pg_probackup

pg_probackup — manage backup and recovery of Postgres Pro database clusters

Synopsis

pg_probackup init -B backupdir

pg_probackup add-instance -B backupdir -D datadir --instance instance_name

pg_probackup del-instance -B backupdir --instance instance_name

pg_probackup set-config -B backupdir --instance instance_name [option...]

pg_probackup show-config -B backupdir --instance instance_name [--format=format]

pg_probackup backup -B backupdir --instance instance_name -b backup_mode [option...]

pg_probackup merge -B backupdir --instance instance_name -i backup_id [option...]

pg_probackup restore -B backupdir --instance instance_name [option...]

pg_probackup validate -B backupdir [option...]

pg_probackup show -B backupdir [option...]

pg_probackup delete -B backupdir --instance instance_name { -i backup_id | --wal | --expired }

pg_probackup archive-push -B backupdir --instance instance_name --wal-file-path %p --wal-file-name %f [option...]

pg_probackup archive-get -B backupdir --instance instance_name --wal-file-path %p --wal-file-name %f

pg_probackup version

pg_probackup help [command]

Description

pg_probackup is a utility to manage backup and recovery of Postgres Pro database clusters. It is designed to perform periodic backups of the Postgres Pro instance that enable you to restore the server in case of a failure. pg_probackup supports Postgres Pro 9.5 or higher.

Overview

As compared to other backup solutions, pg_probackup offers the following benefits that can help you implement different backup strategies and deal with large amounts of data:

  • Choosing between full and page-level incremental backups to speed up backup and recovery

  • Implementing a single backup strategy for multi-server Postgres Pro clusters

  • Automatic data consistency checks and on-demand backup validation without actual data recovery

  • Managing backups in accordance with retention policy

  • Running backup, restore, and validation processes on multiple parallel threads

  • Storing backup data in a compressed state to save disk space

  • Taking backups from a standby server to avoid extra load on the master server

  • Extended logging settings

  • Custom commands to simplify WAL log archiving

To manage backup data, pg_probackup creates a backup catalog. This directory stores all backup files with additional meta information, as well as WAL archives required for point-in-time recovery. You can store backups for different instances in separate subdirectories of a single backup catalog.

Using pg_probackup, you can take full or incremental backups:

  • Full backups contain all the data files required to restore the database cluster from scratch.

  • Incremental backups only store the data that has changed since the previous backup. It allows to decrease the backup size and speed up backup operations. pg_probackup supports the following modes of incremental backups:

    • PAGE backup. In this mode, pg_probackup scans all WAL files in the archive from the moment the previous full or incremental backup was taken. Newly created backups contain only the pages that were mentioned in WAL records. This requires all the WAL files since the previous backup to be present in the WAL archive. If the size of these files is comparable to the total size of the database cluster files, speedup is smaller, but the backup still takes less space.

    • DELTA backup. In this mode, pg_probackup reads all data files in the data directory and copies only those pages that has changed since the previous backup. Continuous archiving is not necessary for this mode to operate. Note that this mode can impose read-only I/O pressure equal to a full backup.

    • PTRACK backup. In this mode, Postgres Pro tracks page changes on the fly. Continuous archiving is not necessary for it to operate. Each time a relation page is updated, this page is marked in a special PTRACK bitmap for this relation. As one page requires just one bit in the PTRACK fork, such bitmaps are quite small. Tracking implies some minor overhead on the database server operation, but speeds up incremental backups significantly.

Regardless of the chosen backup type, all backups taken with pg_probackup support the following archiving strategies:

  • Autonomous backups include all the files required to restore the cluster to a consistent state at the time the backup was taken. Even if continuous archiving is not set up, the required WAL segments are included into the backup.

  • Archive backups rely on continuous archiving. Such backups enable cluster recovery to an arbitrary point after the backup was taken (point-in-time recovery).

See Also

Creating Backups

Limitations

pg_probackup currently has the following limitations:

  • Creating backups from a remote server is currently not supported.

  • The server from which the backup was taken and the restored server must be compatible by the block_size and wal_block_size parameters and have the same major release number.

  • Configuration files outside of Postgres Pro data directory are not included into the backup and should be backed up separately.

Installation and Setup

The pg_probackup package is provided as part of the Postgres Pro distribution. Once you have pg_probackup installed, complete the following setup:

Initializing the Backup Catalog

pg_probackup stores all WAL and backup files in the corresponding subdirectories of the backup catalog.

To initialize the backup catalog, run the following command:

pg_probackup init -B backupdir

where backupdir is the backup catalog. If the backupdir already exists, it must be empty. Otherwise, pg_probackup returns an error.

pg_probackup creates the backupdir backup catalog, with the following subdirectories:

  • wal/ — directory for WAL files.

  • backups/ — directory for backup files.

Once the backup catalog is initialized, you can add a new backup instance.

Adding a New Backup Instance

pg_probackup can store backups for multiple database clusters in a single backup catalog. To set up the required subdirectories, you must add a backup instance to the backup catalog for each database cluster you are going to back up.

To add a new backup instance, run the following command:

pg_probackup add-instance -B backupdir -D datadir --instance instance_name

where:

  • datadir is the data directory of the cluster you are going to back up. To set up and use pg_probackup, write access to this directory is required.

  • instance_name is the name of the subdirectories that will store WAL and backup files for this cluster.

pg_probackup creates the instance_name subdirectories under the backups/ and wal/ directories of the backup catalog. The backups/instance_name directory contains the pg_probackup.conf configuration file that controls backup and restore settings for this backup instance. For details on how to fine-tune pg_probackup configuration, see the section called “Configuring pg_probackup”.

The backup catalog must belong to the file system of the database server. The user launching pg_probackup must have full access to the contents of the backup catalog. If you specify the path to the backup catalog in the BACKUP_PATH environment variable, you can omit the corresponding option when running pg_probackup commands.

Since pg_probackup uses a regular PostgreSQL connection and the replication protocol, pg_probackup commands require connection options. To avoid specifying these options each time on the command line, you can set them in the pg_probackup.conf configuration file using the set-config command. For details, see the section called “Configuring pg_probackup”.

Configuring the Database Cluster

Although pg_probackup can be used by a superuser, it is recommended to create a separate user or role with the minimum permissions required for the chosen backup strategy. In these configuration instructions, the backup role is used as an example.

To enable backups, the following rights are required:

CREATE ROLE backup WITH LOGIN;
GRANT USAGE ON SCHEMA pg_catalog TO backup;
GRANT EXECUTE ON FUNCTION current_setting(text) TO backup;
GRANT EXECUTE ON FUNCTION pg_is_in_recovery() TO backup;
GRANT EXECUTE ON FUNCTION pg_start_backup(text, boolean, boolean) TO backup;
GRANT EXECUTE ON FUNCTION pg_stop_backup() TO backup;
GRANT EXECUTE ON FUNCTION pg_stop_backup(boolean) TO backup;
GRANT EXECUTE ON FUNCTION pg_create_restore_point(text) TO backup;
GRANT EXECUTE ON FUNCTION pg_switch_xlog() TO backup;
GRANT EXECUTE ON FUNCTION txid_current() TO backup;
GRANT EXECUTE ON FUNCTION txid_current_snapshot() TO backup;
GRANT EXECUTE ON FUNCTION txid_snapshot_xmax(txid_snapshot) TO backup;

Depending on whether you are going to use autonomous or archive backup strategies, Postgres Pro cluster configuration will differ, as specified in the sections below. To back up the database cluster from a standby server or create PTRACK backups, additional setup is required. For details, see the section called “PTRACK Backup” and the section called “Backup from Standby”.

Setting up Autonomous Backups

To set up the cluster for autonomous backups, complete the following steps:

  1. Grant the REPLICATION privilege to the backup role:

    ALTER ROLE backup WITH REPLICATION;
    
  2. In the pg_hba.conf file, allow replication on behalf of the backup role.

  3. Modify the postgresql.conf configuration file of the Postgres Pro server, as follows:

    • Make sure the max_wal_senders parameter is set high enough to leave at least one session available for the backup process.

    • Set the wal_level parameter to be replica or higher.

Setting up Archive Backups

To set up the cluster for archive backups, complete the following steps:

  1. Configure the following parameters in postgresql.conf to enable continuous archiving on the Postgres Pro server:

    • Make sure the wal_level parameter is set to replica or higher.

    • Set archive_mode to on.

    • Set the archive_command variable, as follows:

      archive_command = 'pg_probackup archive-push -B backupdir --instance instance_name --wal-file-path %p --wal-file-name %f'
      

      where backupdir and instance_name refer to the already initialized backup catalog instance for this database cluster.

Backup from Standby

For Postgres Pro 9.6 or higher, pg_probackup can take backups from a standby server. This requires the following additional setup:

  1. On the standby server, allow replication connections:

    • Set the max_wal_senders and hot_standby parameters in postgresql.conf.

    • Configure host-based authentication in pg_hba.conf.

  2. On the master server, enable full_page_writes in postgresql.conf.

Note

Archive backup from the standby server has the following limitations:

  • If the standby is promoted to the master during archive backup, the backup fails.

  • All WAL records required for the backup must contain sufficient full-page writes. This requires you to enable full_page_writes on the master, and not to use a tool like pg_compresslog as archive_command to remove full-page writes from WAL files.

PTRACK Backup

If you are going to use PTRACK backups, complete the following additional steps:

  1. In postgresql.conf, set ptrack_enable to on.

  2. Grant the rights to execute ptrack functions to the backup role:

GRANT EXECUTE ON FUNCTION pg_ptrack_clear() TO backup;
GRANT EXECUTE ON FUNCTION pg_ptrack_get_and_clear(oid, oid) TO backup;

The backup role must have access to all the databases of the cluster.

Command-Line Reference

Commands

This section describes pg_probackup commands. Some commands require mandatory options and can take additional options. For detailed descriptions, see the section called “Options”.

init

Syntax:

pg_probackup init -B backupdir

Initializes the backupdir backup catalog that will store backup copies, WAL archive, and meta information for the backed up database clusters. If the specified backupdir already exists, it must be empty. Otherwise, pg_probackup displays a corresponding error message.

add-instance

Syntax:

pg_probackup add-instance -B backupdir -D datadir --instance instance_name

Initializes a new backup instance inside the backup catalog backupdir and generates the pg_probackup.conf configuration file that controls backup and restore settings for the cluster with the specified datadir data directory. For details, see the section called “Adding a New Backup Instance”.

del-instance

Syntax:

pg_probackup del-instance -B backupdir --instance instance_name

Deletes all backup and WAL files associated with the specified instance.

set-config

Syntax:

pg_probackup set-config -B backupdir --instance instance_name
[--log-level-console=log_level] [--log-level-file=log_level] [--log-filename=log_filename]
[--error-log-filename=error_log_filename] [--log-directory=log_directory]
[--log-rotation-size=log_rotation_size] [--log-rotation-age=log_rotation_age]
[--retention-redundancy=redundancy][--retention-window=window]
[--compress-algorithm=compression_algorithm] [--compress-level=compression_level]
[-d dbname] [-h host] [-p port] [-U username]
[--master-db=dbname] [--master-host=host]
[--master-port=port] [--master-user=username]
[--replica-timeout=timeout] [-archive-timeout=timeout]

Adds the specified connection, retention, logging or replica, and compression settings into the pg_probackup.conf configuration file, or modifies the previously defined values.

show-config

Syntax:

pg_probackup show-config -B backupdir --instance instance_name [--format=plain|json]

Displays the contents of the pg_probackup.conf configuration file located in the backupdir/backups/instance_name directory. You can specify the --format=json option to return the result in the JSON format. By default, configuration settings are shown as plain text.

To edit pg_probackup.conf, use the set-config command. It is not allowed to edit pg_probackup.conf directly.

backup

Syntax:

pg_probackup backup -B backupdir -b backup_mode --instance instance_name
[-C] [--stream [-S slot_name]] [--backup-pg-log]
[--delete-expired] [--delete-wal] [--skip-block-validation]
[--retention-redundancy=redundancy] [--retention-window=window]
[-d dbname] [-h host] [-p port] [-U username]
[-w --no-password] [-W --password]
[--master-db=dbname] [--master-host=host]
[--master-port=port] [--master-user=username]
[--replica-timeout=timeout] [-archive-timeout=timeout]
[--compress] [--compress-algorithm=compression_algorithm] [--compress-level=compression_level]
[-j num_threads][--progress] [-q] [-v]
[logging_options]

Creates a backup copy of the Postgres Pro instance. The backup_mode option specifies the backup mode to use. For details, see the section called “Creating a Backup”.

merge

Syntax:

pg_probackup merge -B backupdir --instance instance_name -i backup_id
[-j num_threads][--progress]
[logging_options]

Merges the specified incremental backup to its parent full backup, together with all incremental backups between them, if any. As a result, the full backup takes in all the merged data, and the incremental backups are removed as redundant. For details, see the section called “Merging Backups”.

restore

Syntax:

pg_probackup restore -B backupdir --instance instance_name
[-D datadir]
[ -i backup_id | --immediate | [{--time=time | --xid=xid | --lsn=lsn | --recovery-target-name=recovery_target_name } [--inclusive=boolean]]]
[--timeline=timeline] [-T OLDDIR=NEWDIR]
[--recovery-target-action=pause|promote|shutdown]
[-R | --restore-as-replica] [--no-validate] [--skip-block-validation]
[-j num_threads] [--progress] [-q] [-v]
[logging_options]

Restores the Postgres Pro instance from a backup copy located in the backupdir backup catalog. If you specify a recovery target option, pg_probackup restores the database cluster up to the corresponding recovery target. Otherwise, the most recent backup is used.

validate

Syntax:

pg_probackup validate -B backupdir
[--instance instance_name
[ -i backup_id | [{--time=time | --xid=xid | --lsn=lsn | --recovery-target-name=recovery_target_name }
[--inclusive=boolean]]]]
[--timeline=timeline] [--skip-block-validation]
[-j num_threads] [--progress] [-q] [-v]

Verifies that all the files required to restore the cluster are present and not corrupted. If you specify the instance_name without any additional options, pg_probackup validates the most recent backup available in this backup instance. If you specify the instance_name with a recovery target option or a backup_id, pg_probackup checks whether it is possible to restore the cluster using these options. If instance_name is not specified, pg_probackup validates all backups available in the backup catalog.

show

Syntax:

pg_probackup show -B backupdir
[--instance instance_name [-i backup_id]] [--format=plain|json]

Shows the contents of the backup catalog. If instance_name and backup_id are specified, shows detailed information about this backup. You can specify the --format=json option to return the result in the JSON format. By default, the contents of the backup catalog is shown as plain text.

delete

Syntax:

pg_probackup delete -B backupdir --instance instance_name
 [--wal] {-i backup_id | --expired}

Deletes backup or WAL files of the specified backup instance from the backupdir backup catalog:

  • The wal option removes the WAL files that are no longer required to restore the cluster from any of the existing backups.

  • The -i option removes the specified backup copy.

  • The expired option removes the backups that are expired according to the current retention policy.

archive-push

Syntax:

pg_probackup archive-push -B backupdir --instance instance_name
--wal-file-path %p --wal-file-name %f'
[--compress][--compress-algorithm=compression_algorithm][--compress-level=compression_level] [--overwrite]

Stores WAL files in the corresponding subdirectory of the backup catalog. Can be set as archive_command in postgresql.conf to perform archive backups. In addition to copying files, this command also validates the instance by instance_name, system-identifier and PGDATA. If parameters of the backup instance and the cluster do not match, this command will fail with the following error message: Refuse to push WAL segment segment_name into archive. Instance parameters mismatch. For each WAL file moved to the backup catalog, you will see the following message in Postgres Pro logfile: pg_probackup archive-push completed successfully.

archive-get

Syntax:

pg_probackup archive-get -B backupdir --instance instance_name
--wal-file-path %p --wal-file-name %f'

Moves WAL files from the corresponding subdirectory of the backup catalog to the cluster's write-ahead log location. This command is automatically set by pg_probackup as restore_command in recovery.conf when restoring archive backups. You do not need to set it manually.

version

Syntax:

pg_probackup version

Prints pg_probackup version.

help

Syntax:

pg_probackup help [command]

Displays the synopsis of pg_probackup commands. If one of the pg_probackup commands is specified, shows detailed information about the options that can be used with this command.

Options

This section describes all command-line options for pg_probackup commands. If the option value can be derived from an environment variable, this variable is specified below the command-line option, in the uppercase. Some values can be taken from the pg_probackup.conf configuration file located in the backup catalog. For details, see the section called “Configuring pg_probackup”.

If an option is specified using more than one method, command-line input has the highest priority, while the pg_probackup.conf settings have the lowest priority.

Common Options

-B directory
--backup-path=directory
BACKUP_PATH

Specifies the absolute path to the backup catalog. Backup catalog is a directory where all backup files and meta information are stored. Since this option is required for most of the pg_probackup commands, you are recommended to specify it once in the BACKUP_PATH environment variable. In this case, you do not need to use this option each time on the command line.

-D directory
--pgdata=directory
PGDATA

Specifies the absolute path to the data directory of the database cluster. This option is mandatory only for the init command. Other commands can take its value from the PGDATA environment variable, or from the pg_probackup.conf configuration file.

-i backup_id
-backup-id=backup_id

Specifies the unique identifier of the backup.

-j num_threads
--threads=num_threads

Sets the number of parallel threads for backup, recovery, and backup validation processes.

--progress

Shows the progress of operations.

-q
--quiet

Enables the silent mode that does not display any messages about the current process.

-v
--verbose

Prints detailed information about the current process.

Backup Options

The following options can be used together with the backup command.

-b mode
--backup-mode=mode

Specifies the backup mode to use. Possible values are:

  • FULL — creates a full backup that contains all the data files of the cluster to be restored.

  • DELTA — reads all data files in the data directory and creates an incremental backup for pages that have changed since the previous backup.

  • PAGE — creates an incremental PAGE backup based on the WAL files that have changed since the previous full or incremental backup was taken.

  • PTRACK — creates an incremental PTRACK backup tracking page changes on the fly.

For details, see the section called “Creating a Backup”.

-C
--smooth-checkpoint
SMOOTH_CHECKPOINT

Spreads out the checkpoint over a period of time. By default, pg_probackup tries to complete the checkpoint as soon as possible.

--stream

Makes an autonomous backup that includes all the necessary WAL files by streaming them from the database server via replication protocol.

-S slot_name
--slot=slot_name

Specifies the replication slot for WAL streaming. This option can only be used together with the --stream option.

--backup-pg-log

Includes the pg_log directory into the backup. This directory usually contains log messages. By default, pg_log directory is excluded.

--archive-timeout=wait_time

Sets the timeout for WAL segment archiving, in seconds. By default, pg_probackup waits 300 seconds.

--delete-expired

After a backup copy is successfully created, deletes backups that are expired according to the current retention policy. You can also clean up the expired backups by running the delete command with the expired option. For details, see the section called “Configuring Backup Retention Policy”.

--delete-wal

After a backup copy is successfully created, removes redundant WAL files in accordance with the current retention policy. You can also clean up the expired WAL files by running the delete command with the wal option. For details, see the section called “Configuring Backup Retention Policy”.

Restore Options

--immediate

Stops recovery as soon as a consistent state is reached.

Alternatively, you can specify the backup ID up to which to restore the data, or one of the recovery target options.

--recovery-target-action=pause|promote|shutdown

Specifies the action the server should take when the recovery target is reached, similar to the recovery_target_action option in the recovery.conf configuration file.

Default: pause

-R | --restore-as-replica

Writes a minimal recovery.conf in the output directory to facilitate setting up a standby server. The password is not included. If the replication connection requires a password, you must specify the password manually.

-T OLDDIR=NEWDIR
--tablespace-mapping=OLDDIR=NEWDIR

Relocates the tablespace from the OLDDIR to the NEWDIR directory at the time of recovery. Both OLDDIR and NEWDIR must be absolute paths. If the path contains the equals sign (=), escape it with a backslash. This option can be specified multiple times for multiple tablespaces.

--timeline=timeline

Specifies a particular timeline to restore the cluster into. By default, the timeline of the specified backup is used.

--no-validate

Skips backup validation. You can use this option if you validate backups regularly and would like to save time when restoring the cluster.

--skip-block-validation

Disables block-level checksum verification to speed up validation. If this option is used, only file-level checksums will be verified. You can use this option with backup, restore, and validate commands.

Recovery Target Options

If the archive backup strategy is configured, you can use one of these options together with restore or validate commands to specify the moment up to which the database cluster must be restored.

--lsn=lsn

Specifies the LSN of the write-ahead log location up to which recovery will proceed.

--recovery-target-name=recovery_target_name

Specifies a named savepoint up to which to restore the cluster data.

--time=time

Specifies the timestamp up to which recovery will proceed.

--xid=xid

Specifies the transaction ID up to which recovery will proceed.

--inclusive=boolean

Specifies whether to stop just after the specified recovery target (true), or just before the recovery target (false). This option can only be used together with recovery-target-name, time, lsn, or xid options. The default value is taken from the recovery_target_inclusive variable.

Delete Options

--wal

Deletes WAL files that are no longer required to restore the cluster from any of the existing backups.

--expired

Deletes backups that do not conform to the retention policy defined in the pg_probackup.conf configuration file. For details, see the section called “Configuring Backup Retention Policy”.

Retention Options

For details on configuring retention policy, see the section called “Configuring Backup Retention Policy”.

--retention-redundancy=redundancy

Specifies the number of full backup copies to keep in the data directory. Must be a positive integer. The zero value disables this setting.

Default: 0

--retention-window=window

Number of days of recoverability. The zero value disables this setting.

Default: 0

Logging Options

--log-level-console=log_level

Controls which message levels are sent to the console log. Valid values are verbose, log, info, notice, warning, error, and off. Each level includes all the levels that follow it. The later the level, the fewer messages are sent. The off level disables console logging.

Default: info

--log-level-file=log_level

Controls which message levels are sent to a log file. Valid values are verbose, log, info, notice, warning, error, and off. Each level includes all the levels that follow it. The later the level, the fewer messages are sent. The off level disables file logging.

Default: off

--log-filename=log_filename

Defines the file names of the created log files. The file names are treated as a strftime pattern, so you can use %-escapes to specify time-varying file names. This option takes effect if file logging is enabled by the log-level-file option.

Default: pg_probackup.log

--error-log-filename=error_log_filename

Defines the file names of log files for error messages. The filenames are treated as a strftime pattern, so you can use %-escapes to specify time-varying file names. If error-log-filename is not set, pg_probackup writes all error messages to stderr.

Default: none

--log-directory=log_directory

Defines the directory in which log files will be created. You must specify the absolute path. This directory is created lazily, when the first log message is written.

Default: $BACKUP_PATH/log/

--log-rotation-size=log_rotation_size

Maximum size of an individual log file. If this value is reached, the log file is rotated once a pg_probackup command is launched, except help and version commands. The zero value disables size-based rotation. Supported units: kB, MB, GB, TB (kB by default).

Default: 0

--log-rotation-age=log_rotation_age

Maximum lifetime of an individual log file. If this value is reached, the log file is rotated once a pg_probackup command is launched, except help and version commands. The time of the last log file creation is stored in $BACKUP_PATH/log/log_rotation. The zero value disables time-based rotation. Supported units: ms, s, min, h, d (min by default).

Default: 0

Connection Options

-d dbname
--dbname=dbname
PGDATABASE

Specifies the name of the database to connect to. The connection is used only for managing backup process, so you can connect to any existing database. If this option is not provided on the command line, PGDATABASE environment variable, or the pg_probackup.conf configuration file, pg_probackup tries to take this value from the PGUSER environment variable, or from the current user name if PGUSER variable is not set.

-h host
--host=host
PGHOST

Specifies the host name of the system on which the server is running. If the value begins with a slash, it is used as a directory for the Unix domain socket.

Default: local socket

-p port
--port=port
PGPORT

Specifies the TCP port or the local Unix domain socket file extension on which the server is listening for connections.

Default: 5432

-U username
--username=username
PGUSER

User name to connect as.

-w
--no-password

Disables a password prompt. If the server requires password authentication and a password is not available by other means such as a .pgpass file, the connection attempt will fail. This option can be useful in batch jobs and scripts where no user is present to enter a password.

-W
--password

Forces a password prompt.

Compression Options

--compress

Enables compression for data files. You can specify the compression algorithm and level using the --compress-algorithm and --compress-level options, respectively. If you omit these options, --compress uses zlib compression algorithm with compression level 1.

By default, compression is disabled.

--compress-algorithm=compression_algorithm

Defines the algorithm to use for compressing data files. Possible values are zlib, pglz, and none. If set to zlib or pglz, this option enables compression, regardless of whether the --compress option is specified. By default, compression is disabled.

For the archive-push command, the pglz compression algorithm is not supported.

--compress-level=compression_level

Defines compression level (0 through 9, 0 being no compression and 9 being best compression). This option can only be used together with --compress or --compress-algorithm options.

Default: 1

Replica Options

This section describes the options related to taking a backup from standby. Starting from pg_probackup 2.0.24, these options are no longer required as backups can be taken from the standby server without connecting to the master server. In lower versions, connection options were needed to create a restore point (it could only be done at master), which was used to determine recovery time — the earliest moment for which you can restore a consistent state of the database cluster.

--master-db=dbname

Specifies the name of the database on the master server to connect to. The connection is used only for managing the backup process, so you can connect to any existing database. Can be set in the pg_probackup.conf using the set-config command. Default: postgres, the default Postgres Pro dbname.

--master-host=host

Specifies the host name of the system on which the master server is running.

--master-port=port

Specifies the TCP port or the local Unix domain socket file extension on which the master server is listening for connections. Default: 5432, the Postgres Pro default port.

--master-user=username

User name to connect as. Default: postgres, the Postgres Pro default user name.

--replica-timeout=timeout

Wait time for WAL segment streaming via replication, in seconds. By default, pg_probackup waits 300 seconds. You can also define this parameter in the pg_probackup.conf configuration file using the set-config command.

Archiving Options

--wal-file-path=wal_file_path %p

Provides the path to the WAL file in archive_command and restore_command used by pg_probackup. The %p variable is required for correct processing.

--wal-file-name=wal_file_name %f

Provides the name of the WAL file in archive_command and restore_command used by pg_probackup. The %f variable is required for correct processing.

--overwrite

Overwrites archived WAL file. Use this option together with the archive-push command if the specified subdirectory of the backup catalog already contains this WAL file and needs to be replaced with its newer copy. Otherwise, archive-push reports that a WAL segment already exists, and aborts the operation.

Usage

Creating a Backup

To create a backup, run the following command:

pg_probackup backup -B backupdir --instance instance_name -b backup_mode

where backup_mode can take one of the following values:

  • FULL — creates a full backup that contains all the data files of the cluster to be restored.

  • DELTA — reads all data files in the data directory and creates an incremental backup for pages that have changed since the previous backup.

  • PAGE — creates an incremental PAGE backup based on the WAL files that have changed since the previous full or incremental backup was taken.

  • PTRACK — creates an incremental PTRACK backup tracking page changes on the fly.

When restoring a cluster from an incremental backup, pg_probackup relies on the previous full backup to restore all the data files first. Thus, you must create at least one full backup before taking incremental ones.

If you have configured PTRACK backups, pg_probackup clears PTRACK bitmap of the relation being processed each time a full or an incremental backup is taken. Thus, the next incremental PTRACK backup contains only the pages that have changed since the previous backup. If a backup failed or was interrupted, some relations can already have their PTRACK forks cleared, so the next incremental backup will be incomplete. The same is true if ptrack_enable was turned off for some time. In this case, you must take a full backup before the next incremental PTRACK backup.

To make a backup autonomous, add the --stream option to the above command. For example, to create a full autonomous backup, run:

pg_probackup backup -B backupdir --instance instance_name -b FULL --stream

Autonomous backups include all the WAL segments required to restore the cluster to a consistent state at the time the backup was taken. To restore a cluster from an incremental autonomous backup, pg_probackup still requires the full backup and all the incremental backups it depends on.

Even if you are using continuous archiving, autonomous backups can still be useful in the following cases:

  • Autonomous backups can be restored on the server that has no file access to WAL archive.

  • Autonomous backups enable you to restore the cluster state at the point in time for which WAL files are no longer available.

Validating Backups

When checksums are enabled for the database cluster, pg_probackup uses this information to check correctness of data files. While reading each page, pg_probackup checks whether the calculated checksum coincides with the checksum stored in the page. This guarantees that the backup is free of corrupted pages. Note that pg_probackup reads database files from disk and under heavy write load during backup it can show false positive checksum failures because of partial writes.

Even if page checksums are disabled, pg_probackup calculates checksums for each file in a backup. Checksums are checked immediately after backup is taken and right before restore, to detect possible backup corruptions.

To ensure that all the required backup files are present and can be used to restore the database cluster, you can run the validate command with the exact recovery target options you are going to use for recovery. If you omit all the parameters, all backups are validated.

For example, to check that you can restore the database cluster from a backup copy up to the specified xid transaction ID, run this command:

pg_probackup validate -B backupdir --instance instance_name --xid=xid

If validation completes successfully, pg_probackup displays the corresponding message. If validation fails, you will receive an error message with the exact time and transaction ID up to which the recovery is possible.

Restoring a Cluster

To restore the database cluster from a backup, run the restore command with at least the following options:

pg_probackup restore -B backupdir --instance instance_name -i backup_id

where:

  • backupdir is the backup catalog that stores all backup files and meta information.

  • instance_name is the backup instance for the cluster to be restored.

  • backup_id specifies the backup to restore the cluster from. If you omit this option, pg_probackup uses the latest backup available for the specified instance. If you specify an incremental backup to restore, pg_probackup automatically restores the underlying full backup and then sequentially applies all the necessary increments.

By default, this command validates the specified backup before restoring the cluster. If you run regular backup validations and would like to save time when restoring the cluster, you can specify the --no-validate option to skip validation and speed up the recovery.

If you have configured archive backups, you can restore the cluster to its state at an arbitrary point in time (recovery target) using recovery target options. pg_probackup automatically chooses the backup that is the closest to the specified recovery target and start the recovery process. By default, the recovery_target_inclusive parameter defines whether the recovery target is included into the backup. You can explicitly include or exclude the recovery target using the --inclusive=boolean option.

To restore the cluster state at the exact time, specify the time option, in the timestamp format. For example:

pg_probackup restore -B backupdir --instance instance_name --time='2017-05-18 14:18:11'

To restore the cluster state up to a specific transaction ID, use the xid:

pg_probackup restore -B backupdir --instance instance_name --xid=687

If you know the exact LSN up to which you need to restore the data, use lsn:

pg_probackup restore -B backupdir --instance instance_name --lsn=16/B374D848

If the cluster to restore contains tablespaces, pg_probackup restores them to their original location by default. To restore tablespaces to a different location, use the --tablespace-mapping option. Otherwise, restoring the cluster on the same host will fail if tablespaces are in use, because the backup would have to be written to the same directories.

When using the --tablespace-mapping you must provide absolute paths to the old and new tablespace directories. If a path happens to contain an equals sign (=), escape it with a backslash. This option can be specified multiple times for multiple tablespaces. For example:

pg_probackup restore -B backupdir --instance instance_name -D datadir -j 4 -i backup_id -T tablespace1_dir=tablespace1_newdir -T tablespace2_dir=tablespace2_newdir

Once the restore command is complete, start the database service. Postgres Pro will restore a self-consistent state by replaying WAL files and will be ready to accept connections.

Running pg_probackup on Parallel Threads

Backup, recovery, and validation processes can be executed on several parallel threads. This can significantly speed up pg_probackup operation given enough resources (CPU cores, disk, and network throughput).

Parallel execution is controlled by the -j/--threads command line option. For example, to create a backup using four parallel threads, run:

pg_probackup backup -B backupdir --instance instance_name -b FULL -j 4

Note

Parallel recovery applies only to copying data from the backup catalog to the data directory of the cluster. When Postgres Pro server is started, WAL records need to be replayed, and this cannot be done in parallel.

Configuring pg_probackup

Once the backup catalog is initialized and a new backup instance is added, you can use the pg_probackup.conf configuration file located in the backups/instance_name directory to fine-tune pg_probackup configuration.

Initially, pg_probackup.conf contains the following settings:

  • PGDATA — the path to the data directory of the cluster to back up.

  • system-identifier — the unique identifier of the Postgres Pro instance.

Additionally, you can define connection, retention, logging, and replica settings using the set-config command:

pg_probackup set-config -B backupdir --instance instance_name [connection_options] [retention_options] [logging_options] [replica_options]

To view the current settings, run the following command:

pg_probackup show-config -B backupdir --instance instance_name

Specifying Connection Settings

If you define connection settings in the pg_probackup.conf configuration file, you can omit connection options in all the subsequent pg_probackup commands. However, if the corresponding environment variables are set, they get higher priority. The options provided on the command line overwrite both environment variables and configuration file settings.

If nothing is given, the default values are taken. pg_probackup tries to use local connection and tries to get the database name and the user name from the PGUSER environment variable or the current OS user name.

Configuring Backup Retention Policy

By default, all backup copies created with pg_probackup are stored in the specified backup catalog. To save disk space, you can configure retention policy and periodically clean up redundant backup copies accordingly.

To configure retention policy, set one or more of the following variables in the pg_probackup.conf file:

  • retention-redundancy — specifies the number of full backup copies to keep in the backup catalog.

  • retention-window — defines the earliest point in time for which pg_probackup can complete the recovery. This option is set in the number of days from the current moment. For example, if retention-window=7, pg_probackup must keep at least one full backup copy that is older than seven days, with all the corresponding WAL files.

If both retention-redundancy and retention-window options are set, pg_probackup keeps backup copies that satisfy both conditions. For example, if you set retention-redundancy=2 and retention-window=7, pg_probackup cleans up the backup directory to keep only two full backup copies if at least one of them is older than seven days.

To clean up the backup catalog in accordance with retention policy, run:

pg_probackup delete -B backupdir --instance instance_name --expired

pg_probackup deletes all backup copies that do not conform to the defined retention policy.

If you would like to also remove the WAL files that are no longer required for any of the backups, add the --wal option:

pg_probackup delete -B backupdir --instance instance_name --expired --wal

Alternatively, you can use the --delete-expired and --delete-wal options together with the backup command to remove the outdated backup copies once the new backup is created.

Managing the Backup Catalog

With pg_probackup, you can manage backups from the command line:

Viewing Backup Information

To view the list of existing backups, run the command:

pg_probackup show -B backupdir

pg_probackup displays the list of all the available backups. You will see the following output:

BACKUP INSTANCE 'node'
============================================================================================================================================
 Instance    Version  ID      Recovery time           Mode    WAL      Current/Parent TLI    Time    Data   Start LSN    Stop LSN    Status 
============================================================================================================================================
 node        10       P7XDQV  2018-04-29 05:32:59+03  DELTA   STREAM     1 / 0                11s    19MB   0/15000060   0/15000198  OK
 node        10       P7XDJA  2018-04-29 05:28:36+03  PTRACK  STREAM     1 / 0                21s    32MB   0/13000028   0/13000198  OK
 node        10       P7XDHU  2018-04-29 05:27:59+03  PTRACK  STREAM     1 / 0                31s    33MB   0/11000028   0/110001D0  OK
 node        10       P7XDHB  2018-04-29 05:27:15+03  FULL    STREAM     1 / 0                11s    39MB   0/F000028    0/F000198   OK
 node        10       P7XDFT  2018-04-29 05:26:25+03  PTRACK  STREAM     1 / 0                11s    40MB   0/D000028    0/D000198   OK

For each backup, the following information is provided:

  • Instance — the instance name.

  • Version — Postgres Pro version.

  • ID — the backup identifier.

  • Recovery time — the earliest moment for which you can restore the state of the database cluster.

  • Mode — the method used to take this backup. Possible values: FULL, PAGE, PTRACK.

  • WAL — the way of WAL log handling. Possible values: STREAM for autonomous backups and ARCHIVE for archive backups.

  • Current/Parent TLI — current and parent timelines of the database cluster.

  • Time — the time it took to perform the backup.

  • Data — the size of the data files in this backup. This value does not include the size of WAL files.

  • Start LSNWAL log sequence number corresponding to the start of the backup process.

  • Stop LSNWAL log sequence number corresponding to the end of the backup process.

  • Status — backup status. Possible values:

    • OK — the backup is complete and valid.

    • CORRUPT — some of the backup files are corrupted.

    • DONE — the backup is complete, but was not validated.

    • ERROR — the backup was aborted because of an unexpected error.

    • RUNNING — the backup is in progress.

    • MERGING — the backup is being merged.

    • ORPHAN — the backup is invalid because one of its parent backups is corrupt.

    • DELETING — the backup files are being deleted.

    You can restore the cluster from the backup only if the backup status is OK.

To get more detailed information about the backup, run the show with the backup ID:

pg_probackup show -B backupdir --instance instance_name -i backup_id

The sample output is as follows:

#Configuration
backup-mode = FULL
stream = false

#Compatibility
block-size = 8192
xlog-block-size = 8192
checksum-version = 0

#Result backup info
timelineid = 1
start-lsn = 0/04000028
stop-lsn = 0/040000f8
start-time = '2017-05-16 12:57:29'
end-time = '2017-05-16 12:57:31'
recovery-xid = 597
recovery-time = '2017-05-16 12:57:31'
data-bytes = 22288792
status = OK

Merging Backups

As you take more and more incremental backups, the total size of the backup catalog can substantially grow. To save disk space, you can merge incremental backups to their parent full backup by running the merge command, specifying the backup ID of the most recent incremental backup you would like to merge:

pg_probackup merge -B backupdir --instance instance_name -i backup_id

This command merges the specified incremental backup to its parent full backup, together with all incremental backups between them. Once the merge is complete, the incremental backups are removed as redundant. Thus, the merge operation is virtually equivalent to retaking a full backup and removing all the outdated backups, but it allows to save much time, especially for large data volumes.

Before the merge, pg_probackup validates all the affected backups to ensure that they are valid. You can check the current backup status by running the show command with the backup ID. If the merge is still in progress, the backup status is displayed as MERGING. You can restart the merge if it is interrupted.

Deleting Backups

To delete a backup that is no longer required, run the following command:

pg_probackup delete -B backupdir --instance instance_name -i backup_id

This command will delete the backup with the specified backup_id, together with all the incremental backups that followed, if any. This way, you can delete some recent incremental backups, retaining the underlying full backup and some of the incremental backups that follow it.

Note

In this case, the next PTRACK backup will be incomplete as some changes since the last retained backup will be lost. Either a full backup or an incremental PAGE backup (if all the necessary WAL files are still present in the archive) must be taken then.

To delete obsolete WAL files that are not necessary to restore any of the remaining backups, use the --wal option:

pg_probackup delete -B backupdir --instance instance_name --wal

To delete backups that are expired according to the current retention policy, use the --expired option:

pg_probackup delete -B backupdir --instance instance_name --expired

Authors

Postgres Professional, Moscow, Russia.

Credits

pg_probackup utility is based on pg_arman, that was originally written by NTT and then developed and maintained by Michael Paquier.