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pg_basebackup(1) - phpMan
PG_BASEBACKUP(1) PostgreSQL 12.3 Documentation PG_BASEBACKUP(1)
NAME
pg_basebackup - take a base backup of a PostgreSQL cluster
SYNOPSIS
pg_basebackup [option...]
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:
· 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.
OPTIONS
The following command-line options control the location and format of the output.
-D directory
--pgdata=directory
Directory 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:
p
plain
Write 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.
t
tar
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
Create standby.signal and append connection settings to postgresql.auto.conf in the
output directory (or into the base archive file when using tar format) to ease setting
up a standby server. The postgresql.auto.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.
-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:
n
none
Don't include write-ahead log in the backup.
f
fetch
The 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.
When tar format mode is used, the write-ahead log files will be written to the
base.tar file.
s
stream
Stream 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.
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.
-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|spread
Sets checkpoint mode to fast (immediate) or spread (default) (see Section 25.3.3).
-C
--create-slot
This option causes creation of a replication slot named by the --slot option before
starting the backup. An error is raised if the slot already exists.
-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.
-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.
-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.
-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 primary_slot_name. 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.
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.
-v
--verbose
Enables 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.
--no-slot
This 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.
--no-verify-checksums
Disables verification of checksums, if they are enabled on the server the base backup
is taken from.
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. Checksum verifications failures will also be reported
in the pg_stat_database view.
The following command-line options control the database connection parameters.
-d connstr
--dbname=connstr
Specifies 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=interval
Specifies 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=username
User 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
--password
Force 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
--version
Print the pg_basebackup version and exit.
-?
--help
Show help about pg_basebackup command line arguments, and exit.
ENVIRONMENT
This utility, like most other PostgreSQL utilities, uses the environment variables
supported by libpq (see Section 33.14).
The environment variable PG_COLOR specifies whether to use color in diagnostic messages.
Possible values are always, auto and never.
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 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.
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
SEE ALSO
pg_dump(1)
PostgreSQL 12.3 2020 PG_BASEBACKUP(1)
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