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>Appendix F. Additional Supplied Modules</TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PGSTANDBY"
>F.23. pg_standby</A
></H1
><A
NAME="AEN103329"
></A
><P
> <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> supports creation of a <SPAN
CLASS="QUOTE"
>"warm standby"</SPAN
>
database server. It is designed to be a production-ready program, as well
as a customizable template should you require specific modifications.
</P
><P
> <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> is designed to be a waiting
<TT
CLASS="LITERAL"
>restore_command</TT
>, 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 <A
HREF="warm-standby.html"
>Section 24.4</A
>).
</P
><P
> <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> features include:
</P
><P
></P
><UL
><LI
><P
> Supports copy or link for restoring WAL files
</P
></LI
><LI
><P
> Written in C, so very portable and easy to install
</P
></LI
><LI
><P
> Easy-to-modify source code, with specifically designated
sections to modify for your own needs
</P
></LI
><LI
><P
> Already tested on Linux and Windows
</P
></LI
></UL
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103349"
>F.23.1. Usage</A
></H2
><P
> To configure a standby
server to use <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
>, put this into its
<TT
CLASS="FILENAME"
>recovery.conf</TT
> configuration file:
</P
><PRE
CLASS="PROGRAMLISTING"
>restore_command = 'pg_standby <TT
CLASS="REPLACEABLE"
><I
>archiveDir</I
></TT
> %f %p %r'
</PRE
><P
> where <TT
CLASS="REPLACEABLE"
><I
>archiveDir</I
></TT
> is the directory from which WAL segment
files should be restored.
</P
><P
> The full syntax of <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
>'s command line is
</P
><PRE
CLASS="SYNOPSIS"
>pg_standby [<SPAN
CLASS="OPTIONAL"
> <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> ... </SPAN
>] <TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>nextwalfile</I
></TT
> <TT
CLASS="REPLACEABLE"
><I
>xlogfilepath</I
></TT
> [<SPAN
CLASS="OPTIONAL"
> <TT
CLASS="REPLACEABLE"
><I
>restartwalfile</I
></TT
> </SPAN
>]
</PRE
><P
> When used within <TT
CLASS="LITERAL"
>restore_command</TT
>, the <TT
CLASS="LITERAL"
>%f</TT
> and
<TT
CLASS="LITERAL"
>%p</TT
> macros should be specified for <TT
CLASS="REPLACEABLE"
><I
>nextwalfile</I
></TT
>
and <TT
CLASS="REPLACEABLE"
><I
>xlogfilepath</I
></TT
> respectively, to provide the actual file
and path required for the restore.
</P
><P
> If <TT
CLASS="REPLACEABLE"
><I
>restartwalfile</I
></TT
> is specified, normally by using the
<TT
CLASS="LITERAL"
>%r</TT
> macro, then all WAL files logically preceding this
file will be removed from <TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
>. This minimizes
the number of files that need to be retained, while preserving
crash-restart capability. Use of this parameter is appropriate if the
<TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> is a transient staging area for this
particular standby server, but <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> when the
<TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> is intended as a long-term WAL archive area.
</P
><P
> <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> assumes that
<TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> is a directory readable by the
server-owning user. If <TT
CLASS="REPLACEABLE"
><I
>restartwalfile</I
></TT
> (or <TT
CLASS="LITERAL"
>-k</TT
>)
is specified,
the <TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> directory must be writable too.
</P
><DIV
CLASS="TABLE"
><A
NAME="AEN103387"
></A
><P
><B
>Table F-26. <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> options</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Option</TH
><TH
>Default</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>-c</TT
></TD
><TD
>yes</TD
><TD
> Use <TT
CLASS="LITERAL"
>cp</TT
> or <TT
CLASS="LITERAL"
>copy</TT
> command to restore WAL files
from archive.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-d</TT
></TD
><TD
>no</TD
><TD
>Print lots of debug logging output on <TT
CLASS="FILENAME"
>stderr</TT
>.</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-k</TT
> <TT
CLASS="REPLACEABLE"
><I
>numfiles</I
></TT
></TD
><TD
>0</TD
><TD
> Remove files from <TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
> 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
<TT
CLASS="REPLACEABLE"
><I
>archivelocation</I
></TT
>.
This parameter will be silently ignored if
<TT
CLASS="REPLACEABLE"
><I
>restartwalfile</I
></TT
> is specified, since that
specification method is more accurate in determining the correct
archive cut-off point.
Use of this parameter is <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>deprecated</I
></SPAN
> as of
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.3; it is safer and more efficient to
specify a <TT
CLASS="REPLACEABLE"
><I
>restartwalfile</I
></TT
> 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.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-l</TT
></TD
><TD
>no</TD
><TD
> Use <TT
CLASS="LITERAL"
>ln</TT
> command to restore WAL files from archive.
Link is more efficient than copy, but the default is copy since link
will not work in all scenarios.
On Windows, this option uses the <TT
CLASS="LITERAL"
>mklink</TT
> command
to provide a file-to-file symbolic link. <TT
CLASS="LITERAL"
>-l</TT
> will
not work on versions of Windows prior to Vista.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-r</TT
> <TT
CLASS="REPLACEABLE"
><I
>maxretries</I
></TT
></TD
><TD
>3</TD
><TD
> Set the maximum number of times to retry the copy or link command if it
fails. After each failure, we wait for <TT
CLASS="REPLACEABLE"
><I
>sleeptime</I
></TT
> *
<TT
CLASS="REPLACEABLE"
><I
>num_retries</I
></TT
>
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.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-s</TT
> <TT
CLASS="REPLACEABLE"
><I
>sleeptime</I
></TT
></TD
><TD
>5</TD
><TD
> Set the number of seconds (up to 60) 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 <A
HREF="warm-standby.html"
>Section 24.4</A
> for discussion.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-t</TT
> <TT
CLASS="REPLACEABLE"
><I
>triggerfile</I
></TT
></TD
><TD
>none</TD
><TD
> Specify a trigger file whose presence should cause recovery to end
whether or not the next WAL file is available.
It is recommended that you use a structured filename to
avoid confusion as to which server is being triggered
when multiple servers exist on the same system; for example
<TT
CLASS="FILENAME"
>/tmp/pgsql.trigger.5432</TT
>.
</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>-w</TT
> <TT
CLASS="REPLACEABLE"
><I
>maxwaittime</I
></TT
></TD
><TD
>0</TD
><TD
> Set the maximum number of seconds to wait for the next WAL file,
after which recovery will end and the standby will come up.
A setting of zero (the default) means wait forever.
The default setting is not necessarily recommended;
consult <A
HREF="warm-standby.html"
>Section 24.4</A
> for discussion.
</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> <TT
CLASS="LITERAL"
>--help</TT
> is not supported since
<SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> is not intended for interactive use,
except during development and testing.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103463"
>F.23.2. Examples</A
></H2
><P
>On Linux or Unix systems, you might use:</P
><PRE
CLASS="PROGRAMLISTING"
>archive_command = 'cp %p .../archive/%f'
restore_command = 'pg_standby -l -d -s 2 -t /tmp/pgsql.trigger.5442 .../archive %f %p %r 2>>standby.log'
</PRE
><P
> where the archive directory is physically located on the standby server,
so that the <TT
CLASS="LITERAL"
>archive_command</TT
> is accessing it across NFS,
but the files are local to the standby (enabling use of <TT
CLASS="LITERAL"
>ln</TT
>).
This will:
</P
><P
></P
><UL
><LI
><P
> use the <TT
CLASS="LITERAL"
>ln</TT
> command to restore WAL files from archive
</P
></LI
><LI
><P
> produce debugging output in <TT
CLASS="FILENAME"
>standby.log</TT
>
</P
></LI
><LI
><P
> sleep for 2 seconds between checks for next WAL file availability
</P
></LI
><LI
><P
> stop waiting only when a trigger file called
<TT
CLASS="FILENAME"
>/tmp/pgsql.trigger.5442</TT
> appears
</P
></LI
><LI
><P
> remove no-longer-needed files from the archive directory
</P
></LI
></UL
><P
>On Windows, you might use:</P
><PRE
CLASS="PROGRAMLISTING"
>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'
</PRE
><P
> Note that backslashes need to be doubled in the
<TT
CLASS="LITERAL"
>archive_command</TT
>, but <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> in the
<TT
CLASS="LITERAL"
>restore_command</TT
>. This will:
</P
><P
></P
><UL
><LI
><P
> use the <TT
CLASS="LITERAL"
>copy</TT
> command to restore WAL files from archive
</P
></LI
><LI
><P
> produce debugging output in <TT
CLASS="FILENAME"
>standby.log</TT
>
</P
></LI
><LI
><P
> sleep for 5 seconds between checks for next WAL file availability
</P
></LI
><LI
><P
> stop waiting only when a trigger file called
<TT
CLASS="FILENAME"
>C:\pgsql.trigger.5442</TT
> appears
</P
></LI
><LI
><P
> remove no-longer-needed files from the archive directory
</P
></LI
></UL
><P
> Since the Windows example uses <TT
CLASS="LITERAL"
>copy</TT
> at both ends, either
or both servers might be accessing the archive directory across the
network.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103506"
>F.23.3. Supported server versions</A
></H2
><P
> <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> is designed to work with
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.2 and later.
</P
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.3 provides the <TT
CLASS="LITERAL"
>%r</TT
> macro,
which is designed to let <SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> know the
last file it needs to keep. With <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.2, the
<TT
CLASS="LITERAL"
>-k</TT
> option must be used if archive cleanup is
required. This option remains available in 8.3, but its use is deprecated.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103517"
>F.23.4. Author</A
></H2
><P
> Simon Riggs <CODE
CLASS="EMAIL"
><<A
HREF="mailto:simon@2ndquadrant.com"
>simon@2ndquadrant.com</A
>></CODE
>
</P
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