Index: src/backend/postmaster/postmaster.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/postmaster/postmaster.c,v
retrieving revision 1.285
diff -c -r1.285 postmaster.c
*** src/backend/postmaster/postmaster.c	2002/08/18 03:03:25	1.285
--- src/backend/postmaster/postmaster.c	2002/08/27 21:59:04
***************
*** 151,156 ****
--- 151,168 ----
   */
  int			MaxBackends = DEF_MAXBACKENDS;
  
+ /*
+  * ReservedBackends is the number of backends reserved for superuser use.
+  * This number is taken out of the pool size given by MaxBackends so
+  * number of backend slots available to none super users is
+  * (MaxBackends - ReservedBackends). Note, existing super user
+  * connections are not taken into account once this lower limit has
+  * been reached, i.e. superuser connections made before the lower limit
+  * is reached always count towards that limit and are not taken from
+  * ReservedBackends.
+  */
+ int			ReservedBackends = 2;
+ 
  
  static char *progname = (char *) NULL;
  
***************
*** 566,571 ****
--- 578,589 ----
  	SetDataDir(potential_DataDir);
  
  	ProcessConfigFile(PGC_POSTMASTER);
+ 
+ 	/*
+ 	 * Force an exit if ReservedBackends is not less than MaxBackends.
+ 	 */
+ 	if (ReservedBackends >= MaxBackends)
+ 		elog(FATAL,"superuser_reserved_connections must be less than max_connections.");
  
  	/*
  	 * Now that we are done processing the postmaster arguments, reset
Index: src/backend/storage/ipc/sinval.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/storage/ipc/sinval.c,v
retrieving revision 1.49
diff -c -r1.49 sinval.c
*** src/backend/storage/ipc/sinval.c	2002/06/20 20:29:35	1.49
--- src/backend/storage/ipc/sinval.c	2002/08/27 21:59:04
***************
*** 538,540 ****
--- 538,564 ----
  
  	return NULL;
  }
+ 
+ /*
+  * CountEmptyBackendSlots - count empty slots in backend process table
+  *
+  * Doesn't count since the procState array could be large and we've already
+  * allowed for that by running a freeBackends counter in the SI segment.
+  * Unlike CountActiveBackends() we do not need to interrogate the
+  * backends to determine the free slot count.
+  * Goes for a lock despite being a trival look up in case other backends
+  * are busy starting or exiting since there is scope for confusion.
+  */
+ int
+ CountEmptyBackendSlots(void)
+ {
+ 	int count;
+ 
+ 	LWLockAcquire(SInvalLock, LW_SHARED);
+ 
+ 	count = shmInvalBuffer->freeBackends;
+ 
+ 	LWLockRelease(SInvalLock);
+ 
+ 	return count;
+ }
Index: src/backend/storage/ipc/sinvaladt.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/storage/ipc/sinvaladt.c,v
retrieving revision 1.47
diff -c -r1.47 sinvaladt.c
*** src/backend/storage/ipc/sinvaladt.c	2002/06/20 20:29:35	1.47
--- src/backend/storage/ipc/sinvaladt.c	2002/08/27 21:59:05
***************
*** 60,65 ****
--- 60,66 ----
  	segP->maxMsgNum = 0;
  	segP->lastBackend = 0;
  	segP->maxBackends = maxBackends;
+ 	segP->freeBackends = maxBackends;
  
  	/* The buffer[] array is initially all unused, so we need not fill it */
  
***************
*** 91,96 ****
--- 92,104 ----
  	int			index;
  	ProcState  *stateP = NULL;
  
+ 	if (segP->freeBackends == 0)
+ 	{
+ 		/* out of procState slots */
+ 		MyBackendId = InvalidBackendId;
+ 		return 0;
+ 	}
+ 
  	/* Look for a free entry in the procState array */
  	for (index = 0; index < segP->lastBackend; index++)
  	{
***************
*** 103,120 ****
  
  	if (stateP == NULL)
  	{
! 		if (segP->lastBackend < segP->maxBackends)
! 		{
! 			stateP = &segP->procState[segP->lastBackend];
! 			Assert(stateP->nextMsgNum < 0);
! 			segP->lastBackend++;
! 		}
! 		else
! 		{
! 			/* out of procState slots */
! 			MyBackendId = InvalidBackendId;
! 			return 0;
! 		}
  	}
  
  	MyBackendId = (stateP - &segP->procState[0]) + 1;
--- 111,119 ----
  
  	if (stateP == NULL)
  	{
! 		stateP = &segP->procState[segP->lastBackend];
! 		Assert(stateP->nextMsgNum < 0);
! 		segP->lastBackend++;
  	}
  
  	MyBackendId = (stateP - &segP->procState[0]) + 1;
***************
*** 123,128 ****
--- 122,130 ----
  	elog(DEBUG1, "SIBackendInit: backend id %d", MyBackendId);
  #endif   /* INVALIDDEBUG */
  
+ 	/* Reduce free slot count */
+ 	segP->freeBackends--;
+ 
  	/* mark myself active, with all extant messages already read */
  	stateP->nextMsgNum = segP->maxMsgNum;
  	stateP->resetState = false;
***************
*** 165,170 ****
--- 167,175 ----
  			break;
  	}
  	segP->lastBackend = i;
+ 
+ 	/* Adjust free slot count */
+ 	segP->freeBackends++;
  
  	LWLockRelease(SInvalLock);
  }
Index: src/backend/utils/init/postinit.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/init/postinit.c,v
retrieving revision 1.109
diff -c -r1.109 postinit.c
*** src/backend/utils/init/postinit.c	2002/07/20 05:16:59	1.109
--- src/backend/utils/init/postinit.c	2002/08/27 21:59:05
***************
*** 402,407 ****
--- 402,417 ----
  	/* close the transaction we started above */
  	if (!bootstrap)
  		CommitTransactionCommand();
+ 
+ 	/*
+ 	 * Check a normal user hasn't connected to a superuser reserved slot.
+ 	 * Do this here since we need the user information and that only happens
+ 	 * after we've started bringing the shared memory online. So we wait
+ 	 * until we've registered exit handlers and potentially shut an open
+ 	 * transaction down for an as safety conscious rejection as possible.
+ 	 */
+ 	if (CountEmptyBackendSlots() < ReservedBackends && !superuser())
+ 		elog(ERROR, "Non-superuser connection limit exceeded");
  }
  
  /*
Index: src/backend/utils/misc/guc.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/misc/guc.c,v
retrieving revision 1.84
diff -c -r1.84 guc.c
*** src/backend/utils/misc/guc.c	2002/08/26 17:53:59	1.84
--- src/backend/utils/misc/guc.c	2002/08/27 21:59:09
***************
*** 537,547 ****
  	/*
  	 * Note: There is some postprocessing done in PostmasterMain() to make
  	 * sure the buffers are at least twice the number of backends, so the
! 	 * constraints here are partially unused.
  	 */
  	{
  		{ "max_connections", PGC_POSTMASTER }, &MaxBackends,
  		DEF_MAXBACKENDS, 1, INT_MAX, NULL, NULL
  	},
  
  	{
--- 537,554 ----
  	/*
  	 * Note: There is some postprocessing done in PostmasterMain() to make
  	 * sure the buffers are at least twice the number of backends, so the
! 	 * constraints here are partially unused. Similarly, the superuser
! 	 * reserved number is checked to ensure it is less than the max
! 	 * backends number.
  	 */
  	{
  		{ "max_connections", PGC_POSTMASTER }, &MaxBackends,
  		DEF_MAXBACKENDS, 1, INT_MAX, NULL, NULL
+ 	},
+ 
+ 	{
+ 		{ "superuser_reserved_connections", PGC_POSTMASTER }, &ReservedBackends,
+ 		2, 0, INT_MAX, NULL, NULL
  	},
  
  	{
Index: src/backend/utils/misc/postgresql.conf.sample
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/misc/postgresql.conf.sample,v
retrieving revision 1.48
diff -c -r1.48 postgresql.conf.sample
*** src/backend/utils/misc/postgresql.conf.sample	2002/08/27 14:06:05	1.48
--- src/backend/utils/misc/postgresql.conf.sample	2002/08/27 21:59:09
***************
*** 31,36 ****
--- 31,37 ----
  #ssl = false
  
  #max_connections = 32
+ #superuser_reserved_connections = 2
  
  #port = 5432 
  #hostname_lookup = false
Index: src/include/miscadmin.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/miscadmin.h,v
retrieving revision 1.106
diff -c -r1.106 miscadmin.h
*** src/include/miscadmin.h	2002/06/20 20:29:42	1.106
--- src/include/miscadmin.h	2002/08/27 21:59:11
***************
*** 179,184 ****
--- 179,185 ----
  extern bool EnableSSL;
  extern bool SilentMode;
  extern int	MaxBackends;
+ extern int	ReservedBackends;
  extern int	NBuffers;
  extern int	PostPortNumber;
  extern int	Unix_socket_permissions;
Index: src/include/storage/sinval.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/storage/sinval.h,v
retrieving revision 1.28
diff -c -r1.28 sinval.h
*** src/include/storage/sinval.h	2002/06/20 20:29:52	1.28
--- src/include/storage/sinval.h	2002/08/27 21:59:11
***************
*** 89,92 ****
--- 89,94 ----
  /* Use "struct PGPROC", not PGPROC, to avoid including proc.h here */
  extern struct PGPROC *BackendIdGetProc(BackendId procId);
  
+ extern int CountEmptyBackendSlots(void);
+ 
  #endif   /* SINVAL_H */
Index: src/include/storage/sinvaladt.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/storage/sinvaladt.h,v
retrieving revision 1.32
diff -c -r1.32 sinvaladt.h
*** src/include/storage/sinvaladt.h	2002/06/20 20:29:52	1.32
--- src/include/storage/sinvaladt.h	2002/08/27 21:59:11
***************
*** 85,90 ****
--- 85,91 ----
  	int			lastBackend;	/* index of last active procState entry,
  								 * +1 */
  	int			maxBackends;	/* size of procState array */
+ 	int			freeBackends;	/* number of empty procState slots */
  
  	/*
  	 * Circular buffer holding shared-inval messages