Perform an immediate shutdown if the postmaster.pid file is removed.

The postmaster now checks every minute or so (worst case, at most two
minutes) that postmaster.pid is still there and still contains its own PID.
If not, it performs an immediate shutdown, as though it had received
SIGQUIT.

The original goal behind this change was to ensure that failed buildfarm
runs would get fully cleaned up, even if the test scripts had left a
postmaster running, which is not an infrequent occurrence.  When the
buildfarm script removes a test postmaster's $PGDATA directory, its next
check on postmaster.pid will fail and cause it to exit.  Previously, manual
intervention was often needed to get rid of such orphaned postmasters,
since they'd block new test postmasters from obtaining the expected socket
address.

However, by checking postmaster.pid and not something else, we can provide
additional robustness: manual removal of postmaster.pid is a frequent DBA
mistake, and now we can at least limit the damage that will ensue if a new
postmaster is started while the old one is still alive.

Back-patch to all supported branches, since we won't get the desired
improvement in buildfarm reliability otherwise.

1 files changed, 42 insertions, 12 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index dd87e430434..40e655f6855 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -1372,9 +1372,10 @@ ServerLoop(void)
 	fd_set		readmask;
 	int			nSockets;
 	time_t		now,
+				last_lockfile_recheck_time,
 				last_touch_time;
 
-	last_touch_time = time(NULL);
+	last_lockfile_recheck_time = last_touch_time = time(NULL);
 
 	nSockets = initMasks(&readmask);
 
@@ -1520,27 +1521,56 @@ ServerLoop(void)
 				kill(AutoVacPID, SIGUSR2);
 		}
 
+#ifdef HAVE_PTHREAD_IS_THREADED_NP
+
+		/*
+		 * With assertions enabled, check regularly for appearance of
+		 * additional threads.  All builds check at start and exit.
+		 */
+		Assert(pthread_is_threaded_np() == 0);
+#endif
+
+		/*
+		 * Lastly, check to see if it's time to do some things that we don't
+		 * want to do every single time through the loop, because they're a
+		 * bit expensive.  Note that there's up to a minute of slop in when
+		 * these tasks will be performed, since DetermineSleepTime() will let
+		 * us sleep at most that long.
+		 */
+		now = time(NULL);
+
 		/*
-		 * Touch the socket and lock file every 58 minutes, to ensure that
+		 * Once a minute, verify that postmaster.pid hasn't been removed or
+		 * overwritten.  If it has, we force a shutdown.  This avoids having
+		 * postmasters and child processes hanging around after their database
+		 * is gone, and maybe causing problems if a new database cluster is
+		 * created in the same place.  It also provides some protection
+		 * against a DBA foolishly removing postmaster.pid and manually
+		 * starting a new postmaster.  Data corruption is likely to ensue from
+		 * that anyway, but we can minimize the damage by aborting ASAP.
+		 */
+		if (now - last_lockfile_recheck_time >= 1 * SECS_PER_MINUTE)
+		{
+			if (!RecheckDataDirLockFile())
+			{
+				ereport(LOG,
+						(errmsg("performing immediate shutdown because data directory lock file is invalid")));
+				kill(MyProcPid, SIGQUIT);
+			}
+			last_lockfile_recheck_time = now;
+		}
+
+		/*
+		 * Touch Unix socket and lock file every 58 minutes, to ensure that
 		 * they are not removed by overzealous /tmp-cleaning tasks.  We assume
 		 * no one runs cleaners with cutoff times of less than an hour ...
 		 */
-		now = time(NULL);
 		if (now - last_touch_time >= 58 * SECS_PER_MINUTE)
 		{
 			TouchSocketFile();
 			TouchSocketLockFile();
 			last_touch_time = now;
 		}
-
-#ifdef HAVE_PTHREAD_IS_THREADED_NP
-
-		/*
-		 * With assertions enabled, check regularly for appearance of
-		 * additional threads.  All builds check at start and exit.
-		 */
-		Assert(pthread_is_threaded_np() == 0);
-#endif
 	}
 }