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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PGSTANDBY"
>F.26. pg_standby</A
></H1
><A
NAME="AEN118620"
></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
> 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="AEN118638"
>F.26.1. 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
><P
> There are two ways to fail over to a <SPAN
CLASS="QUOTE"
>"warm standby"</SPAN
> database server
when the master server fails:
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
>Smart Failover</DT
><DD
><P
> In smart failover, the server is brought up after applying all WAL
files available in the archive. This results in zero data loss, even if
the standby server has fallen behind, but if there is a lot of
unapplied WAL it can be a long time before the standby server becomes
ready. To trigger a smart failover, create a trigger file containing
the word <TT
CLASS="LITERAL"
>smart</TT
>, or just create it and leave it empty.
</P
></DD
><DT
>Fast Failover</DT
><DD
><P
> In fast failover, the server is brought up immediately. Any WAL files
in the archive that have not yet been applied will be ignored, and
all transactions in those files are lost. To trigger a fast failover,
create a trigger file and write the word <TT
CLASS="LITERAL"
>fast</TT
> into it.
<SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> can also be configured to execute a fast
failover automatically if no new WAL file appears within a defined
interval.
</P
></DD
></DL
></DIV
><P>
</P
><DIV
CLASS="TABLE"
><A
NAME="AEN118690"
></A
><P
><B
>Table F-23. <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"
>-r</TT
> <TT
CLASS="REPLACEABLE"
><I
>maxretries</I
></TT
></TD
><TD
>3</TD
><TD
> Set the maximum number of times to retry the copy 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 failover.
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 a fast failover will be performed.
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
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118754"
>F.26.2. 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 -d -s 2 -t /tmp/pgsql.trigger.5442 .../archive %f %p %r 2>>standby.log'
recovery_end_command = 'rm -f /tmp/pgsql.trigger.5442'
</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
> 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,
and perform failover according to its content
</P
></LI
><LI
><P
> remove the trigger file when recovery ends
</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'
recovery_end_command = 'del C:\pgsql.trigger.5442'
</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
> or <TT
CLASS="LITERAL"
>recovery_end_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,
and perform failover according to its content
</P
></LI
><LI
><P
> remove the trigger file when recovery ends
</P
></LI
><LI
><P
> remove no-longer-needed files from the archive directory
</P
></LI
></UL
><P
> The <TT
CLASS="LITERAL"
>copy</TT
> command on Windows sets the final file size
before the file is completely copied, which would ordinarily confuse
<SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
>. Therefore
<SPAN
CLASS="APPLICATION"
>pg_standby</SPAN
> waits <TT
CLASS="LITERAL"
>sleeptime</TT
>
seconds once it sees the proper file size. GNUWin32's <TT
CLASS="LITERAL"
>cp</TT
>
sets the file size only after the file copy is complete.
</P
><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="AEN118805"
>F.26.3. 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
><P
> <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.4 provides the
<TT
CLASS="LITERAL"
>recovery_end_command</TT
> option. Without this option
a leftover trigger file can be hazardous.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118819"
>F.26.4. 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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