Provided by: postgresql-contrib-9.5_9.5.25-0ubuntu0.16.04.1_amd64 
NAME
pg_standby - supports the creation of a PostgreSQL warm standby server
SYNOPSIS
pg_standby [option...] archivelocation nextwalfile xlogfilepath [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 25.2, “Log-Shipping Standby Servers”, in the
documentation).
To configure a standby server to use pg_standby, put this into its recovery.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 25.2, “Log-Shipping Standby Servers”, in the documentation 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 25.2, “Log-Shipping Standby Servers”, in the documentation 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:
• produce debugging output in standby.log
• sleep for 2 seconds between checks for next WAL file availability
• stop waiting only when a trigger file called /tmp/pgsql.trigger.5442 appears, and perform failover
according to its content
• remove the trigger file when recovery ends
• 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:
• use the copy command to restore WAL files from archive
• produce debugging output in standby.log
• sleep for 5 seconds between checks for next WAL file availability
• stop waiting only when a trigger file called C:\pgsql.trigger.5442 appears, and perform failover
according to its content
• remove the trigger file when recovery ends
• 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)