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pg_basebackup(1)         PostgreSQL 12.6 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:

       o   The backup history file is not created in the database cluster
           backed up.

       o   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.

       o   If the standby is promoted to the master during online backup, the
           backup fails.

       o   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; 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, 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 12.6                      2021                     pg_basebackup(1)

postgresql 12.6 - Generated Tue Feb 16 08:46:00 CST 2021
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