diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 04d8e6f09f..956883579a 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.47.2.2 2010/05/01 22:46:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/sysv_shmem.c,v 1.47.2.3 2010/07/23 13:53:29 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -49,6 +49,9 @@ typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
 
 unsigned long UsedShmemSegID = 0;
 void	   *UsedShmemSegAddr = NULL;
+#ifdef WIN32
+Size		UsedShmemSegSize = 0;
+#endif
 
 static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
 static void IpcMemoryDetach(int status, Datum shmaddr);
@@ -446,6 +449,9 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 	/* Save info for possible future use */
 	UsedShmemSegAddr = memAddress;
 	UsedShmemSegID = (unsigned long) NextShmemSegID;
+#ifdef WIN32
+	UsedShmemSegSize = size;
+#endif
 
 	return hdr;
 }
diff --git a/src/backend/port/win32/shmem.c b/src/backend/port/win32/shmem.c
index c7865bda32..2ba144c9a4 100644
--- a/src/backend/port/win32/shmem.c
+++ b/src/backend/port/win32/shmem.c
@@ -6,14 +6,17 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/win32/shmem.c,v 1.13.2.1 2009/05/04 08:36:42 mha Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/win32/shmem.c,v 1.13.2.2 2010/07/23 13:53:30 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
+#include "miscadmin.h"
 
 static DWORD s_segsize = 0;
+extern void *UsedShmemSegAddr;
+extern Size UsedShmemSegSize;
 
 /* Detach from a shared mem area based on its address */
 int
@@ -29,6 +32,13 @@ shmdt(const void *shmaddr)
 void *
 shmat(int memId, void *shmaddr, int flag)
 {
+	/* Release the memory region reserved in the postmaster */
+	if (IsUnderPostmaster)
+	{
+		if (VirtualFree(shmaddr, 0, MEM_RELEASE) == 0)
+			elog(FATAL, "failed to release reserved memory region (addr=%p): %lu",
+				 shmaddr, GetLastError());
+	}
 	/* TODO -- shmat needs to count # attached to shared mem */
 	void	   *lpmem = MapViewOfFileEx((HANDLE) memId,
 										FILE_MAP_WRITE | FILE_MAP_READ,
@@ -128,3 +138,53 @@ shmget(int memKey, int size, int flag)
 
 	return (int) hmap;
 }
+
+/*
+ * pgwin32_ReserveSharedMemoryRegion(hChild)
+ *
+ * Reserve the memory region that will be used for shared memory in a child
+ * process. It is called before the child process starts, to make sure the
+ * memory is available.
+ *
+ * Once the child starts, DLLs loading in different order or threads getting
+ * scheduled differently may allocate memory which can conflict with the
+ * address space we need for our shared memory. By reserving the shared
+ * memory region before the child starts, and freeing it only just before we
+ * attempt to get access to the shared memory forces these allocations to
+ * be given different address ranges that don't conflict.
+ *
+ * NOTE! This function executes in the postmaster, and should for this
+ * reason not use elog(FATAL) since that would take down the postmaster.
+ */
+int
+pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
+{
+	void *address;
+
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(UsedShmemSegSize != 0);
+
+	address = VirtualAllocEx(hChild, UsedShmemSegAddr, UsedShmemSegSize,
+								MEM_RESERVE, PAGE_READWRITE);
+	if (address == NULL) {
+		/* Don't use FATAL since we're running in the postmaster */
+		elog(LOG, "could not reserve shared memory region (addr=%p) for child %lu: %lu",
+			 UsedShmemSegAddr, hChild, GetLastError());
+		return false;
+	}
+	if (address != UsedShmemSegAddr)
+	{
+		/*
+		 * Should never happen - in theory if allocation granularity causes strange
+		 * effects it could, so check just in case.
+		 *
+		 * Don't use FATAL since we're running in the postmaster.
+		 */
+	    elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
+			 address, UsedShmemSegAddr);
+		VirtualFreeEx(hChild, address, 0, MEM_RELEASE);
+		return false;
+	}
+
+	return true;
+}
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 69f37c02ad..583604fcdf 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.505.2.8 2010/04/01 20:12:42 heikki Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.505.2.9 2010/07/23 13:53:30 mha Exp $
  *
  * NOTES
  *
@@ -3186,7 +3186,7 @@ internal_forkexec(int argc, char *argv[], Port *port)
 		return -1;				/* log made by save_backend_variables */
 	}
 
-	/* Drop the shared memory that is now inherited to the backend */
+	/* Drop the parameter shared memory that is now inherited to the backend */
 	if (!UnmapViewOfFile(param))
 		elog(LOG, "could not unmap view of backend parameter file: error code %d",
 			 (int) GetLastError());
@@ -3194,6 +3194,25 @@ internal_forkexec(int argc, char *argv[], Port *port)
 		elog(LOG, "could not close handle to backend parameter file: error code %d",
 			 (int) GetLastError());
 
+	/*
+	 * Reserve the memory region used by our main shared memory segment before we
+	 * resume the child process.
+	 */
+	if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))
+	{
+		/*
+		 * Failed to reserve the memory, so terminate the newly created
+		 * process and give up.
+		 */
+		if (!TerminateProcess(pi.hProcess, 255))
+			ereport(ERROR,
+					(errmsg_internal("could not terminate process that failed to reserve memory: error code %d",
+									 (int) GetLastError())));
+		CloseHandle(pi.hProcess);
+		CloseHandle(pi.hThread);
+		return -1;			/* logging done made by pgwin32_ReserveSharedMemoryRegion() */
+	}
+
 	/*
 	 * Now that the backend variables are written out, we start the child
 	 * thread so it can start initializing while we set up the rest of the
diff --git a/src/include/port/win32.h b/src/include/port/win32.h
index 514efcdb2d..50c711e121 100644
--- a/src/include/port/win32.h
+++ b/src/include/port/win32.h
@@ -1,4 +1,4 @@
-/* $PostgreSQL: pgsql/src/include/port/win32.h,v 1.63.2.3 2007/11/29 16:44:26 mha Exp $ */
+/* $PostgreSQL: pgsql/src/include/port/win32.h,v 1.63.2.4 2010/07/23 13:53:30 mha Exp $ */
 
 #if defined(_MSC_VER) || defined(__BORLANDC__)
 #define WIN32_ONLY_COMPILER
@@ -263,6 +263,9 @@ extern int	pgwin32_is_admin(void);
 extern int	pgwin32_is_service(void);
 #endif
 
+/* in backend/port/win32/shmem.c */
+extern int	pgwin32_ReserveSharedMemoryRegion(HANDLE);
+
 /* in port/win32error.c */
 extern void _dosmaperr(unsigned long);