pgbackrest/INSTALL.md

PgBackRest Installation

sample ubuntu 12.04 install

1. Starting from a clean install, update the OS:

apt-get update
apt-get upgrade (reboot if required)

2. Install ssh, git and cpanminus

apt-get install ssh
apt-get install git
apt-get install cpanminus

3. Install Postgres (instructions from http://www.postgresql.org/download/linux/ubuntu/)

Create the file /etc/apt/sources.list.d/pgdg.list, and add a line for the repository:

deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main

Then run the following:

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
sudo apt-get update

apt-get install postgresql-9.3
apt-get install postgresql-server-dev-9.3

4. Install required Perl modules:

cpanm JSON
cpanm Net::OpenSSH
cpanm DBI
cpanm DBD::Pg
cpanm IPC::System::Simple
cpanm Digest::SHA
cpanm IO::Compress::Gzip
cpanm IO::Uncompress::Gunzip

5. Install PgBackRest

Backrest can be installed by downloading the most recent release:

https://github.com/pgmasters/backrest/releases

6. To run unit tests:

• Create backrest_dev user
• Setup trusted ssh between test user account and backrest_dev
• Backrest user and test user must be in the same group

configuration examples

PgBackRest takes some command-line parameters, but depends on a configuration file for most of the settings. The default location for the configuration file is /etc/pg_backrest.conf.

confguring postgres for archiving with backrest

Modify the following settings in postgresql.conf:

wal_level = archive
archive_mode = on
archive_command = '/path/to/backrest/bin/pg_backrest.pl --stanza=db archive-push %p'

Replace the path with the actual location where PgBackRest was installed. The stanza parameter should be changed to the actual stanza name you used for your database in pg_backrest.conf.

simple single host install

This configuration is appropriate for a small installation where backups are being made locally or to a remote file system that is mounted locally.

/etc/pg_backrest.conf:

[global:command]
psql=/usr/bin/psql

[global:backup]
path=/var/lib/postgresql/backup

[global:retention]
full-retention=2
differential-retention=2
archive-retention-type=diff
archive-retention=2

[db]
path=/var/lib/postgresql/9.3/main

simple multiple host install

This configuration is appropriate for a small installation where backups are being made remotely. Make sure that postgres@db-host has trusted ssh to backrest@backup-host and vice versa. This configuration assumes that you have pg_backrest_remote.pl and pg_backrest.pl in the same path on both servers.

/etc/pg_backrest.conf on the db host:

[global:command]
psql=/usr/bin/psql

[global:backup]
host=backup-host@mydomain.com
user=postgres
path=/var/lib/postgresql/backup

[db]
path=/var/lib/postgresql/9.3/main

/etc/pg_backrest.conf on the backup host:

[global:command]
psql=/usr/bin/psql

[global:backup]
path=/var/lib/postgresql/backup

[global:retention]
full-retention=2
archive-retention-type=full

[db]
host=db-host@mydomain.com
user=postgres
path=/var/lib/postgresql/9.3/main

running

PgBackRest is intended to be run from a scheduler like cron as there is no built-in scheduler. Postgres does backup rotation, but it is not concerned with when the backups were created. So if two full backups are configured in rentention, PgBackRest will keep two full backup no matter whether they occur 2 hours apart or two weeks apart.

There are four basic operations:

1. Backup

/path/to/pg_backrest.pl --stanza=db --type=full backup

Run a full backup on the db stanza. --type can also be set to incr or diff for incremental or differential backups. However, if now full backup exists then a full backup will be forced even if incr

2. Archive Push

/path/to/pg_backrest.pl --stanza=db archive-push %p

Accepts an archive file from Postgres and pushes it to the backup. %p is how Postgres specifies the location of the file to be archived. This command has no other purpose.

3. Archive Get

/path/to/pg_backrest.pl --stanza=db archive-get %f %p

Retrieves an archive log from the backup. This is used in restore.conf to restore a backup to that last archive log, do PITR, or as an alternative to streaming for keep a replica up to date. %f is how Postgres specifies the archive log it needs, and %p is the location where it should be copied.

3. Backup Expire

/path/to/pg_backrest.pl --stanza=db expire

Expire (rotate) any backups that exceed the defined retention. Expiration is run after every backup, so there's no need to run this command on its own unless you have reduced rentention, usually to free up some space.

structure

PgBackRest stores files in a way that is easy for users to work with directly. Each backup directory has two files and two subdirectories:

1. backup.manifest file

Stores information about all the directories, links, and files in the backup. The file is plaintext and should be very clear, but documentation of the format is planned in a future release.

2. version file

Contains the PgBackRest version that was used to create the backup.

3. base directory

Contains the Postgres data directory as defined by the data_directory setting in postgresql.conf

4. tablespace directory

Contains each tablespace in a separate subdirectory. The links in base/pg_tblspc are rewritten to this directory.

restoring

PgBackRest does not currently have a restore command - this is planned for the near future. However, PgBackRest stores backups in a way that makes restoring very easy. If compress=n it is even possible to start Postgres directly on the backup directory.

In order to restore a backup, simply rsync the files from the base backup directory to your data directory. If you have used compression, then recursively ungzip the files. If you have tablespaces, repeat the process for each tablespace in the backup tablespace directory.

It's best to practice restoring backups in advance of needing to do so.

[reference this when writing about tablespace remapping]

http://www.databasesoup.com/2013/11/moving-tablespaces.html

configuration options

Each section defines important aspects of the backup. All configuration sections below should be prefixed with global: as demonstrated in the configuration samples.

command section

The command section defines external commands that are used by PgBackRest.

psql key

Defines the full path to psql. psql is used to call pg_start_backup() and pg_stop_backup().

required: y
example: psql=/usr/bin/psql

remote key

Defines the file path to pg_backrest_remote.pl.

Required only if the path to pg_backrest_remote.pl is different on the local and remote systems. If not defined, the remote path will be assumed to be the same as the local path.

required: n
example: remote=/home/postgres/backrest/bin/pg_backrest_remote.pl

command-option section

The command-option section allows abitrary options to be passed to any command in the command section.

psql key

Allows command line parameters to be passed to psql.

required: no
example: psql=--port=5433

log section

The log section defines logging-related settings. The following log levels are supported:

• off - No logging at all (not recommended)
• error - Log only errors
• warn - Log warnings and errors
• info - Log info, warnings, and errors
• debug - Log debug, info, warnings, and errors
• trace - Log trace (very verbose debugging), debug, info, warnings, and errors

level-file

Sets file log level.

default: info
example: level-file=warn

level-console

Sets console log level.

default: error
example: level-file=info

backup section

The backup section defines settings related to backup and archiving.

host

Sets the backup host.

required: n (but must be set if user is defined)
example: host=backup.mydomain.com

user

Sets user account on the backup host.

required: n (but must be set if host is defined)
example: user=backrest

path

Path where backups are stored on the local or remote host.

required: y
example: path=/backup/backrest

compress

Enable gzip compression. Files stored in the backup are compatible with command-line gzip tools.

default: y
example: compress=n

checksum

Enable SHA-1 checksums. Backup checksums are stored in backup.manifest while archive checksums are stored in the filename.

default: y
example: checksum=n

start-fast

Forces an immediate checkpoint (by passing true to the fast parameter of pg_start_backup()) so the backup begins immediately.

default: n
example: start-fast=y

hardlink

Enable hard-linking of files in differential and incremental backups to their full backups. This gives the appearance that each backup is a full backup. Be care though, because modifying files that are hard-linked can affect all the backups in the set.

default: y
example: hardlink=n

thread-max

Defines the number of threads to use for backup. Each thread will perform compression and transfer to make the backup run faster, but don't set thread-max so high that it impacts database performance.

default: 1
example: thread-max=4

thread-timeout

Maximum amount of time (in seconds) that a backup thread should run. This limits the amount of time that a thread might be stuck due to unforeseen issues during the backup.

default: <none>
example: thread-timeout=86400

archive-required

Are archive logs required to to complete the backup? It's a good idea to leave this as the default unless you are using another method for archiving.

default: y
example: archive-required=n

archive section

The archive section defines parameters when doing async archiving. This means that the archive files will be stored locally, then a background process will pick them and move them to the backup.

path

Path where archive logs are stored before being asynchronously transferred to the backup. Make sure this is not the same path as the backup is using if the backup is local.

required: y
example: path=/backup/archive

compress-async

When set then archive logs are not compressed immediately, but are instead compressed when copied to the backup host. This means that more space will be used on local storage, but the initial archive process will complete more quickly allowing greater throughput from Postgres.

default: n
example: compress-async=y

archive-max-mb

Limits the amount of archive log that will be written locally. After the limit is reached, the following will happen:

1. PgBackRest will notify Postgres that the archive was succesfully backed up, then DROP IT.
2. An error will be logged to the console and also to the Postgres log.
3. A stop file will be written in the lock directory and no more archive files will be backed up until it is removed.

If this occurs then the archive log stream will be interrupted and PITR will not be possible past that point. A new backup will be required to regain full restore capability.

The purpose of this feature is to prevent the log volume from filling up at which point Postgres will stop all operation. Better to lose the backup than have the database go down completely.

To start normal archiving again you'll need to remove the stop file which will be located at ${archive-path}/lock/${stanza}-archive.stop where ${archive-path} is the path set in the archive section, and ${stanza} is the backup stanza.

required: n
example: archive-max-mb=1024

retention section

The rentention section defines how long backups will be retained. Expiration only occurs when the number of complete backups exceeds the allowed retention. In other words, if full-retention is set to 2, then there must be 3 complete backups before the oldest will be expired. Make sure you always have enough space for rentention + 1 backups.

full-retention

Number of full backups to keep. When a full backup expires, all differential and incremental backups associated with the full backup will also expire. When not defined then all full backups will be kept.

required: n
example: full-retention=2

differential-retention

Number of differential backups to keep. When a differential backup expires, all incremental backups associated with the differential backup will also expire. When not defined all differential backups will be kept.

required: n
example: differential-retention=3

archive-retention-type

Type of backup to use for archive retention (full or differential). If set to full, then PgBackRest will keep archive logs for the number of full backups defined by archive-retention. If set to differential, then PgBackRest will keep archive logs for the number of differential backups defined by archive-retention.

If not defined then archive logs will be kept indefinitely. In general it is not useful to keep archive logs that are older than the oldest backup, but there may be reasons for doing so.

required: n
example: archive-retention-type=full

archive-retention

Number of backups worth of archive log to keep. If not defined, then full-retention will be used when archive-retention-type=full and differential-retention will be used when archive-retention-type=differential.

required: n
example: archive-retention=2

stanza sections

A stanza defines a backup for a specific database. The stanza section must define the base database path and host/user if the database is remote. Also, any global configuration sections can be overridden to define stanza-specific settings.

host

Sets the database host.

required: n (but must be set if user is defined)
example: host=db.mydomain.com

user

Sets user account on the db host.

required: n (but must be set if host is defined)
example: user=postgres

path

Path to the db data directory (data_directory setting in postgresql.conf).

required: y
example: path=/var/postgresql/data