Rearrange handling of MAXBACKENDS a little bit. The default setting

of MAXBACKENDS is now 1024, since all it's costing is about 32 bytes of memory
per array slot.  configure's --with-maxbackends switch now controls DEF_MAXBACKENDS
which is simply the default value of the postmaster's -N switch.  Thus,
the out-of-the-box configuration will still limit you to 64 backends,
but you can go up to 1024 backends simply by restarting the postmaster with
a different -N switch --- no rebuild required.

src/backend/postmaster/postmaster.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.102 1999/02/19 06:06:00 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/postmaster/postmaster.c,v 1.103 1999/02/21 01:41:43 tgl Exp $
  *
  * NOTES
  *
@@ -162,14 +162,15 @@ static IpcMemoryKey ipc_key;
   * adding to this.
   */
 
-static int	MaxBackends = MAXBACKENDS;
+static int	MaxBackends = DEF_MAXBACKENDS;
 
  /* 
-  * MaxBackends is the actual soft limit on the number of backends
-  * we will start.  It defaults to the hard limit established at compilation
-  * time, but can be readjusted with postmaster's xxx switch.
-  * One reason to reduce MaxBackends is to allow startup under a kernel
-  * that won't let us get MAXBACKENDS semaphores!
+  * MaxBackends is the actual limit on the number of backends we will start.
+  * The default is established by configure, but it can be readjusted 
+  * from 1..MAXBACKENDS with the postmaster -N switch.
+  * Note that a larger MaxBackends value will increase the size of the
+  * shared memory area as well as cause the postmaster to grab more
+  * kernel semaphores, even if you never actually use that many backends.
   */
 
 static int	NextBackendTag = MAXINT;		/* XXX why count down not up? */
@@ -641,8 +642,8 @@ usage(const char *progname)
 	fprintf(stderr, "\t-b backend\tuse a specific backend server executable\n");
 	fprintf(stderr, "\t-d [1|2|3]\tset debugging level\n");
 	fprintf(stderr, "\t-i \t\tlisten on TCP/IP sockets as well as Unix domain socket\n");
-	fprintf(stderr, "\t-N nprocs\tset max number of backend servers (1..%d)\n",
-			MAXBACKENDS);
+	fprintf(stderr, "\t-N nprocs\tset max number of backends (1..%d, default %d)\n",
+			MAXBACKENDS, DEF_MAXBACKENDS);
 	fprintf(stderr, "\t-n \t\tdon't reinitialize shared memory after abnormal exit\n");
 	fprintf(stderr, "\t-o option\tpass 'option' to each backend servers\n");
 	fprintf(stderr, "\t-p port\tspecify port for postmaster to listen on\n");

src/backend/storage/ipc/ipc.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipc.c,v 1.35 1999/02/13 23:18:09 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipc.c,v 1.36 1999/02/21 01:41:44 tgl Exp $
  *
  * NOTES
  *
@@ -677,9 +677,10 @@ struct ipcdummy
 	SLock	   *free;
 	int			unused;
 	slock_t		memlock;
-	SLock		slocks[NSLOCKS];
+	SLock		slocks[MAX_SPINS + 1];
 };
-static int	SLockMemorySize = sizeof(struct ipcdummy);
+
+#define	SLOCKMEMORYSIZE		sizeof(struct ipcdummy)
 
 void
 CreateAndInitSLockMemory(IPCKey key)
@@ -688,7 +689,7 @@ CreateAndInitSLockMemory(IPCKey key)
 	SLock	   *slckP;
 
 	SLockMemoryId = IpcMemoryCreate(key,
-									SLockMemorySize,
+									SLOCKMEMORYSIZE,
 									0700);
 	AttachSLockMemory(key);
 	*FreeSLockPP = NULL;
@@ -713,7 +714,7 @@ AttachSLockMemory(IPCKey key)
 	struct ipcdummy *slockM;
 
 	if (SLockMemoryId == -1)
-		SLockMemoryId = IpcMemoryIdGet(key, SLockMemorySize);
+		SLockMemoryId = IpcMemoryIdGet(key, SLOCKMEMORYSIZE);
 	if (SLockMemoryId == -1)
 		elog(FATAL, "SLockMemory not in shared memory");
 	slockM = (struct ipcdummy *) IpcMemoryAttach(SLockMemoryId);

src/backend/storage/ipc/ipci.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipci.c,v 1.20 1999/02/19 07:10:47 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipci.c,v 1.21 1999/02/21 01:41:44 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -72,7 +72,7 @@ CreateSharedMemoryAndSemaphores(IPCKey key, int maxBackends)
 	 * ----------------
 	 */
 	CreateSpinlocks(IPCKeyGetSpinLockSemaphoreKey(key));
-	size = BufferShmemSize() + LockShmemSize();
+	size = BufferShmemSize() + LockShmemSize(maxBackends);
 
 #ifdef STABLE_MEMORY_STORAGE
 	size += MMShmemSize();
@@ -113,15 +113,13 @@ CreateSharedMemoryAndSemaphores(IPCKey key, int maxBackends)
 void
 AttachSharedMemoryAndSemaphores(IPCKey key)
 {
-	int			size;
-
 	/* ----------------
 	 *	create rather than attach if using private key
 	 * ----------------
 	 */
 	if (key == PrivateIPCKey)
 	{
-		CreateSharedMemoryAndSemaphores(key, 1);
+		CreateSharedMemoryAndSemaphores(key, 16);
 		return;
 	}
 
@@ -136,8 +134,7 @@ AttachSharedMemoryAndSemaphores(IPCKey key)
 	 *	attach the buffer manager buffer pool (and semaphore)
 	 * ----------------
 	 */
-	size = BufferShmemSize() + LockShmemSize();
-	InitShmem(key, size);
+	InitShmem(key, 0);
 	InitBufferPool(key);
 
 	/* ----------------

src/backend/storage/lmgr/lock.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lock.c,v 1.42 1999/02/19 06:06:06 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lock.c,v 1.43 1999/02/21 01:41:46 tgl Exp $
  *
  * NOTES
  *	  Outside modules can create a lock table and acquire/release
@@ -1478,36 +1478,37 @@ next_item:
 }
 
 int
-LockShmemSize()
+LockShmemSize(int maxBackends)
 {
 	int			size = 0;
+	int			nLockEnts = NLOCKENTS(maxBackends);
 	int			nLockBuckets,
 				nLockSegs;
 	int			nXidBuckets,
 				nXidSegs;
 
-	nLockBuckets = 1 << (int) my_log2((NLOCKENTS - 1) / DEF_FFACTOR + 1);
+	nLockBuckets = 1 << (int) my_log2((nLockEnts - 1) / DEF_FFACTOR + 1);
 	nLockSegs = 1 << (int) my_log2((nLockBuckets - 1) / DEF_SEGSIZE + 1);
 
 	nXidBuckets = 1 << (int) my_log2((NLOCKS_PER_XACT - 1) / DEF_FFACTOR + 1);
 	nXidSegs = 1 << (int) my_log2((nLockBuckets - 1) / DEF_SEGSIZE + 1);
 
-	size += MAXALIGN(MAXBACKENDS * sizeof(PROC)); /* each MyProc */
-	size += MAXALIGN(MAXBACKENDS * sizeof(LOCKMETHODCTL));		/* each
+	size += MAXALIGN(maxBackends * sizeof(PROC)); /* each MyProc */
+	size += MAXALIGN(maxBackends * sizeof(LOCKMETHODCTL));		/* each
 																 * lockMethodTable->ctl */
 	size += MAXALIGN(sizeof(PROC_HDR)); /* ProcGlobal */
 
-	size += MAXALIGN(my_log2(NLOCKENTS) * sizeof(void *));
+	size += MAXALIGN(my_log2(nLockEnts) * sizeof(void *));
 	size += MAXALIGN(sizeof(HHDR));
 	size += nLockSegs * MAXALIGN(DEF_SEGSIZE * sizeof(SEGMENT));
-	size += NLOCKENTS *			/* XXX not multiple of BUCKET_ALLOC_INCR? */
+	size += nLockEnts *			/* XXX not multiple of BUCKET_ALLOC_INCR? */
 		(MAXALIGN(sizeof(BUCKET_INDEX)) +
 		 MAXALIGN(sizeof(LOCK)));		/* contains hash key */
 
-	size += MAXALIGN(my_log2(MAXBACKENDS) * sizeof(void *));
+	size += MAXALIGN(my_log2(maxBackends) * sizeof(void *));
 	size += MAXALIGN(sizeof(HHDR));
 	size += nXidSegs * MAXALIGN(DEF_SEGSIZE * sizeof(SEGMENT));
-	size += MAXBACKENDS *		/* XXX not multiple of BUCKET_ALLOC_INCR? */
+	size += maxBackends *		/* XXX not multiple of BUCKET_ALLOC_INCR? */
 		(MAXALIGN(sizeof(BUCKET_INDEX)) +
 		 MAXALIGN(sizeof(XIDLookupEnt)));		/* contains hash key */
 
@@ -1673,8 +1674,8 @@ DeadLockCheck(SHM_QUEUE *lockQueue, LOCK *findlock, bool skip_check)
 							break;
 					if (j >= nprocs && lock != findlock)
 					{
+						Assert(nprocs < MAXBACKENDS);
 						checked_procs[nprocs++] = proc;
-						Assert(nprocs <= MAXBACKENDS);
 
 						/*
 						 * For non-MyProc entries, we are looking only

src/backend/storage/lmgr/proc.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.50 1999/02/19 07:10:48 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.51 1999/02/21 01:41:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -46,7 +46,7 @@
  *		This is so that we can support more backends. (system-wide semaphore
  *		sets run out pretty fast.)				  -ay 4/95
  *
- * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.50 1999/02/19 07:10:48 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.51 1999/02/21 01:41:45 tgl Exp $
  */
 #include <sys/time.h>
 #include <unistd.h>
@@ -154,23 +154,28 @@ InitProcGlobal(IPCKey key, int maxBackends)
 		 */
 		on_shmem_exit(ProcFreeAllSemaphores, NULL);
 
-		/* Pre-create the semaphores for the first maxBackends processes */
-		for (i = 0;
-			 i < (maxBackends+PROC_NSEMS_PER_SET-1) / PROC_NSEMS_PER_SET;
-			 i++)
+		/* Pre-create the semaphores for the first maxBackends processes,
+		 * unless we are running as a standalone backend.
+		 */
+		if (key != PrivateIPCKey)
 		{
-			IPCKey		semKey = ProcGlobal->currKey + i;
-			int			semId;
-			int			semstat;
-
-			semId = IpcSemaphoreCreate(semKey,
-									   PROC_NSEMS_PER_SET,
-									   IPCProtection,
-									   IpcSemaphoreDefaultStartValue,
-									   0,
-									   &semstat);
-			/* mark this sema set allocated */
-			ProcGlobal->freeSemMap[i] = (1 << PROC_NSEMS_PER_SET);
+			for (i = 0;
+				 i < (maxBackends+PROC_NSEMS_PER_SET-1) / PROC_NSEMS_PER_SET;
+				 i++)
+			{
+				IPCKey		semKey = ProcGlobal->currKey + i;
+				int			semId;
+				int			semstat;
+
+				semId = IpcSemaphoreCreate(semKey,
+										   PROC_NSEMS_PER_SET,
+										   IPCProtection,
+										   IpcSemaphoreDefaultStartValue,
+										   0,
+										   &semstat);
+				/* mark this sema set allocated */
+				ProcGlobal->freeSemMap[i] = (1 << PROC_NSEMS_PER_SET);
+			}
 		}
 	}
 }

src/configure

@@ -31,7 +31,7 @@ ac_help="$ac_help
 ac_help="$ac_help
   --with-pgport=<portnum> change default startup port "
 ac_help="$ac_help
-  --with-maxbackends=<n>  set maximum number of server processes "
+  --with-maxbackends=<n>  set default maximum number of server processes "
 ac_help="$ac_help
   --with-tcl              build Tcl interfaces and pgtclsh "
 ac_help="$ac_help
@@ -879,18 +879,18 @@ EOF
 fi
 
 
-echo $ac_n "checking setting MAXBACKENDS""... $ac_c" 1>&6
-echo "configure:884: checking setting MAXBACKENDS" >&5
+echo $ac_n "checking setting DEF_MAXBACKENDS""... $ac_c" 1>&6
+echo "configure:884: checking setting DEF_MAXBACKENDS" >&5
 # Check whether --with-maxbackends or --without-maxbackends was given.
 if test "${with_maxbackends+set}" = set; then
   withval="$with_maxbackends"
   cat >> confdefs.h <<EOF
-#define MAXBACKENDS ${withval}
+#define DEF_MAXBACKENDS ${withval}
 EOF
  echo "$ac_t""$with_maxbackends" 1>&6
 else
   cat >> confdefs.h <<EOF
-#define MAXBACKENDS 64
+#define DEF_MAXBACKENDS 64
 EOF
  echo "$ac_t""64" 1>&6
 

src/configure.in

@@ -255,13 +255,13 @@ AC_ARG_WITH(
    AC_DEFINE_UNQUOTED(DEF_PGPORT, "5432") AC_MSG_RESULT(5432)
 )
 
-dnl MAXBACKENDS can be set by --with-maxbackends.  Default value is 64.
-AC_MSG_CHECKING(setting MAXBACKENDS)
+dnl DEF_MAXBACKENDS can be set by --with-maxbackends.  Default value is 64.
+AC_MSG_CHECKING(setting DEF_MAXBACKENDS)
 AC_ARG_WITH(
    maxbackends,
-   [  --with-maxbackends=<n>  set maximum number of server processes ],
-   AC_DEFINE_UNQUOTED(MAXBACKENDS, ${withval}) AC_MSG_RESULT($with_maxbackends),
-   AC_DEFINE_UNQUOTED(MAXBACKENDS, 64) AC_MSG_RESULT(64)
+   [  --with-maxbackends=<n>  set default maximum number of server processes ],
+   AC_DEFINE_UNQUOTED(DEF_MAXBACKENDS, ${withval}) AC_MSG_RESULT($with_maxbackends),
+   AC_DEFINE_UNQUOTED(DEF_MAXBACKENDS, 64) AC_MSG_RESULT(64)
 )
 
 dnl We exclude tcl support unless user says --with-tcl

src/include/config.h.in

@@ -9,10 +9,17 @@
 #define CONFIG_H
 
 /*
- * Maximum number of backend server processes per postmaster.
+ * Default runtime limit on number of backend server processes per postmaster;
+ * this is just the default setting for the postmaster's -N switch.
  * (Actual value is set by configure script.)
  */
-#undef MAXBACKENDS
+#undef DEF_MAXBACKENDS
+
+/*
+ * Hard limit on number of backend server processes per postmaster.
+ * Increasing this costs about 32 bytes per process slot as of v 6.5.
+ */
+#define MAXBACKENDS	(DEF_MAXBACKENDS > 1024 ? DEF_MAXBACKENDS : 1024)
 
 /*
  * Size of a disk block --- currently, this limits the size of a tuple.

src/include/storage/ipc.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: ipc.h,v 1.33 1999/02/19 06:06:33 tgl Exp $
+ * $Id: ipc.h,v 1.34 1999/02/21 01:41:47 tgl Exp $
  *
  * NOTES
  *	  This file is very architecture-specific.	This stuff should actually
@@ -96,7 +96,6 @@ extern void AttachSLockMemory(IPCKey key);
 
 #ifdef HAS_TEST_AND_SET
 
-#define NSLOCKS			2048
 #define NOLOCK			0
 #define SHAREDLOCK		1
 #define EXCLUSIVELOCK	2

src/include/storage/lock.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: lock.h,v 1.22 1999/02/19 06:06:35 tgl Exp $
+ * $Id: lock.h,v 1.23 1999/02/21 01:41:47 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -28,14 +28,14 @@ typedef int MASK;
 /* ----------------------
  * The following defines are used to estimate how much shared
  * memory the lock manager is going to require.
+ * See LockShmemSize() in lock.c.
  *
- * MAXBACKENDS - The max number of concurrently running backends (config.h)
  * NLOCKS_PER_XACT - The number of unique locks acquired in a transaction
  * NLOCKENTS - The maximum number of lock entries in the lock table.
  * ----------------------
  */
-#define NLOCKS_PER_XACT	40
-#define NLOCKENTS		(NLOCKS_PER_XACT*MAXBACKENDS)
+#define NLOCKS_PER_XACT			40
+#define NLOCKENTS(maxBackends)	(NLOCKS_PER_XACT*(maxBackends))
 
 typedef int LOCKMODE;
 typedef int LOCKMETHOD;
@@ -242,7 +242,7 @@ extern bool LockRelease(LOCKMETHOD lockmethod, LOCKTAG *locktag,
 			LOCKMODE lockmode);
 extern void GrantLock(LOCK *lock, LOCKMODE lockmode);
 extern bool LockReleaseAll(LOCKMETHOD lockmethod, SHM_QUEUE *lockQueue);
-extern int	LockShmemSize(void);
+extern int	LockShmemSize(int maxBackends);
 extern bool LockingDisabled(void);
 extern bool DeadLockCheck(SHM_QUEUE *lockQueue, LOCK *findlock,
 			  bool skip_check);