Re: Setting oom_adj on linux?

On Fri, Jan 8, 2010 at 07:27, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Then, somebody who wants the feature would build with, say,
>        -DLINUX_OOM_ADJ=0
> or another value if they want that.

Here is a stab at that.

It sets oom_adj for:
autovacuum workers
archivers (pgarch.c)
regular backends

Also it updates the contrib linux starup script to start under an oom_adj of -17

Comments?

*** a/contrib/start-scripts/linux
--- b/contrib/start-scripts/linux
***************
*** 53,58 **** DAEMON="$prefix/bin/postmaster"
--- 53,63 ----
# What to use to shut down the postmaster
PGCTL="$prefix/bin/pg_ctl"

+ # Adjust oom_adj on linux to avoid the postmaster from be killed
+ # note you probably want to compile postgres with -DLINUX_OOM_ADJ=0
+ # so that regular backends will be killed on oom
+ OOM_ADJ=-17
+
set -e

# Only start if we can find the postmaster.
***************
*** 62,67 **** test -x $DAEMON || exit 0
--- 67,73 ----
case $1 in
start)
echo -n "Starting PostgreSQL: "
+ echo $OOM_ADJ > /proc/self/oom_adj
su - $PGUSER -c "$DAEMON -D '$PGDATA' &" >>$PGLOG 2>&1
echo "ok"
;;
*** a/src/backend/postmaster/autovacuum.c
--- b/src/backend/postmaster/autovacuum.c
***************
*** 1403,1408 **** StartAutoVacWorker(void)
--- 1403,1411 ----
/* Lose the postmaster's on-exit routines */
on_exit_reset();

+ /* allow us to be killed on oom */
+ oom_adjust();
+
AutoVacWorkerMain(0, NULL);
break;
#endif
*** a/src/backend/postmaster/fork_process.c
--- b/src/backend/postmaster/fork_process.c
***************
*** 66,68 **** fork_process(void)
--- 66,97 ----
}

#endif /* ! WIN32 */
+
+ #if defined(__linux__) && defined(LINUX_OOM_ADJ)
+ /*
+ * By default linux really likes to kill the postmaster on oom.
+ * Because linux does not take SYSV shared mem into account it
+ * (almost) always will SIGKILL the postmaster on an oom event.
+ *
+ * In the event you started the postmaster under a low (negative)
+ * oom_adj. This will adjust regular backends, autovac and archivers
+ * to LINUX_OOM_ADJ on fork(). Allowing them to be killed in an oom
+ * event.
+ *
+ * Later we might add other OS oom type stuff here.
+ */
+ void
+ oom_adjust(void)
+ {
+ FILE *oom = fopen("/proc/self/oom_adj", "w");
+
+ /* ignore errors we dont really care */
+ if (oom)
+ {
+ fprintf(oom, "%d\n", LINUX_OOM_ADJ);
+ fclose(oom);
+ }
+ }
+ #else
+ void oom_adjust(void) { }
+ #endif
*** a/src/backend/postmaster/pgarch.c
--- b/src/backend/postmaster/pgarch.c
***************
*** 170,175 **** pgarch_start(void)
--- 170,178 ----
/* Drop our connection to postmaster's shared memory, as well */
PGSharedMemoryDetach();

+ /* allow us to be killed on oom */
+ oom_adjust();
+
PgArchiverMain(0, NULL);
break;
#endif
*** a/src/backend/postmaster/postmaster.c
--- b/src/backend/postmaster/postmaster.c
***************
*** 3076,3081 **** BackendStartup(Port *port)
--- 3076,3084 ----
/* Perform additional initialization and collect startup packet */
BackendInitialize(port);

+ /* allow us to be killed on oom */
+ oom_adjust();
+
/* And run the backend */
proc_exit(BackendRun(port));
}
*** a/src/include/postmaster/fork_process.h
--- b/src/include/postmaster/fork_process.h
***************
*** 13,17 ****
--- 13,18 ----
#define FORK_PROCESS_H

extern pid_t fork_process(void);
+ extern void oom_adjust(void);

#endif /* FORK_PROCESS_H */