If the stats collector dies during Hot Standby, restart it.

robertmhaas · robertmhaas · commit e927f55ffffb · 2016-10-27T14:56:42.000-04:00
This bug exists as far back as 9.0, when Hot Standby was introduced,
so back-patch to all supported branches.

Report and patch by Takayuki Tsunakawa, reviewed by Michael Paquier
and Kuntal Ghosh.
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
@@ -1754,7 +1754,8 @@ ServerLoop(void)
 			PgArchPID = pgarch_start();
 
 		/* If we have lost the stats collector, try to start a new one */
-		if (PgStatPID == 0 && pmState == PM_RUN)
+		if (PgStatPID == 0 &&
+			(pmState == PM_RUN || pmState == PM_HOT_STANDBY))
 			PgStatPID = pgstat_start();
 
 		/* If we need to signal the autovacuum launcher, do so now */
@@ -2902,7 +2903,7 @@ reaper(SIGNAL_ARGS)
 			if (!EXIT_STATUS_0(exitstatus))
 				LogChildExit(LOG, _("statistics collector process"),
 							 pid, exitstatus);
-			if (pmState == PM_RUN)
+			if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
 				PgStatPID = pgstat_start();
 			continue;
 		}
