- buster 11.9-0+deb10u1
|PG_BASEBACKUP(1)||PostgreSQL 11.9 Documentation||PG_BASEBACKUP(1)|
NAME¶pg_basebackup - take a base backup of a PostgreSQL cluster
DESCRIPTION¶pg_basebackup is used to take base backups of a running PostgreSQL database cluster. These are taken without affecting other clients to the database, and can be used both for point-in-time recovery (see Section 25.3) and as the starting point for a log shipping or streaming replication standby servers (see Section 26.2).
pg_basebackup makes a binary copy of the database cluster files, while making sure the system is put in and out of backup mode automatically. Backups are always taken of the entire database cluster; it is not possible to back up individual databases or database objects. For individual database backups, a tool such as pg_dump(1) must be used.
The backup is made over a regular PostgreSQL connection, and uses the replication protocol. The connection must be made with a superuser or a user having REPLICATION permissions (see Section 21.2), and pg_hba.conf must explicitly permit the replication connection. The server must also be configured with max_wal_senders set high enough to leave at least one session available for the backup and one for WAL streaming (if used).
There can be multiple pg_basebackups running at the same time, but it is better from a performance point of view to take only one backup, and copy the result.
pg_basebackup can make a base backup from not only the master but also the standby. To take a backup from the standby, set up the standby so that it can accept replication connections (that is, set max_wal_senders and hot_standby, and configure host-based authentication). You will also need to enable full_page_writes on the master.
Note that there are some limitations in an online backup from the standby:
OPTIONS¶The following command-line options control the location and format of the output.
When the backup is in tar mode, and the directory is specified as - (dash), the tar file will be written to stdout.
This option is required.
This is the default format.
If the value - (dash) is specified as target directory, the tar contents will be written to standard output, suitable for piping to for example gzip. This is only possible if the cluster has no additional tablespaces and WAL streaming is not used.
The purpose is to limit the impact of pg_basebackup on the running server.
This option always affects transfer of the data directory. Transfer of WAL files is only affected if the collection method is fetch.
If a tablespace is relocated in this way, the symbolic links inside the main data directory are updated to point to the new location. So the new data directory is ready to be used for a new server instance with all tablespaces in the updated locations.
The following methods for collecting the write-ahead logs are supported:
When tar format mode is used, the write-ahead log files will be written to the base.tar file.
When tar format mode is used, the write-ahead log files will be written to a separate file named pg_wal.tar (if the server is a version earlier than 10, the file will be named pg_xlog.tar).
This value is the default.
The following command-line options control the generation of the backup and the running of the program.
Note that tablespace directories are not cleaned up either way.
When this is enabled, the backup will start by enumerating the size of the entire database, and then go back and send the actual contents. This may make the backup take slightly longer, and in particular it will take longer before the first data is sent.
The specified replication slot has to exist unless the option -C is also used.
If this option is not specified and the server supports temporary replication slots (version 10 and later), then a temporary replication slot is automatically used for WAL streaming.
Temporary replication slots are created by default if no slot name is given with the option -S when using log streaming.
The main purpose of this option is to allow taking a base backup when the server is out of free replication slots. Using replication slots is almost always preferred, because it prevents needed WAL from being removed by the server during the backup.
By default, checksums are verified and checksum failures will result in a non-zero exit status. However, the base backup will not be removed in such a case, as if the --no-clean option had been used.
The following command-line options control the database connection parameters.
The option is called --dbname for consistency with other client applications, but because pg_basebackup doesn't connect to any particular database in the cluster, database name in the connection string will be ignored.
This option is never essential, since pg_basebackup will automatically prompt for a password if the server demands password authentication. However, pg_basebackup will waste a connection attempt finding out that the server wants a password. In some cases it is worth typing -W to avoid the extra connection attempt.
Other options are also available:
ENVIRONMENT¶This utility, like most other PostgreSQL utilities, uses the environment variables supported by libpq (see Section 34.14).
NOTES¶At the beginning of the backup, a checkpoint needs to be written on the server the backup is taken from. Especially if the option --checkpoint=fast is not used, this can take some time during which pg_basebackup will be appear to be idle.
The backup will include all files in the data directory and tablespaces, including the configuration files and any additional files placed in the directory by third parties, except certain temporary files managed by PostgreSQL. But only regular files and directories are copied, except that symbolic links used for tablespaces are preserved. Symbolic links pointing to certain directories known to PostgreSQL are copied as empty directories. Other symbolic links and special device files are skipped. See Section 53.4 for the precise details.
Tablespaces will in plain format by default be backed up to the same path they have on the server, unless the option --tablespace-mapping is used. Without this option, running a plain format base backup on the same host as the server will not work if tablespaces are in use, because the backup would have to be written to the same directory locations as the original tablespaces.
When tar format mode is used, it is the user's responsibility to unpack each tar file before starting the PostgreSQL server. If there are additional tablespaces, the tar files for them need to be unpacked in the correct locations. In this case the symbolic links for those tablespaces will be created by the server according to the contents of the tablespace_map file that is included in the base.tar file.
pg_basebackup works with servers of the same or an older major version, down to 9.1. However, WAL streaming mode (-X stream) only works with server version 9.3 and later, and tar format mode (--format=tar) of the current version only works with server version 9.5 or later.
pg_basebackup will preserve group permissions in both the plain and tar formats if group permissions are enabled on the source cluster.
EXAMPLES¶To create a base backup of the server at mydbserver and store it in the local directory /usr/local/pgsql/data:
$ pg_basebackup -h mydbserver -D /usr/local/pgsql/data
To create a backup of the local server with one compressed tar file for each tablespace, and store it in the directory backup, showing a progress report while running:
$ pg_basebackup -D backup -Ft -z -P
To create a backup of a single-tablespace local database and compress this with bzip2:
$ pg_basebackup -D - -Ft -X fetch | bzip2 > backup.tar.bz2
(This command will fail if there are multiple tablespaces in the database.)
To create a backup of a local database where the tablespace in /opt/ts is relocated to ./backup/ts:
$ pg_basebackup -D backup/data -T /opt/ts=$(pwd)/backup/ts