From 958db06181a41ac3d63bb55478fbad9b55b58e6a Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 28 Mar 2008 15:00:28 +0000
Subject: [PATCH] Clarify documentation on PITR and warm standby on the fact
that the standby restore_command should report failure on non-existent
.backup and .history files. Tidy up some related text along the way.
Patch by Markus Bertheau, with some editing by Simon Riggs and myself.
---
doc/src/sgml/backup.sgml | 50 ++++++++++++++++++++++------------------
1 file changed, 27 insertions(+), 23 deletions(-)
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index 8131bcdf84..9f369f8e6d 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.115 2008/03/07 01:46:41 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.116 2008/03/28 15:00:28 heikki Exp $ -->
<chapter id="backup">
<title>Backup and Restore</title>
@@ -577,11 +577,10 @@ cp -i pg_xlog/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900
<para>
It is important that the archive command return zero exit status if and
only if it succeeded. Upon getting a zero result,
- <productname>PostgreSQL</> will assume that the WAL segment file has been
- successfully archived, and will remove or recycle it.
- However, a nonzero status tells
- <productname>PostgreSQL</> that the file was not archived; it will try
- again periodically until it succeeds.
+ <productname>PostgreSQL</> will assume that the file has been
+ successfully archived, and will remove or recycle it. However, a nonzero
+ status tells <productname>PostgreSQL</> that the file was not archived;
+ it will try again periodically until it succeeds.
</para>
<para>
@@ -1001,11 +1000,13 @@ restore_command = 'cp /mnt/server/archivedir/%f %p'
<para>
It is important that the command return nonzero exit status on failure.
- The command <emphasis>will</> be asked for log files that are not present
+ The command <emphasis>will</> be asked for files that are not present
in the archive; it must return nonzero when so asked. This is not an
- error condition. Be aware also that the base name of the <literal>%p</>
- path will be different from <literal>%f</>; do not expect them to be
- interchangeable.
+ error condition. Not all of the requested files will be WAL segment
+ files; you should also expect requests for files with a suffix of
+ <literal>.backup</> or <literal>.history</>. Also be aware that
+ the base name of the <literal>%p</> path will be different from
+ <literal>%f</>; do not expect them to be interchangeable.
</para>
<para>
@@ -1576,19 +1577,21 @@ archive_command = 'local_backup_script.sh'
<para>
The magic that makes the two loosely coupled servers work together is
- simply a <varname>restore_command</> used on the standby that waits
- for the next WAL file to become available from the primary. The
- <varname>restore_command</> is specified in the
+ simply a <varname>restore_command</> used on the standby that,
+ when asked for the next WAL file, waits for it to become available from
+ the primary. The <varname>restore_command</> is specified in the
<filename>recovery.conf</> file on the standby server. Normal recovery
processing would request a file from the WAL archive, reporting failure
if the file was unavailable. For standby processing it is normal for
- the next file to be unavailable, so we must be patient and wait for
- it to appear. A waiting <varname>restore_command</> can be written as
- a custom script that loops after polling for the existence of the next
- WAL file. There must also be some way to trigger failover, which should
- interrupt the <varname>restore_command</>, break the loop and return
- a file-not-found error to the standby server. This ends recovery and
- the standby will then come up as a normal server.
+ the next WAL file to be unavailable, so we must be patient and wait for
+ it to appear. For files ending in <literal>.backup</> or
+ <literal>.history</> there is no need to wait, and a non-zero return
+ code must be returned. A waiting <varname>restore_command</> can be
+ written as a custom script that loops after polling for the existence of
+ the next WAL file. There must also be some way to trigger failover, which
+ should interrupt the <varname>restore_command</>, break the loop and
+ return a file-not-found error to the standby server. This ends recovery
+ and the standby will then come up as a normal server.
</para>
<para>
@@ -1608,9 +1611,10 @@ if (!triggered)
<para>
A working example of a waiting <varname>restore_command</> is provided
- as a <filename>contrib</> module named <application>pg_standby</>. This
- example can be extended as needed to support specific configurations or
- environments.
+ as a <filename>contrib</> module named <application>pg_standby</>. It
+ should be used as a reference on how to correctly implement the logic
+ described above. It can also be extended as needed to support specific
+ configurations or environments.
</para>
<para>
--
2.49.0