Back-patch fix to cause stats processes to detach from shared memory,

so that they do not prevent the postmaster from deleting the shmem segment
during crash recovery.

src/backend/port/sysv_shmem.c

@@ -10,7 +10,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.4 2002/09/04 20:31:24 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.4.2.1 2003/11/30 21:56:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,6 +41,9 @@ typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
 #define IPCProtection	(0600)	/* access/modify by user only */
 
 
+static IpcMemoryKey UsedShmemSegID = 0;
+static void	   *UsedShmemSegAddr = NULL;
+
 static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size);
 static void IpcMemoryDetach(int status, Datum shmaddr);
 static void IpcMemoryDelete(int status, Datum shmId);
@@ -395,5 +398,29 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 	hdr->totalsize = size;
 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
 
+	/* Save info for possible future use */
+	UsedShmemSegAddr = memAddress;
+	UsedShmemSegID = NextShmemSegID;
+
 	return hdr;
 }
+
+/*
+ * PGSharedMemoryDetach
+ *
+ * Detach from the shared memory segment, if still attached.  This is not
+ * intended for use by the process that originally created the segment
+ * (it will have an on_shmem_exit callback registered to do that).  Rather,
+ * this is for subprocesses that have inherited an attachment and want to
+ * get rid of it.
+ */
+void
+PGSharedMemoryDetach(void)
+{
+	if (UsedShmemSegAddr != NULL)
+	{
+		if (shmdt(UsedShmemSegAddr) < 0)
+			elog(LOG, "shmdt(%p) failed: %m", UsedShmemSegAddr);
+		UsedShmemSegAddr = NULL;
+	}
+}

src/backend/postmaster/pgstat.c

@@ -16,7 +16,7 @@
  *
  *	Copyright (c) 2001, PostgreSQL Global Development Group
  *
- *	$Header: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v 1.31.2.2 2003/07/22 19:13:25 tgl Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v 1.31.2.3 2003/11/30 21:56:36 tgl Exp $
  * ----------
  */
 #include "postgres.h"
@@ -42,6 +42,7 @@
 #include "utils/memutils.h"
 #include "storage/backendid.h"
 #include "storage/ipc.h"
+#include "storage/pg_shmem.h"
 #include "utils/rel.h"
 #include "utils/hsearch.h"
 #include "utils/ps_status.h"
@@ -324,6 +325,9 @@ pgstat_start(void)
 	/* Close the postmaster's sockets, except for pgstat link */
 	ClosePostmasterPorts(false);
 
+	/* Drop our connection to postmaster's shared memory, as well */
+	PGSharedMemoryDetach();
+
 	pgstat_main();
 
 	exit(0);

src/include/storage/pg_shmem.h

@@ -17,7 +17,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: pg_shmem.h,v 1.4 2002/09/04 20:31:45 momjian Exp $
+ * $Id: pg_shmem.h,v 1.4.2.1 2003/11/30 21:56:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -37,5 +37,6 @@ typedef struct PGShmemHeader	/* standard header for all Postgres shmem */
 extern PGShmemHeader *PGSharedMemoryCreate(uint32 size, bool makePrivate,
 					 int port);
 extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
+extern void PGSharedMemoryDetach(void);
 
 #endif   /* PG_SHMEM_H */