From: Simon Riggs <simon@2ndquadrant.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: pgsql-docs@postgresql.org
Subject: Re: PITR Doc clarifications
Date: Wed, 28 Nov 2007 13:39:32 +0000
Message-ID: <1196257173.4246.1226.camel@ebony.site> (raw)
In-Reply-To: <20071128131231.GI5118@alvh.no-ip.org>
References: <1196255311.4246.1197.camel@ebony.site>
<20071128131231.GI5118@alvh.no-ip.org>
On Wed, 2007-11-28 at 10:12 -0300, Alvaro Herrera wrote:
> Simon Riggs wrote:
> >
> > A few docs changes, as mentioned.
> >
> > Comments?
>
> You forgot the patch :-)
No, just a very short patch. :-)
This patch is slightly longer...
--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.comAttachments:pitr_docs.v1.patch (text/x-patch, 7.4K) download
Index: doc/src/sgml/backup.sgml
===================================================================
RCS file: /home/sriggs/pg/REPOSITORY/pgsql/doc/src/sgml/backup.sgml,v
retrieving revision 2.107
diff -c -r2.107 backup.sgml
*** doc/src/sgml/backup.sgml 16 Oct 2007 19:44:18 -0000 2.107
--- doc/src/sgml/backup.sgml 28 Nov 2007 12:58:27 -0000
***************
*** 641,650 ****
<para>
Also, you can force a segment switch manually with
<function>pg_switch_xlog</>, if you want to ensure that a
! just-finished transaction is archived immediately. Other utility
functions related to WAL management are listed in <xref
linkend="functions-admin-backup-table">.
</para>
</sect2>
<sect2 id="backup-base-backup">
--- 641,660 ----
<para>
Also, you can force a segment switch manually with
<function>pg_switch_xlog</>, if you want to ensure that a
! just-finished transaction is archived as soon as possible. Other utility
functions related to WAL management are listed in <xref
linkend="functions-admin-backup-table">.
</para>
+ + <para>+ When <varname>archive_mode</> is off certain SQL operations are optimized+ to avoid writing WAL, as described in <xref linkend="populate-pitr">. If + archiving were enabled during execution of one of these statements then it+ would be possible to write data that would not then be part of any + concurrent backup because the WAL for those changes had been optimized away. + So it is possible to alter <varname>archive_command</> with a reload, but + <varname>archive_mode</> cannot be changed except at server start. + </para>
</sect2>
<sect2 id="backup-base-backup">
***************
*** 973,986 ****
<para>
Normally, recovery will proceed through all available WAL segments,
thereby restoring the database to the current point in time (or as
! close as we can get given the available WAL segments). But if you want
! to recover to some previous point in time (say, right before the junior
! DBA dropped your main transaction table), just specify the required
! stopping point in <filename>recovery.conf</>. You can specify the stop
! point, known as the <quote>recovery target</>, either by date/time or
! by completion of a specific transaction ID. As of this writing only
! the date/time option is very usable, since there are no tools to help
! you identify with any accuracy which transaction ID to use.
</para>
<note>
--- 983,1006 ----
<para>
Normally, recovery will proceed through all available WAL segments,
thereby restoring the database to the current point in time (or as
! close as we can get given the available WAL segments). So a normal
! recovery will end with a "file not found" message, the exact text
! of the error message depending upon your choice of
! <varname>restore_command</>. You may also see an error message
! at the start of recovery for a file named something like
! <filename>00000001.history</>. This is also normal and does not
! indicate a problem in simple recovery situations. See
! <xref linkend="backup-timelines"> for discussion.
! </para>
!
! <para>
! If you want to recover to some previous point in time (say, right before
! the junior DBA dropped your main transaction table), just specify the
! required stopping point in <filename>recovery.conf</>. You can specify
! the stop point, known as the <quote>recovery target</>, either by
! date/time or by completion of a specific transaction ID. As of this
! writing only the date/time option is very usable, since there are no tools
! to help you identify with any accuracy which transaction ID to use.
</para>
<note>
***************
*** 1214,1219 ****
--- 1234,1324 ----
</para>
</sect2>
+ <sect2 id="backup-tips">+ <title>Tips and Examples</title>+ + <para>+ Some examples of configuring Continuous Archiving are given here.+ </para>+ + <sect3 id="backup-standalone">+ <title>Recovery Settings</title>+ + <para>+ It is possible to use the existing backup facilities to produce+ standalone hot backups. These are backups that cannot be used for+ Point in Time Recovery, yet are much faster to backup and restore+ than <application>pg_dump</>.+ </para>+ + <para>+ To configure standalone backups you should use a switch file. If the+ file exists then archives are made, otherwise archiving is ignored.+ <programlisting>+ archive_command = 'test -f /var/lib/pgsql/backup_in_progress && cp -i %p /var/lib/pgsql/archive/%f </dev/null'+ </programlisting>+ Backup can then be taken using a script like the following:+ <programlisting>+ touch /var/lib/pgsql/backup_in_progress+ psql -c "select pg_start_backup('hot_backup');"+ tar -cvf /var/lib/pgsql/backup.tar /var/lib/pgsql/data/+ psql -c "select pg_stop_backup();"+ sleep 20+ rm /var/lib/pgsql/backup_in_progress+ tar -rvf /var/lib/pgsql/backup.tar /var/lib/pgsql/archive/+ </programlisting>+ The switch file /var/lib/pgsql/backup_in_progress is created+ first, allowing archiving to start prior to the backup. After the+ backup the switch file is removed. Archived WAL files are then added+ into the archive so that both Base Backup and all required WAL files+ are part of the same tar file.+ </para>+ </sect3>+ + <sect3 id="backup-scripts">+ <title><varname>archive_command</varname> scripts</title>+ + <para>+ Many people choose to use scripts to define their + <varname>archive_command</varname>, so that their+ <filename>postgresql.conf</> looks very simple:+ <programlisting>+ archive_command = 'local_backup_script.sh'+ </programlisting>+ This allows all complexity to be managed within the script, which could+ be written in a popular scripting language such as bash or perl etc..+ Statements echoed to stderr will appear in the database server log, + allowing complex configurations to be easily diagnosed if they should fail.+ </para>+ <para>+ Example of how scripts might be used include+ <itemizedlist>+ <listitem>+ <para>+ Copying data to a secure off-site data storage provider.+ </para>+ </listitem>+ <listitem>+ <para>+ Batching WAL files so they are transferred every 3 hours, rather than+ one at a time as they fill.+ </para>+ </listitem>+ <listitem>+ <para>+ Interfaces with other Backup and Recovery software.+ </para>+ </listitem>+ <listitem>+ <para>+ Interfaces with monitoring software to report errors directly.+ </para>+ </listitem>+ </itemizedlist>+ </para>+ </sect3>+ </sect2>+
<sect2 id="continuous-archiving-caveats">
<title>Caveats</title>
***************
*** 1435,1441 ****
Pseudocode for a suitable <varname>restore_command</> is:
<programlisting>
triggered = false;
! while (!NextWALFileReady() && !triggered)
{
sleep(100000L); /* wait for ~0.1 sec */
if (CheckForExternalTrigger())
--- 1540,1546 ----
Pseudocode for a suitable <varname>restore_command</> is:
<programlisting>
triggered = false;
! while (!NextWALFileReady() && !triggered)
{
sleep(100000L); /* wait for ~0.1 sec */
if (CheckForExternalTrigger())
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To: pgsql-docs@postgresql.org
Cc: simon@2ndquadrant.com, alvherre@alvh.no-ip.org
Subject: Re: PITR Doc clarifications
In-Reply-To: <1196257173.4246.1226.camel@ebony.site>
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