Simplify LWLock tranche machinery by removing array_base/array_stride.

array_base and array_stride were added so that we could identify the
offset of an LWLock within a tranche, but this facility is only very
marginally used apart from the main tranche.  So, give every lock in
the main tranche its own tranche ID and get rid of array_base,
array_stride, and all that's attached.  For debugging facilities
(Trace_lwlocks and LWLOCK_STATS) print the pointer address of the
LWLock using %p instead of the offset.  This is arguably more useful,
and certainly a lot cheaper.  Drop the offset-within-tranche from
the information reported to dtrace and from one can't-happen message
inside lwlock.c.

The main user-visible impact of this change is that pg_stat_activity
will now report all waits for LWLocks as "LWLock" rather than
reporting some as "LWLockTranche" and others as "LWLockNamed".

The main motivation for this change is that the need to specify an
array_base and an array_stride is awkward for parallel query.  There
is only a very limited supply of tranche IDs so we can't just keep
allocating new ones, and if we try to use the same tranche IDs every
time then we run into trouble when multiple parallel contexts are
use simultaneously.  So if we didn't get rid of this mechanism we'd
have to make it even more complicated.  By simplifying it in this
way, we instead reduce the size of the generated code for lwlock.c
by about 5%.

Discussion: http://postgr.es/m/CA+TgmoYsFn6NUW1x0AZtupJGUAs1UDY4dJtCN47_Q6D0sP80PA@mail.gmail.com

doc/src/sgml/monitoring.sgml

@@ -646,18 +646,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
        <itemizedlist>
         <listitem>
          <para>
-          <literal>LWLockNamed</>: The backend is waiting for a specific named
-          lightweight lock.  Each such lock protects a particular data
-          structure in shared memory.  <literal>wait_event</> will contain
-          the name of the lightweight lock.
-         </para>
-        </listitem>
-        <listitem>
-         <para>
-          <literal>LWLockTranche</>: The backend is waiting for one of a
-          group of related lightweight locks.  All locks in the group perform
-          a similar function; <literal>wait_event</> will identify the general
-          purpose of locks in that group.
+          <literal>LWLock</>: The backend is waiting for a lightweight lock.
+          Each such lock protects a particular data structure in shared memory.
+          <literal>wait_event</> will contain a name identifying the purpose
+          of the lightweight lock.  (Some locks have specific names; others
+          are part of a group of locks each with a similar purpose.)
          </para>
         </listitem>
         <listitem>
@@ -825,7 +818,7 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
 
       <tbody>
        <row>
-        <entry morerows="41"><literal>LWLockNamed</></entry>
+        <entry morerows="57"><literal>LWLock</></entry>
         <entry><literal>ShmemIndexLock</></entry>
         <entry>Waiting to find or allocate space in shared memory.</entry>
        </row>
@@ -1011,7 +1004,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry>Waiting to read or update old snapshot control information.</entry>
         </row>
         <row>
-         <entry morerows="15"><literal>LWLockTranche</></entry>
          <entry><literal>clog</></entry>
          <entry>Waiting for I/O on a clog (transaction status) buffer.</entry>
         </row>
@@ -1279,7 +1271,7 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
  pid  | wait_event_type |  wait_event
 ------+-----------------+---------------
  2540 | Lock            | relation
- 6644 | LWLockNamed     | ProcArrayLock
+ 6644 | LWLock          | ProcArrayLock
 (2 rows)
 </programlisting>
    </para>
@@ -3347,55 +3339,49 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
     </row>
     <row>
      <entry><literal>lwlock-acquire</literal></entry>
-     <entry><literal>(char *, int, LWLockMode)</literal></entry>
+     <entry><literal>(char *, LWLockMode)</literal></entry>
      <entry>Probe that fires when an LWLock has been acquired.
       arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.
-      arg2 is the requested lock mode, either exclusive or shared.</entry>
+      arg1 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry><literal>lwlock-release</literal></entry>
-     <entry><literal>(char *, int)</literal></entry>
+     <entry><literal>(char *)</literal></entry>
      <entry>Probe that fires when an LWLock has been released (but note
       that any released waiters have not yet been awakened).
-      arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.</entry>
+      arg0 is the LWLock's tranche.</entry>
     </row>
     <row>
      <entry><literal>lwlock-wait-start</literal></entry>
-     <entry><literal>(char *, int, LWLockMode)</literal></entry>
+     <entry><literal>(char *, LWLockMode)</literal></entry>
      <entry>Probe that fires when an LWLock was not immediately available and
       a server process has begun to wait for the lock to become available.
       arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.
-      arg2 is the requested lock mode, either exclusive or shared.</entry>
+      arg1 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry><literal>lwlock-wait-done</literal></entry>
-     <entry><literal>(char *, int, LWLockMode)</literal></entry>
+     <entry><literal>(char *, LWLockMode)</literal></entry>
      <entry>Probe that fires when a server process has been released from its
       wait for an LWLock (it does not actually have the lock yet).
       arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.
-      arg2 is the requested lock mode, either exclusive or shared.</entry>
+      arg1 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry><literal>lwlock-condacquire</literal></entry>
-     <entry><literal>(char *, int, LWLockMode)</literal></entry>
+     <entry><literal>(char *, LWLockMode)</literal></entry>
      <entry>Probe that fires when an LWLock was successfully acquired when the
       caller specified no waiting.
       arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.
-      arg2 is the requested lock mode, either exclusive or shared.</entry>
+      arg1 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry><literal>lwlock-condacquire-fail</literal></entry>
-     <entry><literal>(char *, int, LWLockMode)</literal></entry>
+     <entry><literal>(char *, LWLockMode)</literal></entry>
      <entry>Probe that fires when an LWLock was not successfully acquired when
       the caller specified no waiting.
       arg0 is the LWLock's tranche.
-      arg1 is the LWLock's offset within its tranche.
-      arg2 is the requested lock mode, either exclusive or shared.</entry>
+      arg1 is the requested lock mode, either exclusive or shared.</entry>
     </row>
     <row>
      <entry><literal>lock-wait-start</literal></entry>

src/backend/access/transam/slru.c

@@ -216,9 +216,6 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 		Assert(strlen(name) + 1 < SLRU_MAX_NAME_LENGTH);
 		strlcpy(shared->lwlock_tranche_name, name, SLRU_MAX_NAME_LENGTH);
 		shared->lwlock_tranche_id = tranche_id;
-		shared->lwlock_tranche.name = shared->lwlock_tranche_name;
-		shared->lwlock_tranche.array_base = shared->buffer_locks;
-		shared->lwlock_tranche.array_stride = sizeof(LWLockPadded);
 
 		ptr += BUFFERALIGN(offset);
 		for (slotno = 0; slotno < nslots; slotno++)
@@ -237,7 +234,8 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 		Assert(found);
 
 	/* Register SLRU tranche in the main tranches array */
-	LWLockRegisterTranche(shared->lwlock_tranche_id, &shared->lwlock_tranche);
+	LWLockRegisterTranche(shared->lwlock_tranche_id,
+						  shared->lwlock_tranche_name);
 
 	/*
 	 * Initialize the unshared control struct, including directory path. We

src/backend/access/transam/xlog.c

@@ -517,7 +517,6 @@ typedef struct XLogCtlInsert
 	 * WAL insertion locks.
 	 */
 	WALInsertLockPadded *WALInsertLocks;
-	LWLockTranche WALInsertLockTranche;
 } XLogCtlInsert;
 
 /*
@@ -4688,7 +4687,7 @@ XLOGShmemInit(void)
 		/* Initialize local copy of WALInsertLocks and register the tranche */
 		WALInsertLocks = XLogCtl->Insert.WALInsertLocks;
 		LWLockRegisterTranche(LWTRANCHE_WAL_INSERT,
-							  &XLogCtl->Insert.WALInsertLockTranche);
+							  "wal_insert");
 		return;
 	}
 	memset(XLogCtl, 0, sizeof(XLogCtlData));
@@ -4711,11 +4710,7 @@ XLOGShmemInit(void)
 		(WALInsertLockPadded *) allocptr;
 	allocptr += sizeof(WALInsertLockPadded) * NUM_XLOGINSERT_LOCKS;
 
-	XLogCtl->Insert.WALInsertLockTranche.name = "wal_insert";
-	XLogCtl->Insert.WALInsertLockTranche.array_base = WALInsertLocks;
-	XLogCtl->Insert.WALInsertLockTranche.array_stride = sizeof(WALInsertLockPadded);
-
-	LWLockRegisterTranche(LWTRANCHE_WAL_INSERT, &XLogCtl->Insert.WALInsertLockTranche);
+	LWLockRegisterTranche(LWTRANCHE_WAL_INSERT, "wal_insert");
 	for (i = 0; i < NUM_XLOGINSERT_LOCKS; i++)
 	{
 		LWLockInitialize(&WALInsertLocks[i].l.lock, LWTRANCHE_WAL_INSERT);

src/backend/postmaster/pgstat.c

@@ -3152,11 +3152,8 @@ pgstat_get_wait_event_type(uint32 wait_event_info)
 
 	switch (classId)
 	{
-		case PG_WAIT_LWLOCK_NAMED:
-			event_type = "LWLockNamed";
-			break;
-		case PG_WAIT_LWLOCK_TRANCHE:
-			event_type = "LWLockTranche";
+		case PG_WAIT_LWLOCK:
+			event_type = "LWLock";
 			break;
 		case PG_WAIT_LOCK:
 			event_type = "Lock";
@@ -3209,8 +3206,7 @@ pgstat_get_wait_event(uint32 wait_event_info)
 
 	switch (classId)
 	{
-		case PG_WAIT_LWLOCK_NAMED:
-		case PG_WAIT_LWLOCK_TRANCHE:
+		case PG_WAIT_LWLOCK:
 			event_name = GetLWLockIdentifier(classId, eventId);
 			break;
 		case PG_WAIT_LOCK:

src/backend/replication/logical/origin.c

@@ -143,7 +143,6 @@ typedef struct ReplicationStateOnDisk
 typedef struct ReplicationStateCtl
 {
 	int			tranche_id;
-	LWLockTranche tranche;
 	ReplicationState states[FLEXIBLE_ARRAY_MEMBER];
 } ReplicationStateCtl;
 
@@ -474,11 +473,6 @@ ReplicationOriginShmemInit(void)
 		int			i;
 
 		replication_states_ctl->tranche_id = LWTRANCHE_REPLICATION_ORIGIN;
-		replication_states_ctl->tranche.name = "replication_origin";
-		replication_states_ctl->tranche.array_base =
-			&replication_states[0].lock;
-		replication_states_ctl->tranche.array_stride =
-			sizeof(ReplicationState);
 
 		MemSet(replication_states, 0, ReplicationOriginShmemSize());
 
@@ -488,7 +482,7 @@ ReplicationOriginShmemInit(void)
 	}
 
 	LWLockRegisterTranche(replication_states_ctl->tranche_id,
-						  &replication_states_ctl->tranche);
+						  "replication_origin");
 }
 
 /* ---------------------------------------------------------------------------

src/backend/replication/slot.c

@@ -98,8 +98,6 @@ ReplicationSlot *MyReplicationSlot = NULL;
 int			max_replication_slots = 0;	/* the maximum number of replication
 										 * slots */
 
-static LWLockTranche ReplSlotIOLWLockTranche;
-
 static void ReplicationSlotDropAcquired(void);
 static void ReplicationSlotDropPtr(ReplicationSlot *slot);
 
@@ -141,12 +139,8 @@ ReplicationSlotsShmemInit(void)
 		ShmemInitStruct("ReplicationSlot Ctl", ReplicationSlotsShmemSize(),
 						&found);
 
-	ReplSlotIOLWLockTranche.name = "replication_slot_io";
-	ReplSlotIOLWLockTranche.array_base =
-		((char *) ReplicationSlotCtl) + offsetof(ReplicationSlotCtlData, replication_slots) +offsetof(ReplicationSlot, io_in_progress_lock);
-	ReplSlotIOLWLockTranche.array_stride = sizeof(ReplicationSlot);
 	LWLockRegisterTranche(LWTRANCHE_REPLICATION_SLOT_IO_IN_PROGRESS,
-						  &ReplSlotIOLWLockTranche);
+						  "replication_slot_io");
 
 	if (!found)
 	{

src/backend/storage/buffer/buf_init.c

@@ -21,8 +21,6 @@
 BufferDescPadded *BufferDescriptors;
 char	   *BufferBlocks;
 LWLockMinimallyPadded *BufferIOLWLockArray = NULL;
-LWLockTranche BufferIOLWLockTranche;
-LWLockTranche BufferContentLWLockTranche;
 WritebackContext BackendWritebackContext;
 CkptSortItem *CkptBufferIds;
 
@@ -90,18 +88,8 @@ InitBufferPool(void)
 						NBuffers * (Size) sizeof(LWLockMinimallyPadded),
 						&foundIOLocks);
 
-	BufferIOLWLockTranche.name = "buffer_io";
-	BufferIOLWLockTranche.array_base = BufferIOLWLockArray;
-	BufferIOLWLockTranche.array_stride = sizeof(LWLockMinimallyPadded);
-	LWLockRegisterTranche(LWTRANCHE_BUFFER_IO_IN_PROGRESS,
-						  &BufferIOLWLockTranche);
-
-	BufferContentLWLockTranche.name = "buffer_content";
-	BufferContentLWLockTranche.array_base =
-		((char *) BufferDescriptors) + offsetof(BufferDesc, content_lock);
-	BufferContentLWLockTranche.array_stride = sizeof(BufferDescPadded);
-	LWLockRegisterTranche(LWTRANCHE_BUFFER_CONTENT,
-						  &BufferContentLWLockTranche);
+	LWLockRegisterTranche(LWTRANCHE_BUFFER_IO_IN_PROGRESS, "buffer_io");
+	LWLockRegisterTranche(LWTRANCHE_BUFFER_CONTENT, "buffer_content");
 
 	/*
 	 * The array used to sort to-be-checkpointed buffer ids is located in

src/backend/storage/ipc/procarray.c

@@ -106,9 +106,6 @@ static TransactionId *KnownAssignedXids;
 static bool *KnownAssignedXidsValid;
 static TransactionId latestObservedXid = InvalidTransactionId;
 
-/* LWLock tranche for backend locks */
-static LWLockTranche ProcLWLockTranche;
-
 /*
  * If we're in STANDBY_SNAPSHOT_PENDING state, standbySnapshotPendingXmin is
  * the highest xid that might still be running that we don't have in
@@ -266,11 +263,7 @@ CreateSharedProcArray(void)
 	}
 
 	/* Register and initialize fields of ProcLWLockTranche */
-	ProcLWLockTranche.name = "proc";
-	ProcLWLockTranche.array_base = (char *) (ProcGlobal->allProcs) +
-		offsetof(PGPROC, backendLock);
-	ProcLWLockTranche.array_stride = sizeof(PGPROC);
-	LWLockRegisterTranche(LWTRANCHE_PROC, &ProcLWLockTranche);
+	LWLockRegisterTranche(LWTRANCHE_PROC, "proc");
 }
 
 /*

src/backend/utils/mmgr/dsa.c

@@ -362,9 +362,6 @@ struct dsa_area
 	/* Pointer to the control object in shared memory. */
 	dsa_area_control *control;
 
-	/* The lock tranche for this process. */
-	LWLockTranche lwlock_tranche;
-
 	/* Has the mapping been pinned? */
 	bool		mapping_pinned;
 
@@ -1207,10 +1204,8 @@ create_internal(void *place, size_t size,
 	area->mapping_pinned = false;
 	memset(area->segment_maps, 0, sizeof(dsa_segment_map) * DSA_MAX_SEGMENTS);
 	area->high_segment_index = 0;
-	area->lwlock_tranche.array_base = &area->control->pools[0];
-	area->lwlock_tranche.array_stride = sizeof(dsa_area_pool);
-	area->lwlock_tranche.name = control->lwlock_tranche_name;
-	LWLockRegisterTranche(control->lwlock_tranche_id, &area->lwlock_tranche);
+	LWLockRegisterTranche(control->lwlock_tranche_id,
+						  control->lwlock_tranche_name);
 	LWLockInitialize(&control->lock, control->lwlock_tranche_id);
 	for (i = 0; i < DSA_NUM_SIZE_CLASSES; ++i)
 		LWLockInitialize(DSA_SCLASS_LOCK(area, i),
@@ -1267,10 +1262,8 @@ attach_internal(void *place, dsm_segment *segment, dsa_handle handle)
 	memset(&area->segment_maps[0], 0,
 		   sizeof(dsa_segment_map) * DSA_MAX_SEGMENTS);
 	area->high_segment_index = 0;
-	area->lwlock_tranche.array_base = &area->control->pools[0];
-	area->lwlock_tranche.array_stride = sizeof(dsa_area_pool);
-	area->lwlock_tranche.name = control->lwlock_tranche_name;
-	LWLockRegisterTranche(control->lwlock_tranche_id, &area->lwlock_tranche);
+	LWLockRegisterTranche(control->lwlock_tranche_id,
+						  control->lwlock_tranche_name);
 
 	/* Set up the segment map for this process's mapping. */
 	segment_map = &area->segment_maps[0];

src/backend/utils/probes.d

@@ -28,14 +28,14 @@ provider postgresql {
 	probe transaction__commit(LocalTransactionId);
 	probe transaction__abort(LocalTransactionId);
 
-	probe lwlock__acquire(const char *, int, LWLockMode);
-	probe lwlock__release(const char *, int);
-	probe lwlock__wait__start(const char *, int, LWLockMode);
-	probe lwlock__wait__done(const char *, int, LWLockMode);
-	probe lwlock__condacquire(const char *, int, LWLockMode);
-	probe lwlock__condacquire__fail(const char *, int, LWLockMode);
-	probe lwlock__acquire__or__wait(const char *, int, LWLockMode);
-	probe lwlock__acquire__or__wait__fail(const char *, int, LWLockMode);
+	probe lwlock__acquire(const char *, LWLockMode);
+	probe lwlock__release(const char *);
+	probe lwlock__wait__start(const char *, LWLockMode);
+	probe lwlock__wait__done(const char *, LWLockMode);
+	probe lwlock__condacquire(const char *, LWLockMode);
+	probe lwlock__condacquire__fail(const char *, LWLockMode);
+	probe lwlock__acquire__or__wait(const char *, LWLockMode);
+	probe lwlock__acquire__or__wait__fail(const char *, LWLockMode);
 
 	probe lock__wait__start(unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, LOCKMODE);
 	probe lock__wait__done(unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, LOCKMODE);

src/include/access/slru.h

@@ -104,7 +104,6 @@ typedef struct SlruSharedData
 
 	/* LWLocks */
 	int			lwlock_tranche_id;
-	LWLockTranche lwlock_tranche;
 	char		lwlock_tranche_name[SLRU_MAX_NAME_LENGTH];
 	LWLockPadded *buffer_locks;
 } SlruSharedData;

src/include/pgstat.h

@@ -715,8 +715,7 @@ typedef enum BackendState
  * Wait Classes
  * ----------
  */
-#define PG_WAIT_LWLOCK_NAMED		0x01000000U
-#define PG_WAIT_LWLOCK_TRANCHE		0x02000000U
+#define PG_WAIT_LWLOCK				0x01000000U
 #define PG_WAIT_LOCK				0x03000000U
 #define PG_WAIT_BUFFER_PIN			0x04000000U
 #define PG_WAIT_ACTIVITY			0x05000000U

src/include/storage/lwlock.h

@@ -24,32 +24,6 @@
 
 struct PGPROC;
 
-/*
- * Prior to PostgreSQL 9.4, every lightweight lock in the system was stored
- * in a single array.  For convenience and for compatibility with past
- * releases, we still have a main array, but it's now also permissible to
- * store LWLocks elsewhere in the main shared memory segment or in a dynamic
- * shared memory segment.  Each array of lwlocks forms a separate "tranche".
- *
- * It's occasionally necessary to identify a particular LWLock "by name"; e.g.
- * because we wish to report the lock to dtrace.  We could store a name or
- * other identifying information in the lock itself, but since it's common
- * to have many nearly-identical locks (e.g. one per buffer) this would end
- * up wasting significant amounts of memory.  Instead, each lwlock stores a
- * tranche ID which tells us which array it's part of.  Based on that, we can
- * figure out where the lwlock lies within the array using the data structure
- * shown below; the lock is then identified based on the tranche name and
- * computed array index.  We need the array stride because the array might not
- * be an array of lwlocks, but rather some larger data structure that includes
- * one or more lwlocks per element.
- */
-typedef struct LWLockTranche
-{
-	const char *name;
-	void	   *array_base;
-	Size		array_stride;
-} LWLockTranche;
-
 /*
  * Code outside of lwlock.c should not manipulate the contents of this
  * structure directly, but we have to declare it here to allow LWLocks to be
@@ -118,8 +92,8 @@ extern char *MainLWLockNames[];
 /* struct for storing named tranche information */
 typedef struct NamedLWLockTranche
 {
-	LWLockTranche lwLockTranche;
 	int			trancheId;
+	char	   *trancheName;
 } NamedLWLockTranche;
 
 extern PGDLLIMPORT NamedLWLockTranche *NamedLWLockTrancheArray;
@@ -199,9 +173,9 @@ extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name);
  * There is another, more flexible method of obtaining lwlocks. First, call
  * LWLockNewTrancheId just once to obtain a tranche ID; this allocates from
  * a shared counter.  Next, each individual process using the tranche should
- * call LWLockRegisterTranche() to associate that tranche ID with appropriate
- * metadata.  Finally, LWLockInitialize should be called just once per lwlock,
- * passing the tranche ID as an argument.
+ * call LWLockRegisterTranche() to associate that tranche ID with a name.
+ * Finally, LWLockInitialize should be called just once per lwlock, passing
+ * the tranche ID as an argument.
  *
  * It may seem strange that each process using the tranche must register it
  * separately, but dynamic shared memory segments aren't guaranteed to be
@@ -209,17 +183,18 @@ extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name);
  * registration in the main shared memory segment wouldn't work for that case.
  */
 extern int	LWLockNewTrancheId(void);
-extern void LWLockRegisterTranche(int tranche_id, LWLockTranche *tranche);
+extern void LWLockRegisterTranche(int tranche_id, char *tranche_name);
 extern void LWLockInitialize(LWLock *lock, int tranche_id);
 
 /*
- * We reserve a few predefined tranche IDs.  A call to LWLockNewTrancheId
- * will never return a value less than LWTRANCHE_FIRST_USER_DEFINED.
+ * Every tranche ID less than NUM_INDIVIDUAL_LWLOCKS is reserved; also,
+ * we reserve additional tranche IDs for builtin tranches not included in
+ * the set of individual LWLocks.  A call to LWLockNewTrancheId will never
+ * return a value less than LWTRANCHE_FIRST_USER_DEFINED.
  */
 typedef enum BuiltinTrancheIds
 {
-	LWTRANCHE_MAIN,
-	LWTRANCHE_CLOG_BUFFERS,
+	LWTRANCHE_CLOG_BUFFERS = NUM_INDIVIDUAL_LWLOCKS,
 	LWTRANCHE_COMMITTS_BUFFERS,
 	LWTRANCHE_SUBTRANS_BUFFERS,
 	LWTRANCHE_MXACTOFFSET_BUFFERS,