dynamic shared memory

diff --git a/configure b/configure
index c685ca3..97d2f68 100755
--- a/configure
+++ b/configure
@@ -8384,6 +8384,180 @@ if test "$ac_res" != no; then
 
 fi
 
+{ $as_echo "$as_me:$LINENO: checking for library containing shm_open" >&5
+$as_echo_n "checking for library containing shm_open... " >&6; }
+if test "${ac_cv_search_shm_open+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  ac_func_search_save_LIBS=$LIBS
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char shm_open ();
+int
+main ()
+{
+return shm_open ();
+  ;
+  return 0;
+}
+_ACEOF
+for ac_lib in '' rt; do
+  if test -z "$ac_lib"; then
+    ac_res="none required"
+  else
+    ac_res=-l$ac_lib
+    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
+  fi
+  rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  ac_cv_search_shm_open=$ac_res
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext
+  if test "${ac_cv_search_shm_open+set}" = set; then
+  break
+fi
+done
+if test "${ac_cv_search_shm_open+set}" = set; then
+  :
+else
+  ac_cv_search_shm_open=no
+fi
+rm conftest.$ac_ext
+LIBS=$ac_func_search_save_LIBS
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_search_shm_open" >&5
+$as_echo "$ac_cv_search_shm_open" >&6; }
+ac_res=$ac_cv_search_shm_open
+if test "$ac_res" != no; then
+  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+
+fi
+
+{ $as_echo "$as_me:$LINENO: checking for library containing shm_unlink" >&5
+$as_echo_n "checking for library containing shm_unlink... " >&6; }
+if test "${ac_cv_search_shm_unlink+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  ac_func_search_save_LIBS=$LIBS
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char shm_unlink ();
+int
+main ()
+{
+return shm_unlink ();
+  ;
+  return 0;
+}
+_ACEOF
+for ac_lib in '' rt; do
+  if test -z "$ac_lib"; then
+    ac_res="none required"
+  else
+    ac_res=-l$ac_lib
+    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
+  fi
+  rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  ac_cv_search_shm_unlink=$ac_res
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext
+  if test "${ac_cv_search_shm_unlink+set}" = set; then
+  break
+fi
+done
+if test "${ac_cv_search_shm_unlink+set}" = set; then
+  :
+else
+  ac_cv_search_shm_unlink=no
+fi
+rm conftest.$ac_ext
+LIBS=$ac_func_search_save_LIBS
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_search_shm_unlink" >&5
+$as_echo "$ac_cv_search_shm_unlink" >&6; }
+ac_res=$ac_cv_search_shm_unlink
+if test "$ac_res" != no; then
+  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+
+fi
+
 # Solaris:
 { $as_echo "$as_me:$LINENO: checking for library containing fdatasync" >&5
 $as_echo_n "checking for library containing fdatasync... " >&6; }
@@ -19763,7 +19937,8 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
 
 
-for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
+
+for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid shm_open sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
 do
 as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { $as_echo "$as_me:$LINENO: checking for $ac_func" >&5
diff --git a/configure.in b/configure.in
index 82771bd..ead0908 100644
--- a/configure.in
+++ b/configure.in
@@ -883,6 +883,8 @@ case $host_os in
 esac
 AC_SEARCH_LIBS(getopt_long, [getopt gnugetopt])
 AC_SEARCH_LIBS(crypt, crypt)
+AC_SEARCH_LIBS(shm_open, rt)
+AC_SEARCH_LIBS(shm_unlink, rt)
 # Solaris:
 AC_SEARCH_LIBS(fdatasync, [rt posix4])
 # Required for thread_test.c on Solaris 2.5:
@@ -1230,7 +1232,7 @@ PGAC_FUNC_GETTIMEOFDAY_1ARG
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
+AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid shm_open sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in
diff --git a/contrib/dsm_demo/Makefile b/contrib/dsm_demo/Makefile
new file mode 100644
index 0000000..dd9ea92
--- /dev/null
+++ b/contrib/dsm_demo/Makefile
@@ -0,0 +1,17 @@
+# contrib/dsm_demo/Makefile
+
+MODULES = dsm_demo
+
+EXTENSION = dsm_demo
+DATA = dsm_demo--1.0.sql
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/dsm_demo
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/dsm_demo/dsm_demo--1.0.sql b/contrib/dsm_demo/dsm_demo--1.0.sql
new file mode 100644
index 0000000..7ad6ab1
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo--1.0.sql
@@ -0,0 +1,14 @@
+/* contrib/dsm_demo/dsm_demo--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION dsm_demo" to load this file. \quit
+
+CREATE FUNCTION dsm_demo_create(pg_catalog.text)
+RETURNS pg_catalog.int8 STRICT
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION dsm_demo_read(pg_catalog.int8)
+RETURNS pg_catalog.text STRICT
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
diff --git a/contrib/dsm_demo/dsm_demo.c b/contrib/dsm_demo/dsm_demo.c
new file mode 100644
index 0000000..0ebbd68
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo.c
@@ -0,0 +1,97 @@
+/* -------------------------------------------------------------------------
+ *
+ * dsm_demo.c
+ *		Dynamic shared memory demonstration.
+ *
+ * Copyright (C) 2013, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		contrib/dsm_demo/dsm_demo.c
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "storage/dsm.h"
+#include "fmgr.h"
+
+PG_MODULE_MAGIC;
+
+void		_PG_init(void);
+Datum		dsm_demo_create(PG_FUNCTION_ARGS);
+Datum		dsm_demo_read(PG_FUNCTION_ARGS);
+
+PG_FUNCTION_INFO_V1(dsm_demo_create);
+PG_FUNCTION_INFO_V1(dsm_demo_read);
+
+#define		DSM_DEMO_MAGIC			0x44454D4F
+
+typedef struct
+{
+	uint32	magic;
+	int32	len;
+	char	data[FLEXIBLE_ARRAY_MEMBER];
+} dsm_demo_payload;
+
+Datum
+dsm_demo_create(PG_FUNCTION_ARGS)
+{
+	text	   *txt = PG_GETARG_TEXT_PP(0);
+	int			len = VARSIZE_ANY(txt);
+	uint64		seglen;
+	dsm_segment *seg;
+	dsm_demo_payload *payload;
+
+	seglen = offsetof(dsm_demo_payload, data) + len;
+	seg = dsm_create(seglen);
+	dsm_keep_mapping(seg);
+
+	payload = dsm_segment_address(seg);
+	payload->magic = DSM_DEMO_MAGIC;
+	payload->len = len;
+	memcpy(payload->data, txt, len);
+
+	PG_RETURN_INT64(dsm_segment_handle(seg));
+}
+
+Datum
+dsm_demo_read(PG_FUNCTION_ARGS)
+{
+	dsm_handle	h = PG_GETARG_INT64(0);
+	dsm_segment *seg;
+	bool		needs_detach = false;
+	text	   *txt = NULL;
+	dsm_demo_payload *payload;
+
+	/*
+	 * We could be called from the same sesion that called dsm_demo_create(),
+	 * so search for an existing mapping.  If we don't find one, attach the
+	 * segment.
+	 */
+	seg = dsm_find_mapping(h);
+	if (seg == NULL)
+	{
+		seg = dsm_attach(h);
+		if (!seg)
+			PG_RETURN_NULL();
+		needs_detach = true;
+	}
+
+	/* Extract data, after checking magic number. */
+	payload = dsm_segment_address(seg);
+	if (payload->magic == DSM_DEMO_MAGIC)
+	{
+		txt = palloc(payload->len);
+		memcpy(txt, payload->data, payload->len);
+	}
+
+	/* Detach, if there was no existing mapping. */
+	if (needs_detach)
+		dsm_detach(seg);
+
+	if (txt == NULL)
+		PG_RETURN_NULL();
+
+	PG_RETURN_TEXT_P(txt);
+}
diff --git a/contrib/dsm_demo/dsm_demo.control b/contrib/dsm_demo/dsm_demo.control
new file mode 100644
index 0000000..4060791
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo.control
@@ -0,0 +1,5 @@
+# dsm_demo extension
+comment = 'Dynamic shared memory demonstration'
+default_version = '1.0'
+module_pathname = 'dsm_demo'
+relocatable = true
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 20e3c32..b604407 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -29,6 +29,7 @@
 #endif
 
 #include "miscadmin.h"
+#include "portability/mem.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 
@@ -36,31 +37,6 @@
 typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
 typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
 
-#define IPCProtection	(0600)	/* access/modify by user only */
-
-#ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
-#define PG_SHMAT_FLAGS			SHM_SHARE_MMU
-#else
-#define PG_SHMAT_FLAGS			0
-#endif
-
-/* Linux prefers MAP_ANONYMOUS, but the flag is called MAP_ANON on other systems. */
-#ifndef MAP_ANONYMOUS
-#define MAP_ANONYMOUS			MAP_ANON
-#endif
-
-/* BSD-derived systems have MAP_HASSEMAPHORE, but it's not present (or needed) on Linux. */
-#ifndef MAP_HASSEMAPHORE
-#define MAP_HASSEMAPHORE		0
-#endif
-
-#define PG_MMAP_FLAGS			(MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
-
-/* Some really old systems don't define MAP_FAILED. */
-#ifndef MAP_FAILED
-#define MAP_FAILED ((void *) -1)
-#endif
-
 
 unsigned long UsedShmemSegID = 0;
 void	   *UsedShmemSegAddr = NULL;
diff --git a/src/backend/storage/ipc/Makefile b/src/backend/storage/ipc/Makefile
index 743f30e..873dd60 100644
--- a/src/backend/storage/ipc/Makefile
+++ b/src/backend/storage/ipc/Makefile
@@ -15,7 +15,7 @@ override CFLAGS+= -fno-inline
 endif
 endif
 
-OBJS = ipc.o ipci.o pmsignal.o procarray.o procsignal.o shmem.o shmqueue.o \
-	sinval.o sinvaladt.o standby.o
+OBJS = dsm_impl.o dsm.o ipc.o ipci.o pmsignal.o procarray.o procsignal.o \
+	shmem.o shmqueue.o sinval.o sinvaladt.o standby.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
new file mode 100644
index 0000000..60c239f
--- /dev/null
+++ b/src/backend/storage/ipc/dsm.c
@@ -0,0 +1,975 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm.c
+ *	  manage dynamic shared memory segments
+ *
+ * This file provides a set of services to make programming with dynamic
+ * shared memory segments more convenient.  Unlike the low-level
+ * facilities provided by dsm_impl.h and dsm_impl.c, mappings and segments
+ * created using this module will be cleaned up automatically.  Mappings
+ * will be removed when the resource owner under which they were created
+ * is cleaned up, unless dsm_keep_mapping() is used, in which case they
+ * have session lifespan.  Segments will be removed when there are no
+ * remaining mappings, or at postmaster shutdown in any case.  After a
+ * hard postmaster crash, remaining segments will be removed, if they
+ * still exist, at the next postmaster startup.
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/ipc/dsm.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#ifndef WIN32
+#include <sys/mman.h>
+#endif
+#include <sys/stat.h>
+
+#include "lib/ilist.h"
+#include "miscadmin.h"
+#include "storage/dsm.h"
+#include "storage/ipc.h"
+#include "storage/lwlock.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+#include "utils/resowner_private.h"
+
+#define PG_DYNSHMEM_STATE_FILE			PG_DYNSHMEM_DIR "/state"
+#define PG_DYNSHMEM_NEW_STATE_FILE		PG_DYNSHMEM_DIR "/state.new"
+#define PG_DYNSHMEM_STATE_BUFSIZ		512
+#define PG_DYNSHMEM_CONTROL_MAGIC		0x9a503d32
+
+/*
+ * There's no point in getting too cheap here, because the minimum allocation
+ * is one OS page, which is probably at least 4KB and could easily be as high
+ * as 64KB.  Each currently sizeof(dsm_control_item), currently 8 bytes.
+ */
+#define PG_DYNSHMEM_FIXED_SLOTS			64
+#define PG_DYNSHMEM_SLOTS_PER_BACKEND	2
+
+#define INVALID_CONTROL_SLOT		((uint32) -1)
+
+struct dsm_segment
+{
+	dlist_node	node;				/* List link in dsm_segment_list. */
+	ResourceOwner resowner;			/* Resource owner. */
+	dsm_handle	handle;				/* Segment name. */
+	uint32		control_slot;		/* Slot in control segment. */
+	void       *impl_private;		/* Implementation-specific private data. */
+	void	   *mapped_address;		/* Mapping address, or NULL if unmapped. */
+	uint64		mapped_size;		/* Size of our mapping. */
+};
+
+typedef struct dsm_control_item
+{
+	dsm_handle	handle;
+	uint32		refcnt;				/* 2+ = active, 1 = moribund, 0 = gone */
+} dsm_control_item;
+
+typedef struct dsm_control_header
+{
+	uint32		magic;
+	uint32		nitems;
+	uint32		maxitems;
+	dsm_control_item	item[FLEXIBLE_ARRAY_MEMBER];
+} dsm_control_header;
+
+static void dsm_cleanup_using_control_segment(void);
+static void dsm_cleanup_for_mmap(void);
+static bool dsm_read_state_file(dsm_handle *h);
+static void dsm_write_state_file(dsm_handle h);
+static void dsm_postmaster_shutdown(int code, Datum arg);
+static void dsm_backend_shutdown(int code, Datum arg);
+static dsm_segment *dsm_create_descriptor(void);
+static bool dsm_control_segment_sane(dsm_control_header *control,
+						 uint64 mapped_size);
+static uint64 dsm_control_bytes_needed(uint32 nitems);
+
+/* Has this backend initialized the dynamic shared memory system yet? */
+static bool dsm_init_done = false;
+
+/*
+ * List of dynamic shared memory segments used by this backend.
+ *
+ * At process exit time, we must decrement the reference count of each
+ * segment we have attached; this list makes it possible to find all such
+ * segments.
+ *
+ * This list should always be empty in the postmaster.  We could probably
+ * allow the postmaster to map dynamic shared memory segments before it
+ * begins to start child processes, provided that each process adjusted
+ * the reference counts for those segments in the control segment at
+ * startup time, but there's no obvious need for such a facility, which
+ * would also be complex to handle in the EXEC_BACKEND case.  Once the
+ * postmaster has begun spawning children, there's an additional problem:
+ * each new mapping would require an update to the control segment,
+ * which requires locking, in which the postmaster must not be involved.
+ */
+static dlist_head dsm_segment_list = DLIST_STATIC_INIT(dsm_segment_list);
+
+/*
+ * Control segment information.
+ *
+ * Unlike ordinary shared memory segments, the control segment is not
+ * reference counted; instead, it lasts for the postmaster's entire
+ * life cycle.  For simplicity, it doesn't have a dsm_segment object either.
+ */
+static dsm_handle dsm_control_handle;
+static dsm_control_header *dsm_control;
+static uint64 dsm_control_mapped_size = 0;
+static void	*dsm_control_impl_private = NULL;
+
+/*
+ * Start up the dynamic shared memory system.
+ *
+ * This is called just once during each cluster lifetime, at postmaster
+ * startup time.
+ */
+void
+dsm_postmaster_startup(void)
+{
+	void	   *dsm_control_address = NULL;
+	uint32		maxitems;
+	uint64		segsize;
+
+	Assert(!IsUnderPostmaster);
+
+	/* If dynamic shared memory is disabled, there's nothing to do. */
+	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
+		return;
+
+	/*
+	 * Check for, and remove, shared memory segments left behind by a dead
+	 * postmaster.  This isn't necessary on Windows, which always removes them
+	 * when the last reference is gone.
+	 */
+	switch (dynamic_shared_memory_type)
+	{
+		case DSM_IMPL_POSIX:
+		case DSM_IMPL_SYSV:
+			dsm_cleanup_using_control_segment();
+			break;
+		case DSM_IMPL_MMAP:
+			dsm_cleanup_for_mmap();
+			break;
+		case DSM_IMPL_WINDOWS:
+			/* Nothing to do. */
+			break;
+		default:
+			elog(ERROR, "unknown dynamic shared memory type: %d",
+				 dynamic_shared_memory_type);
+	}
+
+	/* Determine size for new control segment. */
+	maxitems = PG_DYNSHMEM_FIXED_SLOTS
+		+ PG_DYNSHMEM_SLOTS_PER_BACKEND * MaxBackends;
+	elog(DEBUG2, "dynamic shared memory system will support %lu segments",
+		(unsigned long) maxitems);
+	segsize = dsm_control_bytes_needed(maxitems);
+
+	/* Create new control segment. */
+	for (;;)
+	{
+		Assert(dsm_control_address == NULL);
+		Assert(dsm_control_mapped_size == 0);
+		dsm_control_handle = random();
+		if (dsm_impl_op(DSM_OP_CREATE, dsm_control_handle, segsize,
+						&dsm_control_impl_private, &dsm_control_address,
+						&dsm_control_mapped_size, ERROR))
+			break;
+	}
+	dsm_control = dsm_control_address;
+	on_shmem_exit(dsm_postmaster_shutdown, 0);
+	elog(DEBUG2, "created dynamic shared memory control segment %lu ("
+		UINT64_FORMAT " bytes)", (unsigned long) dsm_control_handle,
+		segsize);
+	dsm_write_state_file(dsm_control_handle);
+
+	/* Initialize control segment. */
+	dsm_control->magic = PG_DYNSHMEM_CONTROL_MAGIC;
+	dsm_control->nitems = 0;
+	dsm_control->maxitems = maxitems;
+}
+
+/*
+ * Determine whether the control segment from the previous postmaster
+ * invocation still exists.  If so, remove the dynamic shared memory
+ * segments to which it refers, and then the control segment itself.
+ */
+static void
+dsm_cleanup_using_control_segment(void)
+{
+	void	   *mapped_address = NULL;
+	void	   *junk_mapped_address = NULL;
+	void	   *impl_private = NULL;
+	void	   *junk_impl_private = NULL;
+	uint64		mapped_size = 0;
+	uint64		junk_mapped_size = 0;
+	uint32		nitems;
+	uint32		i;
+	dsm_handle	old_control_handle;
+	dsm_control_header *old_control;
+
+	/*
+	 * Read the state file.  If it doesn't exist or is empty, there's nothing
+	 * more to do.
+	 */
+	if (!dsm_read_state_file(&old_control_handle))
+		return;
+
+	/*
+	 * Try to attach the segment.  If this fails, it probably just means that
+	 * the operating system has been rebooted and the segment no longer exists,
+	 * or an unrelated proces has used the same shm ID.  So just fall out
+	 * quietly.
+	 */
+	if (!dsm_impl_op(DSM_OP_ATTACH, old_control_handle, 0, &impl_private,
+					 &mapped_address, &mapped_size, DEBUG1))
+		return;
+
+	/*
+	 * We've managed to reattach it, but the contents might not be sane.
+	 * If they aren't, we disregard the segment after all.
+	 */
+	old_control = (dsm_control_header *) mapped_address;
+	if (!dsm_control_segment_sane(old_control, mapped_size))
+	{
+		dsm_impl_op(DSM_OP_DETACH, old_control_handle, 0, &impl_private,
+					&mapped_address, &mapped_size, LOG);
+		return;
+	}
+
+	/*
+	 * OK, the control segment looks basically valid, so we can get use
+	 * it to get a list of segments that need to be removed.
+	 */
+	nitems = old_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		dsm_handle		handle;
+
+		/* If the reference count is 0, the slot is actually unused. */
+		if (old_control->item[i].refcnt == 0)
+			continue;
+
+		/* Log debugging information. */
+		handle = old_control->item[i].handle;
+		elog(DEBUG2, "cleaning up orphaned dynamic shared memory with ID %lu",
+			(unsigned long) handle);
+
+		/* Destroy the referenced segment. */
+		dsm_impl_op(DSM_OP_DESTROY, handle, 0, &junk_impl_private,
+					&junk_mapped_address, &junk_mapped_size, LOG);
+	}
+
+	/* Destroy the old control segment, too. */
+	elog(DEBUG2,
+		 "cleaning up dynamic shared memory control segment with ID %lu",
+		 (unsigned long) old_control_handle);
+	dsm_impl_op(DSM_OP_DESTROY, old_control_handle, 0, &impl_private,
+				&mapped_address, &mapped_size, LOG);
+}
+
+/*
+ * When we're using the mmap shared memory implementation, "shared memory"
+ * segments might even manage to survive an operating system reboot.
+ * But there's no guarantee as to exactly what will survive: some segments
+ * may survive, and others may not, and the contents of some may be out
+ * of date.  In particular, the control segment may be out of date, so we
+ * can't rely on it to figure out what to remove.  However, since we know
+ * what directory contains the files we used as shared memory, we can simply
+ * scan the directory and blow everything away that shouldn't be there.
+ */
+static void
+dsm_cleanup_for_mmap(void)
+{
+	DIR	   *dir;
+	struct dirent *dent;
+
+	/* Open the directory; can't use AllocateDir in postmaster. */
+	if ((dir = opendir(PG_DYNSHMEM_DIR)) == NULL)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open directory \"%s\": %m",
+					PG_DYNSHMEM_DIR)));
+
+	/* Scan for something with a name of the correct format. */
+	while ((dent = readdir(dir)) != NULL)
+	{
+		if (strncmp(dent->d_name, PG_DYNSHMEM_MMAP_FILE_PREFIX,
+				strlen(PG_DYNSHMEM_MMAP_FILE_PREFIX)) == 0)
+		{
+			char buf[MAXPGPATH];
+			snprintf(buf, MAXPGPATH, PG_DYNSHMEM_DIR "/%s", dent->d_name);
+
+			elog(DEBUG2, "removing file \"%s\"", buf);
+
+			/* We found a matching file; so remove it. */
+			if (unlink(buf) != 0)
+			{
+				int		save_errno;
+
+				save_errno = errno;
+				closedir(dir);
+				errno = save_errno;
+
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\": %m", buf)));
+			}
+		}
+	}
+
+	/* Cleanup complete. */
+	closedir(dir);
+}
+
+/*
+ * Read and parse the state file.
+ *
+ * If the state file is empty or the contents are garbled, it probably means
+ * that the operating system rebooted before the data written by the previous
+ * postmaster made it to disk.  In that case, we can just ignore it; any shared
+ * memory from before the reboot should be gone anyway.
+ */
+static bool
+dsm_read_state_file(dsm_handle *h)
+{
+	int			statefd;
+	char		statebuf[PG_DYNSHMEM_STATE_BUFSIZ];
+	int			nbytes = 0;
+	char	   *endptr,
+			   *s;
+	dsm_handle	handle;
+
+	/* Read the state file to get the ID of the old control segment. */
+	statefd = open(PG_DYNSHMEM_STATE_FILE, O_RDONLY, 0);
+	if (statefd < 0)
+	{
+		if (errno == ENOENT)
+			return false;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+	}
+	nbytes = read(statefd, statebuf, PG_DYNSHMEM_STATE_BUFSIZ - 1);
+	if (nbytes < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+	/* make sure buffer is NUL terminated */
+	statebuf[nbytes] = '\0';
+	close(statefd);
+
+	/*
+	 * We expect to find the handle of the old control segment here,
+	 * on a line by itself.
+	 */
+	handle = strtoul(statebuf, &endptr, 10);
+	for (s = endptr; *s == ' ' || *s == '\t'; ++s)
+		;
+	if (*s != '\n' && *s != '\0')
+		return false;
+
+	/* Looks good. */
+	*h = handle;
+	return true;
+}
+
+/*
+ * Write our control segment handle to the state file, so that if the
+ * postmaster is killed without running it's on_shmem_exit hooks, the
+ * next postmaster can clean things up after restart.
+ */
+static void
+dsm_write_state_file(dsm_handle h)
+{
+	int			statefd;
+	char		statebuf[PG_DYNSHMEM_STATE_BUFSIZ];
+	int			nbytes;
+
+	/* Create or truncate the file. */
+	statefd = open(PG_DYNSHMEM_NEW_STATE_FILE, O_RDWR|O_CREAT|O_TRUNC, 0600);
+	if (statefd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+
+	/* Write contents. */
+	snprintf(statebuf, PG_DYNSHMEM_STATE_BUFSIZ, "%lu\n",
+			 (unsigned long) dsm_control_handle);
+	nbytes = strlen(statebuf);
+	if (write(statefd, statebuf, nbytes) != nbytes)
+	{
+		if (errno == 0)
+			errno = ENOSPC;		/* if no error signalled, assume no space */
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+	}
+
+	/* Close file. */
+	close(statefd);
+
+	/*
+	 * Atomically rename file into place, so that no one ever sees a partially
+	 * written state file.
+	 */
+	if (rename(PG_DYNSHMEM_NEW_STATE_FILE, PG_DYNSHMEM_STATE_FILE) < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not rename file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+}
+
+/*
+ * At shutdown time, we iterate over the control segment and remove all
+ * remaining dynamic shared memory segments.  We avoid throwing errors here;
+ * the postmaster is shutting down either way, and this is just non-critical
+ * resource cleanup.
+ */
+static void
+dsm_postmaster_shutdown(int code, Datum arg)
+{
+	uint32		nitems;
+	uint32		i;
+	void	   *dsm_control_address;
+	void	   *junk_mapped_address = NULL;
+	void	   *junk_impl_private = NULL;
+	uint64		junk_mapped_size = 0;
+
+	/* If dynamic shared memory is disabled, there's nothing to do. */
+	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
+		return;
+
+	/*
+	 * If some other backend exited uncleanly, it might have corrupted the
+	 * control segment while it was dying.  In that case, we warn and ignore
+	 * the contents of the control segment.  This may end up leaving behind
+	 * stray shared memory segments, but there's not much we can do about
+	 * that if the metadata is gone.
+	 */
+	nitems = dsm_control->nitems;
+	if (!dsm_control_segment_sane(dsm_control, dsm_control_mapped_size))
+	{
+		ereport(LOG,
+				(errmsg("dynamic shared memory control segment is corrupt")));
+		return;
+	}
+
+	/* Remove any remaining segments. */
+	for (i = 0; i < nitems; ++i)
+	{
+		dsm_handle	handle;
+
+		/* If the reference count is 0, the slot is actually unused. */
+		if (dsm_control->item[i].refcnt == 0)
+			continue;
+
+		/* Log debugging information. */
+		handle = dsm_control->item[i].handle;
+		elog(DEBUG2, "cleaning up orphaned dynamic shared memory with ID %lu",
+			(unsigned long) handle);
+
+		/* Destroy the segment. */
+		dsm_impl_op(DSM_OP_DESTROY, handle, 0, &junk_impl_private,
+					&junk_mapped_address, &junk_mapped_size, LOG);
+	}
+
+	/* Remove the control segment itself. */
+	elog(DEBUG2,
+		 "cleaning up dynamic shared memory control segment with ID %lu",
+		 (unsigned long) dsm_control_handle);
+	dsm_control_address = dsm_control;
+	dsm_impl_op(DSM_OP_DESTROY, dsm_control_handle, 0,
+				&dsm_control_impl_private, &dsm_control_address,
+				&dsm_control_mapped_size, LOG);
+	dsm_control = dsm_control_address;
+
+	/* And, finally, remove the state file. */
+	if (unlink(PG_DYNSHMEM_STATE_FILE) < 0)
+		ereport(LOG,
+				(errcode_for_file_access(),
+				 errmsg("could not unlink file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+}
+
+/*
+ * Prepare this backend for dynamic shared memory usage.  Under EXEC_BACKEND,
+ * we must reread the state file and map the control segment; in other cases,
+ * we'll have inherited the postmaster's mapping and global variables.
+ */
+static void
+dsm_backend_startup(void)
+{
+	/* If dynamic shared memory is disabled, reject this. */
+	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("dynamic shared memory is disabled"),
+				 errhint("Set dynamic_shared_memory_type to a value other than \"one\".")));
+
+#ifdef EXEC_BACKEND
+	{
+		dsm_handle	control_handle;
+		void	   *control_address = NULL;
+
+		/* Read the control segment information from the state file. */
+		if (!dsm_read_state_file(&control_handle))
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("could not parse dynamic shared memory state file")));
+
+		/* Attach control segment. */
+		dsm_impl_op(DSM_OP_ATTACH, control_handle, 0,
+					&dsm_control_impl_private, &control_address,
+					&dsm_control_mapped_size, ERROR);
+		dsm_control_handle = control_handle;
+		dsm_control = control_address;
+		/* If control segment doesn't look sane, something is badly wrong. */
+		if (!dsm_control_segment_sane(dsm_control, dsm_control_mapped_size))
+		{
+			dsm_impl_op(DSM_OP_DETACH, control_handle, 0,
+					    &dsm_control_impl_private, &control_address,
+						&dsm_control_mapped_size, WARNING);
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("dynamic shared memory control segment is not valid")));
+		}
+	}
+#endif
+
+	/* Arrange to detach segments on exit. */
+	on_shmem_exit(dsm_backend_shutdown, 0);
+
+	dsm_init_done = true;
+}
+
+/*
+ * Create a new dynamic shared memory segment.
+ */
+dsm_segment *
+dsm_create(uint64 size)
+{
+	dsm_segment	   *seg = dsm_create_descriptor();
+	uint32			i;
+	uint32			nitems;
+
+	/* Unsafe in postmaster (and pointless in a stand-alone backend). */
+	Assert(IsUnderPostmaster);
+
+	if (!dsm_init_done)
+		dsm_backend_startup();
+
+	/* Loop until we find an unused segment identifier. */
+	for (;;)
+	{
+		Assert(seg->mapped_address == NULL && seg->mapped_size == 0);
+		seg->handle = random();
+		if (dsm_impl_op(DSM_OP_CREATE, seg->handle, size, &seg->impl_private,
+						&seg->mapped_address, &seg->mapped_size, ERROR))
+			break;
+	}
+
+	/* Lock the control segment so we can register the new segment. */
+	LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+
+	/* Search the control segment for an unused slot. */
+	nitems = dsm_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		if (dsm_control->item[i].refcnt == 0)
+		{
+			dsm_control->item[i].handle = seg->handle;
+			/* refcnt of 1 triggers destruction, so start at 2 */
+			dsm_control->item[i].refcnt = 2;
+			seg->control_slot = i;
+			LWLockRelease(DynamicSharedMemoryControlLock);
+			return seg;
+		}
+	}
+
+	/* Verify that we can support an additional mapping. */
+	if (nitems >= dsm_control->maxitems)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+				 errmsg("too many dynamic shared memory segments")));
+
+	/* Enter the handle into a new array slot. */
+	dsm_control->item[nitems].handle = seg->handle;
+	/* refcnt of 1 triggers destruction, so start at 2 */
+	dsm_control->item[nitems].refcnt = 2;
+	seg->control_slot = nitems;
+	dsm_control->nitems++;
+	LWLockRelease(DynamicSharedMemoryControlLock);
+
+	return seg;
+}
+
+/*
+ * Attach a dynamic shared memory segment.
+ *
+ * See comments for dsm_segment_handle() for an explanation of how this
+ * is intended to be used.
+ *
+ * This function will return NULL if the segment isn't known to the system.
+ * This can happen if we're asked to attach the segment, but then everyone
+ * else detaches it (causing it to be destroyed) before we get around to
+ * attaching it.
+ */
+dsm_segment *
+dsm_attach(dsm_handle h)
+{
+	dsm_segment	   *seg;
+	dlist_iter		iter;
+	uint32			i;
+	uint32			nitems;
+
+	/* Unsafe in postmaster (and pointless in a stand-alone backend). */
+	Assert(IsUnderPostmaster);
+
+	if (!dsm_init_done)
+		dsm_backend_startup();
+
+	/*
+	 * Since this is just a debugging cross-check, we could leave it out
+	 * altogether, or include it only in assert-enabled builds.  But since
+	 * the list of attached segments should normally be very short, let's
+	 * include it always for right now.
+	 *
+	 * If you're hitting this error, you probably want to attempt to
+	 * find an existing mapping via dsm_find_mapping() before calling
+	 * dsm_attach() to create a new one.
+	 */
+	dlist_foreach(iter, &dsm_segment_list)
+	{
+		seg = dlist_container(dsm_segment, node, iter.cur);
+		if (seg->handle == h)
+			elog(ERROR, "can't attach the same segment more than once");
+	}
+
+	/* Create a new segment descriptor. */
+	seg = dsm_create_descriptor();
+	seg->handle = h;
+
+	/* Bump reference count for this segment in shared memory. */
+	LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+	nitems = dsm_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		/* If the reference count is 0, the slot is actually unused. */
+		if (dsm_control->item[i].refcnt == 0)
+			continue;
+
+		/*
+		 * If the reference count is 1, the slot is still in use, but the
+		 * segment is in the process of going away.  Treat that as if we
+		 * didn't find a match.
+		 */
+		if (dsm_control->item[i].refcnt == 1)
+			break;
+
+		/* Otherwise, if the descriptor matches, we've found a match. */
+		if (dsm_control->item[i].handle == seg->handle)
+		{
+			dsm_control->item[i].refcnt++;
+			seg->control_slot = i;
+			break;
+		}
+	}
+	LWLockRelease(DynamicSharedMemoryControlLock);
+
+	/*
+	 * If we didn't find the handle we're looking for in the control
+	 * segment, it probably means that everyone else who had it mapped,
+	 * including the original creator, died before we got to this point.
+	 * It's up to the caller to decide what to do about that.
+	 */
+	if (seg->control_slot == INVALID_CONTROL_SLOT)
+	{
+		dsm_detach(seg);
+		return NULL;
+	}
+
+	/* Here's where we actually try to map the segment. */
+	dsm_impl_op(DSM_OP_ATTACH, seg->handle, 0, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+
+	return seg;
+}
+
+/*
+ * At backend shutdown time, detach any segments that are still attached.
+ */
+static void
+dsm_backend_shutdown(int code, Datum arg)
+{
+	while (!dlist_is_empty(&dsm_segment_list))
+	{
+		dsm_segment	   *seg;
+
+		seg = dlist_head_element(dsm_segment, node, &dsm_segment_list);
+		dsm_detach(seg);
+	}
+}
+
+/*
+ * Resize an existing shared memory segment.
+ *
+ * This may cause the shared memory segment to be remapped at a different
+ * address.  For the caller's convenience, we return the mapped address.
+ */
+void *
+dsm_resize(dsm_segment *seg, uint64 size)
+{
+	Assert(seg->control_slot != INVALID_CONTROL_SLOT);
+	dsm_impl_op(DSM_OP_RESIZE, seg->handle, size, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+	return seg->mapped_address;
+}
+
+/*
+ * Remap an existing shared memory segment.
+ *
+ * This is intended to be used when some other process has extended the
+ * mapping using dsm_resize(), but we've still only got the initial
+ * portion mapped.  Since this might change the address at which the
+ * segment is mapped, we return the new mapped address.
+ */
+void *
+dsm_remap(dsm_segment *seg)
+{
+	if (!dsm_impl_can_resize())
+		return seg->mapped_address;
+
+	dsm_impl_op(DSM_OP_ATTACH, seg->handle, 0, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+
+	return seg->mapped_address;
+}
+
+/*
+ * Detach from a shared memory segment, destroying the segment if we
+ * remove the last reference.
+ *
+ * This function should never fail.  It will often be invoked when aborting
+ * a transaction, and a further error won't serve any purpose.  It's not a
+ * complete disaster if we fail to unmap or destroy the segment; it means a
+ * resource leak, but that doesn't necessarily preclude further operations.
+ */
+void
+dsm_detach(dsm_segment *seg)
+{
+	/*
+	 * Try to remove the mapping, if one exists.  Normally, there will be,
+	 * but maybe not, if we failed partway through a create or attach
+	 * operation.  We remove the mapping before decrementing the reference
+	 * count so that the process that sees a zero reference count can be
+	 * certain that no remaining mappings exist.  Even if this fails, we
+	 * pretend that it works, because retrying is likely to fail in the
+	 * same way.
+	 */
+	if (seg->mapped_address != NULL)
+	{
+		dsm_impl_op(DSM_OP_DETACH, seg->handle, 0, &seg->impl_private,
+					&seg->mapped_address, &seg->mapped_size, WARNING);
+		seg->impl_private = NULL;
+		seg->mapped_address = NULL;
+		seg->mapped_size = 0;
+	}
+
+	/* Reduce reference count, if we previously increased it. */
+	if (seg->control_slot != INVALID_CONTROL_SLOT)
+	{
+		uint32	refcnt;
+		uint32	control_slot = seg->control_slot;
+
+		LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+		Assert(dsm_control->item[control_slot].handle == seg->handle);
+		Assert(dsm_control->item[control_slot].refcnt > 1);
+		refcnt = --dsm_control->item[control_slot].refcnt;
+		seg->control_slot = INVALID_CONTROL_SLOT;
+		LWLockRelease(DynamicSharedMemoryControlLock);
+
+		/* If new reference count is 1, try to destroy the segment. */
+		if (refcnt == 1)
+		{
+			/*
+			 * If we fail to destroy the segment here, or are killed before
+			 * we finish doing so, the reference count will remain at 1, which
+			 * will mean that nobody else can attach to the segment.  At
+			 * postmaster shutdown time, or when a new postmaster is started
+			 * after a hard kill, another attempt will be made to remove the
+			 * segment.
+			 *
+			 * The main case we're worried about here is being killed by
+			 * a signal before we can finish removing the segment.  In that
+			 * case, it's important to be sure that the segment still gets
+			 * removed. If we actually fail to remove the segment for some
+			 * other reason, the postmaster may not have any better luck than
+			 * we did.  There's not much we can do about that, though.
+			 */
+			if (dsm_impl_op(DSM_OP_DESTROY, seg->handle, 0, &seg->impl_private,
+							&seg->mapped_address, &seg->mapped_size, WARNING))
+			{
+				LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+				Assert(dsm_control->item[control_slot].handle == seg->handle);
+				Assert(dsm_control->item[control_slot].refcnt == 1);
+				dsm_control->item[control_slot].refcnt = 0;
+				LWLockRelease(DynamicSharedMemoryControlLock);
+			}
+		}
+	}
+
+	/* Clean up our remaining backend-private data structures. */
+	if (seg->resowner != NULL)
+		ResourceOwnerForgetDSM(seg->resowner, seg);
+	dlist_delete(&seg->node);
+	pfree(seg);
+}
+
+/*
+ * Keep a dynamic shared memory mapping until end of session.
+ *
+ * By default, mappings are owned by the current resource owner, which
+ * typically means they stick around for the duration of the current query
+ * only.
+ */
+void
+dsm_keep_mapping(dsm_segment *seg)
+{
+	if (seg->resowner != NULL)
+	{
+		ResourceOwnerForgetDSM(seg->resowner, seg);
+		seg->resowner = NULL;
+	}
+}
+
+/*
+ * Find an existing mapping for a shared memory segment, if there is one.
+ */
+dsm_segment *
+dsm_find_mapping(dsm_handle h)
+{
+	dlist_iter		iter;
+	dsm_segment	   *seg;
+
+	dlist_foreach(iter, &dsm_segment_list)
+	{
+		seg = dlist_container(dsm_segment, node, iter.cur);
+		if (seg->handle == h)
+			return seg;
+	}
+
+	return NULL;
+}
+
+/*
+ * Get the address at which a dynamic shared memory segment is mapped.
+ */
+void *
+dsm_segment_address(dsm_segment *seg)
+{
+	Assert(seg->mapped_address != NULL);
+	return seg->mapped_address;
+}
+
+/*
+ * Get the size of a mapping.
+ */
+uint64
+dsm_segment_map_length(dsm_segment *seg)
+{
+	Assert(seg->mapped_address != NULL);
+	return seg->mapped_size;
+}
+
+/*
+ * Get a handle for a mapping.
+ *
+ * To establish communication via dynamic shared memory between two backends,
+ * one of them should first call dsm_create() to establish a new shared
+ * memory mapping.  That process should then call dsm_segment_handle() to
+ * obtain a handle for the mapping, and pass that handle to the
+ * coordinating backend via some means (e.g. bgw_main_arg, or via the
+ * main shared memory segment).  The recipient, once in position of the
+ * handle, should call dsm_attach().
+ */
+dsm_handle
+dsm_segment_handle(dsm_segment *seg)
+{
+	return seg->handle;
+}
+
+/*
+ * Create a segment descriptor.
+ */
+static dsm_segment *
+dsm_create_descriptor(void)
+{
+	dsm_segment	   *seg;
+
+	ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
+
+	seg = MemoryContextAlloc(TopMemoryContext, sizeof(dsm_segment));
+	dlist_push_head(&dsm_segment_list, &seg->node);
+
+	/* seg->handle must be initialized by the caller */
+	seg->control_slot = INVALID_CONTROL_SLOT;
+	seg->impl_private = NULL;
+	seg->mapped_address = NULL;
+	seg->mapped_size = 0;
+
+	seg->resowner = CurrentResourceOwner;
+	ResourceOwnerRememberDSM(CurrentResourceOwner, seg);
+
+	return seg;
+}
+
+/*
+ * Sanity check a control segment.
+ *
+ * The goal here isn't to detect everything that could possibly be wrong with
+ * the control segment; there's not enough information for that.  Rather, the
+ * goal is to make sure that someone can iterate over the items in the segment
+ * without overrunning the end of the mapping and crashing.  We also check
+ * the magic number since, if that's messed up, this may not even be one of
+ * our segments at all.
+ */
+static bool
+dsm_control_segment_sane(dsm_control_header *control, uint64 mapped_size)
+{
+	if (mapped_size < offsetof(dsm_control_header, item))
+		return false;			/* Mapped size too short to read header. */
+	if (control->magic != PG_DYNSHMEM_CONTROL_MAGIC)
+		return false;			/* Magic number doesn't match. */
+	if (dsm_control_bytes_needed(control->maxitems) > mapped_size)
+		return false;			/* Max item count won't fit in map. */
+	if (control->nitems > control->maxitems)
+		return false;			/* Overfull. */
+	return true;
+}
+
+/*
+ * Compute the number of control-segment bytes needed to store a given
+ * number of items.
+ */
+static uint64
+dsm_control_bytes_needed(uint32 nitems)
+{
+	return offsetof(dsm_control_header, item)
+		+ sizeof(dsm_control_item) * (uint64) nitems;
+}
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
new file mode 100644
index 0000000..8005fd9
--- /dev/null
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -0,0 +1,986 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm_impl.c
+ *	  manage dynamic shared memory segments
+ *
+ * This file provides low-level APIs for creating and destroying shared
+ * memory segments using several different possible techniques.  We refer
+ * to these segments as dynamic because they can be created, altered, and
+ * destroyed at any point during the server life cycle.  This is unlike
+ * the main shared memory segment, of which there is always exactly one
+ * and which is always mapped at a fixed address in every PostgreSQL
+ * background process.
+ *
+ * Because not all systems provide the same primitives in this area, nor
+ * do all primitives behave the saem way on all systems, we provide
+ * several implementations of this facility.  Many systems implement
+ * POSIX shared memory (shm_open etc.), which is well-suited to our needs
+ * in this area, with the exception that shared memory identifiers live
+ * in a flat system-wide namespace, raising the uncomfortable prospect of
+ * name collisions with other processes (including other copies of
+ * PostgreSQL) running on the same system.  Some systems only support
+ * the older System V shared memory interface (shmget etc.) which is
+ * also usable; however, the default allocation limits are often quite
+ * small, and the namespace is even more restricted.
+ *
+ * We also provide an mmap-based shared memory implementation.  This may
+ * be useful on systems that provide shared memory via a special-purpose
+ * filesystem; by opting for this implementation, the user can even
+ * control precisely where their shared memory segments are placed.  It
+ * can also be used as a fallback for systems where shm_open and shmget
+ * are not available or can't be used for some reason.  Of course,
+ * mapping a file residing on an actual spinning disk is a fairly poor
+ * approximation for shared memory because writeback may hurt performance
+ * substantially, but there should be few systems where we must make do
+ * with such poor tools.
+ *
+ * As ever, Windows requires its own implemetation.
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/ipc/dsm.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#ifndef WIN32
+#include <sys/mman.h>
+#endif
+#include <sys/stat.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SHM_H
+#include <sys/shm.h>
+#endif
+
+#include "portability/mem.h"
+#include "storage/dsm_impl.h"
+#include "storage/fd.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+
+#ifdef USE_DSM_POSIX
+static bool dsm_impl_posix(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address,
+			   uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_SYSV
+static bool dsm_impl_sysv(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address,
+			   uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_WINDOWS
+static bool dsm_impl_windows(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address,
+			  uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_MMAP
+static bool dsm_impl_mmap(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address,
+			  uint64 *mapped_size, int elevel);
+#endif
+static int errcode_for_dynamic_shared_memory(void);
+
+const struct config_enum_entry dynamic_shared_memory_options[] = {
+#ifdef USE_DSM_POSIX
+	{ "posix", DSM_IMPL_POSIX, false},
+#endif
+#ifdef USE_DSM_SYSV
+	{ "sysv", DSM_IMPL_SYSV, false},
+#endif
+#ifdef USE_DSM_WINDOWS
+	{ "windows", DSM_IMPL_WINDOWS, false},
+#endif
+#ifdef USE_DSM_MMAP
+	{ "mmap", DSM_IMPL_MMAP, false},
+#endif
+	{ "none", DSM_IMPL_NONE, false},
+	{NULL, 0, false}
+};
+
+/* Implementation selector. */
+int dynamic_shared_memory_type;
+
+/* Size of buffer to be used for zero-filling. */
+#define ZBUFFER_SIZE				8192
+
+/*------
+ * Perform a low-level shared memory operation in a platform-specific way,
+ * as dictated by the selected implementation.  Each implementation is
+ * required to implement the following primitives.
+ *
+ * DSM_OP_CREATE.  Create a segment whose size is the request_size and
+ * map it.
+ *
+ * DSM_OP_ATTACH.  Map the segment, whose size must be the request_size.
+ * The segment may already be mapped; any existing mapping should be removed
+ * before creating a new one.
+ *
+ * DSM_OP_DETACH.  Unmap the segment.
+ *
+ * DSM_OP_RESIZE.  Resize the segment to the given request_size and
+ * remap the segment at that new size.
+ *
+ * DSM_OP_DESTROY.  Unmap the segment, if it is mapped.  Destroy the
+ * segment.
+ *
+ * Arguments:
+ *   op: The operation to be performed.
+ *   handle: The handle of an existing object, or for DSM_OP_CREATE, the
+ *     a new handle the caller wants created.
+ *   request_size: For DSM_OP_CREATE, the requested size.  For DSM_OP_RESIZE,
+ *     the new size.  Otherwise, 0.
+ *   impl_private: Private, implementation-specific data.  Will be a pointer
+ *     to NULL for the first operation on a shared memory segment within this
+ *     backend; thereafter, it will point to the value to which it was set
+ *     on the previous call.
+ *   mapped_address: Pointer to start of current mapping; pointer to NULL
+ *     if none.  Updated with new mapping address.
+ *   mapped_size: Pointer to size of current mapping; pointer to 0 if none.
+ *     Updated with new mapped size.
+ *   elevel: Level at which to log errors.
+ *
+ * Return value: true on success, false on failure.  When false is returned,
+ * a message should first be logged at the specified elevel, except in the
+ * case where DSM_OP_CREATE experiences a name collision, which should
+ * silently return false.
+ *-----
+ */
+bool
+dsm_impl_op(dsm_op op, dsm_handle handle, uint64 request_size,
+			void **impl_private, void **mapped_address, uint64 *mapped_size,
+			int elevel)
+{
+	Assert(op == DSM_OP_CREATE || op == DSM_OP_RESIZE || request_size == 0);
+	Assert((op != DSM_OP_CREATE && op != DSM_OP_ATTACH) ||
+			(*mapped_address == NULL && *mapped_size == 0));
+
+	if (request_size > (size_t) -1)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("requested shared memory size overflows size_t")));
+
+	switch (dynamic_shared_memory_type)
+	{
+#ifdef USE_DSM_POSIX
+		case DSM_IMPL_POSIX:
+			return dsm_impl_posix(op, handle, request_size, impl_private,
+								  mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_SYSV
+		case DSM_IMPL_SYSV:
+			return dsm_impl_sysv(op, handle, request_size, impl_private,
+								 mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_WINDOWS
+		case DSM_IMPL_WINDOWS:
+			return dsm_impl_windows(op, handle, request_size, impl_private,
+									mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_MMAP
+		case DSM_IMPL_MMAP:
+			return dsm_impl_mmap(op, handle, request_size, impl_private,
+								 mapped_address, mapped_size, elevel);
+#endif
+	}
+	elog(ERROR, "unexpected dynamic shared memory type: %d",
+		 dynamic_shared_memory_type);
+}
+
+/*
+ * Does the current dynamic shared memory implementation support resizing
+ * segments?  (The answer here could be platform-dependent in the future,
+ * since AIX allows shmctl(shmid, SHM_RESIZE, &buffer), though you apparently
+ * can't resize segments to anything larger than 256MB that way.  For now,
+ * we keep it simple.)
+ */
+bool
+dsm_impl_can_resize(void)
+{
+	switch (dynamic_shared_memory_type)
+	{
+		case DSM_IMPL_NONE:
+			return false;
+		case DSM_IMPL_SYSV:
+			return false;
+		case DSM_IMPL_WINDOWS:
+			return false;
+		default:
+			return true;
+	}
+}
+
+#ifdef USE_DSM_POSIX
+/*
+ * Operating system primitives to support POSIX shared memory.
+ *
+ * POSIX shared memory segments are created and attached using shm_open()
+ * and shm_unlink(); other operations, such as sizing or mapping the
+ * segment, are performed as if the shared memory segments were files.
+ *
+ * Indeed, on some platforms, they may be implemented that way.  While
+ * POSIX shared memory segments seem intended to exist in a flat namespace,
+ * some operating systems may implement them as files, even going so far
+ * to treat a request for /xyz as a request to create a file by that name
+ * in the root directory.  Users of such broken platforms should select
+ * a different shared memory implementation.
+ */
+static bool
+dsm_impl_posix(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address, uint64 *mapped_size,
+			   int elevel)
+{
+	char	name[64];
+	int		flags;
+	int		fd;
+	char   *address;
+
+	snprintf(name, 64, "/PostgreSQL.%lu", (unsigned long) handle);
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& munmap(*mapped_address, *mapped_size) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && shm_unlink(name) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/*
+	 * Create new segment or open an existing one for attach or resize.
+	 *
+	 * Even though we're not going through fd.c, we should be safe against
+	 * running out of file descriptors, because of NUM_RESERVED_FDS.  We're
+	 * only opening one extra descriptor here, and we'll close it before
+	 * returning.
+	 */
+	flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
+	if ((fd = shm_open(name, flags, 0600)) == -1)
+	{
+		if (errno != EEXIST)
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * If we're attaching the segment, determine the current size; if we are
+	 * creating or resizing the segment, set the size to the requested value.
+	 */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct stat st;
+
+		if (fstat(fd, &st) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			close(fd);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = st.st_size;
+	}
+	else if (*mapped_size != request_size && ftruncate(fd, request_size))
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+					name, request_size)));
+		return false;
+	}
+
+	/*
+	 * If we're reattaching or resizing, we must remove any existing mapping,
+	 * unless we've already got the right thing mapped.
+	 */
+	if (*mapped_address != NULL)
+	{
+		if (*mapped_size == request_size)
+			return true;
+		if (munmap(*mapped_address, *mapped_size) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			close(fd);
+			if (op == DSM_OP_CREATE)
+				shm_unlink(name);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+	}
+
+	/* Map it. */
+	address = mmap(NULL, request_size, PROT_READ|PROT_WRITE,
+				   MAP_SHARED|MAP_HASSEMAPHORE, fd, 0);
+	if (address == MAP_FAILED)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+	close(fd);
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_SYSV
+/*
+ * Operating system primitives to support System V shared memory.
+ *
+ * System V shared memory segments are manipulated using shmget(), shmat(),
+ * shmdt(), and shmctl().  There's no portable way to resize such
+ * segments.  As the default allocation limits for System V shared memory
+ * are usually quite low, the POSIX facilities may be preferable; but
+ * those are not supported everywhere.
+ */
+static bool
+dsm_impl_sysv(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address, uint64 *mapped_size,
+			  int elevel)
+{
+	key_t	key;
+	int		ident;
+	char   *address;
+	char	name[64];
+	int	   *ident_cache;
+
+	/* Resize is not supported for System V shared memory. */
+	if (op == DSM_OP_RESIZE)
+	{
+		elog(elevel, "System V shared memory segments cannot be resized");
+		return false;
+	}
+
+	/* Since resize isn't supported, reattach is a no-op. */
+	if (op == DSM_OP_ATTACH && *mapped_address != NULL)
+		return true;
+
+	/*
+	 * POSIX shared memory and mmap-based shared memory identify segments
+	 * with names.  To avoid needless error message variation, we use the
+	 * handle as the name.
+	 */
+	snprintf(name, 64, "%lu", (unsigned long) handle);
+
+	/*
+	 * The System V shared memory namespace is very restricted; names are
+	 * of type key_t, which is expected to be some sort of integer data type,
+	 * but not necessarily the same one as dsm_handle.  Since we use
+	 * dsm_handle to identify shared memory segments across processes, this
+	 * might seem like a problem, but it's really not.  If dsm_handle is
+	 * bigger than key_t, the cast below might truncate away some bits from
+	 * the handle the user-provided, but it'll truncate exactly the same bits
+	 * away in exactly the same fashion every time we use that handle, which
+	 * is all that really matters.  Conversely, if dsm_handle is smaller than
+	 * key_t, we won't use the full range of available key space, but that's
+	 * no big deal either.
+	 *
+	 * We do make sure that the key isn't negative, because that might not
+	 * be portable.
+	 */
+	key = (key_t) handle;
+	if (key < 1)		/* avoid compiler warning if type is unsigned */
+		key = -key;
+
+	/*
+	 * There's one special key, IPC_PRIVATE, which can't be used.  If we end
+	 * up with that value by chance during a create operation, just pretend
+	 * it already exists, so that caller will retry.  If we run into it
+	 * anywhere else, the caller has passed a handle that doesn't correspond
+	 * to anything we ever created, which should not happen.
+	 */
+	if (key == IPC_PRIVATE)
+	{
+		if (op != DSM_OP_CREATE)
+			elog(elevel, "System V shared memory key may not be IPC_PRIVATE");
+		errno = EEXIST;
+		return false;
+	}
+
+	/*
+	 * Before we can do anything with a shared memory segment, we have to
+	 * map the shared memory key to a shared memory identifier using shmget().
+	 * To avoid repeated lookups, we store the key using impl_private.
+	 */
+	if (*impl_private != NULL)
+	{
+		ident_cache = *impl_private;
+		ident = *ident_cache;
+	}
+	else
+	{
+		int		flags = IPCProtection;
+		size_t	segsize;
+
+		/*
+		 * Allocate the memory BEFORE acquiring the resource, so that we don't
+		 * leak the resource if memory allocation fails.
+		 */
+		ident_cache = MemoryContextAlloc(TopMemoryContext, sizeof(int));
+
+		/*
+		 * When using shmget to find an existing segment, we must pass the
+		 * size as 0.  Passing a non-zero size which is greater than the
+		 * actual size will result in EINVAL.
+		 */
+		segsize = 0;
+
+		if (op == DSM_OP_CREATE)
+		{
+			flags |= IPC_CREAT | IPC_EXCL;
+			segsize = request_size;
+		}
+
+		if ((ident = shmget(key, segsize, flags)) == -1)
+		{
+			if (errno != EEXIST)
+			{
+				int		save_errno = errno;
+				pfree(ident_cache);
+				errno = save_errno;
+				ereport(elevel,
+						(errcode_for_dynamic_shared_memory(),
+						 errmsg("could not get shared memory segment: %m")));
+			}
+			return false;
+		}
+
+		*ident_cache = ident;
+		*impl_private = ident_cache;
+	}
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		pfree(ident_cache);
+		*impl_private = NULL;
+		if (*mapped_address != NULL && shmdt(*mapped_address) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && shmctl(ident, IPC_RMID, NULL) < 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/* If we're attaching it, we must use IPC_STAT to determine the size. */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct shmid_ds shm;
+
+		if (shmctl(ident, IPC_STAT, &shm) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			if (op == DSM_OP_CREATE)
+				shmctl(ident, IPC_RMID, NULL);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = shm.shm_segsz;
+	}
+
+	/* Map it. */
+	address = shmat(ident, NULL, PG_SHMAT_FLAGS);
+	if (address == (void *) -1)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		if (op == DSM_OP_CREATE)
+			shmctl(ident, IPC_RMID, NULL);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_WINDOWS
+/*
+ * Operating system primitives to support Windows shared memory.
+ *
+ * Windows shared memory implementation is done using file mapping
+ * which can be backed by either physical file or system paging file.
+ * Current implementation uses system paging file as other effects
+ * like performance are not clear for physical file and it is used in similar
+ * way for main shared memory in windows.
+ *
+ * A memory mapping object is a kernel object - they always get deleted when
+ * the last reference to them goes away, either explicitly via a CloseHandle or
+ * when the process containing the reference exits.
+ */
+static bool
+dsm_impl_windows(dsm_op op, dsm_handle handle, uint64 request_size,
+				 void **impl_private, void **mapped_address,
+				 uint64 *mapped_size, int elevel)
+{
+	char   *address;
+	HANDLE		hmap;
+	char	name[64];
+	MEMORY_BASIC_INFORMATION info;
+
+	/* Resize is not supported for Windows shared memory. */
+	if (op == DSM_OP_RESIZE)
+	{
+		elog(elevel, "Windows shared memory segments cannot be resized");
+		return false;
+	}
+
+	/* Since resize isn't supported, reattach is a no-op. */
+	if (op == DSM_OP_ATTACH && *mapped_address != NULL)
+		return true;
+
+	/*
+	 * Storing the shared memory segment in the Global\ namespace, can
+	 * allow any process running in any session to access that file
+	 * mapping object provided that the caller has the required access rights.
+	 * But to avoid issues faced in main shared memory, we are using the naming
+	 * convention similar to main shared memory. We can change here once
+	 * issue mentioned in GetSharedMemName is resolved.
+	 */
+	snprintf(name, 64, "Global/PostgreSQL.%lu", (unsigned long) handle);
+
+	/*
+	 * Handle teardown cases.  Since Windows automatically destroys the object
+	 * when no references reamin, we can treat it the same as detach.
+	 */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& UnmapViewOfFile(*mapped_address) == 0)
+		{
+			_dosmaperr(GetLastError());
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		if (*impl_private != NULL
+			&& CloseHandle(*impl_private) == 0)
+		{
+			_dosmaperr(GetLastError());
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+
+		*impl_private = NULL;
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		return true;
+	}
+
+	/* Create new segment or open an existing one for attach. */
+	if (op == DSM_OP_CREATE)
+	{
+		DWORD		size_high = (DWORD) (request_size >> 32);
+		DWORD		size_low = (DWORD) request_size;
+		hmap = CreateFileMapping(INVALID_HANDLE_VALUE,	/* Use the pagefile */
+								 NULL,			/* Default security attrs */
+								 PAGE_READWRITE,	/* Memory is read/write */
+								 size_high, 	/* Upper 32 bits of size */
+								 size_low,		/* Lower 32 bits of size */
+								 name);
+		_dosmaperr(GetLastError());
+		if (errno == EEXIST)
+		{
+			/*
+			 * On Windows, when the segment already exists, a handle for the
+			 * existing segment is returned.  We must close it before
+			 * returning.  We don't do _dosmaperr here, so errno won't be
+			 * modified.
+			 */
+			CloseHandle(hmap);
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+	}
+	else
+	{
+		hmap = OpenFileMapping(FILE_MAP_WRITE | FILE_MAP_READ,
+							   FALSE,		/* do not inherit the name */
+							   name);		/* name of mapping object */
+		_dosmaperr(GetLastError());
+	}
+
+	if (!hmap)
+	{
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not open shared memory segment \"%s\": %m",
+					name)));
+		return false;
+	}
+
+	/* Map it. */
+	address = MapViewOfFile(hmap, FILE_MAP_WRITE | FILE_MAP_READ,
+							0, 0, 0);
+	if (!address)
+	{
+		int		save_errno;
+
+		_dosmaperr(GetLastError());
+		/* Back out what's already been done. */
+		save_errno = errno;
+		CloseHandle(hmap);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * VirtualQuery gives size in page_size units, which is 4K for Windows.
+	 * We need size only when we are attaching, but it's better to get the
+	 * size when creating new segment to keep size consistent both for
+	 * DSM_OP_CREATE and DSM_OP_ATTACH.
+	 */
+	if (VirtualQuery(address, &info, sizeof(info)) == 0)
+	{
+		int		save_errno;
+
+		_dosmaperr(GetLastError());
+		/* Back out what's already been done. */
+		save_errno = errno;
+		UnmapViewOfFile(address);
+		CloseHandle(hmap);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				errmsg("could not stat shared memory segment \"%s\": %m",
+					name)));
+		return false;
+	}
+
+	*mapped_address = address;
+	*mapped_size = info.RegionSize;
+	*impl_private = hmap;
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_MMAP
+/*
+ * Operating system primitives to support mmap-based shared memory.
+ *
+ * Calling this "shared memory" is somewhat of a misnomer, because what
+ * we're really doing is creating a bunch of files and mapping them into
+ * our address space.  The operating system may feel obliged to
+ * synchronize the contents to disk even if nothing is being paged out,
+ * which will not serve us well.  The user can relocate the pg_dynshmem
+ * directory to a ramdisk to avoid this problem, if available.
+ */
+static bool
+dsm_impl_mmap(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address, uint64 *mapped_size,
+			  int elevel)
+{
+	char	name[64];
+	int		flags;
+	int		fd;
+	char   *address;
+
+	snprintf(name, 64, PG_DYNSHMEM_DIR "/" PG_DYNSHMEM_MMAP_FILE_PREFIX "%lu",
+		(unsigned long) handle);
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& munmap(*mapped_address, *mapped_size) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && unlink(name) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/* Create new segment or open an existing one for attach or resize. */
+	flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
+	if ((fd = OpenTransientFile(name, flags, 0600)) == -1)
+	{
+		if (errno != EEXIST)
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * If we're attaching the segment, determine the current size; if we are
+	 * creating or resizing the segment, set the size to the requested value.
+	 */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct stat st;
+
+		if (fstat(fd, &st) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = st.st_size;
+	}
+	else if (*mapped_size > request_size && ftruncate(fd, request_size))
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+					name, request_size)));
+		return false;
+	}
+	else if (*mapped_size < request_size)
+	{
+		/*
+		 * Allocate a buffer full of zeros.
+		 *
+		 * Note: palloc zbuffer, instead of just using a local char array,
+		 * to ensure it is reasonably well-aligned; this may save a few
+		 * cycles transferring data to the kernel.
+		 */
+		char   *zbuffer = (char *) palloc0(ZBUFFER_SIZE);
+		uint32	remaining = request_size;
+		bool	success = true;
+
+		/*
+		 * Zero-fill the file. We have to do this the hard way to ensure
+		 * that all the file space has really been allocated, so that we
+		 * don't later seg fault when accessing the memory mapping.  This
+		 * is pretty pessimal.
+		 */
+		while (success && remaining > 0)
+		{
+			uint64	goal = remaining;
+
+			if (goal > ZBUFFER_SIZE)
+				goal = ZBUFFER_SIZE;
+			if (write(fd, zbuffer, goal) == goal)
+				remaining -= goal;
+			else
+				success = false;
+		}
+
+		if (!success)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			if (op == DSM_OP_CREATE)
+				unlink(name);
+			errno = save_errno ? save_errno : ENOSPC;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+						name, request_size)));
+			return false;
+		}
+	}
+
+	/*
+	 * If we're reattaching or resizing, we must remove any existing mapping,
+	 * unless we've already got the right thing mapped.
+	 */
+	if (*mapped_address != NULL)
+	{
+		if (*mapped_size == request_size)
+			return true;
+		if (munmap(*mapped_address, *mapped_size) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			if (op == DSM_OP_CREATE)
+				unlink(name);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+	}
+
+	/* Map it. */
+	address = mmap(NULL, request_size, PROT_READ|PROT_WRITE,
+				   MAP_SHARED|MAP_HASSEMAPHORE, fd, 0);
+	if (address == MAP_FAILED)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		CloseTransientFile(fd);
+		if (op == DSM_OP_CREATE)
+			unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+	CloseTransientFile(fd);
+
+	return true;
+}
+#endif
+
+static int
+errcode_for_dynamic_shared_memory()
+{
+	if (errno == EFBIG || errno == ENOMEM)
+		return errcode(ERRCODE_OUT_OF_MEMORY);
+	else
+		return errcode_for_file_access();
+}
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index a0b741b..040c7aa 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -30,6 +30,7 @@
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
 #include "storage/bufmgr.h"
+#include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 #include "storage/pmsignal.h"
@@ -249,6 +250,10 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		ShmemBackendArrayAllocation();
 #endif
 
+	/* Initialize dynamic shared memory facilities. */
+	if (!IsUnderPostmaster)
+		dsm_postmaster_startup();
+
 	/*
 	 * Now give loadable modules a chance to set up their shmem allocations
 	 */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 7d297bc..4dfb3cc 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -61,6 +61,7 @@
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
 #include "storage/bufmgr.h"
+#include "storage/dsm_impl.h"
 #include "storage/standby.h"
 #include "storage/fd.h"
 #include "storage/proc.h"
@@ -385,6 +386,7 @@ static const struct config_enum_entry synchronous_commit_options[] = {
  */
 extern const struct config_enum_entry wal_level_options[];
 extern const struct config_enum_entry sync_method_options[];
+extern const struct config_enum_entry dynamic_shared_memory_options[];
 
 /*
  * GUC option variables that are exported from this module
@@ -3324,6 +3326,16 @@ static struct config_enum ConfigureNamesEnum[] =
 	},
 
 	{
+		{"dynamic_shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Selects the dynamic shared memory implementation used."),
+			NULL
+		},
+		&dynamic_shared_memory_type,
+		DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE, dynamic_shared_memory_options,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"wal_sync_method", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Selects the method used for forcing WAL updates to disk."),
 			NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index d69a02b..c9cea28 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -123,6 +123,13 @@
 #work_mem = 1MB				# min 64kB
 #maintenance_work_mem = 16MB		# min 1MB
 #max_stack_depth = 2MB			# min 100kB
+#dynamic_shared_memory_type = posix # the default is the first option
+					# supported by the operating system:
+					#   posix
+					#   sysv
+					#   windows
+					#   mmap
+					# use none to disable dynamic shared memory
 
 # - Disk -
 
diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c
index e7ec393..43542cf 100644
--- a/src/backend/utils/resowner/resowner.c
+++ b/src/backend/utils/resowner/resowner.c
@@ -98,6 +98,11 @@ typedef struct ResourceOwnerData
 	int			nfiles;			/* number of owned temporary files */
 	File	   *files;			/* dynamically allocated array */
 	int			maxfiles;		/* currently allocated array size */
+
+	/* We have built-in support for remembering dynamic shmem segments */
+	int			ndsms;			/* number of owned shmem segments */
+	dsm_segment **dsms;			/* dynamically allocated array */
+	int			maxdsms;		/* currently allocated array size */
 }	ResourceOwnerData;
 
 
@@ -132,6 +137,7 @@ static void PrintPlanCacheLeakWarning(CachedPlan *plan);
 static void PrintTupleDescLeakWarning(TupleDesc tupdesc);
 static void PrintSnapshotLeakWarning(Snapshot snapshot);
 static void PrintFileLeakWarning(File file);
+static void PrintDSMLeakWarning(dsm_segment *seg);
 
 
 /*****************************************************************************
@@ -271,6 +277,21 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 				PrintRelCacheLeakWarning(owner->relrefs[owner->nrelrefs - 1]);
 			RelationClose(owner->relrefs[owner->nrelrefs - 1]);
 		}
+
+		/*
+		 * Release dynamic shared memory segments.  Note that dsm_detach()
+		 * will remove the segment from my list, so I just have to iterate
+		 * until there are none.
+		 *
+		 * As in the preceding cases, warn if there are leftover at commit
+		 * time.
+		 */
+		while (owner->ndsms > 0)
+		{
+			if (isCommit)
+				PrintDSMLeakWarning(owner->dsms[owner->ndsms - 1]);
+			dsm_detach(owner->dsms[owner->ndsms - 1]);
+		}
 	}
 	else if (phase == RESOURCE_RELEASE_LOCKS)
 	{
@@ -438,6 +459,8 @@ ResourceOwnerDelete(ResourceOwner owner)
 		pfree(owner->snapshots);
 	if (owner->files)
 		pfree(owner->files);
+	if (owner->dsms)
+		pfree(owner->dsms);
 
 	pfree(owner);
 }
@@ -1230,3 +1253,88 @@ PrintFileLeakWarning(File file)
 		 "temporary file leak: File %d still referenced",
 		 file);
 }
+
+/*
+ * Make sure there is room for at least one more entry in a ResourceOwner's
+ * dynamic shmem segment reference array.
+ *
+ * This is separate from actually inserting an entry because if we run out
+ * of memory, it's critical to do so *before* acquiring the resource.
+ */
+void
+ResourceOwnerEnlargeDSMs(ResourceOwner owner)
+{
+	int			newmax;
+
+	if (owner->ndsms < owner->maxdsms)
+		return;					/* nothing to do */
+
+	if (owner->dsms == NULL)
+	{
+		newmax = 16;
+		owner->dsms = (dsm_segment **)
+			MemoryContextAlloc(TopMemoryContext,
+							   newmax * sizeof(dsm_segment *));
+		owner->maxdsms = newmax;
+	}
+	else
+	{
+		newmax = owner->maxdsms * 2;
+		owner->dsms = (dsm_segment **)
+			repalloc(owner->dsms, newmax * sizeof(dsm_segment *));
+		owner->maxdsms = newmax;
+	}
+}
+
+/*
+ * Remember that a dynamic shmem segment is owned by a ResourceOwner
+ *
+ * Caller must have previously done ResourceOwnerEnlargeDSMs()
+ */
+void
+ResourceOwnerRememberDSM(ResourceOwner owner, dsm_segment *seg)
+{
+	Assert(owner->ndsms < owner->maxdsms);
+	owner->dsms[owner->ndsms] = seg;
+	owner->ndsms++;
+}
+
+/*
+ * Forget that a temporary file is owned by a ResourceOwner
+ */
+void
+ResourceOwnerForgetDSM(ResourceOwner owner, dsm_segment *seg)
+{
+	dsm_segment **dsms = owner->dsms;
+	int			ns1 = owner->ndsms - 1;
+	int			i;
+
+	for (i = ns1; i >= 0; i--)
+	{
+		if (dsms[i] == seg)
+		{
+			while (i < ns1)
+			{
+				dsms[i] = dsms[i + 1];
+				i++;
+			}
+			owner->ndsms = ns1;
+			return;
+		}
+	}
+	elog(ERROR,
+		 "dynamic shared memory segment %lu is not owned by resource owner %s",
+		 (unsigned long) dsm_segment_handle(seg), owner->name);
+}
+
+
+/*
+ * Debugging subroutine
+ */
+static void
+PrintDSMLeakWarning(dsm_segment *seg)
+{
+	elog(WARNING,
+		 "dynamic shared memory leak: segment %lu still referenced",
+		 (unsigned long) dsm_segment_handle(seg));
+}
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index f66f530..a6eb0d8 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -182,6 +182,7 @@ const char *subdirs[] = {
 	"pg_xlog",
 	"pg_xlog/archive_status",
 	"pg_clog",
+	"pg_dynshmem",
 	"pg_notify",
 	"pg_serial",
 	"pg_snapshots",
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 8aabf3c..5eac52d 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -424,6 +424,9 @@
 /* Define to 1 if you have the `setsid' function. */
 #undef HAVE_SETSID
 
+/* Define to 1 if you have the `shm_open' function. */
+#undef HAVE_SHM_OPEN
+
 /* Define to 1 if you have the `sigprocmask' function. */
 #undef HAVE_SIGPROCMASK
 
diff --git a/src/include/portability/mem.h b/src/include/portability/mem.h
new file mode 100644
index 0000000..2a07c10
--- /dev/null
+++ b/src/include/portability/mem.h
@@ -0,0 +1,40 @@
+/*-------------------------------------------------------------------------
+ *
+ * mem.h
+ *	  portability definitions for various memory operations
+ *
+ * Copyright (c) 2001-2013, PostgreSQL Global Development Group
+ *
+ * src/include/portability/mem.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef MEM_H
+#define MEM_H
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
+#define PG_SHMAT_FLAGS			SHM_SHARE_MMU
+#else
+#define PG_SHMAT_FLAGS			0
+#endif
+
+/* Linux prefers MAP_ANONYMOUS, but the flag is called MAP_ANON on other systems. */
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS			MAP_ANON
+#endif
+
+/* BSD-derived systems have MAP_HASSEMAPHORE, but it's not present (or needed) on Linux. */
+#ifndef MAP_HASSEMAPHORE
+#define MAP_HASSEMAPHORE		0
+#endif
+
+#define PG_MMAP_FLAGS			(MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
+
+/* Some really old systems don't define MAP_FAILED. */
+#ifndef MAP_FAILED
+#define MAP_FAILED ((void *) -1)
+#endif
+
+#endif   /* MEM_H */
diff --git a/src/include/storage/dsm.h b/src/include/storage/dsm.h
new file mode 100644
index 0000000..2b5e722
--- /dev/null
+++ b/src/include/storage/dsm.h
@@ -0,0 +1,39 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm.h
+ *	  manage dynamic shared memory segments
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/dsm.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSM_H
+#define DSM_H
+
+#include "storage/dsm_impl.h"
+
+typedef struct dsm_segment dsm_segment;
+
+/* Initialization function. */
+extern void dsm_postmaster_startup(void);
+
+/* Functions that create, update, or remove mappings. */
+extern dsm_segment *dsm_create(uint64 size);
+extern dsm_segment *dsm_attach(dsm_handle h);
+extern void *dsm_resize(dsm_segment *seg, uint64 size);
+extern void *dsm_remap(dsm_segment *seg);
+extern void dsm_detach(dsm_segment *seg);
+
+/* Resource management functions. */
+extern void dsm_keep_mapping(dsm_segment *seg);
+extern dsm_segment *dsm_find_mapping(dsm_handle h);
+
+/* Informational functions. */
+extern void *dsm_segment_address(dsm_segment *seg);
+extern uint64 dsm_segment_map_length(dsm_segment *seg);
+extern dsm_handle dsm_segment_handle(dsm_segment *seg);
+
+#endif   /* DSM_H */
diff --git a/src/include/storage/dsm_impl.h b/src/include/storage/dsm_impl.h
new file mode 100644
index 0000000..13f1f48
--- /dev/null
+++ b/src/include/storage/dsm_impl.h
@@ -0,0 +1,75 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm_impl.h
+ *	  low-level dynamic shared memory primitives
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/dsm_impl.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSM_IMPL_H
+#define DSM_IMPL_H
+
+/* Dynamic shared memory implementations. */
+#define DSM_IMPL_NONE			0
+#define DSM_IMPL_POSIX			1
+#define DSM_IMPL_SYSV			2
+#define DSM_IMPL_WINDOWS		3
+#define DSM_IMPL_MMAP			4
+
+/*
+ * Determine which dynamic shared memory implementations will be supported
+ * on this platform, and which one will be the default.
+ */
+#ifdef WIN32
+#define USE_DSM_WINDOWS
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_WINDOWS
+#else
+#ifdef HAVE_SHM_OPEN
+#define USE_DSM_POSIX
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_POSIX
+#endif
+#define USE_DSM_SYSV
+#ifndef DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_SYSV
+#endif
+#define USE_DSM_MMAP
+#endif
+
+/* GUC. */
+extern int dynamic_shared_memory_type;
+
+/*
+ * Directory for on-disk state.
+ *
+ * This is used by all implementations for crash recovery and by the mmap
+ * implementation for storage.
+ */
+#define PG_DYNSHMEM_DIR					"pg_dynshmem"
+#define PG_DYNSHMEM_MMAP_FILE_PREFIX	"mmap."
+
+/* A "name" for a dynamic shared memory segment. */
+typedef uint32 dsm_handle;
+
+/* All the shared-memory operations we know about. */
+typedef enum
+{
+	DSM_OP_CREATE,
+	DSM_OP_ATTACH,
+	DSM_OP_DETACH,
+	DSM_OP_RESIZE,
+	DSM_OP_DESTROY
+} dsm_op;
+
+/* Create, attach to, detach from, resize, or destroy a segment. */
+extern bool dsm_impl_op(dsm_op op, dsm_handle handle, uint64 request_size,
+			void **impl_private, void **mapped_address, uint64 *mapped_size,
+			int elevel);
+
+/* Some implementations cannot resize segments.  Can this one? */
+extern bool dsm_impl_can_resize(void);
+
+#endif   /* DSM_IMPL_H */
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 39415a3..730c47b 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -80,6 +80,7 @@ typedef enum LWLockId
 	OldSerXidLock,
 	SyncRepLock,
 	BackgroundWorkerLock,
+	DynamicSharedMemoryControlLock,
 	/* Individual lock IDs end here */
 	FirstBufMappingLock,
 	FirstLockMgrLock = FirstBufMappingLock + NUM_BUFFER_PARTITIONS,
diff --git a/src/include/utils/resowner_private.h b/src/include/utils/resowner_private.h
index a5d8707..6693483 100644
--- a/src/include/utils/resowner_private.h
+++ b/src/include/utils/resowner_private.h
@@ -16,6 +16,7 @@
 #ifndef RESOWNER_PRIVATE_H
 #define RESOWNER_PRIVATE_H
 
+#include "storage/dsm.h"
 #include "storage/fd.h"
 #include "storage/lock.h"
 #include "utils/catcache.h"
@@ -80,4 +81,11 @@ extern void ResourceOwnerRememberFile(ResourceOwner owner,
 extern void ResourceOwnerForgetFile(ResourceOwner owner,
 						File file);
 
+/* support for dynamic shared memory management */
+extern void ResourceOwnerEnlargeDSMs(ResourceOwner owner);
+extern void ResourceOwnerRememberDSM(ResourceOwner owner,
+						  dsm_segment *);
+extern void ResourceOwnerForgetDSM(ResourceOwner owner,
+						dsm_segment *);
+
 #endif   /* RESOWNER_PRIVATE_H */

diff --git a/configure b/configure
index c685ca3..97d2f68 100755
--- a/configure
+++ b/configure
@@ -8384,6 +8384,180 @@ if test "$ac_res" != no; then
 
 fi
 
+{ $as_echo "$as_me:$LINENO: checking for library containing shm_open" >&5
+$as_echo_n "checking for library containing shm_open... " >&6; }
+if test "${ac_cv_search_shm_open+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  ac_func_search_save_LIBS=$LIBS
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char shm_open ();
+int
+main ()
+{
+return shm_open ();
+  ;
+  return 0;
+}
+_ACEOF
+for ac_lib in '' rt; do
+  if test -z "$ac_lib"; then
+    ac_res="none required"
+  else
+    ac_res=-l$ac_lib
+    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
+  fi
+  rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  ac_cv_search_shm_open=$ac_res
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext
+  if test "${ac_cv_search_shm_open+set}" = set; then
+  break
+fi
+done
+if test "${ac_cv_search_shm_open+set}" = set; then
+  :
+else
+  ac_cv_search_shm_open=no
+fi
+rm conftest.$ac_ext
+LIBS=$ac_func_search_save_LIBS
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_search_shm_open" >&5
+$as_echo "$ac_cv_search_shm_open" >&6; }
+ac_res=$ac_cv_search_shm_open
+if test "$ac_res" != no; then
+  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+
+fi
+
+{ $as_echo "$as_me:$LINENO: checking for library containing shm_unlink" >&5
+$as_echo_n "checking for library containing shm_unlink... " >&6; }
+if test "${ac_cv_search_shm_unlink+set}" = set; then
+  $as_echo_n "(cached) " >&6
+else
+  ac_func_search_save_LIBS=$LIBS
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+/* Override any GCC internal prototype to avoid an error.
+   Use char because int might match the return type of a GCC
+   builtin and then its argument prototype would still apply.  */
+#ifdef __cplusplus
+extern "C"
+#endif
+char shm_unlink ();
+int
+main ()
+{
+return shm_unlink ();
+  ;
+  return 0;
+}
+_ACEOF
+for ac_lib in '' rt; do
+  if test -z "$ac_lib"; then
+    ac_res="none required"
+  else
+    ac_res=-l$ac_lib
+    LIBS="-l$ac_lib  $ac_func_search_save_LIBS"
+  fi
+  rm -f conftest.$ac_objext conftest$ac_exeext
+if { (ac_try="$ac_link"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_link") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest$ac_exeext && {
+	 test "$cross_compiling" = yes ||
+	 $as_test_x conftest$ac_exeext
+       }; then
+  ac_cv_search_shm_unlink=$ac_res
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+
+fi
+
+rm -rf conftest.dSYM
+rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
+      conftest$ac_exeext
+  if test "${ac_cv_search_shm_unlink+set}" = set; then
+  break
+fi
+done
+if test "${ac_cv_search_shm_unlink+set}" = set; then
+  :
+else
+  ac_cv_search_shm_unlink=no
+fi
+rm conftest.$ac_ext
+LIBS=$ac_func_search_save_LIBS
+fi
+{ $as_echo "$as_me:$LINENO: result: $ac_cv_search_shm_unlink" >&5
+$as_echo "$ac_cv_search_shm_unlink" >&6; }
+ac_res=$ac_cv_search_shm_unlink
+if test "$ac_res" != no; then
+  test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
+
+fi
+
 # Solaris:
 { $as_echo "$as_me:$LINENO: checking for library containing fdatasync" >&5
 $as_echo_n "checking for library containing fdatasync... " >&6; }
@@ -19763,7 +19937,8 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
 
 
-for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
+
+for ac_func in cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid shm_open sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l
 do
 as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { $as_echo "$as_me:$LINENO: checking for $ac_func" >&5
diff --git a/configure.in b/configure.in
index 82771bd..ead0908 100644
--- a/configure.in
+++ b/configure.in
@@ -883,6 +883,8 @@ case $host_os in
 esac
 AC_SEARCH_LIBS(getopt_long, [getopt gnugetopt])
 AC_SEARCH_LIBS(crypt, crypt)
+AC_SEARCH_LIBS(shm_open, rt)
+AC_SEARCH_LIBS(shm_unlink, rt)
 # Solaris:
 AC_SEARCH_LIBS(fdatasync, [rt posix4])
 # Required for thread_test.c on Solaris 2.5:
@@ -1230,7 +1232,7 @@ PGAC_FUNC_GETTIMEOFDAY_1ARG
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
+AC_CHECK_FUNCS([cbrt dlopen fdatasync getifaddrs getpeerucred getrlimit mbstowcs_l memmove poll pstat readlink setproctitle setsid shm_open sigprocmask symlink sync_file_range towlower utime utimes wcstombs wcstombs_l])
 
 AC_REPLACE_FUNCS(fseeko)
 case $host_os in
diff --git a/contrib/dsm_demo/Makefile b/contrib/dsm_demo/Makefile
new file mode 100644
index 0000000..dd9ea92
--- /dev/null
+++ b/contrib/dsm_demo/Makefile
@@ -0,0 +1,17 @@
+# contrib/dsm_demo/Makefile
+
+MODULES = dsm_demo
+
+EXTENSION = dsm_demo
+DATA = dsm_demo--1.0.sql
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/dsm_demo
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/dsm_demo/dsm_demo--1.0.sql b/contrib/dsm_demo/dsm_demo--1.0.sql
new file mode 100644
index 0000000..7ad6ab1
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo--1.0.sql
@@ -0,0 +1,14 @@
+/* contrib/dsm_demo/dsm_demo--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION dsm_demo" to load this file. \quit
+
+CREATE FUNCTION dsm_demo_create(pg_catalog.text)
+RETURNS pg_catalog.int8 STRICT
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
+
+CREATE FUNCTION dsm_demo_read(pg_catalog.int8)
+RETURNS pg_catalog.text STRICT
+AS 'MODULE_PATHNAME'
+LANGUAGE C;
diff --git a/contrib/dsm_demo/dsm_demo.c b/contrib/dsm_demo/dsm_demo.c
new file mode 100644
index 0000000..0ebbd68
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo.c
@@ -0,0 +1,97 @@
+/* -------------------------------------------------------------------------
+ *
+ * dsm_demo.c
+ *		Dynamic shared memory demonstration.
+ *
+ * Copyright (C) 2013, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		contrib/dsm_demo/dsm_demo.c
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "storage/dsm.h"
+#include "fmgr.h"
+
+PG_MODULE_MAGIC;
+
+void		_PG_init(void);
+Datum		dsm_demo_create(PG_FUNCTION_ARGS);
+Datum		dsm_demo_read(PG_FUNCTION_ARGS);
+
+PG_FUNCTION_INFO_V1(dsm_demo_create);
+PG_FUNCTION_INFO_V1(dsm_demo_read);
+
+#define		DSM_DEMO_MAGIC			0x44454D4F
+
+typedef struct
+{
+	uint32	magic;
+	int32	len;
+	char	data[FLEXIBLE_ARRAY_MEMBER];
+} dsm_demo_payload;
+
+Datum
+dsm_demo_create(PG_FUNCTION_ARGS)
+{
+	text	   *txt = PG_GETARG_TEXT_PP(0);
+	int			len = VARSIZE_ANY(txt);
+	uint64		seglen;
+	dsm_segment *seg;
+	dsm_demo_payload *payload;
+
+	seglen = offsetof(dsm_demo_payload, data) + len;
+	seg = dsm_create(seglen);
+	dsm_keep_mapping(seg);
+
+	payload = dsm_segment_address(seg);
+	payload->magic = DSM_DEMO_MAGIC;
+	payload->len = len;
+	memcpy(payload->data, txt, len);
+
+	PG_RETURN_INT64(dsm_segment_handle(seg));
+}
+
+Datum
+dsm_demo_read(PG_FUNCTION_ARGS)
+{
+	dsm_handle	h = PG_GETARG_INT64(0);
+	dsm_segment *seg;
+	bool		needs_detach = false;
+	text	   *txt = NULL;
+	dsm_demo_payload *payload;
+
+	/*
+	 * We could be called from the same sesion that called dsm_demo_create(),
+	 * so search for an existing mapping.  If we don't find one, attach the
+	 * segment.
+	 */
+	seg = dsm_find_mapping(h);
+	if (seg == NULL)
+	{
+		seg = dsm_attach(h);
+		if (!seg)
+			PG_RETURN_NULL();
+		needs_detach = true;
+	}
+
+	/* Extract data, after checking magic number. */
+	payload = dsm_segment_address(seg);
+	if (payload->magic == DSM_DEMO_MAGIC)
+	{
+		txt = palloc(payload->len);
+		memcpy(txt, payload->data, payload->len);
+	}
+
+	/* Detach, if there was no existing mapping. */
+	if (needs_detach)
+		dsm_detach(seg);
+
+	if (txt == NULL)
+		PG_RETURN_NULL();
+
+	PG_RETURN_TEXT_P(txt);
+}
diff --git a/contrib/dsm_demo/dsm_demo.control b/contrib/dsm_demo/dsm_demo.control
new file mode 100644
index 0000000..4060791
--- /dev/null
+++ b/contrib/dsm_demo/dsm_demo.control
@@ -0,0 +1,5 @@
+# dsm_demo extension
+comment = 'Dynamic shared memory demonstration'
+default_version = '1.0'
+module_pathname = 'dsm_demo'
+relocatable = true
diff --git a/src/backend/port/sysv_shmem.c b/src/backend/port/sysv_shmem.c
index 20e3c32..b604407 100644
--- a/src/backend/port/sysv_shmem.c
+++ b/src/backend/port/sysv_shmem.c
@@ -29,6 +29,7 @@
 #endif
 
 #include "miscadmin.h"
+#include "portability/mem.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 
@@ -36,31 +37,6 @@
 typedef key_t IpcMemoryKey;		/* shared memory key passed to shmget(2) */
 typedef int IpcMemoryId;		/* shared memory ID returned by shmget(2) */
 
-#define IPCProtection	(0600)	/* access/modify by user only */
-
-#ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
-#define PG_SHMAT_FLAGS			SHM_SHARE_MMU
-#else
-#define PG_SHMAT_FLAGS			0
-#endif
-
-/* Linux prefers MAP_ANONYMOUS, but the flag is called MAP_ANON on other systems. */
-#ifndef MAP_ANONYMOUS
-#define MAP_ANONYMOUS			MAP_ANON
-#endif
-
-/* BSD-derived systems have MAP_HASSEMAPHORE, but it's not present (or needed) on Linux. */
-#ifndef MAP_HASSEMAPHORE
-#define MAP_HASSEMAPHORE		0
-#endif
-
-#define PG_MMAP_FLAGS			(MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
-
-/* Some really old systems don't define MAP_FAILED. */
-#ifndef MAP_FAILED
-#define MAP_FAILED ((void *) -1)
-#endif
-
 
 unsigned long UsedShmemSegID = 0;
 void	   *UsedShmemSegAddr = NULL;
diff --git a/src/backend/storage/ipc/Makefile b/src/backend/storage/ipc/Makefile
index 743f30e..873dd60 100644
--- a/src/backend/storage/ipc/Makefile
+++ b/src/backend/storage/ipc/Makefile
@@ -15,7 +15,7 @@ override CFLAGS+= -fno-inline
 endif
 endif
 
-OBJS = ipc.o ipci.o pmsignal.o procarray.o procsignal.o shmem.o shmqueue.o \
-	sinval.o sinvaladt.o standby.o
+OBJS = dsm_impl.o dsm.o ipc.o ipci.o pmsignal.o procarray.o procsignal.o \
+	shmem.o shmqueue.o sinval.o sinvaladt.o standby.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
new file mode 100644
index 0000000..fa9e003
--- /dev/null
+++ b/src/backend/storage/ipc/dsm.c
@@ -0,0 +1,976 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm.c
+ *	  manage dynamic shared memory segments
+ *
+ * This file provides a set of services to make programming with dynamic
+ * shared memory segments more convenient.  Unlike the low-level
+ * facilities provided by dsm_impl.h and dsm_impl.c, mappings and segments
+ * created using this module will be cleaned up automatically.  Mappings
+ * will be removed when the resource owner under which they were created
+ * is cleaned up, unless dsm_keep_mapping() is used, in which case they
+ * have session lifespan.  Segments will be removed when there are no
+ * remaining mappings, or at postmaster shutdown in any case.  After a
+ * hard postmaster crash, remaining segments will be removed, if they
+ * still exist, at the next postmaster startup.
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/ipc/dsm.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#ifndef WIN32
+#include <sys/mman.h>
+#endif
+#include <sys/stat.h>
+
+#include "lib/ilist.h"
+#include "miscadmin.h"
+#include "storage/dsm.h"
+#include "storage/ipc.h"
+#include "storage/lwlock.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+#include "utils/resowner_private.h"
+
+#define PG_DYNSHMEM_STATE_FILE			PG_DYNSHMEM_DIR "/state"
+#define PG_DYNSHMEM_NEW_STATE_FILE		PG_DYNSHMEM_DIR "/state.new"
+#define PG_DYNSHMEM_STATE_BUFSIZ		512
+#define PG_DYNSHMEM_CONTROL_MAGIC		0x9a503d32
+
+/*
+ * There's no point in getting too cheap here, because the minimum allocation
+ * is one OS page, which is probably at least 4KB and could easily be as high
+ * as 64KB.  Each currently sizeof(dsm_control_item), currently 8 bytes.
+ */
+#define PG_DYNSHMEM_FIXED_SLOTS			64
+#define PG_DYNSHMEM_SLOTS_PER_BACKEND	2
+
+#define INVALID_CONTROL_SLOT		((uint32) -1)
+
+/* Backend-local state for a dynamic shared memory segment. */
+struct dsm_segment
+{
+	dlist_node	node;				/* List link in dsm_segment_list. */
+	ResourceOwner resowner;			/* Resource owner. */
+	dsm_handle	handle;				/* Segment name. */
+	uint32		control_slot;		/* Slot in control segment. */
+	void       *impl_private;		/* Implementation-specific private data. */
+	void	   *mapped_address;		/* Mapping address, or NULL if unmapped. */
+	uint64		mapped_size;		/* Size of our mapping. */
+};
+
+/* Shared-memory state for a dynamic shared memory segment. */
+typedef struct dsm_control_item
+{
+	dsm_handle	handle;
+	uint32		refcnt;				/* 2+ = active, 1 = moribund, 0 = gone */
+} dsm_control_item;
+
+/* Layout of the dynamic shared memory control segment. */
+typedef struct dsm_control_header
+{
+	uint32		magic;
+	uint32		nitems;
+	uint32		maxitems;
+	dsm_control_item	item[FLEXIBLE_ARRAY_MEMBER];
+} dsm_control_header;
+
+static void dsm_cleanup_using_control_segment(void);
+static void dsm_cleanup_for_mmap(void);
+static bool dsm_read_state_file(dsm_handle *h);
+static void dsm_write_state_file(dsm_handle h);
+static void dsm_postmaster_shutdown(int code, Datum arg);
+static void dsm_backend_shutdown(int code, Datum arg);
+static dsm_segment *dsm_create_descriptor(void);
+static bool dsm_control_segment_sane(dsm_control_header *control,
+						 uint64 mapped_size);
+static uint64 dsm_control_bytes_needed(uint32 nitems);
+
+/* Has this backend initialized the dynamic shared memory system yet? */
+static bool dsm_init_done = false;
+
+/*
+ * List of dynamic shared memory segments used by this backend.
+ *
+ * At process exit time, we must decrement the reference count of each
+ * segment we have attached; this list makes it possible to find all such
+ * segments.
+ *
+ * This list should always be empty in the postmaster.  We could probably
+ * allow the postmaster to map dynamic shared memory segments before it
+ * begins to start child processes, provided that each process adjusted
+ * the reference counts for those segments in the control segment at
+ * startup time, but there's no obvious need for such a facility, which
+ * would also be complex to handle in the EXEC_BACKEND case.  Once the
+ * postmaster has begun spawning children, there's an additional problem:
+ * each new mapping would require an update to the control segment,
+ * which requires locking, in which the postmaster must not be involved.
+ */
+static dlist_head dsm_segment_list = DLIST_STATIC_INIT(dsm_segment_list);
+
+/*
+ * Control segment information.
+ *
+ * Unlike ordinary shared memory segments, the control segment is not
+ * reference counted; instead, it lasts for the postmaster's entire
+ * life cycle.  For simplicity, it doesn't have a dsm_segment object either.
+ */
+static dsm_handle dsm_control_handle;
+static dsm_control_header *dsm_control;
+static uint64 dsm_control_mapped_size = 0;
+static void	*dsm_control_impl_private = NULL;
+
+/*
+ * Start up the dynamic shared memory system.
+ *
+ * This is called just once during each cluster lifetime, at postmaster
+ * startup time.
+ */
+void
+dsm_postmaster_startup(void)
+{
+	void	   *dsm_control_address = NULL;
+	uint32		maxitems;
+	uint64		segsize;
+
+	Assert(!IsUnderPostmaster);
+
+	/* If dynamic shared memory is disabled, there's nothing to do. */
+	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
+		return;
+
+	/*
+	 * Check for, and remove, shared memory segments left behind by a dead
+	 * postmaster.  This isn't necessary on Windows, which always removes them
+	 * when the last reference is gone.
+	 */
+	switch (dynamic_shared_memory_type)
+	{
+		case DSM_IMPL_POSIX:
+		case DSM_IMPL_SYSV:
+			dsm_cleanup_using_control_segment();
+			break;
+		case DSM_IMPL_MMAP:
+			dsm_cleanup_for_mmap();
+			break;
+		case DSM_IMPL_WINDOWS:
+			/* Nothing to do. */
+			break;
+		default:
+			elog(ERROR, "unknown dynamic shared memory type: %d",
+				 dynamic_shared_memory_type);
+	}
+
+	/* Determine size for new control segment. */
+	maxitems = PG_DYNSHMEM_FIXED_SLOTS
+		+ PG_DYNSHMEM_SLOTS_PER_BACKEND * MaxBackends;
+	elog(DEBUG2, "dynamic shared memory system will support %lu segments",
+		(unsigned long) maxitems);
+	segsize = dsm_control_bytes_needed(maxitems);
+
+	/* Loop until we find an unused identifier for the new control segment. */
+	for (;;)
+	{
+		Assert(dsm_control_address == NULL);
+		Assert(dsm_control_mapped_size == 0);
+		dsm_control_handle = random();
+		if (dsm_impl_op(DSM_OP_CREATE, dsm_control_handle, segsize,
+						&dsm_control_impl_private, &dsm_control_address,
+						&dsm_control_mapped_size, ERROR))
+			break;
+	}
+	dsm_control = dsm_control_address;
+	on_shmem_exit(dsm_postmaster_shutdown, 0);
+	elog(DEBUG2, "created dynamic shared memory control segment %lu ("
+		UINT64_FORMAT " bytes)", (unsigned long) dsm_control_handle,
+		segsize);
+	dsm_write_state_file(dsm_control_handle);
+
+	/* Initialize control segment. */
+	dsm_control->magic = PG_DYNSHMEM_CONTROL_MAGIC;
+	dsm_control->nitems = 0;
+	dsm_control->maxitems = maxitems;
+}
+
+/*
+ * Determine whether the control segment from the previous postmaster
+ * invocation still exists.  If so, remove the dynamic shared memory
+ * segments to which it refers, and then the control segment itself.
+ */
+static void
+dsm_cleanup_using_control_segment(void)
+{
+	void	   *mapped_address = NULL;
+	void	   *junk_mapped_address = NULL;
+	void	   *impl_private = NULL;
+	void	   *junk_impl_private = NULL;
+	uint64		mapped_size = 0;
+	uint64		junk_mapped_size = 0;
+	uint32		nitems;
+	uint32		i;
+	dsm_handle	old_control_handle;
+	dsm_control_header *old_control;
+
+	/*
+	 * Read the state file.  If it doesn't exist or is empty, there's nothing
+	 * more to do.
+	 */
+	if (!dsm_read_state_file(&old_control_handle))
+		return;
+
+	/*
+	 * Try to attach the segment.  If this fails, it probably just means that
+	 * the operating system has been rebooted and the segment no longer exists,
+	 * or an unrelated proces has used the same shm ID.  So just fall out
+	 * quietly.
+	 */
+	if (!dsm_impl_op(DSM_OP_ATTACH, old_control_handle, 0, &impl_private,
+					 &mapped_address, &mapped_size, DEBUG1))
+		return;
+
+	/*
+	 * We've managed to reattach it, but the contents might not be sane.
+	 * If they aren't, we disregard the segment after all.
+	 */
+	old_control = (dsm_control_header *) mapped_address;
+	if (!dsm_control_segment_sane(old_control, mapped_size))
+	{
+		dsm_impl_op(DSM_OP_DETACH, old_control_handle, 0, &impl_private,
+					&mapped_address, &mapped_size, LOG);
+		return;
+	}
+
+	/*
+	 * OK, the control segment looks basically valid, so we can get use
+	 * it to get a list of segments that need to be removed.
+	 */
+	nitems = old_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		dsm_handle		handle;
+		uint32			refcnt;
+
+		/* If the reference count is 0, the slot is actually unused. */
+		refcnt = old_control->item[i].refcnt;
+		if (refcnt == 0)
+			continue;
+
+		/* Log debugging information. */
+		handle = old_control->item[i].handle;
+		elog(DEBUG2, "cleaning up orphaned dynamic shared memory with ID %lu (reference count %lu)",
+			(unsigned long) handle, (unsigned long) refcnt);
+
+		/* Destroy the referenced segment. */
+		dsm_impl_op(DSM_OP_DESTROY, handle, 0, &junk_impl_private,
+					&junk_mapped_address, &junk_mapped_size, LOG);
+	}
+
+	/* Destroy the old control segment, too. */
+	elog(DEBUG2,
+		 "cleaning up dynamic shared memory control segment with ID %lu",
+		 (unsigned long) old_control_handle);
+	dsm_impl_op(DSM_OP_DESTROY, old_control_handle, 0, &impl_private,
+				&mapped_address, &mapped_size, LOG);
+}
+
+/*
+ * When we're using the mmap shared memory implementation, "shared memory"
+ * segments might even manage to survive an operating system reboot.
+ * But there's no guarantee as to exactly what will survive: some segments
+ * may survive, and others may not, and the contents of some may be out
+ * of date.  In particular, the control segment may be out of date, so we
+ * can't rely on it to figure out what to remove.  However, since we know
+ * what directory contains the files we used as shared memory, we can simply
+ * scan the directory and blow everything away that shouldn't be there.
+ */
+static void
+dsm_cleanup_for_mmap(void)
+{
+	DIR	   *dir;
+	struct dirent *dent;
+
+	/* Open the directory; can't use AllocateDir in postmaster. */
+	if ((dir = opendir(PG_DYNSHMEM_DIR)) == NULL)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open directory \"%s\": %m",
+					PG_DYNSHMEM_DIR)));
+
+	/* Scan for something with a name of the correct format. */
+	while ((dent = readdir(dir)) != NULL)
+	{
+		if (strncmp(dent->d_name, PG_DYNSHMEM_MMAP_FILE_PREFIX,
+				strlen(PG_DYNSHMEM_MMAP_FILE_PREFIX)) == 0)
+		{
+			char buf[MAXPGPATH];
+			snprintf(buf, MAXPGPATH, PG_DYNSHMEM_DIR "/%s", dent->d_name);
+
+			elog(DEBUG2, "removing file \"%s\"", buf);
+
+			/* We found a matching file; so remove it. */
+			if (unlink(buf) != 0)
+			{
+				int		save_errno;
+
+				save_errno = errno;
+				closedir(dir);
+				errno = save_errno;
+
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not remove file \"%s\": %m", buf)));
+			}
+		}
+	}
+
+	/* Cleanup complete. */
+	closedir(dir);
+}
+
+/*
+ * Read and parse the state file.
+ *
+ * If the state file is empty or the contents are garbled, it probably means
+ * that the operating system rebooted before the data written by the previous
+ * postmaster made it to disk.  In that case, we can just ignore it; any shared
+ * memory from before the reboot should be gone anyway.
+ */
+static bool
+dsm_read_state_file(dsm_handle *h)
+{
+	int			statefd;
+	char		statebuf[PG_DYNSHMEM_STATE_BUFSIZ];
+	int			nbytes = 0;
+	char	   *endptr,
+			   *s;
+	dsm_handle	handle;
+
+	/* Read the state file to get the ID of the old control segment. */
+	statefd = open(PG_DYNSHMEM_STATE_FILE, O_RDONLY, 0);
+	if (statefd < 0)
+	{
+		if (errno == ENOENT)
+			return false;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+	}
+	nbytes = read(statefd, statebuf, PG_DYNSHMEM_STATE_BUFSIZ - 1);
+	if (nbytes < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+	/* make sure buffer is NUL terminated */
+	statebuf[nbytes] = '\0';
+	close(statefd);
+
+	/*
+	 * We expect to find the handle of the old control segment here,
+	 * on a line by itself.
+	 */
+	handle = strtoul(statebuf, &endptr, 10);
+	for (s = endptr; *s == ' ' || *s == '\t'; ++s)
+		;
+	if (*s != '\n' && *s != '\0')
+		return false;
+
+	/* Looks good. */
+	*h = handle;
+	return true;
+}
+
+/*
+ * Write our control segment handle to the state file, so that if the
+ * postmaster is killed without running it's on_shmem_exit hooks, the
+ * next postmaster can clean things up after restart.
+ */
+static void
+dsm_write_state_file(dsm_handle h)
+{
+	int			statefd;
+	char		statebuf[PG_DYNSHMEM_STATE_BUFSIZ];
+	int			nbytes;
+
+	/* Create or truncate the file. */
+	statefd = open(PG_DYNSHMEM_NEW_STATE_FILE, O_RDWR|O_CREAT|O_TRUNC, 0600);
+	if (statefd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+
+	/* Write contents. */
+	snprintf(statebuf, PG_DYNSHMEM_STATE_BUFSIZ, "%lu\n",
+			 (unsigned long) dsm_control_handle);
+	nbytes = strlen(statebuf);
+	if (write(statefd, statebuf, nbytes) != nbytes)
+	{
+		if (errno == 0)
+			errno = ENOSPC;		/* if no error signalled, assume no space */
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+	}
+
+	/* Close file. */
+	close(statefd);
+
+	/*
+	 * Atomically rename file into place, so that no one ever sees a partially
+	 * written state file.
+	 */
+	if (rename(PG_DYNSHMEM_NEW_STATE_FILE, PG_DYNSHMEM_STATE_FILE) < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not rename file \"%s\": %m",
+					PG_DYNSHMEM_NEW_STATE_FILE)));
+}
+
+/*
+ * At shutdown time, we iterate over the control segment and remove all
+ * remaining dynamic shared memory segments.  We avoid throwing errors here;
+ * the postmaster is shutting down either way, and this is just non-critical
+ * resource cleanup.
+ */
+static void
+dsm_postmaster_shutdown(int code, Datum arg)
+{
+	uint32		nitems;
+	uint32		i;
+	void	   *dsm_control_address;
+	void	   *junk_mapped_address = NULL;
+	void	   *junk_impl_private = NULL;
+	uint64		junk_mapped_size = 0;
+
+	/*
+	 * If some other backend exited uncleanly, it might have corrupted the
+	 * control segment while it was dying.  In that case, we warn and ignore
+	 * the contents of the control segment.  This may end up leaving behind
+	 * stray shared memory segments, but there's not much we can do about
+	 * that if the metadata is gone.
+	 */
+	nitems = dsm_control->nitems;
+	if (!dsm_control_segment_sane(dsm_control, dsm_control_mapped_size))
+	{
+		ereport(LOG,
+				(errmsg("dynamic shared memory control segment is corrupt")));
+		return;
+	}
+
+	/* Remove any remaining segments. */
+	for (i = 0; i < nitems; ++i)
+	{
+		dsm_handle	handle;
+
+		/* If the reference count is 0, the slot is actually unused. */
+		if (dsm_control->item[i].refcnt == 0)
+			continue;
+
+		/* Log debugging information. */
+		handle = dsm_control->item[i].handle;
+		elog(DEBUG2, "cleaning up orphaned dynamic shared memory with ID %lu",
+			(unsigned long) handle);
+
+		/* Destroy the segment. */
+		dsm_impl_op(DSM_OP_DESTROY, handle, 0, &junk_impl_private,
+					&junk_mapped_address, &junk_mapped_size, LOG);
+	}
+
+	/* Remove the control segment itself. */
+	elog(DEBUG2,
+		 "cleaning up dynamic shared memory control segment with ID %lu",
+		 (unsigned long) dsm_control_handle);
+	dsm_control_address = dsm_control;
+	dsm_impl_op(DSM_OP_DESTROY, dsm_control_handle, 0,
+				&dsm_control_impl_private, &dsm_control_address,
+				&dsm_control_mapped_size, LOG);
+	dsm_control = dsm_control_address;
+
+	/* And, finally, remove the state file. */
+	if (unlink(PG_DYNSHMEM_STATE_FILE) < 0)
+		ereport(LOG,
+				(errcode_for_file_access(),
+				 errmsg("could not unlink file \"%s\": %m",
+					PG_DYNSHMEM_STATE_FILE)));
+}
+
+/*
+ * Prepare this backend for dynamic shared memory usage.  Under EXEC_BACKEND,
+ * we must reread the state file and map the control segment; in other cases,
+ * we'll have inherited the postmaster's mapping and global variables.
+ */
+static void
+dsm_backend_startup(void)
+{
+	/* If dynamic shared memory is disabled, reject this. */
+	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("dynamic shared memory is disabled"),
+				 errhint("Set dynamic_shared_memory_type to a value other than \"one\".")));
+
+#ifdef EXEC_BACKEND
+	{
+		dsm_handle	control_handle;
+		void	   *control_address = NULL;
+
+		/* Read the control segment information from the state file. */
+		if (!dsm_read_state_file(&control_handle))
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("could not parse dynamic shared memory state file")));
+
+		/* Attach control segment. */
+		dsm_impl_op(DSM_OP_ATTACH, control_handle, 0,
+					&dsm_control_impl_private, &control_address,
+					&dsm_control_mapped_size, ERROR);
+		dsm_control_handle = control_handle;
+		dsm_control = control_address;
+		/* If control segment doesn't look sane, something is badly wrong. */
+		if (!dsm_control_segment_sane(dsm_control, dsm_control_mapped_size))
+		{
+			dsm_impl_op(DSM_OP_DETACH, control_handle, 0,
+					    &dsm_control_impl_private, &control_address,
+						&dsm_control_mapped_size, WARNING);
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("dynamic shared memory control segment is not valid")));
+		}
+	}
+#endif
+
+	/* Arrange to detach segments on exit. */
+	on_shmem_exit(dsm_backend_shutdown, 0);
+
+	dsm_init_done = true;
+}
+
+/*
+ * Create a new dynamic shared memory segment.
+ */
+dsm_segment *
+dsm_create(uint64 size)
+{
+	dsm_segment	   *seg = dsm_create_descriptor();
+	uint32			i;
+	uint32			nitems;
+
+	/* Unsafe in postmaster (and pointless in a stand-alone backend). */
+	Assert(IsUnderPostmaster);
+
+	if (!dsm_init_done)
+		dsm_backend_startup();
+
+	/* Loop until we find an unused segment identifier. */
+	for (;;)
+	{
+		Assert(seg->mapped_address == NULL && seg->mapped_size == 0);
+		seg->handle = random();
+		if (dsm_impl_op(DSM_OP_CREATE, seg->handle, size, &seg->impl_private,
+						&seg->mapped_address, &seg->mapped_size, ERROR))
+			break;
+	}
+
+	/* Lock the control segment so we can register the new segment. */
+	LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+
+	/* Search the control segment for an unused slot. */
+	nitems = dsm_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		if (dsm_control->item[i].refcnt == 0)
+		{
+			dsm_control->item[i].handle = seg->handle;
+			/* refcnt of 1 triggers destruction, so start at 2 */
+			dsm_control->item[i].refcnt = 2;
+			seg->control_slot = i;
+			LWLockRelease(DynamicSharedMemoryControlLock);
+			return seg;
+		}
+	}
+
+	/* Verify that we can support an additional mapping. */
+	if (nitems >= dsm_control->maxitems)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
+				 errmsg("too many dynamic shared memory segments")));
+
+	/* Enter the handle into a new array slot. */
+	dsm_control->item[nitems].handle = seg->handle;
+	/* refcnt of 1 triggers destruction, so start at 2 */
+	dsm_control->item[nitems].refcnt = 2;
+	seg->control_slot = nitems;
+	dsm_control->nitems++;
+	LWLockRelease(DynamicSharedMemoryControlLock);
+
+	return seg;
+}
+
+/*
+ * Attach a dynamic shared memory segment.
+ *
+ * See comments for dsm_segment_handle() for an explanation of how this
+ * is intended to be used.
+ *
+ * This function will return NULL if the segment isn't known to the system.
+ * This can happen if we're asked to attach the segment, but then everyone
+ * else detaches it (causing it to be destroyed) before we get around to
+ * attaching it.
+ */
+dsm_segment *
+dsm_attach(dsm_handle h)
+{
+	dsm_segment	   *seg;
+	dlist_iter		iter;
+	uint32			i;
+	uint32			nitems;
+
+	/* Unsafe in postmaster (and pointless in a stand-alone backend). */
+	Assert(IsUnderPostmaster);
+
+	if (!dsm_init_done)
+		dsm_backend_startup();
+
+	/*
+	 * Since this is just a debugging cross-check, we could leave it out
+	 * altogether, or include it only in assert-enabled builds.  But since
+	 * the list of attached segments should normally be very short, let's
+	 * include it always for right now.
+	 *
+	 * If you're hitting this error, you probably want to attempt to
+	 * find an existing mapping via dsm_find_mapping() before calling
+	 * dsm_attach() to create a new one.
+	 */
+	dlist_foreach(iter, &dsm_segment_list)
+	{
+		seg = dlist_container(dsm_segment, node, iter.cur);
+		if (seg->handle == h)
+			elog(ERROR, "can't attach the same segment more than once");
+	}
+
+	/* Create a new segment descriptor. */
+	seg = dsm_create_descriptor();
+	seg->handle = h;
+
+	/* Bump reference count for this segment in shared memory. */
+	LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+	nitems = dsm_control->nitems;
+	for (i = 0; i < nitems; ++i)
+	{
+		/* If the reference count is 0, the slot is actually unused. */
+		if (dsm_control->item[i].refcnt == 0)
+			continue;
+
+		/*
+		 * If the reference count is 1, the slot is still in use, but the
+		 * segment is in the process of going away.  Treat that as if we
+		 * didn't find a match.
+		 */
+		if (dsm_control->item[i].refcnt == 1)
+			break;
+
+		/* Otherwise, if the descriptor matches, we've found a match. */
+		if (dsm_control->item[i].handle == seg->handle)
+		{
+			dsm_control->item[i].refcnt++;
+			seg->control_slot = i;
+			break;
+		}
+	}
+	LWLockRelease(DynamicSharedMemoryControlLock);
+
+	/*
+	 * If we didn't find the handle we're looking for in the control
+	 * segment, it probably means that everyone else who had it mapped,
+	 * including the original creator, died before we got to this point.
+	 * It's up to the caller to decide what to do about that.
+	 */
+	if (seg->control_slot == INVALID_CONTROL_SLOT)
+	{
+		dsm_detach(seg);
+		return NULL;
+	}
+
+	/* Here's where we actually try to map the segment. */
+	dsm_impl_op(DSM_OP_ATTACH, seg->handle, 0, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+
+	return seg;
+}
+
+/*
+ * At backend shutdown time, detach any segments that are still attached.
+ */
+static void
+dsm_backend_shutdown(int code, Datum arg)
+{
+	while (!dlist_is_empty(&dsm_segment_list))
+	{
+		dsm_segment	   *seg;
+
+		seg = dlist_head_element(dsm_segment, node, &dsm_segment_list);
+		dsm_detach(seg);
+	}
+}
+
+/*
+ * Resize an existing shared memory segment.
+ *
+ * This may cause the shared memory segment to be remapped at a different
+ * address.  For the caller's convenience, we return the mapped address.
+ */
+void *
+dsm_resize(dsm_segment *seg, uint64 size)
+{
+	Assert(seg->control_slot != INVALID_CONTROL_SLOT);
+	dsm_impl_op(DSM_OP_RESIZE, seg->handle, size, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+	return seg->mapped_address;
+}
+
+/*
+ * Remap an existing shared memory segment.
+ *
+ * This is intended to be used when some other process has extended the
+ * mapping using dsm_resize(), but we've still only got the initial
+ * portion mapped.  Since this might change the address at which the
+ * segment is mapped, we return the new mapped address.
+ */
+void *
+dsm_remap(dsm_segment *seg)
+{
+	if (!dsm_impl_can_resize())
+		return seg->mapped_address;
+
+	dsm_impl_op(DSM_OP_ATTACH, seg->handle, 0, &seg->impl_private,
+				&seg->mapped_address, &seg->mapped_size, ERROR);
+
+	return seg->mapped_address;
+}
+
+/*
+ * Detach from a shared memory segment, destroying the segment if we
+ * remove the last reference.
+ *
+ * This function should never fail.  It will often be invoked when aborting
+ * a transaction, and a further error won't serve any purpose.  It's not a
+ * complete disaster if we fail to unmap or destroy the segment; it means a
+ * resource leak, but that doesn't necessarily preclude further operations.
+ */
+void
+dsm_detach(dsm_segment *seg)
+{
+	/*
+	 * Try to remove the mapping, if one exists.  Normally, there will be,
+	 * but maybe not, if we failed partway through a create or attach
+	 * operation.  We remove the mapping before decrementing the reference
+	 * count so that the process that sees a zero reference count can be
+	 * certain that no remaining mappings exist.  Even if this fails, we
+	 * pretend that it works, because retrying is likely to fail in the
+	 * same way.
+	 */
+	if (seg->mapped_address != NULL)
+	{
+		dsm_impl_op(DSM_OP_DETACH, seg->handle, 0, &seg->impl_private,
+					&seg->mapped_address, &seg->mapped_size, WARNING);
+		seg->impl_private = NULL;
+		seg->mapped_address = NULL;
+		seg->mapped_size = 0;
+	}
+
+	/* Reduce reference count, if we previously increased it. */
+	if (seg->control_slot != INVALID_CONTROL_SLOT)
+	{
+		uint32	refcnt;
+		uint32	control_slot = seg->control_slot;
+
+		LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+		Assert(dsm_control->item[control_slot].handle == seg->handle);
+		Assert(dsm_control->item[control_slot].refcnt > 1);
+		refcnt = --dsm_control->item[control_slot].refcnt;
+		seg->control_slot = INVALID_CONTROL_SLOT;
+		LWLockRelease(DynamicSharedMemoryControlLock);
+
+		/* If new reference count is 1, try to destroy the segment. */
+		if (refcnt == 1)
+		{
+			/*
+			 * If we fail to destroy the segment here, or are killed before
+			 * we finish doing so, the reference count will remain at 1, which
+			 * will mean that nobody else can attach to the segment.  At
+			 * postmaster shutdown time, or when a new postmaster is started
+			 * after a hard kill, another attempt will be made to remove the
+			 * segment.
+			 *
+			 * The main case we're worried about here is being killed by
+			 * a signal before we can finish removing the segment.  In that
+			 * case, it's important to be sure that the segment still gets
+			 * removed. If we actually fail to remove the segment for some
+			 * other reason, the postmaster may not have any better luck than
+			 * we did.  There's not much we can do about that, though.
+			 */
+			if (dsm_impl_op(DSM_OP_DESTROY, seg->handle, 0, &seg->impl_private,
+							&seg->mapped_address, &seg->mapped_size, WARNING))
+			{
+				LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE);
+				Assert(dsm_control->item[control_slot].handle == seg->handle);
+				Assert(dsm_control->item[control_slot].refcnt == 1);
+				dsm_control->item[control_slot].refcnt = 0;
+				LWLockRelease(DynamicSharedMemoryControlLock);
+			}
+		}
+	}
+
+	/* Clean up our remaining backend-private data structures. */
+	if (seg->resowner != NULL)
+		ResourceOwnerForgetDSM(seg->resowner, seg);
+	dlist_delete(&seg->node);
+	pfree(seg);
+}
+
+/*
+ * Keep a dynamic shared memory mapping until end of session.
+ *
+ * By default, mappings are owned by the current resource owner, which
+ * typically means they stick around for the duration of the current query
+ * only.
+ */
+void
+dsm_keep_mapping(dsm_segment *seg)
+{
+	if (seg->resowner != NULL)
+	{
+		ResourceOwnerForgetDSM(seg->resowner, seg);
+		seg->resowner = NULL;
+	}
+}
+
+/*
+ * Find an existing mapping for a shared memory segment, if there is one.
+ */
+dsm_segment *
+dsm_find_mapping(dsm_handle h)
+{
+	dlist_iter		iter;
+	dsm_segment	   *seg;
+
+	dlist_foreach(iter, &dsm_segment_list)
+	{
+		seg = dlist_container(dsm_segment, node, iter.cur);
+		if (seg->handle == h)
+			return seg;
+	}
+
+	return NULL;
+}
+
+/*
+ * Get the address at which a dynamic shared memory segment is mapped.
+ */
+void *
+dsm_segment_address(dsm_segment *seg)
+{
+	Assert(seg->mapped_address != NULL);
+	return seg->mapped_address;
+}
+
+/*
+ * Get the size of a mapping.
+ */
+uint64
+dsm_segment_map_length(dsm_segment *seg)
+{
+	Assert(seg->mapped_address != NULL);
+	return seg->mapped_size;
+}
+
+/*
+ * Get a handle for a mapping.
+ *
+ * To establish communication via dynamic shared memory between two backends,
+ * one of them should first call dsm_create() to establish a new shared
+ * memory mapping.  That process should then call dsm_segment_handle() to
+ * obtain a handle for the mapping, and pass that handle to the
+ * coordinating backend via some means (e.g. bgw_main_arg, or via the
+ * main shared memory segment).  The recipient, once in position of the
+ * handle, should call dsm_attach().
+ */
+dsm_handle
+dsm_segment_handle(dsm_segment *seg)
+{
+	return seg->handle;
+}
+
+/*
+ * Create a segment descriptor.
+ */
+static dsm_segment *
+dsm_create_descriptor(void)
+{
+	dsm_segment	   *seg;
+
+	ResourceOwnerEnlargeDSMs(CurrentResourceOwner);
+
+	seg = MemoryContextAlloc(TopMemoryContext, sizeof(dsm_segment));
+	dlist_push_head(&dsm_segment_list, &seg->node);
+
+	/* seg->handle must be initialized by the caller */
+	seg->control_slot = INVALID_CONTROL_SLOT;
+	seg->impl_private = NULL;
+	seg->mapped_address = NULL;
+	seg->mapped_size = 0;
+
+	seg->resowner = CurrentResourceOwner;
+	ResourceOwnerRememberDSM(CurrentResourceOwner, seg);
+
+	return seg;
+}
+
+/*
+ * Sanity check a control segment.
+ *
+ * The goal here isn't to detect everything that could possibly be wrong with
+ * the control segment; there's not enough information for that.  Rather, the
+ * goal is to make sure that someone can iterate over the items in the segment
+ * without overrunning the end of the mapping and crashing.  We also check
+ * the magic number since, if that's messed up, this may not even be one of
+ * our segments at all.
+ */
+static bool
+dsm_control_segment_sane(dsm_control_header *control, uint64 mapped_size)
+{
+	if (mapped_size < offsetof(dsm_control_header, item))
+		return false;			/* Mapped size too short to read header. */
+	if (control->magic != PG_DYNSHMEM_CONTROL_MAGIC)
+		return false;			/* Magic number doesn't match. */
+	if (dsm_control_bytes_needed(control->maxitems) > mapped_size)
+		return false;			/* Max item count won't fit in map. */
+	if (control->nitems > control->maxitems)
+		return false;			/* Overfull. */
+	return true;
+}
+
+/*
+ * Compute the number of control-segment bytes needed to store a given
+ * number of items.
+ */
+static uint64
+dsm_control_bytes_needed(uint32 nitems)
+{
+	return offsetof(dsm_control_header, item)
+		+ sizeof(dsm_control_item) * (uint64) nitems;
+}
diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
new file mode 100644
index 0000000..b00e63a
--- /dev/null
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -0,0 +1,990 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm_impl.c
+ *	  manage dynamic shared memory segments
+ *
+ * This file provides low-level APIs for creating and destroying shared
+ * memory segments using several different possible techniques.  We refer
+ * to these segments as dynamic because they can be created, altered, and
+ * destroyed at any point during the server life cycle.  This is unlike
+ * the main shared memory segment, of which there is always exactly one
+ * and which is always mapped at a fixed address in every PostgreSQL
+ * background process.
+ *
+ * Because not all systems provide the same primitives in this area, nor
+ * do all primitives behave the same way on all systems, we provide
+ * several implementations of this facility.  Many systems implement
+ * POSIX shared memory (shm_open etc.), which is well-suited to our needs
+ * in this area, with the exception that shared memory identifiers live
+ * in a flat system-wide namespace, raising the uncomfortable prospect of
+ * name collisions with other processes (including other copies of
+ * PostgreSQL) running on the same system.  Some systems only support
+ * the older System V shared memory interface (shmget etc.) which is
+ * also usable; however, the default allocation limits are often quite
+ * small, and the namespace is even more restricted.
+ *
+ * We also provide an mmap-based shared memory implementation.  This may
+ * be useful on systems that provide shared memory via a special-purpose
+ * filesystem; by opting for this implementation, the user can even
+ * control precisely where their shared memory segments are placed.  It
+ * can also be used as a fallback for systems where shm_open and shmget
+ * are not available or can't be used for some reason.  Of course,
+ * mapping a file residing on an actual spinning disk is a fairly poor
+ * approximation for shared memory because writeback may hurt performance
+ * substantially, but there should be few systems where we must make do
+ * with such poor tools.
+ *
+ * As ever, Windows requires its own implemetation.
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/storage/ipc/dsm.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#ifndef WIN32
+#include <sys/mman.h>
+#endif
+#include <sys/stat.h>
+#ifdef HAVE_SYS_IPC_H
+#include <sys/ipc.h>
+#endif
+#ifdef HAVE_SYS_SHM_H
+#include <sys/shm.h>
+#endif
+
+#include "portability/mem.h"
+#include "storage/dsm_impl.h"
+#include "storage/fd.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+
+#ifdef USE_DSM_POSIX
+static bool dsm_impl_posix(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address,
+			   uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_SYSV
+static bool dsm_impl_sysv(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address,
+			   uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_WINDOWS
+static bool dsm_impl_windows(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address,
+			  uint64 *mapped_size, int elevel);
+#endif
+#ifdef USE_DSM_MMAP
+static bool dsm_impl_mmap(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address,
+			  uint64 *mapped_size, int elevel);
+#endif
+static int errcode_for_dynamic_shared_memory(void);
+
+const struct config_enum_entry dynamic_shared_memory_options[] = {
+#ifdef USE_DSM_POSIX
+	{ "posix", DSM_IMPL_POSIX, false},
+#endif
+#ifdef USE_DSM_SYSV
+	{ "sysv", DSM_IMPL_SYSV, false},
+#endif
+#ifdef USE_DSM_WINDOWS
+	{ "windows", DSM_IMPL_WINDOWS, false},
+#endif
+#ifdef USE_DSM_MMAP
+	{ "mmap", DSM_IMPL_MMAP, false},
+#endif
+	{ "none", DSM_IMPL_NONE, false},
+	{NULL, 0, false}
+};
+
+/* Implementation selector. */
+int dynamic_shared_memory_type;
+
+/* Size of buffer to be used for zero-filling. */
+#define ZBUFFER_SIZE				8192
+
+/*------
+ * Perform a low-level shared memory operation in a platform-specific way,
+ * as dictated by the selected implementation.  Each implementation is
+ * required to implement the following primitives.
+ *
+ * DSM_OP_CREATE.  Create a segment whose size is the request_size and
+ * map it.
+ *
+ * DSM_OP_ATTACH.  Map the segment, whose size must be the request_size.
+ * The segment may already be mapped; any existing mapping should be removed
+ * before creating a new one.
+ *
+ * DSM_OP_DETACH.  Unmap the segment.
+ *
+ * DSM_OP_RESIZE.  Resize the segment to the given request_size and
+ * remap the segment at that new size.
+ *
+ * DSM_OP_DESTROY.  Unmap the segment, if it is mapped.  Destroy the
+ * segment.
+ *
+ * Arguments:
+ *   op: The operation to be performed.
+ *   handle: The handle of an existing object, or for DSM_OP_CREATE, the
+ *     a new handle the caller wants created.
+ *   request_size: For DSM_OP_CREATE, the requested size.  For DSM_OP_RESIZE,
+ *     the new size.  Otherwise, 0.
+ *   impl_private: Private, implementation-specific data.  Will be a pointer
+ *     to NULL for the first operation on a shared memory segment within this
+ *     backend; thereafter, it will point to the value to which it was set
+ *     on the previous call.
+ *   mapped_address: Pointer to start of current mapping; pointer to NULL
+ *     if none.  Updated with new mapping address.
+ *   mapped_size: Pointer to size of current mapping; pointer to 0 if none.
+ *     Updated with new mapped size.
+ *   elevel: Level at which to log errors.
+ *
+ * Return value: true on success, false on failure.  When false is returned,
+ * a message should first be logged at the specified elevel, except in the
+ * case where DSM_OP_CREATE experiences a name collision, which should
+ * silently return false.
+ *-----
+ */
+bool
+dsm_impl_op(dsm_op op, dsm_handle handle, uint64 request_size,
+			void **impl_private, void **mapped_address, uint64 *mapped_size,
+			int elevel)
+{
+	Assert(op == DSM_OP_CREATE || op == DSM_OP_RESIZE || request_size == 0);
+	Assert((op != DSM_OP_CREATE && op != DSM_OP_ATTACH) ||
+			(*mapped_address == NULL && *mapped_size == 0));
+
+	if (request_size > (size_t) -1)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("requested shared memory size overflows size_t")));
+
+	switch (dynamic_shared_memory_type)
+	{
+#ifdef USE_DSM_POSIX
+		case DSM_IMPL_POSIX:
+			return dsm_impl_posix(op, handle, request_size, impl_private,
+								  mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_SYSV
+		case DSM_IMPL_SYSV:
+			return dsm_impl_sysv(op, handle, request_size, impl_private,
+								 mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_WINDOWS
+		case DSM_IMPL_WINDOWS:
+			return dsm_impl_windows(op, handle, request_size, impl_private,
+									mapped_address, mapped_size, elevel);
+#endif
+#ifdef USE_DSM_MMAP
+		case DSM_IMPL_MMAP:
+			return dsm_impl_mmap(op, handle, request_size, impl_private,
+								 mapped_address, mapped_size, elevel);
+#endif
+	}
+	elog(ERROR, "unexpected dynamic shared memory type: %d",
+		 dynamic_shared_memory_type);
+}
+
+/*
+ * Does the current dynamic shared memory implementation support resizing
+ * segments?  (The answer here could be platform-dependent in the future,
+ * since AIX allows shmctl(shmid, SHM_RESIZE, &buffer), though you apparently
+ * can't resize segments to anything larger than 256MB that way.  For now,
+ * we keep it simple.)
+ */
+bool
+dsm_impl_can_resize(void)
+{
+	switch (dynamic_shared_memory_type)
+	{
+		case DSM_IMPL_NONE:
+			return false;
+		case DSM_IMPL_POSIX:
+			return true;
+		case DSM_IMPL_SYSV:
+			return false;
+		case DSM_IMPL_WINDOWS:
+			return false;
+		case DSM_IMPL_MMAP:
+			return false;
+		default:
+			return false;		/* should not happen */
+	}
+}
+
+#ifdef USE_DSM_POSIX
+/*
+ * Operating system primitives to support POSIX shared memory.
+ *
+ * POSIX shared memory segments are created and attached using shm_open()
+ * and shm_unlink(); other operations, such as sizing or mapping the
+ * segment, are performed as if the shared memory segments were files.
+ *
+ * Indeed, on some platforms, they may be implemented that way.  While
+ * POSIX shared memory segments seem intended to exist in a flat namespace,
+ * some operating systems may implement them as files, even going so far
+ * to treat a request for /xyz as a request to create a file by that name
+ * in the root directory.  Users of such broken platforms should select
+ * a different shared memory implementation.
+ */
+static bool
+dsm_impl_posix(dsm_op op, dsm_handle handle, uint64 request_size,
+			   void **impl_private, void **mapped_address, uint64 *mapped_size,
+			   int elevel)
+{
+	char	name[64];
+	int		flags;
+	int		fd;
+	char   *address;
+
+	snprintf(name, 64, "/PostgreSQL.%lu", (unsigned long) handle);
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& munmap(*mapped_address, *mapped_size) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && shm_unlink(name) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/*
+	 * Create new segment or open an existing one for attach or resize.
+	 *
+	 * Even though we're not going through fd.c, we should be safe against
+	 * running out of file descriptors, because of NUM_RESERVED_FDS.  We're
+	 * only opening one extra descriptor here, and we'll close it before
+	 * returning.
+	 */
+	flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
+	if ((fd = shm_open(name, flags, 0600)) == -1)
+	{
+		if (errno != EEXIST)
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * If we're attaching the segment, determine the current size; if we are
+	 * creating or resizing the segment, set the size to the requested value.
+	 */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct stat st;
+
+		if (fstat(fd, &st) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			close(fd);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = st.st_size;
+	}
+	else if (*mapped_size != request_size && ftruncate(fd, request_size))
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+					name, request_size)));
+		return false;
+	}
+
+	/*
+	 * If we're reattaching or resizing, we must remove any existing mapping,
+	 * unless we've already got the right thing mapped.
+	 */
+	if (*mapped_address != NULL)
+	{
+		if (*mapped_size == request_size)
+			return true;
+		if (munmap(*mapped_address, *mapped_size) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			close(fd);
+			if (op == DSM_OP_CREATE)
+				shm_unlink(name);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+	}
+
+	/* Map it. */
+	address = mmap(NULL, request_size, PROT_READ|PROT_WRITE,
+				   MAP_SHARED|MAP_HASSEMAPHORE, fd, 0);
+	if (address == MAP_FAILED)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+	close(fd);
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_SYSV
+/*
+ * Operating system primitives to support System V shared memory.
+ *
+ * System V shared memory segments are manipulated using shmget(), shmat(),
+ * shmdt(), and shmctl().  There's no portable way to resize such
+ * segments.  As the default allocation limits for System V shared memory
+ * are usually quite low, the POSIX facilities may be preferable; but
+ * those are not supported everywhere.
+ */
+static bool
+dsm_impl_sysv(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address, uint64 *mapped_size,
+			  int elevel)
+{
+	key_t	key;
+	int		ident;
+	char   *address;
+	char	name[64];
+	int	   *ident_cache;
+
+	/* Resize is not supported for System V shared memory. */
+	if (op == DSM_OP_RESIZE)
+	{
+		elog(elevel, "System V shared memory segments cannot be resized");
+		return false;
+	}
+
+	/* Since resize isn't supported, reattach is a no-op. */
+	if (op == DSM_OP_ATTACH && *mapped_address != NULL)
+		return true;
+
+	/*
+	 * POSIX shared memory and mmap-based shared memory identify segments
+	 * with names.  To avoid needless error message variation, we use the
+	 * handle as the name.
+	 */
+	snprintf(name, 64, "%lu", (unsigned long) handle);
+
+	/*
+	 * The System V shared memory namespace is very restricted; names are
+	 * of type key_t, which is expected to be some sort of integer data type,
+	 * but not necessarily the same one as dsm_handle.  Since we use
+	 * dsm_handle to identify shared memory segments across processes, this
+	 * might seem like a problem, but it's really not.  If dsm_handle is
+	 * bigger than key_t, the cast below might truncate away some bits from
+	 * the handle the user-provided, but it'll truncate exactly the same bits
+	 * away in exactly the same fashion every time we use that handle, which
+	 * is all that really matters.  Conversely, if dsm_handle is smaller than
+	 * key_t, we won't use the full range of available key space, but that's
+	 * no big deal either.
+	 *
+	 * We do make sure that the key isn't negative, because that might not
+	 * be portable.
+	 */
+	key = (key_t) handle;
+	if (key < 1)		/* avoid compiler warning if type is unsigned */
+		key = -key;
+
+	/*
+	 * There's one special key, IPC_PRIVATE, which can't be used.  If we end
+	 * up with that value by chance during a create operation, just pretend
+	 * it already exists, so that caller will retry.  If we run into it
+	 * anywhere else, the caller has passed a handle that doesn't correspond
+	 * to anything we ever created, which should not happen.
+	 */
+	if (key == IPC_PRIVATE)
+	{
+		if (op != DSM_OP_CREATE)
+			elog(DEBUG4, "System V shared memory key may not be IPC_PRIVATE");
+		errno = EEXIST;
+		return false;
+	}
+
+	/*
+	 * Before we can do anything with a shared memory segment, we have to
+	 * map the shared memory key to a shared memory identifier using shmget().
+	 * To avoid repeated lookups, we store the key using impl_private.
+	 */
+	if (*impl_private != NULL)
+	{
+		ident_cache = *impl_private;
+		ident = *ident_cache;
+	}
+	else
+	{
+		int		flags = IPCProtection;
+		size_t	segsize;
+
+		/*
+		 * Allocate the memory BEFORE acquiring the resource, so that we don't
+		 * leak the resource if memory allocation fails.
+		 */
+		ident_cache = MemoryContextAlloc(TopMemoryContext, sizeof(int));
+
+		/*
+		 * When using shmget to find an existing segment, we must pass the
+		 * size as 0.  Passing a non-zero size which is greater than the
+		 * actual size will result in EINVAL.
+		 */
+		segsize = 0;
+
+		if (op == DSM_OP_CREATE)
+		{
+			flags |= IPC_CREAT | IPC_EXCL;
+			segsize = request_size;
+		}
+
+		if ((ident = shmget(key, segsize, flags)) == -1)
+		{
+			if (errno != EEXIST)
+			{
+				int		save_errno = errno;
+				pfree(ident_cache);
+				errno = save_errno;
+				ereport(elevel,
+						(errcode_for_dynamic_shared_memory(),
+						 errmsg("could not get shared memory segment: %m")));
+			}
+			return false;
+		}
+
+		*ident_cache = ident;
+		*impl_private = ident_cache;
+	}
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		pfree(ident_cache);
+		*impl_private = NULL;
+		if (*mapped_address != NULL && shmdt(*mapped_address) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && shmctl(ident, IPC_RMID, NULL) < 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/* If we're attaching it, we must use IPC_STAT to determine the size. */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct shmid_ds shm;
+
+		if (shmctl(ident, IPC_STAT, &shm) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			if (op == DSM_OP_CREATE)
+				shmctl(ident, IPC_RMID, NULL);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = shm.shm_segsz;
+	}
+
+	/* Map it. */
+	address = shmat(ident, NULL, PG_SHMAT_FLAGS);
+	if (address == (void *) -1)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		if (op == DSM_OP_CREATE)
+			shmctl(ident, IPC_RMID, NULL);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_WINDOWS
+/*
+ * Operating system primitives to support Windows shared memory.
+ *
+ * Windows shared memory implementation is done using file mapping
+ * which can be backed by either physical file or system paging file.
+ * Current implementation uses system paging file as other effects
+ * like performance are not clear for physical file and it is used in similar
+ * way for main shared memory in windows.
+ *
+ * A memory mapping object is a kernel object - they always get deleted when
+ * the last reference to them goes away, either explicitly via a CloseHandle or
+ * when the process containing the reference exits.
+ */
+static bool
+dsm_impl_windows(dsm_op op, dsm_handle handle, uint64 request_size,
+				 void **impl_private, void **mapped_address,
+				 uint64 *mapped_size, int elevel)
+{
+	char   *address;
+	HANDLE		hmap;
+	char	name[64];
+	MEMORY_BASIC_INFORMATION info;
+
+	/* Resize is not supported for Windows shared memory. */
+	if (op == DSM_OP_RESIZE)
+	{
+		elog(elevel, "Windows shared memory segments cannot be resized");
+		return false;
+	}
+
+	/* Since resize isn't supported, reattach is a no-op. */
+	if (op == DSM_OP_ATTACH && *mapped_address != NULL)
+		return true;
+
+	/*
+	 * Storing the shared memory segment in the Global\ namespace, can
+	 * allow any process running in any session to access that file
+	 * mapping object provided that the caller has the required access rights.
+	 * But to avoid issues faced in main shared memory, we are using the naming
+	 * convention similar to main shared memory. We can change here once
+	 * issue mentioned in GetSharedMemName is resolved.
+	 */
+	snprintf(name, 64, "Global/PostgreSQL.%lu", (unsigned long) handle);
+
+	/*
+	 * Handle teardown cases.  Since Windows automatically destroys the object
+	 * when no references reamin, we can treat it the same as detach.
+	 */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& UnmapViewOfFile(*mapped_address) == 0)
+		{
+			_dosmaperr(GetLastError());
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		if (*impl_private != NULL
+			&& CloseHandle(*impl_private) == 0)
+		{
+			_dosmaperr(GetLastError());
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+
+		*impl_private = NULL;
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		return true;
+	}
+
+	/* Create new segment or open an existing one for attach. */
+	if (op == DSM_OP_CREATE)
+	{
+		DWORD		size_high = (DWORD) (request_size >> 32);
+		DWORD		size_low = (DWORD) request_size;
+		hmap = CreateFileMapping(INVALID_HANDLE_VALUE,	/* Use the pagefile */
+								 NULL,			/* Default security attrs */
+								 PAGE_READWRITE,	/* Memory is read/write */
+								 size_high, 	/* Upper 32 bits of size */
+								 size_low,		/* Lower 32 bits of size */
+								 name);
+		_dosmaperr(GetLastError());
+		if (errno == EEXIST)
+		{
+			/*
+			 * On Windows, when the segment already exists, a handle for the
+			 * existing segment is returned.  We must close it before
+			 * returning.  We don't do _dosmaperr here, so errno won't be
+			 * modified.
+			 */
+			CloseHandle(hmap);
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+	}
+	else
+	{
+		hmap = OpenFileMapping(FILE_MAP_WRITE | FILE_MAP_READ,
+							   FALSE,		/* do not inherit the name */
+							   name);		/* name of mapping object */
+		_dosmaperr(GetLastError());
+	}
+
+	if (!hmap)
+	{
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not open shared memory segment \"%s\": %m",
+					name)));
+		return false;
+	}
+
+	/* Map it. */
+	address = MapViewOfFile(hmap, FILE_MAP_WRITE | FILE_MAP_READ,
+							0, 0, 0);
+	if (!address)
+	{
+		int		save_errno;
+
+		_dosmaperr(GetLastError());
+		/* Back out what's already been done. */
+		save_errno = errno;
+		CloseHandle(hmap);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * VirtualQuery gives size in page_size units, which is 4K for Windows.
+	 * We need size only when we are attaching, but it's better to get the
+	 * size when creating new segment to keep size consistent both for
+	 * DSM_OP_CREATE and DSM_OP_ATTACH.
+	 */
+	if (VirtualQuery(address, &info, sizeof(info)) == 0)
+	{
+		int		save_errno;
+
+		_dosmaperr(GetLastError());
+		/* Back out what's already been done. */
+		save_errno = errno;
+		UnmapViewOfFile(address);
+		CloseHandle(hmap);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				errmsg("could not stat shared memory segment \"%s\": %m",
+					name)));
+		return false;
+	}
+
+	*mapped_address = address;
+	*mapped_size = info.RegionSize;
+	*impl_private = hmap;
+
+	return true;
+}
+#endif
+
+#ifdef USE_DSM_MMAP
+/*
+ * Operating system primitives to support mmap-based shared memory.
+ *
+ * Calling this "shared memory" is somewhat of a misnomer, because what
+ * we're really doing is creating a bunch of files and mapping them into
+ * our address space.  The operating system may feel obliged to
+ * synchronize the contents to disk even if nothing is being paged out,
+ * which will not serve us well.  The user can relocate the pg_dynshmem
+ * directory to a ramdisk to avoid this problem, if available.
+ */
+static bool
+dsm_impl_mmap(dsm_op op, dsm_handle handle, uint64 request_size,
+			  void **impl_private, void **mapped_address, uint64 *mapped_size,
+			  int elevel)
+{
+	char	name[64];
+	int		flags;
+	int		fd;
+	char   *address;
+
+	snprintf(name, 64, PG_DYNSHMEM_DIR "/" PG_DYNSHMEM_MMAP_FILE_PREFIX "%lu",
+		(unsigned long) handle);
+
+	/* Handle teardown cases. */
+	if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
+	{
+		if (*mapped_address != NULL
+			&& munmap(*mapped_address, *mapped_size) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+		if (op == DSM_OP_DESTROY && unlink(name) != 0)
+		{
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not remove shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		return true;
+	}
+
+	/* Create new segment or open an existing one for attach or resize. */
+	flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
+	if ((fd = OpenTransientFile(name, flags, 0600)) == -1)
+	{
+		if (errno != EEXIST)
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not open shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+
+	/*
+	 * If we're attaching the segment, determine the current size; if we are
+	 * creating or resizing the segment, set the size to the requested value.
+	 */
+	if (op == DSM_OP_ATTACH)
+	{
+		struct stat st;
+
+		if (fstat(fd, &st) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not stat shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		request_size = st.st_size;
+	}
+	else if (*mapped_size > request_size && ftruncate(fd, request_size))
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		close(fd);
+		if (op == DSM_OP_CREATE)
+			shm_unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+					name, request_size)));
+		return false;
+	}
+	else if (*mapped_size < request_size)
+	{
+		/*
+		 * Allocate a buffer full of zeros.
+		 *
+		 * Note: palloc zbuffer, instead of just using a local char array,
+		 * to ensure it is reasonably well-aligned; this may save a few
+		 * cycles transferring data to the kernel.
+		 */
+		char   *zbuffer = (char *) palloc0(ZBUFFER_SIZE);
+		uint32	remaining = request_size;
+		bool	success = true;
+
+		/*
+		 * Zero-fill the file. We have to do this the hard way to ensure
+		 * that all the file space has really been allocated, so that we
+		 * don't later seg fault when accessing the memory mapping.  This
+		 * is pretty pessimal.
+		 */
+		while (success && remaining > 0)
+		{
+			uint64	goal = remaining;
+
+			if (goal > ZBUFFER_SIZE)
+				goal = ZBUFFER_SIZE;
+			if (write(fd, zbuffer, goal) == goal)
+				remaining -= goal;
+			else
+				success = false;
+		}
+
+		if (!success)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			if (op == DSM_OP_CREATE)
+				unlink(name);
+			errno = save_errno ? save_errno : ENOSPC;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not resize shared memory segment %s to " UINT64_FORMAT " bytes: %m",
+						name, request_size)));
+			return false;
+		}
+	}
+
+	/*
+	 * If we're reattaching or resizing, we must remove any existing mapping,
+	 * unless we've already got the right thing mapped.
+	 */
+	if (*mapped_address != NULL)
+	{
+		if (*mapped_size == request_size)
+			return true;
+		if (munmap(*mapped_address, *mapped_size) != 0)
+		{
+			int		save_errno;
+
+			/* Back out what's already been done. */
+			save_errno = errno;
+			CloseTransientFile(fd);
+			if (op == DSM_OP_CREATE)
+				unlink(name);
+			errno = save_errno;
+
+			ereport(elevel,
+					(errcode_for_dynamic_shared_memory(),
+					 errmsg("could not unmap shared memory segment \"%s\": %m",
+						name)));
+			return false;
+		}
+		*mapped_address = NULL;
+		*mapped_size = 0;
+	}
+
+	/* Map it. */
+	address = mmap(NULL, request_size, PROT_READ|PROT_WRITE,
+				   MAP_SHARED|MAP_HASSEMAPHORE, fd, 0);
+	if (address == MAP_FAILED)
+	{
+		int		save_errno;
+
+		/* Back out what's already been done. */
+		save_errno = errno;
+		CloseTransientFile(fd);
+		if (op == DSM_OP_CREATE)
+			unlink(name);
+		errno = save_errno;
+
+		ereport(elevel,
+				(errcode_for_dynamic_shared_memory(),
+				 errmsg("could not map shared memory segment \"%s\": %m",
+						name)));
+		return false;
+	}
+	*mapped_address = address;
+	*mapped_size = request_size;
+	CloseTransientFile(fd);
+
+	return true;
+}
+#endif
+
+static int
+errcode_for_dynamic_shared_memory()
+{
+	if (errno == EFBIG || errno == ENOMEM)
+		return errcode(ERRCODE_OUT_OF_MEMORY);
+	else
+		return errcode_for_file_access();
+}
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index a0b741b..040c7aa 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -30,6 +30,7 @@
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
 #include "storage/bufmgr.h"
+#include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"
 #include "storage/pmsignal.h"
@@ -249,6 +250,10 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		ShmemBackendArrayAllocation();
 #endif
 
+	/* Initialize dynamic shared memory facilities. */
+	if (!IsUnderPostmaster)
+		dsm_postmaster_startup();
+
 	/*
 	 * Now give loadable modules a chance to set up their shmem allocations
 	 */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 3107f9c..44a0e75 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -61,6 +61,7 @@
 #include "replication/walreceiver.h"
 #include "replication/walsender.h"
 #include "storage/bufmgr.h"
+#include "storage/dsm_impl.h"
 #include "storage/standby.h"
 #include "storage/fd.h"
 #include "storage/proc.h"
@@ -385,6 +386,7 @@ static const struct config_enum_entry synchronous_commit_options[] = {
  */
 extern const struct config_enum_entry wal_level_options[];
 extern const struct config_enum_entry sync_method_options[];
+extern const struct config_enum_entry dynamic_shared_memory_options[];
 
 /*
  * GUC option variables that are exported from this module
@@ -3336,6 +3338,16 @@ static struct config_enum ConfigureNamesEnum[] =
 	},
 
 	{
+		{"dynamic_shared_memory_type", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Selects the dynamic shared memory implementation used."),
+			NULL
+		},
+		&dynamic_shared_memory_type,
+		DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE, dynamic_shared_memory_options,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"wal_sync_method", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Selects the method used for forcing WAL updates to disk."),
 			NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index d69a02b..c9cea28 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -123,6 +123,13 @@
 #work_mem = 1MB				# min 64kB
 #maintenance_work_mem = 16MB		# min 1MB
 #max_stack_depth = 2MB			# min 100kB
+#dynamic_shared_memory_type = posix # the default is the first option
+					# supported by the operating system:
+					#   posix
+					#   sysv
+					#   windows
+					#   mmap
+					# use none to disable dynamic shared memory
 
 # - Disk -
 
diff --git a/src/backend/utils/resowner/resowner.c b/src/backend/utils/resowner/resowner.c
index e7ec393..43542cf 100644
--- a/src/backend/utils/resowner/resowner.c
+++ b/src/backend/utils/resowner/resowner.c
@@ -98,6 +98,11 @@ typedef struct ResourceOwnerData
 	int			nfiles;			/* number of owned temporary files */
 	File	   *files;			/* dynamically allocated array */
 	int			maxfiles;		/* currently allocated array size */
+
+	/* We have built-in support for remembering dynamic shmem segments */
+	int			ndsms;			/* number of owned shmem segments */
+	dsm_segment **dsms;			/* dynamically allocated array */
+	int			maxdsms;		/* currently allocated array size */
 }	ResourceOwnerData;
 
 
@@ -132,6 +137,7 @@ static void PrintPlanCacheLeakWarning(CachedPlan *plan);
 static void PrintTupleDescLeakWarning(TupleDesc tupdesc);
 static void PrintSnapshotLeakWarning(Snapshot snapshot);
 static void PrintFileLeakWarning(File file);
+static void PrintDSMLeakWarning(dsm_segment *seg);
 
 
 /*****************************************************************************
@@ -271,6 +277,21 @@ ResourceOwnerReleaseInternal(ResourceOwner owner,
 				PrintRelCacheLeakWarning(owner->relrefs[owner->nrelrefs - 1]);
 			RelationClose(owner->relrefs[owner->nrelrefs - 1]);
 		}
+
+		/*
+		 * Release dynamic shared memory segments.  Note that dsm_detach()
+		 * will remove the segment from my list, so I just have to iterate
+		 * until there are none.
+		 *
+		 * As in the preceding cases, warn if there are leftover at commit
+		 * time.
+		 */
+		while (owner->ndsms > 0)
+		{
+			if (isCommit)
+				PrintDSMLeakWarning(owner->dsms[owner->ndsms - 1]);
+			dsm_detach(owner->dsms[owner->ndsms - 1]);
+		}
 	}
 	else if (phase == RESOURCE_RELEASE_LOCKS)
 	{
@@ -438,6 +459,8 @@ ResourceOwnerDelete(ResourceOwner owner)
 		pfree(owner->snapshots);
 	if (owner->files)
 		pfree(owner->files);
+	if (owner->dsms)
+		pfree(owner->dsms);
 
 	pfree(owner);
 }
@@ -1230,3 +1253,88 @@ PrintFileLeakWarning(File file)
 		 "temporary file leak: File %d still referenced",
 		 file);
 }
+
+/*
+ * Make sure there is room for at least one more entry in a ResourceOwner's
+ * dynamic shmem segment reference array.
+ *
+ * This is separate from actually inserting an entry because if we run out
+ * of memory, it's critical to do so *before* acquiring the resource.
+ */
+void
+ResourceOwnerEnlargeDSMs(ResourceOwner owner)
+{
+	int			newmax;
+
+	if (owner->ndsms < owner->maxdsms)
+		return;					/* nothing to do */
+
+	if (owner->dsms == NULL)
+	{
+		newmax = 16;
+		owner->dsms = (dsm_segment **)
+			MemoryContextAlloc(TopMemoryContext,
+							   newmax * sizeof(dsm_segment *));
+		owner->maxdsms = newmax;
+	}
+	else
+	{
+		newmax = owner->maxdsms * 2;
+		owner->dsms = (dsm_segment **)
+			repalloc(owner->dsms, newmax * sizeof(dsm_segment *));
+		owner->maxdsms = newmax;
+	}
+}
+
+/*
+ * Remember that a dynamic shmem segment is owned by a ResourceOwner
+ *
+ * Caller must have previously done ResourceOwnerEnlargeDSMs()
+ */
+void
+ResourceOwnerRememberDSM(ResourceOwner owner, dsm_segment *seg)
+{
+	Assert(owner->ndsms < owner->maxdsms);
+	owner->dsms[owner->ndsms] = seg;
+	owner->ndsms++;
+}
+
+/*
+ * Forget that a temporary file is owned by a ResourceOwner
+ */
+void
+ResourceOwnerForgetDSM(ResourceOwner owner, dsm_segment *seg)
+{
+	dsm_segment **dsms = owner->dsms;
+	int			ns1 = owner->ndsms - 1;
+	int			i;
+
+	for (i = ns1; i >= 0; i--)
+	{
+		if (dsms[i] == seg)
+		{
+			while (i < ns1)
+			{
+				dsms[i] = dsms[i + 1];
+				i++;
+			}
+			owner->ndsms = ns1;
+			return;
+		}
+	}
+	elog(ERROR,
+		 "dynamic shared memory segment %lu is not owned by resource owner %s",
+		 (unsigned long) dsm_segment_handle(seg), owner->name);
+}
+
+
+/*
+ * Debugging subroutine
+ */
+static void
+PrintDSMLeakWarning(dsm_segment *seg)
+{
+	elog(WARNING,
+		 "dynamic shared memory leak: segment %lu still referenced",
+		 (unsigned long) dsm_segment_handle(seg));
+}
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index f66f530..a6eb0d8 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -182,6 +182,7 @@ const char *subdirs[] = {
 	"pg_xlog",
 	"pg_xlog/archive_status",
 	"pg_clog",
+	"pg_dynshmem",
 	"pg_notify",
 	"pg_serial",
 	"pg_snapshots",
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 8aabf3c..5eac52d 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -424,6 +424,9 @@
 /* Define to 1 if you have the `setsid' function. */
 #undef HAVE_SETSID
 
+/* Define to 1 if you have the `shm_open' function. */
+#undef HAVE_SHM_OPEN
+
 /* Define to 1 if you have the `sigprocmask' function. */
 #undef HAVE_SIGPROCMASK
 
diff --git a/src/include/portability/mem.h b/src/include/portability/mem.h
new file mode 100644
index 0000000..2a07c10
--- /dev/null
+++ b/src/include/portability/mem.h
@@ -0,0 +1,40 @@
+/*-------------------------------------------------------------------------
+ *
+ * mem.h
+ *	  portability definitions for various memory operations
+ *
+ * Copyright (c) 2001-2013, PostgreSQL Global Development Group
+ *
+ * src/include/portability/mem.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef MEM_H
+#define MEM_H
+
+#define IPCProtection	(0600)	/* access/modify by user only */
+
+#ifdef SHM_SHARE_MMU			/* use intimate shared memory on Solaris */
+#define PG_SHMAT_FLAGS			SHM_SHARE_MMU
+#else
+#define PG_SHMAT_FLAGS			0
+#endif
+
+/* Linux prefers MAP_ANONYMOUS, but the flag is called MAP_ANON on other systems. */
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS			MAP_ANON
+#endif
+
+/* BSD-derived systems have MAP_HASSEMAPHORE, but it's not present (or needed) on Linux. */
+#ifndef MAP_HASSEMAPHORE
+#define MAP_HASSEMAPHORE		0
+#endif
+
+#define PG_MMAP_FLAGS			(MAP_SHARED|MAP_ANONYMOUS|MAP_HASSEMAPHORE)
+
+/* Some really old systems don't define MAP_FAILED. */
+#ifndef MAP_FAILED
+#define MAP_FAILED ((void *) -1)
+#endif
+
+#endif   /* MEM_H */
diff --git a/src/include/storage/dsm.h b/src/include/storage/dsm.h
new file mode 100644
index 0000000..2b5e722
--- /dev/null
+++ b/src/include/storage/dsm.h
@@ -0,0 +1,39 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm.h
+ *	  manage dynamic shared memory segments
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/dsm.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSM_H
+#define DSM_H
+
+#include "storage/dsm_impl.h"
+
+typedef struct dsm_segment dsm_segment;
+
+/* Initialization function. */
+extern void dsm_postmaster_startup(void);
+
+/* Functions that create, update, or remove mappings. */
+extern dsm_segment *dsm_create(uint64 size);
+extern dsm_segment *dsm_attach(dsm_handle h);
+extern void *dsm_resize(dsm_segment *seg, uint64 size);
+extern void *dsm_remap(dsm_segment *seg);
+extern void dsm_detach(dsm_segment *seg);
+
+/* Resource management functions. */
+extern void dsm_keep_mapping(dsm_segment *seg);
+extern dsm_segment *dsm_find_mapping(dsm_handle h);
+
+/* Informational functions. */
+extern void *dsm_segment_address(dsm_segment *seg);
+extern uint64 dsm_segment_map_length(dsm_segment *seg);
+extern dsm_handle dsm_segment_handle(dsm_segment *seg);
+
+#endif   /* DSM_H */
diff --git a/src/include/storage/dsm_impl.h b/src/include/storage/dsm_impl.h
new file mode 100644
index 0000000..13f1f48
--- /dev/null
+++ b/src/include/storage/dsm_impl.h
@@ -0,0 +1,75 @@
+/*-------------------------------------------------------------------------
+ *
+ * dsm_impl.h
+ *	  low-level dynamic shared memory primitives
+ *
+ * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/dsm_impl.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef DSM_IMPL_H
+#define DSM_IMPL_H
+
+/* Dynamic shared memory implementations. */
+#define DSM_IMPL_NONE			0
+#define DSM_IMPL_POSIX			1
+#define DSM_IMPL_SYSV			2
+#define DSM_IMPL_WINDOWS		3
+#define DSM_IMPL_MMAP			4
+
+/*
+ * Determine which dynamic shared memory implementations will be supported
+ * on this platform, and which one will be the default.
+ */
+#ifdef WIN32
+#define USE_DSM_WINDOWS
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_WINDOWS
+#else
+#ifdef HAVE_SHM_OPEN
+#define USE_DSM_POSIX
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_POSIX
+#endif
+#define USE_DSM_SYSV
+#ifndef DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE
+#define DEFAULT_DYNAMIC_SHARED_MEMORY_TYPE		DSM_IMPL_SYSV
+#endif
+#define USE_DSM_MMAP
+#endif
+
+/* GUC. */
+extern int dynamic_shared_memory_type;
+
+/*
+ * Directory for on-disk state.
+ *
+ * This is used by all implementations for crash recovery and by the mmap
+ * implementation for storage.
+ */
+#define PG_DYNSHMEM_DIR					"pg_dynshmem"
+#define PG_DYNSHMEM_MMAP_FILE_PREFIX	"mmap."
+
+/* A "name" for a dynamic shared memory segment. */
+typedef uint32 dsm_handle;
+
+/* All the shared-memory operations we know about. */
+typedef enum
+{
+	DSM_OP_CREATE,
+	DSM_OP_ATTACH,
+	DSM_OP_DETACH,
+	DSM_OP_RESIZE,
+	DSM_OP_DESTROY
+} dsm_op;
+
+/* Create, attach to, detach from, resize, or destroy a segment. */
+extern bool dsm_impl_op(dsm_op op, dsm_handle handle, uint64 request_size,
+			void **impl_private, void **mapped_address, uint64 *mapped_size,
+			int elevel);
+
+/* Some implementations cannot resize segments.  Can this one? */
+extern bool dsm_impl_can_resize(void);
+
+#endif   /* DSM_IMPL_H */
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 39415a3..730c47b 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -80,6 +80,7 @@ typedef enum LWLockId
 	OldSerXidLock,
 	SyncRepLock,
 	BackgroundWorkerLock,
+	DynamicSharedMemoryControlLock,
 	/* Individual lock IDs end here */
 	FirstBufMappingLock,
 	FirstLockMgrLock = FirstBufMappingLock + NUM_BUFFER_PARTITIONS,
diff --git a/src/include/utils/resowner_private.h b/src/include/utils/resowner_private.h
index a5d8707..6693483 100644
--- a/src/include/utils/resowner_private.h
+++ b/src/include/utils/resowner_private.h
@@ -16,6 +16,7 @@
 #ifndef RESOWNER_PRIVATE_H
 #define RESOWNER_PRIVATE_H
 
+#include "storage/dsm.h"
 #include "storage/fd.h"
 #include "storage/lock.h"
 #include "utils/catcache.h"
@@ -80,4 +81,11 @@ extern void ResourceOwnerRememberFile(ResourceOwner owner,
 extern void ResourceOwnerForgetFile(ResourceOwner owner,
 						File file);
 
+/* support for dynamic shared memory management */
+extern void ResourceOwnerEnlargeDSMs(ResourceOwner owner);
+extern void ResourceOwnerRememberDSM(ResourceOwner owner,
+						  dsm_segment *);
+extern void ResourceOwnerForgetDSM(ResourceOwner owner,
+						dsm_segment *);
+
 #endif   /* RESOWNER_PRIVATE_H */

diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index 8e72731..9f1ea5b 100644
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -694,10 +694,6 @@ dsm_impl_windows(dsm_op op, dsm_handle handle, uint64 request_size,
 			 * modified.
 			 */
 			CloseHandle(hmap);
-			ereport(elevel,
-					(errcode_for_dynamic_shared_memory(),
-					 errmsg("could not open shared memory segment \"%s\": %m",
-						name)));
 			return false;
 		}
 	}