max backends checking patch

As of 6.4.2 (and snapshot, I guess), postmaser does not check if the
number of backends exceeds MaxBackendId (defined in
include/storage/sinvaladt.h). As a result (MaxBackendId+1)th backend
gets started but failed in the middle of its initialising process.
Typical error would be:

NOTICE: SIAssignBackendId: discarding tag 2147430138
Connection databese 'request' failed.
FATAL 1: Backend cache invalidation initialization failed

Then postmaster decides to re-initialize the shared memory and all
running backends are killed. Too bad.

Attached patches try to fix the problem.
--
Tatsuo Ishii
-------------------------------- cut here ---------------------------
*** postgresql-6.4.2/src/backend/postmaster/postmaster.c.orig Sun Nov 29 10:52:32 1998
--- postgresql-6.4.2/src/backend/postmaster/postmaster.c Sat Jan 9 18:14:52 1999
***************
*** 238,243 ****
--- 238,244 ----
static long PostmasterRandom(void);
static void RandomSalt(char *salt);
static void SignalChildren(SIGNAL_ARGS);
+ static int CountChildren(void);

#ifdef CYR_RECODE
void GetCharSetByHost(char *, int, char *);
***************
*** 754,764 ****
* by the backend.
*/

! if (BackendStartup(port) != STATUS_OK)
! PacketSendError(&port->pktInfo,
"Backend startup failed");
! else
! status = STATUS_ERROR;
}

/* Close the connection if required. */
--- 755,771 ----
* by the backend.
*/

! if (CountChildren() < MaxBackendId) {
! if (BackendStartup(port) != STATUS_OK)
! PacketSendError(&port->pktInfo,
"Backend startup failed");
! else {
! status = STATUS_ERROR;
! }
! } else {
! PacketSendError(&port->pktInfo,
! "There are too many backends");
! }
}

/* Close the connection if required. */
***************
*** 1617,1620 ****
--- 1624,1655 ----
}

return random() ^ random_seed;
+ }
+
+ /*
+ * Count up number of chidren processes.
+ */
+ static int
+ CountChildren(void)
+ {
+ Dlelem *curr,
+ *next;
+ Backend *bp;
+ int mypid = getpid();
+ int cnt = 0;
+
+ curr = DLGetHead(BackendList);
+ while (curr)
+ {
+ next = DLGetSucc(curr);
+ bp = (Backend *) DLE_VAL(curr);
+
+ if (bp->pid != mypid)
+ {
+ cnt++;
+ }
+
+ curr = next;
+ }
+ return(cnt);
}