Add some simple support and documentation for using process-specific oom_adj
settings to prevent the postmaster from being OOM-killed on Linux systems. Alex Hunsaker and Tom Lane
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Tom Lane
parent
292176a118
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d5e0029862
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@ -24,7 +24,7 @@
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# Original author: Ryan Kirkpatrick <pgsql@rkirkpat.net>
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# $PostgreSQL: pgsql/contrib/start-scripts/linux,v 1.9 2009/08/27 16:59:38 tgl Exp $
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# $PostgreSQL: pgsql/contrib/start-scripts/linux,v 1.10 2010/01/11 18:39:32 tgl Exp $
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## EDIT FROM HERE
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@ -40,6 +40,14 @@ PGUSER=postgres
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# Where to keep a log file
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PGLOG="$PGDATA/serverlog"
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# It's often a good idea to protect the postmaster from being killed by the
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# OOM killer (which will tend to preferentially kill the postmaster because
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# of the way it accounts for shared memory). Setting the OOM_ADJ value to
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# -17 will disable OOM kill altogether. If you enable this, you probably want
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# to compile PostgreSQL with "-DLINUX_OOM_ADJ=0", so that individual backends
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# can still be killed by the OOM killer.
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#OOM_ADJ=-17
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## STOP EDITING HERE
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# The path that is to be used for the script
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@ -62,6 +70,7 @@ test -x $DAEMON || exit 0
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case $1 in
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start)
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echo -n "Starting PostgreSQL: "
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test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
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su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
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echo "ok"
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;;
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@ -73,6 +82,7 @@ case $1 in
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restart)
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echo -n "Restarting PostgreSQL: "
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su - $PGUSER -c "$PGCTL stop -D '$PGDATA' -s -m fast -w"
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test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
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su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
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echo "ok"
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;;
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.429 2009/12/10 06:32:28 petere Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.430 2010/01/11 18:39:32 tgl Exp $ -->
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<chapter Id="runtime">
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<title>Server Setup and Operation</title>
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@ -1244,7 +1244,7 @@ default:\
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this (consult your system documentation and configuration on where
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to look for such a message):
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<programlisting>
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Out of Memory: Killed process 12345 (postgres).
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Out of Memory: Killed process 12345 (postgres).
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</programlisting>
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This indicates that the <filename>postgres</filename> process
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has been terminated due to memory pressure.
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@ -1258,13 +1258,13 @@ Out of Memory: Killed process 12345 (postgres).
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<productname>PostgreSQL</productname> on a machine where you can
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be sure that other processes will not run the machine out of
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memory. If memory is tight, increasing the swap space of the
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operating system can help avoiding the problem, because the
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out-of-memory (OOM) killer is invoked whenever physical memory and
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operating system can help avoid the problem, because the
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out-of-memory (OOM) killer is invoked only when physical memory and
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swap space are exhausted.
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</para>
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<para>
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On Linux 2.6 and later, an additional measure is to modify the
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On Linux 2.6 and later, it is possible to modify the
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kernel's behavior so that it will not <quote>overcommit</> memory.
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Although this setting will not prevent the <ulink
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url="http://lwn.net/Articles/104179/">OOM killer</> from being invoked
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@ -1275,11 +1275,31 @@ Out of Memory: Killed process 12345 (postgres).
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sysctl -w vm.overcommit_memory=2
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</programlisting>
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or placing an equivalent entry in <filename>/etc/sysctl.conf</>.
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You might also wish to modify the related setting
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<literal>vm.overcommit_ratio</>. For details see the kernel documentation
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You might also wish to modify the related setting
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<varname>vm.overcommit_ratio</>. For details see the kernel documentation
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file <filename>Documentation/vm/overcommit-accounting</>.
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</para>
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<para>
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Another approach, which can be used with or without altering
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<varname>vm.overcommit_memory</>, is to set the process-specific
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<varname>oom_adj</> value for the postmaster process to <literal>-17</>,
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thereby guaranteeing it will not be targeted by the OOM killer. The
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simplest way to do this is to execute
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<programlisting>
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echo -17 > /proc/self/oom_adj
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</programlisting>
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in the postmaster's startup script just before invoking the postmaster.
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Note that this action must be done as root, or it will have no effect;
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so a root-owned startup script is the easiest place to do it. If you
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do this, you may also wish to build <productname>PostgreSQL</>
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with <literal>-DLINUX_OOM_ADJ=0</> added to <varname>CFLAGS</>.
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That will cause postmaster child processes to run with the normal
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<varname>oom_adj</> value of zero, so that the OOM killer can still
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target them at need.
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</para>
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<note>
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<para>
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Some vendors' Linux 2.4 kernels are reported to have early versions
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of the 2.6 overcommit <command>sysctl</command> parameter. However, setting
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@ -1294,6 +1314,7 @@ sysctl -w vm.overcommit_memory=2
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feature is there. If in any doubt, consult a kernel expert or your
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kernel vendor.
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</para>
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</note>
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</sect2>
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</sect1>
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@ -7,12 +7,14 @@
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* Copyright (c) 1996-2010, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/postmaster/fork_process.c,v 1.10 2010/01/02 16:57:50 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/postmaster/fork_process.c,v 1.11 2010/01/11 18:39:32 tgl Exp $
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*/
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#include "postgres.h"
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#include "postmaster/fork_process.h"
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#include <fcntl.h>
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#include <time.h>
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#include <sys/stat.h>
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#include <sys/time.h>
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#include <unistd.h>
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@ -60,6 +62,38 @@ fork_process(void)
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setitimer(ITIMER_PROF, &prof_itimer, NULL);
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#endif
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/*
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* By default, Linux tends to kill the postmaster in out-of-memory
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* situations, because it blames the postmaster for the sum of child
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* process sizes *including shared memory*. (This is unbelievably
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* stupid, but the kernel hackers seem uninterested in improving it.)
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* Therefore it's often a good idea to protect the postmaster by
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* setting its oom_adj value negative (which has to be done in a
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* root-owned startup script). If you just do that much, all child
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* processes will also be protected against OOM kill, which might not
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* be desirable. You can then choose to build with LINUX_OOM_ADJ
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* #defined to 0, or some other value that you want child processes
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* to adopt here.
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*/
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#ifdef LINUX_OOM_ADJ
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{
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/*
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* Use open() not stdio, to ensure we control the open flags.
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* Some Linux security environments reject anything but O_WRONLY.
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*/
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int fd = open("/proc/self/oom_adj", O_WRONLY, 0);
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/* We ignore all errors */
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if (fd >= 0)
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{
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char buf[16];
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snprintf(buf, sizeof(buf), "%d\n", LINUX_OOM_ADJ);
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(void) write(fd, buf, strlen(buf));
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close(fd);
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}
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}
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#endif /* LINUX_OOM_ADJ */
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}
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return result;
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