1PG_STANDBY(1)            PostgreSQL 13.4 Documentation           PG_STANDBY(1)
2
3
4

NAME

6       pg_standby - supports the creation of a PostgreSQL warm standby server
7

SYNOPSIS

9       pg_standby [option...] archivelocation nextwalfile walfilepath
10                  [restartwalfile]
11

DESCRIPTION

13       pg_standby supports creation of a “warm standby” database server. It is
14       designed to be a production-ready program, as well as a customizable
15       template should you require specific modifications.
16
17       pg_standby is designed to be a waiting restore_command, which is needed
18       to turn a standard archive recovery into a warm standby operation.
19       Other configuration is required as well, all of which is described in
20       the main server manual (see Section 26.2).
21
22       To configure a standby server to use pg_standby, put this into its
23       postgresql.conf configuration file:
24
25           restore_command = 'pg_standby archiveDir %f %p %r'
26
27       where archiveDir is the directory from which WAL segment files should
28       be restored.
29
30       If restartwalfile is specified, normally by using the %r macro, then
31       all WAL files logically preceding this file will be removed from
32       archivelocation. This minimizes the number of files that need to be
33       retained, while preserving crash-restart capability. Use of this
34       parameter is appropriate if the archivelocation is a transient staging
35       area for this particular standby server, but not when the
36       archivelocation is intended as a long-term WAL archive area.
37
38       pg_standby assumes that archivelocation is a directory readable by the
39       server-owning user. If restartwalfile (or -k) is specified, the
40       archivelocation directory must be writable too.
41
42       There are two ways to fail over to a “warm standby” database server
43       when the master server fails:
44
45       Smart Failover
46           In smart failover, the server is brought up after applying all WAL
47           files available in the archive. This results in zero data loss,
48           even if the standby server has fallen behind, but if there is a lot
49           of unapplied WAL it can be a long time before the standby server
50           becomes ready. To trigger a smart failover, create a trigger file
51           containing the word smart, or just create it and leave it empty.
52
53       Fast Failover
54           In fast failover, the server is brought up immediately. Any WAL
55           files in the archive that have not yet been applied will be
56           ignored, and all transactions in those files are lost. To trigger a
57           fast failover, create a trigger file and write the word fast into
58           it.  pg_standby can also be configured to execute a fast failover
59           automatically if no new WAL file appears within a defined interval.
60

OPTIONS

62       pg_standby accepts the following command-line arguments:
63
64       -c
65           Use cp or copy command to restore WAL files from archive. This is
66           the only supported behavior so this option is useless.
67
68       -d
69           Print lots of debug logging output on stderr.
70
71       -k
72           Remove files from archivelocation so that no more than this many
73           WAL files before the current one are kept in the archive. Zero (the
74           default) means not to remove any files from archivelocation. This
75           parameter will be silently ignored if restartwalfile is specified,
76           since that specification method is more accurate in determining the
77           correct archive cut-off point. Use of this parameter is deprecated
78           as of PostgreSQL 8.3; it is safer and more efficient to specify a
79           restartwalfile parameter. A too small setting could result in
80           removal of files that are still needed for a restart of the standby
81           server, while a too large setting wastes archive space.
82
83       -r maxretries
84           Set the maximum number of times to retry the copy command if it
85           fails (default 3). After each failure, we wait for sleeptime *
86           num_retries so that the wait time increases progressively. So by
87           default, we will wait 5 secs, 10 secs, then 15 secs before
88           reporting the failure back to the standby server. This will be
89           interpreted as end of recovery and the standby will come up fully
90           as a result.
91
92       -s sleeptime
93           Set the number of seconds (up to 60, default 5) to sleep between
94           tests to see if the WAL file to be restored is available in the
95           archive yet. The default setting is not necessarily recommended;
96           consult Section 26.2 for discussion.
97
98       -t triggerfile
99           Specify a trigger file whose presence should cause failover. It is
100           recommended that you use a structured file name to avoid confusion
101           as to which server is being triggered when multiple servers exist
102           on the same system; for example /tmp/pgsql.trigger.5432.
103
104       -V
105       --version
106           Print the pg_standby version and exit.
107
108       -w maxwaittime
109           Set the maximum number of seconds to wait for the next WAL file,
110           after which a fast failover will be performed. A setting of zero
111           (the default) means wait forever. The default setting is not
112           necessarily recommended; consult Section 26.2 for discussion.
113
114       -?
115       --help
116           Show help about pg_standby command line arguments, and exit.
117

NOTES

119       pg_standby is designed to work with PostgreSQL 8.2 and later.
120
121       PostgreSQL 8.3 provides the %r macro, which is designed to let
122       pg_standby know the last file it needs to keep. With PostgreSQL 8.2,
123       the -k option must be used if archive cleanup is required. This option
124       remains available in 8.3, but its use is deprecated.
125
126       PostgreSQL 8.4 provides the recovery_end_command option. Without this
127       option a leftover trigger file can be hazardous.
128
129       pg_standby is written in C and has an easy-to-modify source code, with
130       specifically designated sections to modify for your own needs
131

EXAMPLES

133       On Linux or Unix systems, you might use:
134
135           archive_command = 'cp %p .../archive/%f'
136
137           restore_command = 'pg_standby -d -s 2 -t /tmp/pgsql.trigger.5442 .../archive %f %p %r 2>>standby.log'
138
139           recovery_end_command = 'rm -f /tmp/pgsql.trigger.5442'
140
141       where the archive directory is physically located on the standby
142       server, so that the archive_command is accessing it across NFS, but the
143       files are local to the standby (enabling use of ln). This will:
144
145       •   produce debugging output in standby.log
146
147       •   sleep for 2 seconds between checks for next WAL file availability
148
149       •   stop waiting only when a trigger file called
150           /tmp/pgsql.trigger.5442 appears, and perform failover according to
151           its content
152
153       •   remove the trigger file when recovery ends
154
155       •   remove no-longer-needed files from the archive directory
156
157       On Windows, you might use:
158
159           archive_command = 'copy %p ...\\archive\\%f'
160
161           restore_command = 'pg_standby -d -s 5 -t C:\pgsql.trigger.5442 ...\archive %f %p %r 2>>standby.log'
162
163           recovery_end_command = 'del C:\pgsql.trigger.5442'
164
165       Note that backslashes need to be doubled in the archive_command, but
166       not in the restore_command or recovery_end_command. This will:
167
168       •   use the copy command to restore WAL files from archive
169
170       •   produce debugging output in standby.log
171
172       •   sleep for 5 seconds between checks for next WAL file availability
173
174       •   stop waiting only when a trigger file called C:\pgsql.trigger.5442
175           appears, and perform failover according to its content
176
177       •   remove the trigger file when recovery ends
178
179       •   remove no-longer-needed files from the archive directory
180
181       The copy command on Windows sets the final file size before the file is
182       completely copied, which would ordinarily confuse pg_standby. Therefore
183       pg_standby waits sleeptime seconds once it sees the proper file size.
184       GNUWin32's cp sets the file size only after the file copy is complete.
185
186       Since the Windows example uses copy at both ends, either or both
187       servers might be accessing the archive directory across the network.
188

AUTHOR

190       Simon Riggs <simon@2ndquadrant.com>
191

SEE ALSO

193       pg_archivecleanup(1)
194
195
196
197PostgreSQL 13.4                      2021                        PG_STANDBY(1)
Impressum