pg_basebackuppg_basebackup1Applicationpg_basebackuptake a base backup of a PostgreSQL clusterpg_basebackupoptionDescriptionpg_basebackup is used to take a base backup of
a running PostgreSQL database cluster. The backup
is taken without affecting other clients of the database, and can be used
both for point-in-time recovery (see )
and as the starting point for a log-shipping or streaming-replication standby
server (see ).
pg_basebackup makes an exact copy of the database
cluster's files, while making sure the server is put into 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 selective backups, another tool such as
must be used.
The backup is made over a regular PostgreSQL
connection that uses the replication protocol. The connection must be made
with a user ID that has REPLICATION permissions
(see ) or is a superuser,
and pg_hba.conf
must permit the replication connection. The server must also be configured
with set high enough to provide at
least one walsender for the backup plus one for WAL streaming (if used).
There can be multiple pg_basebackups running at the same time, but it is usually
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 a primary server but also a standby. To take a backup from a standby,
set up the standby so that it can accept replication connections (that is, set
max_wal_senders and ,
and configure its pg_hba.conf appropriately).
You will also need to enable on the primary.
Note that there are some limitations in taking a backup from a standby:
The backup history file is not created in the database cluster backed up.
pg_basebackup cannot force the standby
to switch to a new WAL file at the end of backup.
When you are using -X none, if write activity on
the primary is low, pg_basebackup may
need to wait a long time for the last WAL file required for the backup
to be switched and archived. In this case, it may be useful to run
pg_switch_wal on the primary in order to
trigger an immediate WAL file switch.
If the standby is promoted to be primary during 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 primary.
Whenever pg_basebackup is taking a base
backup, the server's pg_stat_progress_basebackup
view will report the progress of the backup.
See for details.
Options
The following command-line options control the location and format of the
output:
Sets the target directory to write the output to.
pg_basebackup will create this directory
(and any missing parent directories) if it does not exist. If it
already exists, it must be empty.
When the backup is in tar format, the target directory may be
specified as - (dash), causing the tar file to be
written to stdout.
This option is required.
Selects the format for the output. format
can be one of the following:
pplain
Write the output as plain files, with the same layout as the
source server's 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 source server.
(See to change that.)
This is the default format.
ttar
Write the output as tar files in the target directory. The main
data directory's contents will be written to a file named
base.tar, and each other tablespace will be
written to a separate tar file named after that tablespace's OID.
If the target directory is specified as -
(dash), the tar contents will be written to
standard output, suitable for piping to (for example)
gzip. This is only allowed if
the cluster has no additional tablespaces and WAL
streaming is not used.
Creates a
standby.signalstandby.signalpg_basebackup --write-recovery-conf
file and appends
connection settings to the postgresql.auto.conf
file in the target directory (or within the base archive file when
using tar format). This eases setting up a standby server using the
results of the backup.
The postgresql.auto.conf file will record the connection
settings and, if specified, the replication slot
that pg_basebackup is using, so that
streaming replication will use the same settings later on.
Instructs the server where to place the base backup. The default target
is client, which specifies that the backup should
be sent to the machine where pg_basebackup
is running. If the target is instead set to
server:/some/path, the backup will be stored on
the machine where the server is running in the
/some/path directory. Storing a backup on the
server requires superuser privileges or having privileges of the
pg_write_server_files role. If the target is set to
blackhole, the contents are discarded and not
stored anywhere. This should only be used for testing purposes, as you
will not end up with an actual backup.
Since WAL streaming is implemented by
pg_basebackup rather than by the server,
this option cannot be used together with -Xstream.
Since that is the default, when this option is specified, you must also
specify either -Xfetch or -Xnone.
Relocates 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 defined on the source
server. (But it is not an error if there is no tablespace
in olddir on the source server.)
Meanwhile newdir is a directory in the
receiving host's filesystem. As with the main target directory,
newdir need not exist already, but if
it does exist it must be empty.
Both olddir
and newdir must be absolute paths. If
either path needs to contain an equal sign (=),
precede that with a backslash. This option can be specified multiple
times for multiple tablespaces.
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.
Currently, this option only works with plain output format; it is
ignored if tar format is selected.
Sets the directory to write WAL (write-ahead log) files to.
By default WAL files will be placed in
the pg_wal subdirectory of the target
directory, but this option can be used to place them elsewhere.
waldir must be an absolute path.
As with the main target directory,
waldir need not exist already, but if
it does exist it must be empty.
This option can only be specified when
the backup is in plain format.
Includes the required WAL (write-ahead log) 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 in the target
directory without the need to consult the WAL archive, thus
making the output a completely standalone backup.
The following methods for collecting the
write-ahead logs are supported:
nnone
Don't include write-ahead logs in the backup.
ffetch
The write-ahead log files are collected at the end of the backup.
Therefore, it is necessary for the source server's
parameter to be set high
enough that the required log data is not removed before the end
of the backup. If the required log data has been recycled
before it's time to transfer it, the backup will fail and be
unusable.
When tar format is used, the write-ahead log files will be
included in the base.tar file.
sstream
Stream write-ahead log data while the backup is being taken.
This method will open a second connection to the server and
start streaming the write-ahead log in parallel while running
the backup. Therefore, it will require two replication
connections not just one. As long as the client can keep up
with the write-ahead log data, using this method requires no
extra write-ahead logs to be saved on the source server.
When tar format 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.
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.
Requests compression of the backup. If client or
server is included, it specifies where the
compression is to be performed. Compressing on the server will reduce
transfer bandwidth but will increase server CPU consumption. The
default is client except when
--target is used. In that case, the backup is not
being sent to the client, so only server compression is sensible.
When -Xstream, which is the default, is used,
server-side compression will not be applied to the WAL. To compress
the WAL, use client-side compression, or
specify -Xfetch.
The compression method can be set to gzip,
lz4, zstd,
none for no compression or an integer (no
compression if 0, gzip if greater than 0).
A compression detail string can optionally be specified.
If the detail string is an integer, it specifies the compression
level. Otherwise, it should be a comma-separated list of items,
each of the form keyword or
keyword=value.
Currently, the supported keywords are level,
long, and workers.
The detail string cannot be used when the compression method
is specified as a plain integer.
If no compression level is specified, the default compression level
will be used. If only a level is specified without mentioning an
algorithm, gzip compression will be used if the
level is greater than 0, and no compression will be used if the level
is 0.
When the tar format is used with gzip,
lz4, or zstd, the suffix
.gz, .lz4, or
.zst, respectively, will be automatically added to
all tar filenames. When the plain format is used, client-side
compression may not be specified, but it is still possible to request
server-side compression. If this is done, the server will compress the
backup for transmission, and the client will decompress and extract it.
When this option is used in combination with
-Xstream, pg_wal.tar will
be compressed using gzip if client-side gzip
compression is selected, but will not be compressed if any other
compression algorithm is selected, or if server-side compression
is selected.
The following command-line options control the generation of the
backup and the invocation of the program:
Sets checkpoint mode to fast (immediate) or spread (the default)
(see ).
Specifies that the replication slot named by the
--slot option should be created before starting
the backup. An error is raised if the slot already exists.
Sets the label for the backup. If none is specified, a default value of
pg_basebackup base backup will be used.
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, the target
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.
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.
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.
Sets the maximum transfer rate at which data is collected from the
source server. This can be useful to limit the impact
of pg_basebackup on 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.
This option always affects transfer of the data directory. Transfer of
WAL files is only affected if the collection method
is fetch.
This option can only be used together with -X
stream. It causes WAL streaming to use the specified
replication slot. If the base backup is intended to be used as a
streaming-replication standby using a replication slot, the standby
should then use the same replication slot name as
. This ensures that the
primary server does not remove any necessary WAL data in the time
between the end of the base backup and the start of streaming
replication on the new standby.
The specified replication slot has to exist unless the
option 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.
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.
Specifies the checksum algorithm that should be applied to each file
included in the backup manifest. Currently, the available
algorithms are NONE, CRC32C,
SHA224, SHA256,
SHA384, and SHA512.
The default is CRC32C.
If NONE is selected, the backup manifest will
not contain any checksums. Otherwise, it will contain a checksum
of each file in the backup using the specified algorithm. In addition,
the manifest will always contain a SHA256
checksum of its own contents. The SHA algorithms
are significantly more CPU-intensive than CRC32C,
so selecting one of them may increase the time required to complete
the backup.
Using a SHA hash function provides a cryptographically secure digest
of each file for users who wish to verify that the backup has not been
tampered with, while the CRC32C algorithm provides a checksum that is
much faster to calculate; it is good at catching errors due to accidental
changes but is not resistant to malicious modifications. Note that, to
be useful against an adversary who has access to the backup, the backup
manifest would need to be stored securely elsewhere or otherwise
verified not to have been modified since the backup was taken.
can be used to check the
integrity of a backup against the backup manifest.
Forces all filenames in the backup manifest to be hex-encoded.
If this option is not specified, only non-UTF8 filenames are
hex-encoded. This option is mostly intended to test that tools which
read a backup manifest file properly handle this case.
Prevents the server from estimating the total
amount of backup data that will be streamed, resulting in the
backup_total column in the
pg_stat_progress_basebackup view
always being NULL.
Without this option, 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. This option is useful to avoid such estimation
time if it's too long.
This option is not allowed when using .
Disables generation of a backup manifest. If this option is not
specified, the server will generate and send a backup manifest
which can be verified using .
The manifest is a list of every file present in the backup with the
exception of any WAL files that may be included. It also stores the
size, last modification time, and an optional checksum for each file.
Prevents the creation of a temporary replication slot
for the backup.
By default, if log streaming is selected but no slot name is given
with the option, then a temporary replication
slot is created (if supported by the source server).
The main purpose of this option is to allow taking a base backup when
the server has no free replication slots. Using a replication slot
is almost always preferred, because it prevents needed WAL from being
removed by the server during the backup.
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 option
had been used. Checksum verification failures will also be reported
in the
pg_stat_database view.
The following command-line options control the connection to the source
server:
Specifies parameters used to connect to the server, as a connection string; these
will override any conflicting command line options.
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, any database
name in the connection string will be ignored.
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 a Unix domain socket. The default is taken
from the PGHOST environment variable, if set,
else a Unix domain socket connection is attempted.
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.
Specifies the number of seconds between status packets sent back to
the source server. Smaller values allow more accurate monitoring of
backup progress from the server.
A value of zero disables periodic status updates completely,
although an update will still be sent when requested by the server, to
avoid timeout-based disconnects. The default value is 10 seconds.
Specifies the user name to connect as.
Prevents issuing 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.
Forces pg_basebackup to prompt for a
password before connecting to the source server.
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 to avoid the extra
connection attempt.
Other options are also available:
Prints the pg_basebackup version and exits.
Shows help about pg_basebackup command line
arguments, and exits.
Environment
This utility, like most other PostgreSQL utilities,
uses the environment variables supported by libpq
(see ).
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 performed on the
source server. This can take some time (especially if the option
--checkpoint=fast is not used), during
which pg_basebackup will 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 for the precise details.
In plain format, tablespaces will be backed up to the same path
they have on the source 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 is used, it is the user's responsibility to unpack each
tar file before starting a PostgreSQL server that uses the data. 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
(--format=tar) only works with server version 9.5
and later.
pg_basebackup will preserve group permissions
for data files 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
To create a backup of a local server with one tar file for each tablespace
compressed with gzip at level 9, stored in the
directory backup:
$pg_basebackup -D backup -Ft --compress=gzip:9See Also