Fix some sloppiness in the recent multiple-autovacuum-worker patch. It was

not bothering to initialize is_autovacuum for regular backends, meaning there
was a significant chance of the postmaster prematurely sending them SIGTERM
during database shutdown.  Also, leaving the cancel key unset for an autovac
worker meant that any client could send it SIGINT, which doesn't sound
especially good either.

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.537 2007/08/02 23:39:44 adunstan Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.538 2007/08/03 20:06:50 tgl Exp $
  *
  * NOTES
  *
@@ -130,7 +130,7 @@
  * children we have and send them appropriate signals when necessary.
  *
  * "Special" children such as the startup, bgwriter and autovacuum launcher
- * tasks are not in this list.  Autovacuum worker processes are on it.
+ * tasks are not in this list.  Autovacuum worker processes are in it.
  */
 typedef struct bkend
 {
@@ -2705,6 +2705,7 @@ BackendStartup(Port *port)
 	 */
 	bn->pid = pid;
 	bn->cancel_key = MyCancelKey;
+	bn->is_autovacuum = false;
 	DLAddHead(BackendList, DLNewElem(bn));
 #ifdef EXEC_BACKEND
 	ShmemBackendArrayAdd(bn);
@@ -3925,15 +3926,22 @@ StartAutovacuumWorker(void)
 	if (StartupPID != 0 || FatalError || Shutdown != NoShutdown)
 		return;
 
+	/*
+	 * Compute the cancel key that will be assigned to this session.
+	 * We probably don't need cancel keys for autovac workers, but we'd
+	 * better have something random in the field to prevent unfriendly
+	 * people from sending cancels to them.
+	 */
+	MyCancelKey = PostmasterRandom();
+
 	bn = (Backend *) malloc(sizeof(Backend));
 	if (bn)
 	{
 		bn->pid = StartAutoVacWorker();
-		bn->is_autovacuum = true;
-		/* we don't need a cancel key */
-
 		if (bn->pid > 0)
 		{
+			bn->cancel_key = MyCancelKey;
+			bn->is_autovacuum = true;
 			DLAddHead(BackendList, DLNewElem(bn));
 #ifdef EXEC_BACKEND
 			ShmemBackendArrayAdd(bn);
@@ -3949,7 +3957,9 @@ StartAutovacuumWorker(void)
 		free(bn);
 	}
 	else
-		elog(LOG, "out of memory");
+		ereport(LOG,
+				(errcode(ERRCODE_OUT_OF_MEMORY),
+				 errmsg("out of memory")));
 
 	/* report the failure to the launcher */
 	AutoVacWorkerFailed();