Convert the arithmetic for shared memory size calculation from 'int'

to 'Size' (that is, size_t), and install overflow detection checks in it.
This allows us to remove the former arbitrary restrictions on NBuffers
etc.  It won't make any difference in a 32-bit machine, but in a 64-bit
machine you could theoretically have terabytes of shared buffers.
(How efficiently we could manage 'em remains to be seen.)  Similarly,
num_temp_buffers, work_mem, and maintenance_work_mem can be set above
2Gb on a 64-bit machine.  Original patch from Koichi Suzuki, additional
work by moi.

src/backend/utils/hash/dynahash.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.63 2005/06/26 23:32:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.64 2005/08/20 23:26:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -44,6 +44,7 @@
 
 #include "postgres.h"
 
+#include "storage/shmem.h"
 #include "utils/dynahash.h"
 #include "utils/hsearch.h"
 #include "utils/memutils.h"
@@ -391,10 +392,10 @@ init_htab(HTAB *hashp, long nelem)
  * memory; therefore it does not count HTAB which is in local memory.
  * NB: assumes that all hash structure parameters have default values!
  */
-long
+Size
 hash_estimate_size(long num_entries, Size entrysize)
 {
-	long		size = 0;
+	Size		size;
 	long		nBuckets,
 				nSegments,
 				nDirEntries,
@@ -412,17 +413,20 @@ hash_estimate_size(long num_entries, Size entrysize)
 		nDirEntries <<= 1;		/* dir_alloc doubles dsize at each call */
 
 	/* fixed control info */
-	size += MAXALIGN(sizeof(HASHHDR));	/* but not HTAB, per above */
+	size = MAXALIGN(sizeof(HASHHDR));	/* but not HTAB, per above */
 	/* directory */
-	size += MAXALIGN(nDirEntries * sizeof(HASHSEGMENT));
+	size = add_size(size, mul_size(nDirEntries, sizeof(HASHSEGMENT)));
 	/* segments */
-	size += nSegments * MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET));
+	size = add_size(size, mul_size(nSegments,
+								   MAXALIGN(DEF_SEGSIZE * sizeof(HASHBUCKET))));
 	/* elements --- allocated in groups of up to HASHELEMENT_ALLOC_MAX */
 	elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(entrysize);
 	elementAllocCnt = Min(num_entries, HASHELEMENT_ALLOC_MAX);
 	elementAllocCnt = Max(elementAllocCnt, 1);
 	nElementAllocs = (num_entries - 1) / elementAllocCnt + 1;
-	size += nElementAllocs * elementAllocCnt * elementSize;
+	size = add_size(size,
+					mul_size(nElementAllocs,
+							 mul_size(elementAllocCnt, elementSize)));
 
 	return size;
 }

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.283 2005/08/19 18:58:18 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.284 2005/08/20 23:26:26 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -78,6 +78,13 @@
 #define CONFIG_EXEC_PARAMS_NEW "global/config_exec_params.new"
 #endif
 
+/* upper limit for GUC variables measured in kilobytes of memory */
+#if SIZEOF_SIZE_T > 4
+#define MAX_KILOBYTES	INT_MAX
+#else
+#define MAX_KILOBYTES	(INT_MAX / 1024)
+#endif
+
 /* XXX these should appear in other modules' header files */
 extern bool Log_disconnections;
 extern DLLIMPORT bool check_function_bodies;
@@ -1027,6 +1034,10 @@ static struct config_int ConfigureNamesInt[] =
 	 * constraints here are partially unused. Similarly, the superuser
 	 * reserved number is checked to ensure it is less than the max
 	 * backends number.
+	 *
+	 * MaxBackends is limited to INT_MAX/4 because some places compute
+	 * 4*MaxBackends without any overflow check.  Likewise we have to
+	 * limit NBuffers to INT_MAX/2.
 	 */
 	{
 		{"max_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
@@ -1034,7 +1045,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&MaxBackends,
-		100, 1, INT_MAX / BLCKSZ, NULL, NULL
+		100, 1, INT_MAX / 4, NULL, NULL
 	},
 
 	{
@@ -1043,7 +1054,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&ReservedBackends,
-		2, 0, INT_MAX / BLCKSZ, NULL, NULL
+		2, 0, INT_MAX / 4, NULL, NULL
 	},
 
 	{
@@ -1052,7 +1063,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&NBuffers,
-		1000, 16, INT_MAX / BLCKSZ, NULL, NULL
+		1000, 16, INT_MAX / 2, NULL, NULL
 	},
 
 	{
@@ -1061,7 +1072,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&num_temp_buffers,
-		1000, 100, INT_MAX / BLCKSZ, NULL, show_num_temp_buffers
+		1000, 100, INT_MAX / 2, NULL, show_num_temp_buffers
 	},
 
 	{
@@ -1094,7 +1105,7 @@ static struct config_int ConfigureNamesInt[] =
 						 "temporary disk files.")
 		},
 		&work_mem,
-		1024, 8 * BLCKSZ / 1024, INT_MAX / 1024, NULL, NULL
+		1024, 8 * BLCKSZ / 1024, MAX_KILOBYTES, NULL, NULL
 	},
 
 	{
@@ -1103,7 +1114,7 @@ static struct config_int ConfigureNamesInt[] =
 			gettext_noop("This includes operations such as VACUUM and CREATE INDEX.")
 		},
 		&maintenance_work_mem,
-		16384, 1024, INT_MAX / 1024, NULL, NULL
+		16384, 1024, MAX_KILOBYTES, NULL, NULL
 	},
 
 	{
@@ -1112,7 +1123,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&max_stack_depth,
-		2048, 100, INT_MAX / 1024, assign_max_stack_depth, NULL
+		2048, 100, MAX_KILOBYTES, assign_max_stack_depth, NULL
 	},
 
 	{
@@ -1193,7 +1204,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&max_prepared_xacts,
-		50, 0, 10000, NULL, NULL
+		50, 0, INT_MAX, NULL, NULL
 	},
 
 #ifdef LOCK_DEBUG
@@ -1310,7 +1321,7 @@ static struct config_int ConfigureNamesInt[] =
 			NULL
 		},
 		&XLOGbuffers,
-		8, 4, INT_MAX / BLCKSZ, NULL, NULL
+		8, 4, INT_MAX, NULL, NULL
 	},
 
 	{

src/backend/utils/misc/postgresql.conf.sample

@@ -88,7 +88,7 @@
 
 #shared_buffers = 1000			# min 16 or max_connections*2, 8KB each
 #temp_buffers = 1000			# min 100, 8KB each
-#max_prepared_transactions = 50 # 0-10000
+#max_prepared_transactions = 50		# can be 0 or more
 #work_mem = 1024			# min 64, size in KB
 #maintenance_work_mem = 16384		# min 1024, size in KB
 #max_stack_depth = 2048			# min 100, size in KB