Cause stats processes to detach from shared memory when started, so that

they do not prevent the postmaster from deleting the shmem segment during
a post-backend-crash restart cycle.  Per recent discussion.

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 1.24 2003/10/27 18:30:07 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/port/sysv_shmem.c,v 1.25 2003/11/07 21:55:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -134,7 +134,7 @@ InternalIpcMemoryCreate(IpcMemoryKey memKey, uint32 size)
 
 	/* OK, should be able to attach to the segment */
 #ifdef SHM_SHARE_MMU
-	/* use intimate shared memory on SPARC Solaris */
+	/* use intimate shared memory on Solaris */
 	memAddress = shmat(shmid, 0, SHM_SHARE_MMU);
 #else
 	memAddress = shmat(shmid, 0, 0);
@@ -244,7 +244,7 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 	/* Room for a header? */
 	Assert(size > MAXALIGN(sizeof(PGShmemHeader)));
 
-	/* Just attach and return the pointer */
+	/* If Exec case, just attach and return the pointer */
 	if (ExecBackend && UsedShmemSegAddr != NULL && !makePrivate)
 	{
 		if ((hdr = PGSharedMemoryAttach(UsedShmemSegID, &shmid)) == NULL)
@@ -253,6 +253,9 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 		return hdr;
 	}
 
+	/* Make sure PGSharedMemoryAttach doesn't fail without need */
+	UsedShmemSegAddr = NULL;
+
 	/* Loop till we find a free IPC key */
 	NextShmemSegID = port * 1000;
 
@@ -326,16 +329,32 @@ PGSharedMemoryCreate(uint32 size, bool makePrivate, int port)
 	hdr->totalsize = size;
 	hdr->freeoffset = MAXALIGN(sizeof(PGShmemHeader));
 
-
-	if (ExecBackend && UsedShmemSegAddr == NULL && !makePrivate)
-	{
-		UsedShmemSegAddr = memAddress;
-		UsedShmemSegID = NextShmemSegID;
-	}
+	/* 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;
+	}
+}
 
 /*
  * Attach to shared memory and make sure it has a Postgres header

src/backend/postmaster/pgstat.c

@@ -13,7 +13,7 @@
  *
  *	Copyright (c) 2001-2003, PostgreSQL Global Development Group
  *
- *	$Header: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v 1.45 2003/09/25 06:58:01 petere Exp $
+ *	$Header: /cvsroot/pgsql/src/backend/postmaster/pgstat.c,v 1.46 2003/11/07 21:55:50 tgl Exp $
  * ----------
  */
 #include "postgres.h"
@@ -44,6 +44,7 @@
 #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"
@@ -400,6 +401,9 @@ 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) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: pg_shmem.h,v 1.7 2003/08/04 02:40:15 momjian Exp $
+ * $Id: pg_shmem.h,v 1.8 2003/11/07 21:55:50 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -44,5 +44,6 @@ extern void *UsedShmemSegAddr;
 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 */