1- <!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.115 2008/03/07 01:46:41 momjian Exp $ -->
1+ <!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.116 2008/03/28 15:00:28 heikki Exp $ -->
22
33<chapter id="backup">
44 <title>Backup and Restore</title>
@@ -577,11 +577,10 @@ cp -i pg_xlog/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900
577577 <para>
578578 It is important that the archive command return zero exit status if and
579579 only if it succeeded. Upon getting a zero result,
580- <productname>PostgreSQL</> will assume that the WAL segment file has been
581- successfully archived, and will remove or recycle it.
582- However, a nonzero status tells
583- <productname>PostgreSQL</> that the file was not archived; it will try
584- again periodically until it succeeds.
580+ <productname>PostgreSQL</> will assume that the file has been
581+ successfully archived, and will remove or recycle it. However, a nonzero
582+ status tells <productname>PostgreSQL</> that the file was not archived;
583+ it will try again periodically until it succeeds.
585584 </para>
586585
587586 <para>
@@ -1001,11 +1000,13 @@ restore_command = 'cp /mnt/server/archivedir/%f %p'
10011000
10021001 <para>
10031002 It is important that the command return nonzero exit status on failure.
1004- The command <emphasis>will</> be asked forlog files that are not present
1003+ The command <emphasis>will</> be asked for files that are not present
10051004 in the archive; it must return nonzero when so asked. This is not an
1006- error condition. Be aware also that the base name of the <literal>%p</>
1007- path will be different from <literal>%f</>; do not expect them to be
1008- interchangeable.
1005+ error condition. Not all of the requested files will be WAL segment
1006+ files; you should also expect requests for files with a suffix of
1007+ <literal>.backup</> or <literal>.history</>. Also be aware that
1008+ the base name of the <literal>%p</> path will be different from
1009+ <literal>%f</>; do not expect them to be interchangeable.
10091010 </para>
10101011
10111012 <para>
@@ -1576,19 +1577,21 @@ archive_command = 'local_backup_script.sh'
15761577
15771578 <para>
15781579 The magic that makes the two loosely coupled servers work together is
1579- simply a <varname>restore_command</> used on the standby that waits
1580- for the next WAL file the primary. The
1581- <varname>restore_command</> is specified in the
1580+ simply a <varname>restore_command</> used on the standby that,
1581+ when asked for the next WAL file, waits for it to become available from
1582+ the primary. The <varname>restore_command</> is specified in the
15821583 <filename>recovery.conf</> file on the standby server. Normal recovery
15831584 processing would request a file from the WAL archive, reporting failure
15841585 if the file was unavailable. For standby processing it is normal for
1585- the next file to be unavailable, so we must be patient and wait for
1586- it to appear. A waiting <varname>restore_command</> can be written as
1587- a custom script that loops after polling for the existence of the next
1588- WAL file. There must also be some way to trigger failover, which should
1589- interrupt the <varname>restore_command</>, break the loop and return
1590- a file-not-found error to the standby server. This ends recovery and
1591- the standby will then come up as a normal server.
1586+ the next WAL file to be unavailable, so we must be patient and wait for
1587+ it to appear. For files ending in <literal>.backup</> or
1588+ <literal>.history</> there is no need to wait, and a non-zero return
1589+ code must be returned. A waiting <varname>restore_command</> can be
1590+ written as a custom script that loops after polling for the existence of
1591+ the next WAL file. There must also be some way to trigger failover, which
1592+ should interrupt the <varname>restore_command</>, break the loop and
1593+ return a file-not-found error to the standby server. This ends recovery
1594+ and the standby will then come up as a normal server.
15921595 </para>
15931596
15941597 <para>
@@ -1608,9 +1611,10 @@ if (!triggered)
16081611
16091612 <para>
16101613 A working example of a waiting <varname>restore_command</> is provided
1611- as a <filename>contrib</> module named <application>pg_standby</>. This
1612- example can be extended as needed to support specific configurations or
1613- environments.
1614+ as a <filename>contrib</> module named <application>pg_standby</>. It
1615+ should be used as a reference on how to correctly implement the logic
1616+ described above. It can also be extended as needed to support specific
1617+ configurations or environments.
16141618 </para>
16151619
16161620 <para>