diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index 64ce7557ba..ad3559e0a7 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -430,13 +430,13 @@ ifeq ($(enable_tap_tests),yes)
 define prove_installcheck
 rm -rf '$(CURDIR)'/tmp_check
 $(MKDIR_P) '$(CURDIR)'/tmp_check
-cd $(srcdir) && TESTDIR='$(CURDIR)' PATH="$(bindir):$$PATH" PGPORT='6$(DEF_PGPORT)' top_builddir='$(CURDIR)/$(top_builddir)' PG_REGRESS='$(CURDIR)/$(top_builddir)/src/test/regress/pg_regress' REGRESS_SHLIB='$(abs_top_builddir)/src/test/regress/regress$(DLSUFFIX)' $(PROVE) $(PG_PROVE_FLAGS) $(PROVE_FLAGS) $(if $(PROVE_TESTS),$(PROVE_TESTS),t/*.pl)
+cd $(srcdir) && TESTDIR='$(CURDIR)' PATH="$(bindir):$$PATH" PGPORT='6$(DEF_PGPORT)' top_builddir='$(CURDIR)/$(top_builddir)' PG_REGRESS='$(CURDIR)/$(top_builddir)/src/test/regress/pg_regress' $(PROVE) $(PG_PROVE_FLAGS) $(PROVE_FLAGS) $(if $(PROVE_TESTS),$(PROVE_TESTS),t/*.pl)
 endef
 
 define prove_check
 rm -rf '$(CURDIR)'/tmp_check
 $(MKDIR_P) '$(CURDIR)'/tmp_check
-cd $(srcdir) && TESTDIR='$(CURDIR)' $(with_temp_install) PGPORT='6$(DEF_PGPORT)' PG_REGRESS='$(CURDIR)/$(top_builddir)/src/test/regress/pg_regress' REGRESS_SHLIB='$(abs_top_builddir)/src/test/regress/regress$(DLSUFFIX)' $(PROVE) $(PG_PROVE_FLAGS) $(PROVE_FLAGS) $(if $(PROVE_TESTS),$(PROVE_TESTS),t/*.pl)
+cd $(srcdir) && TESTDIR='$(CURDIR)' $(with_temp_install) PGPORT='6$(DEF_PGPORT)' PG_REGRESS='$(CURDIR)/$(top_builddir)/src/test/regress/pg_regress' $(PROVE) $(PG_PROVE_FLAGS) $(PROVE_FLAGS) $(if $(PROVE_TESTS),$(PROVE_TESTS),t/*.pl)
 endef
 
 else
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index a4533046ce..741c455ccb 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -71,26 +71,6 @@
 typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
 typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
 
-/*
- * How does a given IpcMemoryId relate to this PostgreSQL process?
- *
- * One could recycle unattached segments of different data directories if we
- * distinguished that case from other SHMSTATE_FOREIGN cases.  Doing so would
- * cause us to visit less of the key space, making us less likely to detect a
- * SHMSTATE_ATTACHED key.  It would also complicate the concurrency analysis,
- * in that postmasters of different data directories could simultaneously
- * attempt to recycle a given key.  We'll waste keys longer in some cases, but
- * avoiding the problems of the alternative justifies that loss.
- */
-typedef enum
-{
-	SHMSTATE_ANALYSIS_FAILURE,	/* unexpected failure to analyze the ID */
-	SHMSTATE_ATTACHED,			/* pertinent to DataDir, has attached PIDs */
-	SHMSTATE_ENOENT,			/* no segment of that ID */
-	SHMSTATE_FOREIGN,			/* exists, but not pertinent to DataDir */
-	SHMSTATE_UNATTACHED			/* pertinent to DataDir, no attached PIDs */
-} IpcMemoryState;
-
 
 unsigned long UsedShmemSegID = 0;
 void	   *UsedShmemSegAddr = NULL;
@@ -103,8 +83,8 @@ static void *AnonymousShmem = NULL;
 static void *InternalIpcMemoryCreate(IpcMemoryKey memKey, Size size);
 static void IpcMemoryDetach(int status, Datum shmaddr);
 static void IpcMemoryDelete(int status, Datum shmId);
-static IpcMemoryState PGSharedMemoryAttach(IpcMemoryId shmId,
-					 PGShmemHeader **addr);
+static PGShmemHeader *PGSharedMemoryAttach(IpcMemoryKey key,
+					 IpcMemoryId *shmid);
 
 
 /*
@@ -308,36 +288,11 @@ IpcMemoryDelete(int status, Datum shmId)
 bool
 PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2)
 {
-	PGShmemHeader *memAddress;
-	IpcMemoryState state;
-
-	state = PGSharedMemoryAttach((IpcMemoryId) id2, &memAddress);
-	if (memAddress && shmdt(memAddress) < 0)
-		elog(LOG, "shmdt(%p) failed: %m", memAddress);
-	switch (state)
-	{
-		case SHMSTATE_ENOENT:
-		case SHMSTATE_FOREIGN:
-		case SHMSTATE_UNATTACHED:
-			return false;
-		case SHMSTATE_ANALYSIS_FAILURE:
-		case SHMSTATE_ATTACHED:
-			return true;
-	}
-	return true;
-}
-
-/* See comment at IpcMemoryState. */
-static IpcMemoryState
-PGSharedMemoryAttach(IpcMemoryId shmId,
-					 PGShmemHeader **addr)
-{
+	IpcMemoryId shmId = (IpcMemoryId) id2;
 	struct shmid_ds shmStat;
 	struct stat statbuf;
 	PGShmemHeader *hdr;
 
-	*addr = NULL;
-
 	/*
 	 * We detect whether a shared memory segment is in use by seeing whether
 	 * it (a) exists and (b) has any processes attached to it.
@@ -350,7 +305,7 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 		 * exists.
 		 */
 		if (errno == EINVAL)
-			return SHMSTATE_ENOENT;
+			return false;
 
 		/*
 		 * EACCES implies that the segment belongs to some other userid, which
@@ -358,7 +313,7 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 		 * is relevant to our data directory).
 		 */
 		if (errno == EACCES)
-			return SHMSTATE_FOREIGN;
+			return false;
 
 		/*
 		 * Some Linux kernel versions (in fact, all of them as of July 2007)
@@ -369,7 +324,7 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 		 */
 #ifdef HAVE_LINUX_EIDRM_BUG
 		if (errno == EIDRM)
-			return SHMSTATE_ENOENT;
+			return false;
 #endif
 
 		/*
@@ -377,26 +332,25 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 		 * only likely case is EIDRM, which implies that the segment has been
 		 * IPC_RMID'd but there are still processes attached to it.
 		 */
-		return SHMSTATE_ANALYSIS_FAILURE;
+		return true;
 	}
 
+	/* If it has no attached processes, it's not in use */
+	if (shmStat.shm_nattch == 0)
+		return false;
+
 	/*
 	 * Try to attach to the segment and see if it matches our data directory.
 	 * This avoids shmid-conflict problems on machines that are running
 	 * several postmasters under the same userid.
 	 */
 	if (stat(DataDir, &statbuf) < 0)
-		return SHMSTATE_ANALYSIS_FAILURE;	/* can't stat; be conservative */
+		return true;			/* if can't stat, be conservative */
+
+	hdr = (PGShmemHeader *) shmat(shmId, NULL, PG_SHMAT_FLAGS);
 
-	/*
-	 * If we can't attach, be conservative.  This may fail if postmaster.pid
-	 * furnished the shmId and another user created a world-readable segment
-	 * of the same shmId.
-	 */
-	hdr = (PGShmemHeader *) shmat(shmId, UsedShmemSegAddr, PG_SHMAT_FLAGS);
 	if (hdr == (PGShmemHeader *) -1)
-		return SHMSTATE_ANALYSIS_FAILURE;
-	*addr = hdr;
+		return true;			/* if can't attach, be conservative */
 
 	if (hdr->magic != PGShmemMagic ||
 		hdr->device != statbuf.st_dev ||
@@ -404,12 +358,16 @@ PGSharedMemoryAttach(IpcMemoryId shmId,
 	{
 		/*
 		 * It's either not a Postgres segment, or not one for my data
-		 * directory.
+		 * directory.  In either case it poses no threat.
 		 */
-		return SHMSTATE_FOREIGN;
+		shmdt((void *) hdr);
+		return false;
 	}
 
-	return shmStat.shm_nattch == 0 ? SHMSTATE_UNATTACHED : SHMSTATE_ATTACHED;
+	/* Trouble --- looks a lot like there's still live backends */
+	shmdt((void *) hdr);
+
+	return true;
 }
 
 #ifdef USE_ANONYMOUS_SHMEM
@@ -585,21 +543,25 @@ AnonymousShmemDetach(int status, Datum arg)
  * standard header.  Also, register an on_shmem_exit callback to release
  * the storage.
  *
- * Dead Postgres segments pertinent to this DataDir are recycled if found, but
- * we do not fail upon collision with foreign shmem segments.  The idea here
- * is to detect and re-use keys that may have been assigned by a crashed
- * postmaster or backend.
+ * Dead Postgres segments are recycled if found, but we do not fail upon
+ * collision with non-Postgres shmem segments.  The idea here is to detect and
+ * re-use keys that may have been assigned by a crashed postmaster or backend.
+ *
+ * makePrivate means to always create a new segment, rather than attach to
+ * or recycle any existing segment.
  *
  * The port number is passed for possible use as a key (for SysV, we use
- * it to generate the starting shmem key).
+ * it to generate the starting shmem key).  In a standalone backend,
+ * zero will be passed.
  */
 PGShmemHeader *
-PGSharedMemoryCreate(Size size, int port,
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
 					 PGShmemHeader **shim)
 {
 	IpcMemoryKey NextShmemSegID;
 	void	   *memAddress;
 	PGShmemHeader *hdr;
+	IpcMemoryId shmid;
 	struct stat statbuf;
 	Size		sysvsize;
 
@@ -630,20 +592,11 @@ PGSharedMemoryCreate(Size size, int port,
 	/* Make sure PGSharedMemoryAttach doesn't fail without need */
 	UsedShmemSegAddr = NULL;
 
-	/*
-	 * Loop till we find a free IPC key.  Trust CreateDataDirLockFile() to
-	 * ensure no more than one postmaster per data directory can enter this
-	 * loop simultaneously.  (CreateDataDirLockFile() does not ensure that,
-	 * but prefer fixing it over coping here.)
-	 */
-	NextShmemSegID = 1 + port * 1000;
+	/* Loop till we find a free IPC key */
+	NextShmemSegID = port * 1000;
 
-	for (;;)
+	for (NextShmemSegID++;; NextShmemSegID++)
 	{
-		IpcMemoryId shmid;
-		PGShmemHeader *oldhdr;
-		IpcMemoryState state;
-
 		/* Try to create new segment */
 		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
 		if (memAddress)
@@ -651,71 +604,58 @@ PGSharedMemoryCreate(Size size, int port,
 
 		/* Check shared memory and possibly remove and recreate */
 
+		if (makePrivate)		/* a standalone backend shouldn't do this */
+			continue;
+
+		if ((memAddress = PGSharedMemoryAttach(NextShmemSegID, &shmid)) == NULL)
+			continue;			/* can't attach, not one of mine */
+
 		/*
-		 * shmget() failure is typically EACCES, hence SHMSTATE_FOREIGN.
-		 * ENOENT, a narrow possibility, implies SHMSTATE_ENOENT, but one can
-		 * safely treat SHMSTATE_ENOENT like SHMSTATE_FOREIGN.
+		 * If I am not the creator and it belongs to an extant process,
+		 * continue.
 		 */
-		shmid = shmget(NextShmemSegID, sizeof(PGShmemHeader), 0);
-		if (shmid < 0)
+		hdr = (PGShmemHeader *) memAddress;
+		if (hdr->creatorPID != getpid())
 		{
-			oldhdr = NULL;
-			state = SHMSTATE_FOREIGN;
-		}
-		else
-			state = PGSharedMemoryAttach(shmid, &oldhdr);
-
-		switch (state)
-		{
-			case SHMSTATE_ANALYSIS_FAILURE:
-			case SHMSTATE_ATTACHED:
-				ereport(FATAL,
-						(errcode(ERRCODE_LOCK_FILE_EXISTS),
-						 errmsg("pre-existing shared memory block (key %lu, ID %lu) is still in use",
-								(unsigned long) NextShmemSegID,
-								(unsigned long) shmid),
-						 errhint("Terminate any old server processes associated with data directory \"%s\".",
-								 DataDir)));
-				break;
-			case SHMSTATE_ENOENT:
-
-				/*
-				 * To our surprise, some other process deleted since our last
-				 * InternalIpcMemoryCreate().  Moments earlier, we would have
-				 * seen SHMSTATE_FOREIGN.  Try that same ID again.
-				 */
-				elog(LOG,
-					 "shared memory block (key %lu, ID %lu) deleted during startup",
-					 (unsigned long) NextShmemSegID,
-					 (unsigned long) shmid);
-				break;
-			case SHMSTATE_FOREIGN:
-				NextShmemSegID++;
-				break;
-			case SHMSTATE_UNATTACHED:
-
-				/*
-				 * The segment pertains to DataDir, and every process that had
-				 * used it has died or detached.  Zap it, if possible, and any
-				 * associated dynamic shared memory segments, as well.  This
-				 * shouldn't fail, but if it does, assume the segment belongs
-				 * to someone else after all, and try the next candidate.
-				 * Otherwise, try again to create the segment.  That may fail
-				 * if some other process creates the same shmem key before we
-				 * do, in which case we'll try the next key.
-				 */
-				if (oldhdr->dsm_control != 0)
-					dsm_cleanup_using_control_segment(oldhdr->dsm_control);
-				if (shmctl(shmid, IPC_RMID, NULL) < 0)
-					NextShmemSegID++;
-				break;
+			if (kill(hdr->creatorPID, 0) == 0 || errno != ESRCH)
+			{
+				shmdt(memAddress);
+				continue;		/* segment belongs to a live process */
+			}
 		}
 
-		if (oldhdr && shmdt(oldhdr) < 0)
-			elog(LOG, "shmdt(%p) failed: %m", oldhdr);
+		/*
+		 * The segment appears to be from a dead Postgres process, or from a
+		 * previous cycle of life in this same process.  Zap it, if possible,
+		 * and any associated dynamic shared memory segments, as well. This
+		 * probably shouldn't fail, but if it does, assume the segment belongs
+		 * to someone else after all, and continue quietly.
+		 */
+		if (hdr->dsm_control != 0)
+			dsm_cleanup_using_control_segment(hdr->dsm_control);
+		shmdt(memAddress);
+		if (shmctl(shmid, IPC_RMID, NULL) < 0)
+			continue;
+
+		/*
+		 * Now try again to create the segment.
+		 */
+		memAddress = InternalIpcMemoryCreate(NextShmemSegID, sysvsize);
+		if (memAddress)
+			break;				/* successful create and attach */
+
+		/*
+		 * Can only get here if some other process managed to create the same
+		 * shmem key before we did.  Let him have that one, loop around to try
+		 * next key.
+		 */
 	}
 
-	/* Initialize new segment. */
+	/*
+	 * OK, we created a new segment.  Mark it as created by this process. The
+	 * order of assignments here is critical so that another Postgres process
+	 * can't see the header as valid but belonging to an invalid PID!
+	 */
 	hdr = (PGShmemHeader *) memAddress;
 	hdr->creatorPID = getpid();
 	hdr->magic = PGShmemMagic;
@@ -775,8 +715,7 @@ void
 PGSharedMemoryReAttach(void)
 {
 	IpcMemoryId shmid;
-	PGShmemHeader *hdr;
-	IpcMemoryState state;
+	void	   *hdr;
 	void	   *origUsedShmemSegAddr = UsedShmemSegAddr;
 
 	Assert(UsedShmemSegAddr != NULL);
@@ -789,18 +728,14 @@ PGSharedMemoryReAttach(void)
 #endif
 
 	elog(DEBUG3, "attaching to %p", UsedShmemSegAddr);
-	shmid = shmget(UsedShmemSegID, sizeof(PGShmemHeader), 0);
-	if (shmid < 0)
-		state = SHMSTATE_FOREIGN;
-	else
-		state = PGSharedMemoryAttach(shmid, &hdr);
-	if (state != SHMSTATE_ATTACHED)
+	hdr = (void *) PGSharedMemoryAttach((IpcMemoryKey) UsedShmemSegID, &shmid);
+	if (hdr == NULL)
 		elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %m",
 			 (int) UsedShmemSegID, UsedShmemSegAddr);
 	if (hdr != origUsedShmemSegAddr)
 		elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
 			 hdr, origUsedShmemSegAddr);
-	dsm_set_control_handle(hdr->dsm_control);
+	dsm_set_control_handle(((PGShmemHeader *) hdr)->dsm_control);
 
 	UsedShmemSegAddr = hdr;		/* probably redundant */
 }
@@ -876,3 +811,31 @@ PGSharedMemoryDetach(void)
 	}
 #endif
 }
+
+
+/*
+ * Attach to shared memory and make sure it has a Postgres header
+ *
+ * Returns attach address if OK, else NULL
+ */
+static PGShmemHeader *
+PGSharedMemoryAttach(IpcMemoryKey key, IpcMemoryId *shmid)
+{
+	PGShmemHeader *hdr;
+
+	if ((*shmid = shmget(key, sizeof(PGShmemHeader), 0)) < 0)
+		return NULL;
+
+	hdr = (PGShmemHeader *) shmat(*shmid, UsedShmemSegAddr, PG_SHMAT_FLAGS);
+
+	if (hdr == (PGShmemHeader *) -1)
+		return NULL;			/* failed: must be some other app's */
+
+	if (hdr->magic != PGShmemMagic)
+	{
+		shmdt((void *) hdr);
+		return NULL;			/* segment belongs to a non-Postgres app */
+	}
+
+	return hdr;
+}
diff --git a/src/backend/port/win32_shmem.c b/src/backend/port/win32_shmem.c
index 3888c26db5..f8ca52e1af 100644
--- a/src/backend/port/win32_shmem.c
+++ b/src/backend/port/win32_shmem.c
@@ -170,9 +170,14 @@ EnableLockPagesPrivilege(int elevel)
  *
  * Create a shared memory segment of the given size and initialize its
  * standard header.
+ *
+ * makePrivate means to always create a new segment, rather than attach to
+ * or recycle any existing segment. On win32, we always create a new segment,
+ * since there is no need for recycling (segments go away automatically
+ * when the last backend exits)
  */
 PGShmemHeader *
-PGSharedMemoryCreate(Size size, int port,
+PGSharedMemoryCreate(Size size, bool makePrivate, int port,
 					 PGShmemHeader **shim)
 {
 	void	   *memAddress;
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 0f74f243c5..2215ebbb5a 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -2509,7 +2509,7 @@ reset_shared(int port)
 	 * determine IPC keys.  This helps ensure that we will clean up dead IPC
 	 * objects if the postmaster crashes and is restarted.
 	 */
-	CreateSharedMemoryAndSemaphores(port);
+	CreateSharedMemoryAndSemaphores(false, port);
 }
 
 
@@ -4877,7 +4877,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitProcess();
 
 		/* Attach process to shared data structures */
-		CreateSharedMemoryAndSemaphores(0);
+		CreateSharedMemoryAndSemaphores(false, 0);
 
 		/* And run the backend */
 		BackendRun(&port);		/* does not return */
@@ -4891,7 +4891,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitAuxiliaryProcess();
 
 		/* Attach process to shared data structures */
-		CreateSharedMemoryAndSemaphores(0);
+		CreateSharedMemoryAndSemaphores(false, 0);
 
 		AuxiliaryProcessMain(argc - 2, argv + 2);	/* does not return */
 	}
@@ -4904,7 +4904,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitProcess();
 
 		/* Attach process to shared data structures */
-		CreateSharedMemoryAndSemaphores(0);
+		CreateSharedMemoryAndSemaphores(false, 0);
 
 		AutoVacLauncherMain(argc - 2, argv + 2);	/* does not return */
 	}
@@ -4917,7 +4917,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitProcess();
 
 		/* Attach process to shared data structures */
-		CreateSharedMemoryAndSemaphores(0);
+		CreateSharedMemoryAndSemaphores(false, 0);
 
 		AutoVacWorkerMain(argc - 2, argv + 2);	/* does not return */
 	}
@@ -4935,7 +4935,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitProcess();
 
 		/* Attach process to shared data structures */
-		CreateSharedMemoryAndSemaphores(0);
+		CreateSharedMemoryAndSemaphores(false, 0);
 
 		/* Fetch MyBgworkerEntry from shared memory */
 		shmem_slot = atoi(argv[1] + 15);
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 091244dde8..0c86a581c0 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -88,9 +88,12 @@ RequestAddinShmemSpace(Size size)
  * through the same code as before.  (Note that the called routines mostly
  * check IsUnderPostmaster, rather than EXEC_BACKEND, to detect this case.
  * This is a bit code-wasteful and could be cleaned up.)
+ *
+ * If "makePrivate" is true then we only need private memory, not shared
+ * memory.  This is true for a standalone backend, false for a postmaster.
  */
 void
-CreateSharedMemoryAndSemaphores(int port)
+CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 {
 	PGShmemHeader *shim = NULL;
 
@@ -163,7 +166,7 @@ CreateSharedMemoryAndSemaphores(int port)
 		/*
 		 * Create the shmem segment
 		 */
-		seghdr = PGSharedMemoryCreate(size, port, &shim);
+		seghdr = PGSharedMemoryCreate(size, makePrivate, port, &shim);
 
 		InitShmemAccess(seghdr);
 
@@ -184,9 +187,12 @@ CreateSharedMemoryAndSemaphores(int port)
 	{
 		/*
 		 * We are reattaching to an existing shared memory segment. This
-		 * should only be reached in the EXEC_BACKEND case.
+		 * should only be reached in the EXEC_BACKEND case, and even then only
+		 * with makePrivate == false.
 		 */
-#ifndef EXEC_BACKEND
+#ifdef EXEC_BACKEND
+		Assert(!makePrivate);
+#else
 		elog(PANIC, "should be attached to shared memory already");
 #endif
 	}
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 9676fda866..09e0df290d 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -422,11 +422,9 @@ InitCommunication(void)
 	{
 		/*
 		 * We're running a postgres bootstrap process or a standalone backend.
-		 * Though we won't listen on PostPortNumber, use it to select a shmem
-		 * key.  This increases the chance of detecting a leftover live
-		 * backend of this DataDir.
+		 * Create private "shmem" and semaphores.
 		 */
-		CreateSharedMemoryAndSemaphores(PostPortNumber);
+		CreateSharedMemoryAndSemaphores(true, 0);
 	}
 }
 
diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 02f4b1ba79..6a05a89349 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -76,6 +76,6 @@ extern void on_exit_reset(void);
 /* ipci.c */
 extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
 
-extern void CreateSharedMemoryAndSemaphores(int port);
+extern void CreateSharedMemoryAndSemaphores(bool makePrivate, int port);
 
 #endif							/* IPC_H */
diff --git a/src/include/storage/pg_shmem.h b/src/include/storage/pg_shmem.h
index 0a6519650e..6b1e040251 100644
--- a/src/include/storage/pg_shmem.h
+++ b/src/include/storage/pg_shmem.h
@@ -30,7 +30,7 @@ typedef struct PGShmemHeader	/* standard header for all Postgres shmem */
 {
 	int32		magic;			/* magic # to identify Postgres segments */
 #define PGShmemMagic  679834894
-	pid_t		creatorPID;		/* PID of creating process (set but unread) */
+	pid_t		creatorPID;		/* PID of creating process */
 	Size		totalsize;		/* total size of segment */
 	Size		freeoffset;		/* offset to first free space */
 	dsm_handle	dsm_control;	/* ID of dynamic shared memory control seg */
@@ -64,8 +64,8 @@ extern void PGSharedMemoryReAttach(void);
 extern void PGSharedMemoryNoReAttach(void);
 #endif
 
-extern PGShmemHeader *PGSharedMemoryCreate(Size size, int port,
-					 PGShmemHeader **shim);
+extern PGShmemHeader *PGSharedMemoryCreate(Size size, bool makePrivate,
+					 int port, PGShmemHeader **shim);
 extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
 extern void PGSharedMemoryDetach(void);
 
diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index 0335ab22f2..044b07790c 100644
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -104,8 +104,7 @@ our @EXPORT = qw(
   get_new_node
 );
 
-our ($use_tcp, $test_localhost, $test_pghost, $last_host_assigned,
-	$last_port_assigned, @all_nodes, $died);
+our ($test_localhost, $test_pghost, $last_port_assigned, @all_nodes, $died);
 
 # Windows path to virtual file system root
 
@@ -119,14 +118,13 @@ if ($Config{osname} eq 'msys')
 INIT
 {
 
-	# Set PGHOST for backward compatibility.  This doesn't work for own_host
-	# nodes, so prefer to not rely on this when writing new tests.
-	$use_tcp            = $TestLib::windows_os;
-	$test_localhost     = "127.0.0.1";
-	$last_host_assigned = 1;
-	$test_pghost        = $use_tcp ? $test_localhost : TestLib::tempdir_short;
-	$ENV{PGHOST}        = $test_pghost;
-	$ENV{PGDATABASE}    = 'postgres';
+	# PGHOST is set once and for all through a single series of tests when
+	# this module is loaded.
+	$test_localhost = "127.0.0.1";
+	$test_pghost =
+	  $TestLib::windows_os ? $test_localhost : TestLib::tempdir_short;
+	$ENV{PGHOST}     = $test_pghost;
+	$ENV{PGDATABASE} = 'postgres';
 
 	# Tracking of last port value assigned to accelerate free port lookup.
 	$last_port_assigned = int(rand() * 16384) + 49152;
@@ -157,9 +155,7 @@ sub new
 		_host    => $pghost,
 		_basedir => "$TestLib::tmp_check/t_${testname}_${name}_data",
 		_name    => $name,
-		_logfile_generation => 0,
-		_logfile_base       => "$TestLib::log_path/${testname}_${name}",
-		_logfile            => "$TestLib::log_path/${testname}_${name}.log"
+		_logfile => "$TestLib::log_path/${testname}_${name}.log"
 	};
 
 	bless $self, $class;
@@ -477,9 +473,8 @@ sub init
 		print $conf "max_wal_senders = 0\n";
 	}
 
-	if ($use_tcp)
+	if ($TestLib::windows_os)
 	{
-		print $conf "unix_socket_directories = ''\n";
 		print $conf "listen_addresses = '$host'\n";
 	}
 	else
@@ -541,11 +536,12 @@ sub backup
 {
 	my ($self, $backup_name) = @_;
 	my $backup_path = $self->backup_dir . '/' . $backup_name;
+	my $port        = $self->port;
 	my $name        = $self->name;
 
 	print "# Taking pg_basebackup $backup_name from node \"$name\"\n";
-	TestLib::system_or_bail('pg_basebackup', '-D', $backup_path, '-h',
-		$self->host, '-p', $self->port, '--no-sync');
+	TestLib::system_or_bail('pg_basebackup', '-D', $backup_path, '-p', $port,
+		'--no-sync');
 	print "# Backup finished\n";
 	return;
 }
@@ -657,7 +653,6 @@ sub init_from_backup
 {
 	my ($self, $root_node, $backup_name, %params) = @_;
 	my $backup_path = $root_node->backup_dir . '/' . $backup_name;
-	my $host        = $self->host;
 	my $port        = $self->port;
 	my $node_name   = $self->name;
 	my $root_name   = $root_node->name;
@@ -684,15 +679,6 @@ sub init_from_backup
 		qq(
 port = $port
 ));
-	if ($use_tcp)
-	{
-		$self->append_conf('postgresql.conf', "listen_addresses = '$host'");
-	}
-	else
-	{
-		$self->append_conf('postgresql.conf',
-			"unix_socket_directories = '$host'");
-	}
 	$self->enable_streaming($root_node) if $params{has_streaming};
 	$self->enable_restoring($root_node) if $params{has_restoring};
 	return;
@@ -700,45 +686,17 @@ port = $port
 
 =pod
 
-=item $node->rotate_logfile()
-
-Switch to a new PostgreSQL log file.  This does not alter any running
-PostgreSQL process.  Subsequent method calls, including pg_ctl invocations,
-will use the new name.  Return the new name.
-
-=cut
-
-sub rotate_logfile
-{
-	my ($self) = @_;
-	$self->{_logfile} = sprintf('%s_%d.log',
-		$self->{_logfile_base},
-		++$self->{_logfile_generation});
-	return $self->{_logfile};
-}
-
-=pod
-
-=item $node->start(%params) => success_or_failure
+=item $node->start()
 
 Wrapper for pg_ctl start
 
 Start the node and wait until it is ready to accept connections.
 
-=over
-
-=item fail_ok => 1
-
-By default, failure terminates the entire F<prove> invocation.  If given,
-instead return a true or false value to indicate success or failure.
-
-=back
-
 =cut
 
 sub start
 {
-	my ($self, %params) = @_;
+	my ($self) = @_;
 	my $port   = $self->port;
 	my $pgdata = $self->data_dir;
 	my $name   = $self->name;
@@ -751,34 +709,10 @@ sub start
 	{
 		print "# pg_ctl start failed; logfile:\n";
 		print TestLib::slurp_file($self->logfile);
-		BAIL_OUT("pg_ctl start failed") unless $params{fail_ok};
-		return 0;
+		BAIL_OUT("pg_ctl start failed");
 	}
 
 	$self->_update_pid(1);
-	return 1;
-}
-
-=pod
-
-=item $node->kill9()
-
-Send SIGKILL (signal 9) to the postmaster.
-
-Note: if the node is already known stopped, this does nothing.
-However, if we think it's running and it's not, it's important for
-this to fail.  Otherwise, tests might fail to detect server crashes.
-
-=cut
-
-sub kill9
-{
-	my ($self) = @_;
-	my $name = $self->name;
-	return unless defined $self->{_pid};
-	print "### Killing node \"$name\" using signal 9\n";
-	kill(9, $self->{_pid}) or BAIL_OUT("kill(9, $self->{_pid}) failed");
-	$self->{_pid} = undef;
 	return;
 }
 
@@ -974,7 +908,7 @@ sub _update_pid
 
 =pod
 
-=item PostgresNode->get_new_node(node_name, %params)
+=item PostgresNode->get_new_node(node_name)
 
 Build a new object of class C<PostgresNode> (or of a subclass, if you have
 one), assigning a free port number.  Remembers the node, to prevent its port
@@ -983,22 +917,6 @@ shut down when the test script exits.
 
 You should generally use this instead of C<PostgresNode::new(...)>.
 
-=over
-
-=item port => [1,65535]
-
-By default, this function assigns a port number to each node.  Specify this to
-force a particular port number.  The caller is responsible for evaluating
-potential conflicts and privilege requirements.
-
-=item own_host => 1
-
-By default, all nodes use the same PGHOST value.  If specified, generate a
-PGHOST specific to this node.  This allows multiple nodes to use the same
-port.
-
-=back
-
 For backwards compatibility, it is also exported as a standalone function,
 which can only create objects of class C<PostgresNode>.
 
@@ -1007,11 +925,10 @@ which can only create objects of class C<PostgresNode>.
 sub get_new_node
 {
 	my $class = 'PostgresNode';
-	$class = shift if scalar(@_) % 2 != 1;
-	my ($name, %params) = @_;
-	my $port_is_forced = defined $params{port};
-	my $found          = $port_is_forced;
-	my $port = $port_is_forced ? $params{port} : $last_port_assigned;
+	$class = shift if 1 < scalar @_;
+	my $name  = shift;
+	my $found = 0;
+	my $port  = $last_port_assigned;
 
 	while ($found == 0)
 	{
@@ -1028,15 +945,13 @@ sub get_new_node
 			$found = 0 if ($node->port == $port);
 		}
 
-		# Check to see if anything else is listening on this TCP port.  Accept
-		# only ports available for all possible listen_addresses values, so
-		# the caller can harness this port for the widest range of purposes.
-		# This is *necessary* on Windows, and seems like a good idea on Unixen
-		# as well, even though we don't ask the postmaster to open a TCP port
-		# on Unix.
+		# Check to see if anything else is listening on this TCP port.
+		# This is *necessary* on Windows, and seems like a good idea
+		# on Unixen as well, even though we don't ask the postmaster
+		# to open a TCP port on Unix.
 		if ($found == 1)
 		{
-			my $iaddr = inet_aton('0.0.0.0');
+			my $iaddr = inet_aton($test_localhost);
 			my $paddr = sockaddr_in($port, $iaddr);
 			my $proto = getprotobyname("tcp");
 
@@ -1052,35 +967,16 @@ sub get_new_node
 		}
 	}
 
-	print "# Found port $port\n";
-
-	# Select a host.
-	my $host = $test_pghost;
-	if ($params{own_host})
-	{
-		if ($use_tcp)
-		{
-			# This assumes $use_tcp platforms treat every address in
-			# 127.0.0.1/24, not just 127.0.0.1, as a usable loopback.
-			$last_host_assigned++;
-			$last_host_assigned > 254 and BAIL_OUT("too many own_host nodes");
-			$host = '127.0.0.' . $last_host_assigned;
-		}
-		else
-		{
-			$host = "$test_pghost/$name"; # Assume $name =~ /^[-_a-zA-Z0-9]+$/
-			mkdir $host;
-		}
-	}
+	print "# Found free port $port\n";
 
 	# Lock port number found by creating a new node
-	my $node = $class->new($name, $host, $port);
+	my $node = $class->new($name, $test_pghost, $port);
 
 	# Add node to list of nodes
 	push(@all_nodes, $node);
 
 	# And update port for next time
-	$port_is_forced or $last_port_assigned = $port;
+	$last_port_assigned = $port;
 
 	return $node;
 }
@@ -1471,8 +1367,9 @@ $stderr);
 
 =item $node->command_ok(...)
 
-Runs a shell command like TestLib::command_ok, but with PGHOST and PGPORT set
-so that the command will default to connecting to this PostgresNode.
+Runs a shell command like TestLib::command_ok, but with PGPORT
+set so that the command will default to connecting to this
+PostgresNode.
 
 =cut
 
@@ -1480,7 +1377,6 @@ sub command_ok
 {
 	my $self = shift;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	TestLib::command_ok(@_);
@@ -1491,7 +1387,7 @@ sub command_ok
 
 =item $node->command_fails(...)
 
-TestLib::command_fails with our connection parameters. See command_ok(...)
+TestLib::command_fails with our PGPORT. See command_ok(...)
 
 =cut
 
@@ -1499,7 +1395,6 @@ sub command_fails
 {
 	my $self = shift;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	TestLib::command_fails(@_);
@@ -1510,7 +1405,7 @@ sub command_fails
 
 =item $node->command_like(...)
 
-TestLib::command_like with our connection parameters. See command_ok(...)
+TestLib::command_like with our PGPORT. See command_ok(...)
 
 =cut
 
@@ -1518,7 +1413,6 @@ sub command_like
 {
 	my $self = shift;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	TestLib::command_like(@_);
@@ -1529,8 +1423,7 @@ sub command_like
 
 =item $node->command_checks_all(...)
 
-TestLib::command_checks_all with our connection parameters. See
-command_ok(...)
+TestLib::command_checks_all with our PGPORT. See command_ok(...)
 
 =cut
 
@@ -1538,7 +1431,6 @@ sub command_checks_all
 {
 	my $self = shift;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	TestLib::command_checks_all(@_);
@@ -1561,7 +1453,6 @@ sub issues_sql_like
 {
 	my ($self, $cmd, $expected_sql, $test_name) = @_;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	truncate $self->logfile, 0;
@@ -1576,8 +1467,8 @@ sub issues_sql_like
 
 =item $node->run_log(...)
 
-Runs a shell command like TestLib::run_log, but with connection parameters set
-so that the command will default to connecting to this PostgresNode.
+Runs a shell command like TestLib::run_log, but with PGPORT set so
+that the command will default to connecting to this PostgresNode.
 
 =cut
 
@@ -1585,7 +1476,6 @@ sub run_log
 {
 	my $self = shift;
 
-	local $ENV{PGHOST} = $self->host;
 	local $ENV{PGPORT} = $self->port;
 
 	TestLib::run_log(@_);
diff --git a/src/test/recovery/t/017_shm.pl b/src/test/recovery/t/017_shm.pl
deleted file mode 100644
index 8e85d6b7cd..0000000000
--- a/src/test/recovery/t/017_shm.pl
+++ /dev/null
@@ -1,177 +0,0 @@
-#
-# Tests of pg_shmem.h functions
-#
-use strict;
-use warnings;
-use IPC::Run 'run';
-use PostgresNode;
-use Test::More;
-use TestLib;
-
-plan tests => 6;
-
-my $tempdir = TestLib::tempdir;
-my $port;
-
-# Log "ipcs" diffs on a best-effort basis, swallowing any error.
-my $ipcs_before = "$tempdir/ipcs_before";
-eval { run_log [ 'ipcs', '-am' ], '>', $ipcs_before; };
-
-sub log_ipcs
-{
-	eval { run_log [ 'ipcs', '-am' ], '|', [ 'diff', $ipcs_before, '-' ] };
-	return;
-}
-
-# With Unix sockets, choose a port number such that the port number's first
-# IpcMemoryKey candidate is available.  If multiple copies of this test run
-# concurrently, they will pick different ports.  In the absence of collisions
-# from other shmget() activity, gnat starts with key 0x7d001 (512001), and
-# flea starts with key 0x7d002 (512002).  With TCP, the first get_new_node
-# picks a port number.
-my $port_holder;
-if (!$PostgresNode::use_tcp)
-{
-	for ($port = 512; $port < 612; ++$port)
-	{
-		$port_holder = PostgresNode->get_new_node(
-			"port${port}_holder",
-			port     => $port,
-			own_host => 1);
-		$port_holder->init;
-		$port_holder->start;
-		# Match the AddToDataDirLockFile() call in sysv_shmem.c.  Assume all
-		# systems not using sysv_shmem.c do use TCP.
-		my $shmem_key_line_prefix = sprintf("%9lu ", 1 + $port * 1000);
-		last
-		  if slurp_file($port_holder->data_dir . '/postmaster.pid') =~
-		  /^$shmem_key_line_prefix/m;
-		$port_holder->stop;
-	}
-}
-
-# Node setup.
-sub init_start
-{
-	my $name = shift;
-	my $ret = PostgresNode->get_new_node($name, port => $port, own_host => 1);
-	defined($port) or $port = $ret->port;    # same port for all nodes
-	$ret->init;
-	$ret->start;
-	log_ipcs();
-	return $ret;
-}
-my $gnat = init_start 'gnat';
-my $flea = init_start 'flea';
-
-# Upon postmaster death, postmaster children exit automatically.
-$gnat->kill9;
-log_ipcs();
-$flea->restart;       # flea ignores the shm key gnat abandoned.
-log_ipcs();
-poll_start($gnat);    # gnat recycles its former shm key.
-log_ipcs();
-
-# After clean shutdown, the nodes swap shm keys.
-$gnat->stop;
-$flea->restart;
-log_ipcs();
-$gnat->start;
-log_ipcs();
-
-# Scenarios involving no postmaster.pid, dead postmaster, and a live backend.
-# Use a regress.c function to emulate the responsiveness of a backend working
-# through a CPU-intensive task.
-$gnat->safe_psql('postgres', <<EOSQL);
-CREATE FUNCTION wait_pid(int)
-   RETURNS void
-   AS '$ENV{REGRESS_SHLIB}'
-   LANGUAGE C STRICT;
-EOSQL
-my $slow_query = 'SELECT wait_pid(pg_backend_pid())';
-my ($stdout, $stderr);
-my $slow_client = IPC::Run::start(
-	[
-		'psql', '-X', '-qAt', '-d', $gnat->connstr('postgres'),
-		'-c', $slow_query
-	],
-	'<',
-	\undef,
-	'>',
-	\$stdout,
-	'2>',
-	\$stderr,
-	IPC::Run::timeout(900));    # five times the poll_query_until timeout
-ok( $gnat->poll_query_until(
-		'postgres',
-		"SELECT 1 FROM pg_stat_activity WHERE query = '$slow_query'", '1'),
-	'slow query started');
-my $slow_pid = $gnat->safe_psql('postgres',
-	"SELECT pid FROM pg_stat_activity WHERE query = '$slow_query'");
-$gnat->kill9;
-unlink($gnat->data_dir . '/postmaster.pid');
-$gnat->rotate_logfile;    # on Windows, can't open old log for writing
-log_ipcs();
-# Reject ordinary startup.
-ok(!$gnat->start(fail_ok => 1), 'live query blocks restart');
-like(
-	slurp_file($gnat->logfile),
-	qr/pre-existing shared memory block/,
-	'detected live backend via shared memory');
-# Reject single-user startup.
-my $single_stderr;
-ok( !run_log(
-		[ 'postgres', '--single', '-D', $gnat->data_dir, 'template1' ],
-		'<', \('SELECT 1 + 1'), '2>', \$single_stderr),
-	'live query blocks --single');
-print STDERR $single_stderr;
-like(
-	$single_stderr,
-	qr/pre-existing shared memory block/,
-	'single-user mode detected live backend via shared memory');
-log_ipcs();
-# Fail to reject startup if shm key N has become available and we crash while
-# using key N+1.  This is unwanted, but expected.  Windows is immune, because
-# its GetSharedMemName() use DataDir strings, not numeric keys.
-$flea->stop;    # release first key
-is( $gnat->start(fail_ok => 1),
-	$TestLib::windows_os ? 0 : 1,
-	'key turnover fools only sysv_shmem.c');
-$gnat->stop;     # release first key (no-op on $TestLib::windows_os)
-$flea->start;    # grab first key
-# cleanup
-TestLib::system_log('pg_ctl', 'kill', 'QUIT', $slow_pid);
-$slow_client->finish;    # client has detected backend termination
-log_ipcs();
-poll_start($gnat);       # recycle second key
-
-$gnat->stop;
-$flea->stop;
-$port_holder->stop if $port_holder;
-log_ipcs();
-
-
-# When postmaster children are slow to exit after postmaster death, we may
-# need retries to start a new postmaster.
-sub poll_start
-{
-	my ($node) = @_;
-
-	my $max_attempts = 180 * 10;
-	my $attempts     = 0;
-
-	while ($attempts < $max_attempts)
-	{
-		$node->start(fail_ok => 1) && return 1;
-
-		# Wait 0.1 second before retrying.
-		usleep(100_000);
-
-		$attempts++;
-	}
-
-	# No success within 180 seconds.  Try one last time without fail_ok, which
-	# will BAIL_OUT unless it succeeds.
-	$node->start && return 1;
-	return 0;
-}
diff --git a/src/tools/msvc/vcregress.pl b/src/tools/msvc/vcregress.pl
index 3e3a058794..24ac6a5e4d 100644
--- a/src/tools/msvc/vcregress.pl
+++ b/src/tools/msvc/vcregress.pl
@@ -205,7 +205,6 @@ sub tap_check
 	local %ENV = %ENV;
 	$ENV{PERL5LIB}   = "$topdir/src/test/perl;$ENV{PERL5LIB}";
 	$ENV{PG_REGRESS} = "$topdir/$Config/pg_regress/pg_regress";
-	$ENV{REGRESS_SHLIB} = "$topdir/src/test/regress/regress.dll";
 
 	$ENV{TESTDIR} = "$dir";