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pg_standby(1)            PostgreSQL 12.0 Documentation           pg_standby(1)




NAME

       pg_standby - supports the creation of a PostgreSQL warm standby server


SYNOPSIS

       pg_standby [option...] archivelocation nextwalfile walfilepath
                  [restartwalfile]


DESCRIPTION

       pg_standby supports creation of a "warm standby" database server. It is
       designed to be a production-ready program, as well as a customizable
       template should you require specific modifications.

       pg_standby is designed to be a waiting restore_command, which is needed
       to turn a standard archive recovery into a warm standby operation.
       Other configuration is required as well, all of which is described in
       the main server manual (see Section 26.2).

       To configure a standby server to use pg_standby, put this into its
       postgresql.conf configuration file:

           restore_command = 'pg_standby archiveDir %f %p %r'

       where archiveDir is the directory from which WAL segment files should
       be restored.

       If restartwalfile is specified, normally by using the %r macro, then
       all WAL files logically preceding this file will be removed from
       archivelocation. This minimizes the number of files that need to be
       retained, while preserving crash-restart capability. Use of this
       parameter is appropriate if the archivelocation is a transient staging
       area for this particular standby server, but not when the
       archivelocation is intended as a long-term WAL archive area.

       pg_standby assumes that archivelocation is a directory readable by the
       server-owning user. If restartwalfile (or -k) is specified, the
       archivelocation directory must be writable too.

       There are two ways to fail over to a "warm standby" database server
       when the master server fails:

       Smart Failover
           In smart failover, the server is brought up after applying all WAL
           files available in the archive. This results in zero data loss,
           even if the standby server has fallen behind, but if there is a lot
           of unapplied WAL it can be a long time before the standby server
           becomes ready. To trigger a smart failover, create a trigger file
           containing the word smart, or just create it and leave it empty.

       Fast Failover
           In fast failover, the server is brought up immediately. Any WAL
           files in the archive that have not yet been applied will be
           ignored, and all transactions in those files are lost. To trigger a
           fast failover, create a trigger file and write the word fast into
           it.  pg_standby can also be configured to execute a fast failover
           automatically if no new WAL file appears within a defined interval.


OPTIONS

       pg_standby accepts the following command-line arguments:

       -c
           Use cp or copy command to restore WAL files from archive. This is
           the only supported behavior so this option is useless.

       -d
           Print lots of debug logging output on stderr.

       -k
           Remove files from archivelocation so that no more than this many
           WAL files before the current one are kept in the archive. Zero (the
           default) means not to remove any files from archivelocation. This
           parameter will be silently ignored if restartwalfile is specified,
           since that specification method is more accurate in determining the
           correct archive cut-off point. Use of this parameter is deprecated
           as of PostgreSQL 8.3; it is safer and more efficient to specify a
           restartwalfile parameter. A too small setting could result in
           removal of files that are still needed for a restart of the standby
           server, while a too large setting wastes archive space.

       -r maxretries
           Set the maximum number of times to retry the copy command if it
           fails (default 3). After each failure, we wait for sleeptime *
           num_retries so that the wait time increases progressively. So by
           default, we will wait 5 secs, 10 secs, then 15 secs before
           reporting the failure back to the standby server. This will be
           interpreted as end of recovery and the standby will come up fully
           as a result.

       -s sleeptime
           Set the number of seconds (up to 60, default 5) to sleep between
           tests to see if the WAL file to be restored is available in the
           archive yet. The default setting is not necessarily recommended;
           consult Section 26.2 for discussion.

       -t triggerfile
           Specify a trigger file whose presence should cause failover. It is
           recommended that you use a structured file name to avoid confusion
           as to which server is being triggered when multiple servers exist
           on the same system; for example /tmp/pgsql.trigger.5432.

       -V
       --version
           Print the pg_standby version and exit.

       -w maxwaittime
           Set the maximum number of seconds to wait for the next WAL file,
           after which a fast failover will be performed. A setting of zero
           (the default) means wait forever. The default setting is not
           necessarily recommended; consult Section 26.2 for discussion.

       -?
       --help
           Show help about pg_standby command line arguments, and exit.


NOTES

       pg_standby is designed to work with PostgreSQL 8.2 and later.

       PostgreSQL 8.3 provides the %r macro, which is designed to let
       pg_standby know the last file it needs to keep. With PostgreSQL 8.2,
       the -k option must be used if archive cleanup is required. This option
       remains available in 8.3, but its use is deprecated.

       PostgreSQL 8.4 provides the recovery_end_command option. Without this
       option a leftover trigger file can be hazardous.

       pg_standby is written in C and has an easy-to-modify source code, with
       specifically designated sections to modify for your own needs


EXAMPLES

       On Linux or Unix systems, you might use:

           archive_command = 'cp %p .../archive/%f'

           restore_command = 'pg_standby -d -s 2 -t /tmp/pgsql.trigger.5442 .../archive %f %p %r 2>>standby.log'

           recovery_end_command = 'rm -f /tmp/pgsql.trigger.5442'

       where the archive directory is physically located on the standby
       server, so that the archive_command is accessing it across NFS, but the
       files are local to the standby (enabling use of ln). This will:

       o   produce debugging output in standby.log

       o   sleep for 2 seconds between checks for next WAL file availability

       o   stop waiting only when a trigger file called
           /tmp/pgsql.trigger.5442 appears, and perform failover according to
           its content

       o   remove the trigger file when recovery ends

       o   remove no-longer-needed files from the archive directory

       On Windows, you might use:

           archive_command = 'copy %p ...\\archive\\%f'

           restore_command = 'pg_standby -d -s 5 -t C:\pgsql.trigger.5442 ...\archive %f %p %r 2>>standby.log'

           recovery_end_command = 'del C:\pgsql.trigger.5442'

       Note that backslashes need to be doubled in the archive_command, but
       not in the restore_command or recovery_end_command. This will:

       o   use the copy command to restore WAL files from archive

       o   produce debugging output in standby.log

       o   sleep for 5 seconds between checks for next WAL file availability

       o   stop waiting only when a trigger file called C:\pgsql.trigger.5442
           appears, and perform failover according to its content

       o   remove the trigger file when recovery ends

       o   remove no-longer-needed files from the archive directory

       The copy command on Windows sets the final file size before the file is
       completely copied, which would ordinarily confuse pg_standby. Therefore
       pg_standby waits sleeptime seconds once it sees the proper file size.
       GNUWin32's cp sets the file size only after the file copy is complete.

       Since the Windows example uses copy at both ends, either or both
       servers might be accessing the archive directory across the network.


AUTHOR

       Simon Riggs <simon@2ndquadrant.com>


SEE ALSO

       pg_archivecleanup(1)



PostgreSQL 12.0                      2019                        pg_standby(1)

postgresql 12.0 - Generated Tue Oct 29 18:19:22 CDT 2019
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