pg_basebackup Man page

PG_BASEBACKUP(1) PostgreSQL 9.5.5 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 24.3, “Continuous Archiving and Point-in-Time Recovery (PITR)”,
in the documentation) and as the starting point for a log shipping or
streaming replication standby servers (see Section 25.2, “Log-Shipping
Standby Servers”, in the documentation).

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 20.2, “Role
Attributes”, in the documentation), 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.

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.

· There is no guarantee that all WAL files required for the backup
are archived at the end of backup. If you are planning to use the
backup for an archive recovery and want to ensure that all required
files are available at that moment, you need to include them into
the backup by using -x option.

· 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.

-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.

-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.

–xlogdir=xlogdir
Specifies the location for the transaction log directory. xlogdir
must be an absolute path. The transaction log directory can only be
specified when the backup is in plain mode.

-x
–xlog
Using this option is equivalent of using -X with method fetch.

-X method
–xlog-method=method
Includes the required transaction log files (WAL files) in the
backup. This will include all transaction logs generated during the
backup. If this option 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 transaction logs are
supported:

f
fetch
The transaction 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.

s
stream
Stream the transaction log while the backup is created. This
will open a second connection to the server and start streaming
the transaction 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 transaction log received, using this mode requires no
extra transaction logs to be saved on the master.

-z
–gzip
Enables gzip compression of tar file output, with the default
compression level. Compression is only available when using the tar
format.

-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.

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 or spread (default) (see Section
24.3.3, “Making a Base Backup Using the Low Level API”, in the
documentation).

-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.

-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.

-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.

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 31.1.1, “Connection Strings”, in the
documentation 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 31.14,
“Environment Variables”, in the documentation).

NOTES
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. But only regular files and
directories are copied. Symbolic links (other than those used for
tablespaces) and special device files are skipped. (See Section 50.3,
“Streaming Replication Protocol”, in the documentation 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.

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 | 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

PostgreSQL 9.5.5 2016 PG_BASEBACKUP(1)

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