Index: src/backend/storage/ipc/shmem.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/storage/ipc/shmem.c,v
retrieving revision 1.70
diff -u -r1.70 shmem.c
--- src/backend/storage/ipc/shmem.c	4 Aug 2003 02:40:03 -0000	1.70
+++ src/backend/storage/ipc/shmem.c	21 Sep 2003 07:53:13 -0000
@@ -131,6 +131,7 @@
 void *
 ShmemAlloc(Size size)
 {
+	uint32		newStart;
 	uint32		newFree;
 	void	   *newSpace;
 
@@ -146,10 +147,14 @@
 
 	SpinLockAcquire(ShmemLock);
 
-	newFree = shmemseghdr->freeoffset + size;
+	newStart = shmemseghdr->freeoffset;
+	if (size >= BLCKSZ)
+		newStart = BUFFERALIGN(newStart);
+
+	newFree = newStart + size;
 	if (newFree <= shmemseghdr->totalsize)
 	{
-		newSpace = (void *) MAKE_PTR(shmemseghdr->freeoffset);
+		newSpace = (void *) MAKE_PTR(newStart);
 		shmemseghdr->freeoffset = newFree;
 	}
 	else
Index: src/include/c.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/c.h,v
retrieving revision 1.152
diff -u -r1.152 c.h
--- src/include/c.h	4 Aug 2003 02:40:10 -0000	1.152
+++ src/include/c.h	21 Sep 2003 07:53:14 -0000
@@ -529,6 +529,7 @@
 #define LONGALIGN(LEN)			TYPEALIGN(ALIGNOF_LONG, (LEN))
 #define DOUBLEALIGN(LEN)		TYPEALIGN(ALIGNOF_DOUBLE, (LEN))
 #define MAXALIGN(LEN)			TYPEALIGN(MAXIMUM_ALIGNOF, (LEN))
+#define BUFFERALIGN(LEN)		TYPEALIGN(ALIGNOF_BUFFER, (LEN))
 
 
 /* ----------------------------------------------------------------
Index: src/include/pg_config_manual.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/pg_config_manual.h,v
retrieving revision 1.5
diff -u -r1.5 pg_config_manual.h
--- src/include/pg_config_manual.h	4 Aug 2003 00:43:29 -0000	1.5
+++ src/include/pg_config_manual.h	21 Sep 2003 07:53:14 -0000
@@ -176,6 +176,14 @@
  */
 #define MAX_RANDOM_VALUE  (0x7FFFFFFF)
 
+/*
+ * Alignment of the disk blocks in the shared memory area.
+ * A significant amount of the total system time is required for
+ * copying disk blocks between the os buffers and the cache in the
+ * shared memory area. Some cpus (most notably Intel Pentium III)
+ * prefer well-aligned addresses for memory copies.
+ */
+#define ALIGNOF_BUFFER	32
 
 /*
  *------------------------------------------------------------------------