# It's often a good idea to protect the postmaster from being killed by the
# OOM killer (which will tend to preferentially kill the postmaster because
# of the way it accounts for shared memory). Setting the OOM_SCORE_ADJ value
-# to -1000 will disable OOM kill altogether. If you enable this, you probably
-# want to compile PostgreSQL with "-DLINUX_OOM_SCORE_ADJ=0", so that
-# individual backends can still be killed by the OOM killer.
+# to -1000 will disable OOM kill altogether, which is a good thing for the
+# postmaster, but not so much for individual backends. If you enable this,
+# also uncomment the DAEMON_ENV line, which will instruct backends to set
+# their OOM adjustments back to the default setting of zero.
#OOM_SCORE_ADJ=-1000
+#DAEMON_ENV="PG_OOM_ADJUST_FILE=/proc/self/oom_score_adj"
# Older Linux kernels may not have /proc/self/oom_score_adj, but instead
# /proc/self/oom_adj, which works similarly except the disable value is -17.
-# For such a system, enable this and compile with "-DLINUX_OOM_ADJ=0".
+# For such a system, uncomment these two lines instead.
#OOM_ADJ=-17
+#DAEMON_ENV="PG_OOM_ADJUST_FILE=/proc/self/oom_adj"
## STOP EDITING HERE
echo -n "Starting PostgreSQL: "
test x"$OOM_SCORE_ADJ" != x && echo "$OOM_SCORE_ADJ" > /proc/self/oom_score_adj
test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
- su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
+ su - $PGUSER -c "$DAEMON_ENV $DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
echo "ok"
;;
stop)
su - $PGUSER -c "$PGCTL stop -D '$PGDATA' -s -m fast -w"
test x"$OOM_SCORE_ADJ" != x && echo "$OOM_SCORE_ADJ" > /proc/self/oom_score_adj
test x"$OOM_ADJ" != x && echo "$OOM_ADJ" > /proc/self/oom_adj
- su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
+ su - $PGUSER -c "$DAEMON_ENV $DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
echo "ok"
;;
reload)
Another approach, which can be used with or without altering
vm.overcommit_memory, is to set the process-specific
- <varname>oom_score_adj value for the postmaster process to
+ <firstterm>OOM score adjustment value for the postmaster process to
-1000, thereby guaranteeing it will not be targeted by the OOM
killer. The simplest way to do this is to execute
in the postmaster's startup script just before invoking the postmaster.
Note that this action must be done as root, or it will have no effect;
so a root-owned startup script is the easiest place to do it. If you
- do this, you may also wish to build
PostgreSQL- with -DLINUX_OOM_SCORE_ADJ=0 added to CPPFLAGS.
- That will cause postmaster child processes to run with the normal
- oom_score_adj value of zero, so that the OOM killer can still
- target them at need.
+ do this, you should also set these environment variables in the startup
+ script before invoking the postmaster:
+export PG_OOM_ADJUST_FILE=/proc/self/oom_score_adj
+export PG_OOM_ADJUST_VALUE=0
+
+ These settings will cause postmaster child processes to run with the
+ normal OOM score adjustment of zero, so that the OOM killer can still
+ target them at need. You could use some other value for
+ PG_OOM_ADJUST_VALUE if you want the child processes to run
+ with some other OOM score adjustment. (PG_OOM_ADJUST_VALUE
+ can also be omitted, in which case it defaults to zero.) If you do not
+ set PG_OOM_ADJUST_FILE, the child processes will run with the
+ same OOM score adjustment as the postmaster, which is unwise since the
+ whole point is to ensure that the postmaster has a preferential setting.
Older Linux kernels do not offer /proc/self/oom_score_adj,
but may have a previous version of the same functionality called
/proc/self/oom_adj. This works the same except the disable
- value is -17 not -1000. The corresponding
- build flag for
PostgreSQL is- -DLINUX_OOM_ADJ=0.
+ value is -17 not -1000.
fork_process(void)
{
pid_t result;
+ const char *oomfilename;
#ifdef LINUX_PROFILE
struct itimerval prof_itimer;
* process sizes *including shared memory*. (This is unbelievably
* stupid, but the kernel hackers seem uninterested in improving it.)
* Therefore it's often a good idea to protect the postmaster by
- * setting its oom_score_adj value negative (which has to be done in a
- * root-owned startup script). If you just do that much, all child
- * processes will also be protected against OOM kill, which might not
- * be desirable. You can then choose to build with
- * LINUX_OOM_SCORE_ADJ #defined to 0, or to some other value that you
- * want child processes to adopt here.
+ * setting its OOM score adjustment negative (which has to be done in
+ * a root-owned startup script). Since the adjustment is inherited by
+ * child processes, this would ordinarily mean that all the
+ * postmaster's children are equally protected against OOM kill, which
+ * is not such a good idea. So we provide this code to allow the
+ * children to change their OOM score adjustments again. Both the
+ * file name to write to and the value to write are controlled by
+ * environment variables, which can be set by the same startup script
+ * that did the original adjustment.
*/
-#ifdef LINUX_OOM_SCORE_ADJ
- {
- /*
- * Use open() not stdio, to ensure we control the open flags. Some
- * Linux security environments reject anything but O_WRONLY.
- */
- int fd = open("/proc/self/oom_score_adj", O_WRONLY, 0);
-
- /* We ignore all errors */
- if (fd >= 0)
- {
- char buf[16];
- int rc;
+ oomfilename = getenv("PG_OOM_ADJUST_FILE");
- snprintf(buf, sizeof(buf), "%d\n", LINUX_OOM_SCORE_ADJ);
- rc = write(fd, buf, strlen(buf));
- (void) rc;
- close(fd);
- }
- }
-#endif /* LINUX_OOM_SCORE_ADJ */
-
- /*
- * Older Linux kernels have oom_adj not oom_score_adj. This works
- * similarly except with a different scale of adjustment values. If
- * it's necessary to build Postgres to work with either API, you can
- * define both LINUX_OOM_SCORE_ADJ and LINUX_OOM_ADJ.
- */
-#ifdef LINUX_OOM_ADJ
+ if (oomfilename != NULL)
{
/*
* Use open() not stdio, to ensure we control the open flags. Some
* Linux security environments reject anything but O_WRONLY.
*/
- int fd = open("/proc/self/oom_adj", O_WRONLY, 0);
+ int fd = open(oomfilename, O_WRONLY, 0);
/* We ignore all errors */
if (fd >= 0)
{
- char buf[16];
+ const char *oomvalue = getenv("PG_OOM_ADJUST_VALUE");
int rc;
- snprintf(buf, sizeof(buf), "%d\n", LINUX_OOM_ADJ);
- rc = write(fd, buf, strlen(buf));
+ if (oomvalue == NULL) /* supply a useful default */
+ oomvalue = "0";
+
+ rc = write(fd, oomvalue, strlen(oomvalue));
(void) rc;
close(fd);
}
}
-#endif /* LINUX_OOM_ADJ */
/*
* Make sure processes do not share OpenSSL randomness state.
projects / postgresql.git / commitdiff