pg_basebackup — take a base backup of a PostgreSQL cluster
pg_basebackup [option...]
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 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:
The backup history file is not created in the database cluster backed up.
If you are using -X none, there is no guarantee that all
WAL files required for the backup are archived at the end of backup.
If the standby is promoted to the master during online backup, the backup fails.
All WAL records required for the backup must contain sufficient full-page writes,
which 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.
The following command-line options control the location and format of the output.
-D directory--pgdata=directoryDirectory to write the output to. pg_basebackup will create the directory and any parent directories if necessary. The directory may already exist, but it is an error if the directory already exists and is not empty.
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.
-F format--format=format Selects the format for the output. format
can be one of the following:
pplainWrite the output as plain files, with the same layout as the current data directory and tablespaces. When the cluster has no additional tablespaces, the whole database will be placed in the target directory. If the cluster contains additional tablespaces, the main data directory will be placed in the target directory, but all other tablespaces will be placed in the same absolute path as they have on the server.
This is the default format.
ttar Write the output as tar files in the target directory. The main
data directory will be written to a file named
base.tar, and all other tablespaces will
be named after the tablespace OID.
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.
-r rate--max-rate=rate The maximum transfer rate of data transferred from the server. Values are
in kilobytes per second. Use a suffix of M to indicate megabytes
per second. A suffix of k is also accepted, and has no effect.
Valid values are between 32 kilobytes per second and 1024 megabytes per second.
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.
-R--write-recovery-conf Write a minimal recovery.conf in the output
directory (or into the base archive file when using tar format) to
ease setting up a standby server.
The recovery.conf file will record the connection
settings and, if specified, the replication slot
that pg_basebackup is using, so that the
streaming replication will use the same settings later on.
-S slotname--slot=slotname This option can only be used together with -X
stream. It causes the WAL streaming to use the specified
replication slot. If the base backup is intended to be used as a
streaming replication standby using replication slots, it should then
use the same replication slot name
in recovery.conf. That way, it is ensured that
the server does not remove any necessary WAL data in the time between
the end of the base backup and the start of streaming replication.
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.
--no-slotThis option prevents the creation of a temporary replication slot during the backup even if it's supported by the server.
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.
-T olddir=newdir--tablespace-mapping=olddir=newdir Relocate the tablespace in directory olddir
to newdir during the backup. To be
effective, olddir must exactly match the
path specification of the tablespace as it is currently defined. (But
it is not an error if there is no tablespace
in olddir contained in the backup.)
Both olddir
and newdir must be absolute paths. If a
path happens to contain a = sign, escape it with a
backslash. This option can be specified multiple times for multiple
tablespaces. See examples below.
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.
--waldir=waldir Specifies the location for the write-ahead log directory.
waldir must be an absolute path.
The write-ahead log directory can only be specified when
the backup is in plain mode.
-X method--wal-method=method Includes the required write-ahead log files (WAL files) in the
backup. This will include all write-ahead logs generated during
the backup. Unless the method none is specified,
it is possible to start a postmaster directly in the extracted
directory without the need to consult the log archive, thus
making this a completely standalone backup.
The following methods for collecting the write-ahead logs are supported:
nnoneDon't include write-ahead log in the backup.
ffetchThe write-ahead log files are collected at the end of the backup. Therefore, it is necessary for the wal_keep_segments parameter to be set high enough that the log is not removed before the end of the backup. If the log has been rotated when it's time to transfer it, the backup will fail and be unusable.
The write-ahead log files will be written to
the base.tar file.
sstreamStream the write-ahead log while the backup is created. This will open a second connection to the server and start streaming the write-ahead log in parallel while running the backup. Therefore, it will use up two connections configured by the max_wal_senders parameter. As long as the client can keep up with write-ahead log received, using this mode requires no extra write-ahead logs to be saved on the master.
The write-ahead log files are 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.
-z--gzip Enables gzip compression of tar file output, with the default
compression level. Compression is only available when using
the tar format, and the suffix .gz will
automatically be added to all tar filenames.
-Z level--compress=level Enables gzip compression of tar file output, and specifies the
compression level (0 through 9, 0 being no compression and 9 being best
compression). Compression is only available when using the tar
format, and the suffix .gz will
automatically be added to all tar filenames.
The following command-line options control the generation of the backup and the running of the program.
-c fast|spread--checkpoint=fast|spreadSets checkpoint mode to fast (immediate) or spread (default) (see Section 25.3.3).
-l label--label=label Sets the label for the backup. If none is specified, a default value of
“pg_basebackup base backup” will be used.
-n--no-clean By default, when pg_basebackup aborts with an
error, it removes any directories it might have created before
discovering that it cannot finish the job (for example, data directory
and write-ahead log directory). This option inhibits tidying-up and is
thus useful for debugging.
Note that tablespace directories are not cleaned up either way.
-P--progress Enables progress reporting. Turning this on will deliver an approximate
progress report during the backup. Since the database may change during
the backup, this is only an approximation and may not end at exactly
100%. In particular, when WAL log is included in the
backup, the total amount of data cannot be estimated in advance, and
in this case the estimated target size will increase once it passes the
total estimate without WAL.
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.
-N--no-sync By default, pg_basebackup will wait for all files
to be written safely to disk. This option causes
pg_basebackup to return without waiting, which is
faster, but means that a subsequent operating system crash can leave
the base backup corrupt. Generally, this option is useful for testing
but should not be used when creating a production installation.
-v--verboseEnables verbose mode. Will output some extra steps during startup and shutdown, as well as show the exact file name that is currently being processed if progress reporting is also enabled.
The following command-line options control the database connection parameters.
-d connstr--dbname=connstrSpecifies parameters used to connect to the server, as a connection string. See Section 33.1.1 for more information.
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.
-h host--host=host Specifies the host name of the machine on which the server is
running. If the value begins with a slash, it is used as the
directory for the Unix domain socket. The default is taken
from the PGHOST environment variable, if set,
else a Unix domain socket connection is attempted.
-p port--port=port Specifies the TCP port or local Unix domain socket file
extension on which the server is listening for connections.
Defaults to the PGPORT environment variable, if
set, or a compiled-in default.
-s interval--status-interval=intervalSpecifies the number of seconds between status packets sent back to the server. This allows for easier monitoring of the progress from server. A value of zero disables the periodic status updates completely, although an update will still be sent when requested by the server, to avoid timeout disconnect. The default value is 10 seconds.
-U username--username=usernameUser name to connect as.
-w--no-password Never issue 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--passwordForce pg_basebackup to prompt for a password before connecting to a database.
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:
-V--versionPrint the pg_basebackup version and exit.
-?--helpShow help about pg_basebackup command line arguments, and exit.
This utility, like most other PostgreSQL utilities, uses the environment variables supported by libpq (see Section 33.14).
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 52.4 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.
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