target, either as a timestamp or as a
transaction ID; you can also specify whether the recovery target should
be included or not in the recovery.
The recovery target can be specified using one of three mutually
exclusive options:
* --target-time TARGET_TIME: to specify a timestamp
* --target-xid TARGET_XID: to specify a transaction ID
* --target-name TARGET_NAME: to specify a named restore point -
previously created with the pg_create_restore_point(name) function
[Only available for PostgreSQL 9.1 and above users]
You can use the --exclusive option to specify whether to stop
immediately before or immediately after the recovery target.
Barman allows you to specify a target timeline for recovery, using the
target-tli option. The notion of timeline goes beyond the scope of this
document; you can find more details in the PostgreSQL documentation, or
in one of 2ndQuadrant's Recovery training courses.
Retry of copy in backup/recovery operations
As of version 1.3.3, it is possible to take advantage of two new
options in Barman:
* basebackup_retry_times (set to 0 by default)
* basebackup_retry_sleep (set to 30 by default)
When issuing a backup or a recovery, Barman normally tries to copy the
base backup once. If the copy fails (e.g. due to network problems),
Barman terminates the operation with a failure.
By setting basebackup_retry_times, Barman will try to re-execute a copy
operation as many times as requested by the user. The
basebackup_retry_sleep option specifies the number of seconds that
Barman will wait between each attempt.
At any time you can override the configuration option behaviour from
the command line, when issuing barman backup or barman recover, using:
* --retry-times <retry_number> (same logic as basebackup_retry_times)
* --no-retry (same as --retry-times 0)
* --retry-sleep <number_of_seconds> (same logic as
basebackup_retry_sleep)
__________________________________________________________________
Available commands
Barman commands are applied to three different levels:
* general commands, which apply to the backup catalogue
* server commands, which apply to a specific server (list available
backups, execute a backup, etc.)
* backup commands, which apply to a specific backup in the catalogue
(display information, issue a recovery, delete the backup, etc.)
In the following sections the available commands will be described in
detail.
General commands
List available servers
You can display the list of active servers that have been configured
for your backup system with:
barman list-server
Maintenance mode
You can perform maintenance operations, like compressing WAL files and
moving them from the incoming directory to the archived one, with:
barman cron
This command enforces retention policies on those servers that have:
* retention_policy not empty and valid;
* retention_policy_mode set to auto.
Note
This command should be executed in a cron script. Our recommendation is
to schedule barman cron to run every minute.
Server commands
Show the configuration for a given server
You can show the configuration parameters for a given server with:
barman show-server <server_name>
Take a base backup
You can perform a full backup (base backup) for a given server with:
barman backup [--immediate-checkpoint] <server_name>
Tip
You can use barman backup all to sequentially backup all your
configured servers.
Show available backups for a server
You can list the catalogue of available backups for a given server
with:
barman list-backup <server_name>
Check a server is properly working
You can check if the connection to a given server is properly working
with:
barman check <server_name>
Tip
You can use barman check all to check all your configured servers.
From version 1.3.3, you can automatically be notified if the latest
backup of a given server is older than, for example, 7 days.
[This feature is commonly known among the development team members as
smelly backup check]
Barman introduces the option named last_backup_maximum_age having the
following syntax:
last_backup_maximum_age = {value {DAYS | WEEKS | MONTHS}}
where value is a positive integer representing the number of days,
weeks or months of the time frame.
Diagnose a Barman installation
You can gather important information about all the configured server
using:
barman diagnose
The diagnose command also provides other useful information, such as
global configuration, SSH version, Python version, rsync version, as
well as current configuration and status of all servers.
Tip
You can use barman diagnose when you want to ask questions or report
errors to Barman developers, providing them with all the information
about your issue.
Rebuild the WAL archive
At any time, you can regenerate the content of the WAL archive for a
specific server (or every server, using the all shortcut). The WAL
archive is contained in the xlog.db file, and every Barman server has
its own copy. From version 1.2.4 you can now rebuild the xlog.db file
with the rebuild-xlogdb command. This will scan all the archived WAL
files and regenerate the metadata for the archive.
Important
Users of Barman < 1.2.3 might have suffered from a bug due to bad
locking in highly concurrent environments. You can now regenerate the
WAL archive using the rebuild-xlogdb command.
barman rebuild-xlogdb <server_name>
Backup commands
Note
Remember: a backup ID can be retrieved with barman list-backup
<server_name>
Show backup information
You can show all the available information for a particular backup of a
given server with:
barman show-backup <server_name> <backup_id>
From version 1.1.2, in order to show the latest backup, you can issue:
barman show-backup <server_name> latest
Delete a backup
You can delete a given backup with:
barman delete <server_name> <backup_id>
From version 1.1.2, in order to delete the oldest backup, you can
issue:
barman delete <server_name> oldest
Warning
Until retention policies are natively supported, you must use the
oldest shortcut with extreme care and caution. Iteratively executing
this command can easily wipe out your backup archive.
List backup files
You can list the files (base backup and required WAL files) for a given
backup with:
barman list-files [--target TARGET_TYPE] <server_name> <backup_id>
With the --target TARGET_TYPE option, it is possible to choose the
content of the list for a given backup.
Possible values for TARGET_TYPE are:
* data: lists just the data files;
* standalone: lists the base backup files, including required WAL
files;
* wal: lists all WAL files from the beginning of the base backup to
the start of the following one (or until the end of the log);
* full: same as data + wal.
The default value for TARGET_TYPE is standalone.
Important
The list-files command facilitates interaction with external tools, and
therefore can be extremely useful to integrate Barman into your
archiving procedures.
__________________________________________________________________
Main features
Incremental backup
From version 1.4.0, Barman implements file-level incremental backup.
Incremental backup is a kind of full periodical backup which saves only
data changes from the latest full backup available in the catalogue for
a specific PostgreSQL server. It must not be confused with differential
backup, which is implemented by WAL continuous archiving.
The main goals of incremental backup in Barman are:
* Reduce the time taken for the full backup process
* Reduce the disk space occupied by several periodical backups (data
deduplication)
This feature heavily relies on rysnc and [7]hard links, which must be
therefore supported by both the underlying operating system and the
file system where the backup data resides.
The main concept is that two periodical base backups will share those
files that have not changed, leading to relevant savings in disk usage.
This is particularly true of VLDB contexts and, more in general, of
those databases containing a high percentage of read-only historical
tables.
Barman implements incremental backup through a global/server option,
called reuse_backup, that transparently manage the barman backup
command. It accepts three values:
* off: standard full backup (default)
* link: incremental backup, by reusing the last backup for a server
and creating a hard link of the unchanged files (for backup space
and time reduction)
* copy: incremental backup, by reusing the last backup for a server
and creating a copy of the unchanged files (just for backup time
reduction)
The most common scenario is to set reuse_backup to link, as follows:
reuse_backup = link
Setting this at global level will automatically enable incremental
backup for all your servers.
As a final note, users can override the setting of the reuse_backup
option through the --reuse-backup runtime option for the barman backup
command. Similarly, the runtime option accepts three values: off, link
and copy. For example, you can run a one-off incremental backup as
follows:
barman backup --reuse-backup=link <server_name>
WAL compression
The barman cron command (see below) will compress WAL files if the
compression option is set in the configuration file. This option allows
three values:
* gzip: for Gzip compression (requires gzip)
* bzip2: for Bzip2 compression (requires bzip2)
* custom: for custom compression, which requires you to set the
following options as well:
+ custom_compression_filter: a compression filter
+ custom_decompression_filter: a decompression filter
Limiting bandwidth usage
From version 1.2.1, it is possible to limit the usage of I/O bandwidth
through the bandwidth_limit option (global/per server), by specifying
the maximum number of kilobytes per second. By default it is set to 0,
meaning no limit.
In case you have several tablespaces and you prefer to limit the I/O
workload of your backup procedures on one or more tablespaces, you can
use the tablespace_bandwidth_limit option (global/per server):
tablespace_bandwidth_limit = tbname:bwlimit[, tbname:bwlimit, ...]
The option accepts a comma separated list of pairs made up of the
tablespace name and the bandwidth limit (in kilobytes per second).
When backing up a server, Barman will try and locate any existing
tablespace in the above option. If found, the specified bandwidth limit
will be enforced. If not, the default bandwidth limit for that server
will be applied.
Network Compression
From version 1.3.0 it is possible to reduce the size of transferred
data using compression. It can be enabled using the network_compression
option (global/per server):
network_compression = true|false
Setting this option to true will enable data compression during network
transfers (for both backup and recovery). By default it is set to
false.
Backup ID shortcuts
As of version 1.1.2, you can use any of the following shortcuts to
identify a particular backup for a given server:
* latest: the latest available backup for that server, in
chronological order. You can also use the last synonym.
* oldest: the oldest available backup for that server, in
chronological order. You can also use the first synonym.
These aliases can be used with any of the following commands:
show-backup, delete, list-files and recover.
Minimum redundancy safety
From version 1.2.0, you can define the minimum number of periodical
backups for a PostgreSQL server.
You can use the global/per server configuration option called
minimum_redundancy for this purpose, by default set to 0.
By setting this value to any number greater than 0, Barman makes sure
that at any time you will have at least that number of backups in a
server catalogue.
This will protect you from accidental barman delete operations.
Important
Make sure that your policy retention settings do not collide with
minimum redundancy requirements. Regularly check Barman's log for
messages on this topic.
Retention policies
From version 1.2.0, Barman supports retention policies for backups.
A backup retention policy is an user-defined policy that determines how
long backups and related archive logs (Write Ahead Log segments) need
to be retained for recovery procedures.
Based on the user's request, Barman retains the periodical backups
required to satisfy the current retention policy, and any archived WAL
files required for the complete recovery of those backups.
Barman users can define a retention policy in terms of backup
redundancy (how many periodical backups) or a recovery window (how
long).
Retention policy based on redundancy
In a redundancy based retention policy, the user determines how
many periodical backups to keep. A redundancy-based retention
policy is contrasted with retention policies that use a recovery
window.
Retention policy based on recovery window
A recovery window is one type of Barman backup retention policy,
in which the DBA specifies a period of time and Barman ensures
retention of backups and/or archived WAL files required for
point-in-time recovery to any time during the recovery window.
The interval always ends with the current time and extends back
in time for the number of days specified by the user. For
example, if the retention policy is set for a recovery window of
seven days, and the current time is 9:30 AM on Friday, Barman
retains the backups required to allow point-in-time recovery
back to 9:30 AM on the previous Friday.
Scope
Retention policies can be defined for:
* PostgreSQL periodical base backups: through the retention_policy
configuration option;
* Archive logs, for Point-In-Time-Recovery: through the
wal_retention_policy configuration option.
Important
In a temporal dimension, archive logs must be included in the time
window of periodical backups.
There are two typical use cases here: full or partial point-in-time
recovery.
Full point in time recovery scenario
Base backups and archive logs share the same retention policy,
allowing DBAs to recover at any point in time from the first
available backup.
Partial point in time recovery scenario
Base backup retention policy is wider than that of archive logs,
allowing users for example to keep full weekly backups of the
last 6 months, but archive logs for the last 4 weeks (granting
to recover at any point in time starting from the last 4
periodical weekly backups).
Important
Currently, Barman implements only the full point in time recovery
scenario, by constraining the wal_retention_policy option to main.
How they work
Retention policies in Barman can be:
* automated: enforced by barman cron;
* manual: Barman simply reports obsolete backups and allows DBAs to
delete them.
Important
Currently Barman does not implement manual enforcement. This feature
will be available in future versions.
Configuration and syntax
Retention policies can be defined through the following configuration
options:
* retention_policy: for base backup retention;
* wal_retention_policy: for archive logs retention;
* retention_policy_mode: can only be set to auto (retention policies
are automatically enforced by the barman cron command).
These configuration options can be defined both at a global level and a
server level, allowing users maximum flexibility on a multi-server
environment.
Syntax for retention_policy
The general syntax for a base backup retention policy through
retention_policy is the following:
retention_policy = {REDUNDANCY value | RECOVERY WINDOW OF value {DAYS | WEEKS
| MONTHS}}
Where:
* syntax is case insensitive;
* value is an integer and is > 0;
* in case of redundancy retention policy:
+ value must be greater than or equal to the server minimum
redundancy level (if not is is assigned to that value and a
warning is generated);
+ the first valid backup is the value-th backup in a reverse
ordered time series;
* in case of recovery window policy:
+ the point of recoverability is: current time - window;
+ the first valid backup is the first available backup before
the point of recoverability; its value in a reverse ordered
time series must be greater than or equal to the server
minimum redundancy level (if not is is assigned to that value
and a warning is generated).
By default, retention_policy is empty (no retention enforced).
Syntax for wal_retention_policy
Currently, the only allowed value for wal_retention_policy is the
special value main, that maps the retention policy of archive logs to
that of base backups.
Concurrent Backup and backup from a standby
Normally, during backup operations, Barman uses PostgreSQL native
functions pg_start_backup and pg_stop_backup for exclusive backup.
These operations are not allowed on a read-only standby server.
As of version 1.3.1, Barman is also capable of performing backups of
PostgreSQL 9.2/9.3 database servers in a concurrent way, primarily
through the backup_options configuration parameter.
[Concurrent backup is a technology that has been available in
PostgreSQL since version 9.1, through the streaming replication
protocol (using, for example, a tool like pg_basebackup).]
This introduces a new architecture scenario with Barman: backup from a
standby server, using rsync.
Important
Concurrent backup requires users of PostgreSQL 9.2 and 9.3 to install
the pgespresso open source extension on the PostgreSQL server. Detailed
information as well as the source code of pgespresso can be found at
[8]https://github.com/2ndquadrant-it/pgespresso.
By default, backup_options is transparently set to exclusive_backup
(the only supported method by any Barman version prior to 1.3.1).
When backup_options is set to concurrent_backup, Barman activates the
concurrent backup mode for a server and follows these two simple rules:
* ssh_command must point to the destination Postgres server;
* conninfo must point to a database on the destination Postgres 9.2
or 9.3 server where pgespresso is correctly installed through
CREATE EXTENSION.
The destination Postgres server can be either the master or a streaming
replicated standby server.
Note
When backing up from a standby server, continuous archiving of WAL
files must be configured on the master to ship files to the Barman
server (as outlined in the "Continuous WAL archiving" section above).
[ In case of concurrent backup, currently Barman does not have a way to
determine that the closing WAL file of a full backup has actually been
shipped - opposite to the case of an exclusive backup where it is
Postgres itself that makes sure that the WAL file is correctly
archived. Be aware that the full backup cannot be considered consistent
until that WAL file has been received and archived by Barman. We
encourage Barman users to wait to delete the previous backup - at least
until that moment. ]
Hook scripts
Barman allows a database administrator to run hook scripts on these two
events:
* before and after a backup
* before and after a WAL file is archived
Important
No check is performed on the exit code of a script. The result will be
simply written in the log file.
Backup scripts
Version 1.1.0 introduced backup scripts.
These scripts can be configured with the following global configuration
options (which can be overridden on a per server basis):
* pre_backup_script: hook script launched before a base backup
* post_backup_script: hook script launched after a base backup
The script definition is passed to a shell and can return any exit
code.
The shell environment will contain the following variables:
* BARMAN_BACKUP_DIR: backup destination directory
* BARMAN_BACKUP_ID: ID of the backup
* BARMAN_CONFIGURATION: configuration file used by barman
* BARMAN_ERROR: error message, if any (only for the post phase)
* BARMAN_PHASE: phase of the script, either pre or post
* BARMAN_PREVIOUS_ID: ID of the previous backup (if present)
* BARMAN_SERVER: name of the server
* BARMAN_STATUS: status of the backup
* BARMAN_VERSION: version of Barman (from 1.2.1)
WAL archive scripts
Version 1.3.0 introduced WAL archive hook scripts.
Similarly to backup scripts, archive scripts can be configured with
global configuration options (which can be overridden on a per server
basis):
* pre_archive_script: hook script launched before a WAL file is
archived by maintenance (usually barman cron)
* post_archive_script: hook script launched after a WAL file is
archived by maintenance
The script is executed through a shell and can return any exit code.
Archive scripts share with backup scripts some environmental variables:
* BARMAN_CONFIGURATION: configuration file used by barman
* BARMAN_ERROR: error message, if any (only for the post phase)
* BARMAN_PHASE: phase of the script, either pre or post
* BARMAN_SERVER: name of the server
Following variables are specific to archive scripts:
* BARMAN_SEGMENT: name of the WAL file
* BARMAN_FILE: full path of the WAL file
* BARMAN_SIZE: size of the WAL file
* BARMAN_TIMESTAMP: WAL file timestamp
* BARMAN_COMPRESSION: type of compression used for the WAL file
__________________________________________________________________
Support and sponsor opportunities
Barman is free software, written and maintained by 2ndQuadrant. If you
require support on using Barman, or if you need new features, please
get in touch with 2ndQuadrant. You can sponsor the development of new
features of Barman and PostgreSQL which will be made publicly available
as open source.
For further information, please visit our websites:
* Barman website: [9]http://www.pgbarman.org/
* Support section on the website:
[10]http://www.pgbarman.org/support/
* 2ndQuadrant website: [11]http://www.2ndquadrant.com/
Useful information can be found in:
* the FAQ section of the website: [12]http://www.pgbarman.org/faq/
* the "Barman" category of 2ndQuadrant's blog:
[13]http://blog.2ndquadrant.com/tag/barman/
Important
When submitting requests on the mailing list, please always report the
output of the barman diagnose command.
__________________________________________________________________
Submitting a bug
Barman has been extensively tested, and is currently being used in
several production environments. However, as any software, Barman is
not bug free.
If you discover a bug, please follow this procedure:
* execute the barman diagnose command;
* file a bug through the Sourceforge bug tracker, by attaching the
output obtained by the diagnostics command above (barman diagnose).
__________________________________________________________________
Authors
In alphabetical order:
* Gabriele Bartolini <[14]gabriele.bartolini@2ndquadrant.it> (core
team, project leader)
* Giuseppe Broccolo <[15]giuseppe.broccolo@2ndquadrant.it> (core
team, QA/testing)
* Giulio Calacoci <[16]giulio.calacoci@2ndquadrant.it> (core team,
developer)
* Francesco Canovai <[17]francesco.canovai@2ndquadrant.it> (core
team, QA/testing)
* Marco Nenciarini <[18]marco.nenciarini@2ndquadrant.it> (core team,
team leader)
Past contributors:
* Carlo Ascani
__________________________________________________________________
Links
* check-barman: a Nagios plugin for Barman, written by Holger Hamann
([19]https://github.com/hamann/check-barman, MIT license)
* puppet-barman: Barman module for Puppet
([20]https://github.com/2ndquadrant-it/puppet-barman, GPL)
__________________________________________________________________
License and Contributions
Barman is the exclusive property of 2ndQuadrant Italia and its code is
distributed under GNU General Public License 3.
Copyright © 2011-2015 2ndQuadrant.it.
Barman has been partially funded through [21]4CaaSt, a research project
funded by the European Commission's Seventh Framework programme.
Contributions to Barman are welcome, and will be listed in the file
AUTHORS. 2ndQuadrant Italia requires that any contributions provide a
copyright assignment and a disclaimer of any work-for-hire ownership
claims from the employer of the developer. This lets us make sure that
all of the Barman distribution remains free code. Please contact
[22]info@2ndQuadrant.it for a copy of the relevant Copyright Assignment
Form.
__________________________________________________________________
Last updated 2015-01-12 14:33:11 CET
References
1. http://fedoraproject.org/wiki/EPEL
2. http://yum.postgresql.org/
3. http://apt.postgresql.org/
4. https://wiki.postgresql.org/wiki/Apt
5. http://www.postgresql.org/docs/current/static/client-authentication.html
6. http://docs.pgbarman.org/barman.5.html
7. http://en.wikipedia.org/wiki/Hard_link
8. https://github.com/2ndquadrant-it/pgespresso
9. http://www.pgbarman.org/
10. http://www.pgbarman.org/support/
11. http://www.2ndquadrant.com/
12. http://www.pgbarman.org/faq/
13. http://blog.2ndquadrant.com/tag/barman/
14. mailto:gabriele.bartolini@2ndquadrant.it
15. mailto:giuseppe.broccolo@2ndquadrant.it
16. mailto:giulio.calacoci@2ndquadrant.it
17. mailto:francesco.canovai@2ndquadrant.it
18. mailto:marco.nenciarini@2ndquadrant.it
19. https://github.com/hamann/check-barman
20. https://github.com/2ndquadrant-it/puppet-barman
21. http://4caast.morfeo-project.org/
22. mailto:info@2ndQuadrant.it