Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * async.c
4 : * Asynchronous notification: NOTIFY, LISTEN, UNLISTEN
5 : *
6 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
7 : * Portions Copyright (c) 1994, Regents of the University of California
8 : *
9 : * IDENTIFICATION
10 : * src/backend/commands/async.c
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 :
15 : /*-------------------------------------------------------------------------
16 : * Async Notification Model as of 9.0:
17 : *
18 : * 1. Multiple backends on same machine. Multiple backends listening on
19 : * several channels. (Channels are also called "conditions" in other
20 : * parts of the code.)
21 : *
22 : * 2. There is one central queue in disk-based storage (directory pg_notify/),
23 : * with actively-used pages mapped into shared memory by the slru.c module.
24 : * All notification messages are placed in the queue and later read out
25 : * by listening backends.
26 : *
27 : * There is no central knowledge of which backend listens on which channel;
28 : * every backend has its own list of interesting channels.
29 : *
30 : * Although there is only one queue, notifications are treated as being
31 : * database-local; this is done by including the sender's database OID
32 : * in each notification message. Listening backends ignore messages
33 : * that don't match their database OID. This is important because it
34 : * ensures senders and receivers have the same database encoding and won't
35 : * misinterpret non-ASCII text in the channel name or payload string.
36 : *
37 : * Since notifications are not expected to survive database crashes,
38 : * we can simply clean out the pg_notify data at any reboot, and there
39 : * is no need for WAL support or fsync'ing.
40 : *
41 : * 3. Every backend that is listening on at least one channel registers by
42 : * entering its PID into the array in AsyncQueueControl. It then scans all
43 : * incoming notifications in the central queue and first compares the
44 : * database OID of the notification with its own database OID and then
45 : * compares the notified channel with the list of channels that it listens
46 : * to. In case there is a match it delivers the notification event to its
47 : * frontend. Non-matching events are simply skipped.
48 : *
49 : * 4. The NOTIFY statement (routine Async_Notify) stores the notification in
50 : * a backend-local list which will not be processed until transaction end.
51 : *
52 : * Duplicate notifications from the same transaction are sent out as one
53 : * notification only. This is done to save work when for example a trigger
54 : * on a 2 million row table fires a notification for each row that has been
55 : * changed. If the application needs to receive every single notification
56 : * that has been sent, it can easily add some unique string into the extra
57 : * payload parameter.
58 : *
59 : * When the transaction is ready to commit, PreCommit_Notify() adds the
60 : * pending notifications to the head of the queue. The head pointer of the
61 : * queue always points to the next free position and a position is just a
62 : * page number and the offset in that page. This is done before marking the
63 : * transaction as committed in clog. If we run into problems writing the
64 : * notifications, we can still call elog(ERROR, ...) and the transaction
65 : * will roll back.
66 : *
67 : * Once we have put all of the notifications into the queue, we return to
68 : * CommitTransaction() which will then do the actual transaction commit.
69 : *
70 : * After commit we are called another time (AtCommit_Notify()). Here we
71 : * make any actual updates to the effective listen state (listenChannels).
72 : * Then we signal any backends that may be interested in our messages
73 : * (including our own backend, if listening). This is done by
74 : * SignalBackends(), which scans the list of listening backends and sends a
75 : * PROCSIG_NOTIFY_INTERRUPT signal to every listening backend (we don't
76 : * know which backend is listening on which channel so we must signal them
77 : * all). We can exclude backends that are already up to date, though, and
78 : * we can also exclude backends that are in other databases (unless they
79 : * are way behind and should be kicked to make them advance their
80 : * pointers).
81 : *
82 : * Finally, after we are out of the transaction altogether and about to go
83 : * idle, we scan the queue for messages that need to be sent to our
84 : * frontend (which might be notifies from other backends, or self-notifies
85 : * from our own). This step is not part of the CommitTransaction sequence
86 : * for two important reasons. First, we could get errors while sending
87 : * data to our frontend, and it's really bad for errors to happen in
88 : * post-commit cleanup. Second, in cases where a procedure issues commits
89 : * within a single frontend command, we don't want to send notifies to our
90 : * frontend until the command is done; but notifies to other backends
91 : * should go out immediately after each commit.
92 : *
93 : * 5. Upon receipt of a PROCSIG_NOTIFY_INTERRUPT signal, the signal handler
94 : * sets the process's latch, which triggers the event to be processed
95 : * immediately if this backend is idle (i.e., it is waiting for a frontend
96 : * command and is not within a transaction block. C.f.
97 : * ProcessClientReadInterrupt()). Otherwise the handler may only set a
98 : * flag, which will cause the processing to occur just before we next go
99 : * idle.
100 : *
101 : * Inbound-notify processing consists of reading all of the notifications
102 : * that have arrived since scanning last time. We read every notification
103 : * until we reach either a notification from an uncommitted transaction or
104 : * the head pointer's position.
105 : *
106 : * 6. To limit disk space consumption, the tail pointer needs to be advanced
107 : * so that old pages can be truncated. This is relatively expensive
108 : * (notably, it requires an exclusive lock), so we don't want to do it
109 : * often. We make sending backends do this work if they advanced the queue
110 : * head into a new page, but only once every QUEUE_CLEANUP_DELAY pages.
111 : *
112 : * An application that listens on the same channel it notifies will get
113 : * NOTIFY messages for its own NOTIFYs. These can be ignored, if not useful,
114 : * by comparing be_pid in the NOTIFY message to the application's own backend's
115 : * PID. (As of FE/BE protocol 2.0, the backend's PID is provided to the
116 : * frontend during startup.) The above design guarantees that notifies from
117 : * other backends will never be missed by ignoring self-notifies.
118 : *
119 : * The amount of shared memory used for notify management (notify_buffers)
120 : * can be varied without affecting anything but performance. The maximum
121 : * amount of notification data that can be queued at one time is determined
122 : * by max_notify_queue_pages GUC.
123 : *-------------------------------------------------------------------------
124 : */
125 :
126 : #include "postgres.h"
127 :
128 : #include <limits.h>
129 : #include <unistd.h>
130 : #include <signal.h>
131 :
132 : #include "access/parallel.h"
133 : #include "access/slru.h"
134 : #include "access/transam.h"
135 : #include "access/xact.h"
136 : #include "catalog/pg_database.h"
137 : #include "commands/async.h"
138 : #include "common/hashfn.h"
139 : #include "funcapi.h"
140 : #include "libpq/libpq.h"
141 : #include "libpq/pqformat.h"
142 : #include "miscadmin.h"
143 : #include "storage/ipc.h"
144 : #include "storage/lmgr.h"
145 : #include "storage/procsignal.h"
146 : #include "tcop/tcopprot.h"
147 : #include "utils/builtins.h"
148 : #include "utils/guc_hooks.h"
149 : #include "utils/memutils.h"
150 : #include "utils/ps_status.h"
151 : #include "utils/snapmgr.h"
152 : #include "utils/timestamp.h"
153 :
154 :
155 : /*
156 : * Maximum size of a NOTIFY payload, including terminating NULL. This
157 : * must be kept small enough so that a notification message fits on one
158 : * SLRU page. The magic fudge factor here is noncritical as long as it's
159 : * more than AsyncQueueEntryEmptySize --- we make it significantly bigger
160 : * than that, so changes in that data structure won't affect user-visible
161 : * restrictions.
162 : */
163 : #define NOTIFY_PAYLOAD_MAX_LENGTH (BLCKSZ - NAMEDATALEN - 128)
164 :
165 : /*
166 : * Struct representing an entry in the global notify queue
167 : *
168 : * This struct declaration has the maximal length, but in a real queue entry
169 : * the data area is only big enough for the actual channel and payload strings
170 : * (each null-terminated). AsyncQueueEntryEmptySize is the minimum possible
171 : * entry size, if both channel and payload strings are empty (but note it
172 : * doesn't include alignment padding).
173 : *
174 : * The "length" field should always be rounded up to the next QUEUEALIGN
175 : * multiple so that all fields are properly aligned.
176 : */
177 : typedef struct AsyncQueueEntry
178 : {
179 : int length; /* total allocated length of entry */
180 : Oid dboid; /* sender's database OID */
181 : TransactionId xid; /* sender's XID */
182 : int32 srcPid; /* sender's PID */
183 : char data[NAMEDATALEN + NOTIFY_PAYLOAD_MAX_LENGTH];
184 : } AsyncQueueEntry;
185 :
186 : /* Currently, no field of AsyncQueueEntry requires more than int alignment */
187 : #define QUEUEALIGN(len) INTALIGN(len)
188 :
189 : #define AsyncQueueEntryEmptySize (offsetof(AsyncQueueEntry, data) + 2)
190 :
191 : /*
192 : * Struct describing a queue position, and assorted macros for working with it
193 : */
194 : typedef struct QueuePosition
195 : {
196 : int64 page; /* SLRU page number */
197 : int offset; /* byte offset within page */
198 : } QueuePosition;
199 :
200 : #define QUEUE_POS_PAGE(x) ((x).page)
201 : #define QUEUE_POS_OFFSET(x) ((x).offset)
202 :
203 : #define SET_QUEUE_POS(x,y,z) \
204 : do { \
205 : (x).page = (y); \
206 : (x).offset = (z); \
207 : } while (0)
208 :
209 : #define QUEUE_POS_EQUAL(x,y) \
210 : ((x).page == (y).page && (x).offset == (y).offset)
211 :
212 : #define QUEUE_POS_IS_ZERO(x) \
213 : ((x).page == 0 && (x).offset == 0)
214 :
215 : /* choose logically smaller QueuePosition */
216 : #define QUEUE_POS_MIN(x,y) \
217 : (asyncQueuePagePrecedes((x).page, (y).page) ? (x) : \
218 : (x).page != (y).page ? (y) : \
219 : (x).offset < (y).offset ? (x) : (y))
220 :
221 : /* choose logically larger QueuePosition */
222 : #define QUEUE_POS_MAX(x,y) \
223 : (asyncQueuePagePrecedes((x).page, (y).page) ? (y) : \
224 : (x).page != (y).page ? (x) : \
225 : (x).offset > (y).offset ? (x) : (y))
226 :
227 : /*
228 : * Parameter determining how often we try to advance the tail pointer:
229 : * we do that after every QUEUE_CLEANUP_DELAY pages of NOTIFY data. This is
230 : * also the distance by which a backend in another database needs to be
231 : * behind before we'll decide we need to wake it up to advance its pointer.
232 : *
233 : * Resist the temptation to make this really large. While that would save
234 : * work in some places, it would add cost in others. In particular, this
235 : * should likely be less than notify_buffers, to ensure that backends
236 : * catch up before the pages they'll need to read fall out of SLRU cache.
237 : */
238 : #define QUEUE_CLEANUP_DELAY 4
239 :
240 : /*
241 : * Struct describing a listening backend's status
242 : */
243 : typedef struct QueueBackendStatus
244 : {
245 : int32 pid; /* either a PID or InvalidPid */
246 : Oid dboid; /* backend's database OID, or InvalidOid */
247 : ProcNumber nextListener; /* id of next listener, or INVALID_PROC_NUMBER */
248 : QueuePosition pos; /* backend has read queue up to here */
249 : } QueueBackendStatus;
250 :
251 : /*
252 : * Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff)
253 : *
254 : * The AsyncQueueControl structure is protected by the NotifyQueueLock and
255 : * NotifyQueueTailLock.
256 : *
257 : * When holding NotifyQueueLock in SHARED mode, backends may only inspect
258 : * their own entries as well as the head and tail pointers. Consequently we
259 : * can allow a backend to update its own record while holding only SHARED lock
260 : * (since no other backend will inspect it).
261 : *
262 : * When holding NotifyQueueLock in EXCLUSIVE mode, backends can inspect the
263 : * entries of other backends and also change the head pointer. When holding
264 : * both NotifyQueueLock and NotifyQueueTailLock in EXCLUSIVE mode, backends
265 : * can change the tail pointers.
266 : *
267 : * SLRU buffer pool is divided in banks and bank wise SLRU lock is used as
268 : * the control lock for the pg_notify SLRU buffers.
269 : * In order to avoid deadlocks, whenever we need multiple locks, we first get
270 : * NotifyQueueTailLock, then NotifyQueueLock, and lastly SLRU bank lock.
271 : *
272 : * Each backend uses the backend[] array entry with index equal to its
273 : * ProcNumber. We rely on this to make SendProcSignal fast.
274 : *
275 : * The backend[] array entries for actively-listening backends are threaded
276 : * together using firstListener and the nextListener links, so that we can
277 : * scan them without having to iterate over inactive entries. We keep this
278 : * list in order by ProcNumber so that the scan is cache-friendly when there
279 : * are many active entries.
280 : */
281 : typedef struct AsyncQueueControl
282 : {
283 : QueuePosition head; /* head points to the next free location */
284 : QueuePosition tail; /* tail must be <= the queue position of every
285 : * listening backend */
286 : int64 stopPage; /* oldest unrecycled page; must be <=
287 : * tail.page */
288 : ProcNumber firstListener; /* id of first listener, or
289 : * INVALID_PROC_NUMBER */
290 : TimestampTz lastQueueFillWarn; /* time of last queue-full msg */
291 : QueueBackendStatus backend[FLEXIBLE_ARRAY_MEMBER];
292 : } AsyncQueueControl;
293 :
294 : static AsyncQueueControl *asyncQueueControl;
295 :
296 : #define QUEUE_HEAD (asyncQueueControl->head)
297 : #define QUEUE_TAIL (asyncQueueControl->tail)
298 : #define QUEUE_STOP_PAGE (asyncQueueControl->stopPage)
299 : #define QUEUE_FIRST_LISTENER (asyncQueueControl->firstListener)
300 : #define QUEUE_BACKEND_PID(i) (asyncQueueControl->backend[i].pid)
301 : #define QUEUE_BACKEND_DBOID(i) (asyncQueueControl->backend[i].dboid)
302 : #define QUEUE_NEXT_LISTENER(i) (asyncQueueControl->backend[i].nextListener)
303 : #define QUEUE_BACKEND_POS(i) (asyncQueueControl->backend[i].pos)
304 :
305 : /*
306 : * The SLRU buffer area through which we access the notification queue
307 : */
308 : static SlruCtlData NotifyCtlData;
309 :
310 : #define NotifyCtl (&NotifyCtlData)
311 : #define QUEUE_PAGESIZE BLCKSZ
312 :
313 : #define QUEUE_FULL_WARN_INTERVAL 5000 /* warn at most once every 5s */
314 :
315 : /*
316 : * listenChannels identifies the channels we are actually listening to
317 : * (ie, have committed a LISTEN on). It is a simple list of channel names,
318 : * allocated in TopMemoryContext.
319 : */
320 : static List *listenChannels = NIL; /* list of C strings */
321 :
322 : /*
323 : * State for pending LISTEN/UNLISTEN actions consists of an ordered list of
324 : * all actions requested in the current transaction. As explained above,
325 : * we don't actually change listenChannels until we reach transaction commit.
326 : *
327 : * The list is kept in CurTransactionContext. In subtransactions, each
328 : * subtransaction has its own list in its own CurTransactionContext, but
329 : * successful subtransactions attach their lists to their parent's list.
330 : * Failed subtransactions simply discard their lists.
331 : */
332 : typedef enum
333 : {
334 : LISTEN_LISTEN,
335 : LISTEN_UNLISTEN,
336 : LISTEN_UNLISTEN_ALL,
337 : } ListenActionKind;
338 :
339 : typedef struct
340 : {
341 : ListenActionKind action;
342 : char channel[FLEXIBLE_ARRAY_MEMBER]; /* nul-terminated string */
343 : } ListenAction;
344 :
345 : typedef struct ActionList
346 : {
347 : int nestingLevel; /* current transaction nesting depth */
348 : List *actions; /* list of ListenAction structs */
349 : struct ActionList *upper; /* details for upper transaction levels */
350 : } ActionList;
351 :
352 : static ActionList *pendingActions = NULL;
353 :
354 : /*
355 : * State for outbound notifies consists of a list of all channels+payloads
356 : * NOTIFYed in the current transaction. We do not actually perform a NOTIFY
357 : * until and unless the transaction commits. pendingNotifies is NULL if no
358 : * NOTIFYs have been done in the current (sub) transaction.
359 : *
360 : * We discard duplicate notify events issued in the same transaction.
361 : * Hence, in addition to the list proper (which we need to track the order
362 : * of the events, since we guarantee to deliver them in order), we build a
363 : * hash table which we can probe to detect duplicates. Since building the
364 : * hash table is somewhat expensive, we do so only once we have at least
365 : * MIN_HASHABLE_NOTIFIES events queued in the current (sub) transaction;
366 : * before that we just scan the events linearly.
367 : *
368 : * The list is kept in CurTransactionContext. In subtransactions, each
369 : * subtransaction has its own list in its own CurTransactionContext, but
370 : * successful subtransactions add their entries to their parent's list.
371 : * Failed subtransactions simply discard their lists. Since these lists
372 : * are independent, there may be notify events in a subtransaction's list
373 : * that duplicate events in some ancestor (sub) transaction; we get rid of
374 : * the dups when merging the subtransaction's list into its parent's.
375 : *
376 : * Note: the action and notify lists do not interact within a transaction.
377 : * In particular, if a transaction does NOTIFY and then LISTEN on the same
378 : * condition name, it will get a self-notify at commit. This is a bit odd
379 : * but is consistent with our historical behavior.
380 : */
381 : typedef struct Notification
382 : {
383 : uint16 channel_len; /* length of channel-name string */
384 : uint16 payload_len; /* length of payload string */
385 : /* null-terminated channel name, then null-terminated payload follow */
386 : char data[FLEXIBLE_ARRAY_MEMBER];
387 : } Notification;
388 :
389 : typedef struct NotificationList
390 : {
391 : int nestingLevel; /* current transaction nesting depth */
392 : List *events; /* list of Notification structs */
393 : HTAB *hashtab; /* hash of NotificationHash structs, or NULL */
394 : struct NotificationList *upper; /* details for upper transaction levels */
395 : } NotificationList;
396 :
397 : #define MIN_HASHABLE_NOTIFIES 16 /* threshold to build hashtab */
398 :
399 : struct NotificationHash
400 : {
401 : Notification *event; /* => the actual Notification struct */
402 : };
403 :
404 : static NotificationList *pendingNotifies = NULL;
405 :
406 : /*
407 : * Inbound notifications are initially processed by HandleNotifyInterrupt(),
408 : * called from inside a signal handler. That just sets the
409 : * notifyInterruptPending flag and sets the process
410 : * latch. ProcessNotifyInterrupt() will then be called whenever it's safe to
411 : * actually deal with the interrupt.
412 : */
413 : volatile sig_atomic_t notifyInterruptPending = false;
414 :
415 : /* True if we've registered an on_shmem_exit cleanup */
416 : static bool unlistenExitRegistered = false;
417 :
418 : /* True if we're currently registered as a listener in asyncQueueControl */
419 : static bool amRegisteredListener = false;
420 :
421 : /* have we advanced to a page that's a multiple of QUEUE_CLEANUP_DELAY? */
422 : static bool tryAdvanceTail = false;
423 :
424 : /* GUC parameters */
425 : bool Trace_notify = false;
426 :
427 : /* For 8 KB pages this gives 8 GB of disk space */
428 : int max_notify_queue_pages = 1048576;
429 :
430 : /* local function prototypes */
431 : static inline int64 asyncQueuePageDiff(int64 p, int64 q);
432 : static inline bool asyncQueuePagePrecedes(int64 p, int64 q);
433 : static void queue_listen(ListenActionKind action, const char *channel);
434 : static void Async_UnlistenOnExit(int code, Datum arg);
435 : static void Exec_ListenPreCommit(void);
436 : static void Exec_ListenCommit(const char *channel);
437 : static void Exec_UnlistenCommit(const char *channel);
438 : static void Exec_UnlistenAllCommit(void);
439 : static bool IsListeningOn(const char *channel);
440 : static void asyncQueueUnregister(void);
441 : static bool asyncQueueIsFull(void);
442 : static bool asyncQueueAdvance(volatile QueuePosition *position, int entryLength);
443 : static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe);
444 : static ListCell *asyncQueueAddEntries(ListCell *nextNotify);
445 : static double asyncQueueUsage(void);
446 : static void asyncQueueFillWarning(void);
447 : static void SignalBackends(void);
448 : static void asyncQueueReadAllNotifications(void);
449 : static bool asyncQueueProcessPageEntries(QueuePosition *current,
450 : QueuePosition stop,
451 : Snapshot snapshot);
452 : static void asyncQueueAdvanceTail(void);
453 : static void ProcessIncomingNotify(bool flush);
454 : static bool AsyncExistsPendingNotify(Notification *n);
455 : static void AddEventToPendingNotifies(Notification *n);
456 : static uint32 notification_hash(const void *key, Size keysize);
457 : static int notification_match(const void *key1, const void *key2, Size keysize);
458 : static void ClearPendingActionsAndNotifies(void);
459 :
460 : /*
461 : * Compute the difference between two queue page numbers.
462 : * Previously this function accounted for a wraparound.
463 : */
464 : static inline int64
465 0 : asyncQueuePageDiff(int64 p, int64 q)
466 : {
467 0 : return p - q;
468 : }
469 :
470 : /*
471 : * Determines whether p precedes q.
472 : * Previously this function accounted for a wraparound.
473 : */
474 : static inline bool
475 50 : asyncQueuePagePrecedes(int64 p, int64 q)
476 : {
477 50 : return p < q;
478 : }
479 :
480 : /*
481 : * Report space needed for our shared memory area
482 : */
483 : Size
484 4100 : AsyncShmemSize(void)
485 : {
486 : Size size;
487 :
488 : /* This had better match AsyncShmemInit */
489 4100 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
490 4100 : size = add_size(size, offsetof(AsyncQueueControl, backend));
491 :
492 4100 : size = add_size(size, SimpleLruShmemSize(notify_buffers, 0));
493 :
494 4100 : return size;
495 : }
496 :
497 : /*
498 : * Initialize our shared memory area
499 : */
500 : void
501 2200 : AsyncShmemInit(void)
502 : {
503 : bool found;
504 : Size size;
505 :
506 : /*
507 : * Create or attach to the AsyncQueueControl structure.
508 : */
509 2200 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
510 2200 : size = add_size(size, offsetof(AsyncQueueControl, backend));
511 :
512 2200 : asyncQueueControl = (AsyncQueueControl *)
513 2200 : ShmemInitStruct("Async Queue Control", size, &found);
514 :
515 2200 : if (!found)
516 : {
517 : /* First time through, so initialize it */
518 2200 : SET_QUEUE_POS(QUEUE_HEAD, 0, 0);
519 2200 : SET_QUEUE_POS(QUEUE_TAIL, 0, 0);
520 2200 : QUEUE_STOP_PAGE = 0;
521 2200 : QUEUE_FIRST_LISTENER = INVALID_PROC_NUMBER;
522 2200 : asyncQueueControl->lastQueueFillWarn = 0;
523 205146 : for (int i = 0; i < MaxBackends; i++)
524 : {
525 202946 : QUEUE_BACKEND_PID(i) = InvalidPid;
526 202946 : QUEUE_BACKEND_DBOID(i) = InvalidOid;
527 202946 : QUEUE_NEXT_LISTENER(i) = INVALID_PROC_NUMBER;
528 202946 : SET_QUEUE_POS(QUEUE_BACKEND_POS(i), 0, 0);
529 : }
530 : }
531 :
532 : /*
533 : * Set up SLRU management of the pg_notify data. Note that long segment
534 : * names are used in order to avoid wraparound.
535 : */
536 2200 : NotifyCtl->PagePrecedes = asyncQueuePagePrecedes;
537 2200 : SimpleLruInit(NotifyCtl, "notify", notify_buffers, 0,
538 : "pg_notify", LWTRANCHE_NOTIFY_BUFFER, LWTRANCHE_NOTIFY_SLRU,
539 : SYNC_HANDLER_NONE, true);
540 :
541 2200 : if (!found)
542 : {
543 : /*
544 : * During start or reboot, clean out the pg_notify directory.
545 : */
546 2200 : (void) SlruScanDirectory(NotifyCtl, SlruScanDirCbDeleteAll, NULL);
547 : }
548 2200 : }
549 :
550 :
551 : /*
552 : * pg_notify -
553 : * SQL function to send a notification event
554 : */
555 : Datum
556 2108 : pg_notify(PG_FUNCTION_ARGS)
557 : {
558 : const char *channel;
559 : const char *payload;
560 :
561 2108 : if (PG_ARGISNULL(0))
562 6 : channel = "";
563 : else
564 2102 : channel = text_to_cstring(PG_GETARG_TEXT_PP(0));
565 :
566 2108 : if (PG_ARGISNULL(1))
567 12 : payload = "";
568 : else
569 2096 : payload = text_to_cstring(PG_GETARG_TEXT_PP(1));
570 :
571 : /* For NOTIFY as a statement, this is checked in ProcessUtility */
572 2108 : PreventCommandDuringRecovery("NOTIFY");
573 :
574 2108 : Async_Notify(channel, payload);
575 :
576 2090 : PG_RETURN_VOID();
577 : }
578 :
579 :
580 : /*
581 : * Async_Notify
582 : *
583 : * This is executed by the SQL notify command.
584 : *
585 : * Adds the message to the list of pending notifies.
586 : * Actual notification happens during transaction commit.
587 : * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
588 : */
589 : void
590 2226 : Async_Notify(const char *channel, const char *payload)
591 : {
592 2226 : int my_level = GetCurrentTransactionNestLevel();
593 : size_t channel_len;
594 : size_t payload_len;
595 : Notification *n;
596 : MemoryContext oldcontext;
597 :
598 2226 : if (IsParallelWorker())
599 0 : elog(ERROR, "cannot send notifications from a parallel worker");
600 :
601 2226 : if (Trace_notify)
602 0 : elog(DEBUG1, "Async_Notify(%s)", channel);
603 :
604 2226 : channel_len = channel ? strlen(channel) : 0;
605 2226 : payload_len = payload ? strlen(payload) : 0;
606 :
607 : /* a channel name must be specified */
608 2226 : if (channel_len == 0)
609 12 : ereport(ERROR,
610 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
611 : errmsg("channel name cannot be empty")));
612 :
613 : /* enforce length limits */
614 2214 : if (channel_len >= NAMEDATALEN)
615 6 : ereport(ERROR,
616 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
617 : errmsg("channel name too long")));
618 :
619 2208 : if (payload_len >= NOTIFY_PAYLOAD_MAX_LENGTH)
620 0 : ereport(ERROR,
621 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
622 : errmsg("payload string too long")));
623 :
624 : /*
625 : * We must construct the Notification entry, even if we end up not using
626 : * it, in order to compare it cheaply to existing list entries.
627 : *
628 : * The notification list needs to live until end of transaction, so store
629 : * it in the transaction context.
630 : */
631 2208 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
632 :
633 2208 : n = (Notification *) palloc(offsetof(Notification, data) +
634 2208 : channel_len + payload_len + 2);
635 2208 : n->channel_len = channel_len;
636 2208 : n->payload_len = payload_len;
637 2208 : strcpy(n->data, channel);
638 2208 : if (payload)
639 2182 : strcpy(n->data + channel_len + 1, payload);
640 : else
641 26 : n->data[channel_len + 1] = '\0';
642 :
643 2208 : if (pendingNotifies == NULL || my_level > pendingNotifies->nestingLevel)
644 120 : {
645 : NotificationList *notifies;
646 :
647 : /*
648 : * First notify event in current (sub)xact. Note that we allocate the
649 : * NotificationList in TopTransactionContext; the nestingLevel might
650 : * get changed later by AtSubCommit_Notify.
651 : */
652 : notifies = (NotificationList *)
653 120 : MemoryContextAlloc(TopTransactionContext,
654 : sizeof(NotificationList));
655 120 : notifies->nestingLevel = my_level;
656 120 : notifies->events = list_make1(n);
657 : /* We certainly don't need a hashtable yet */
658 120 : notifies->hashtab = NULL;
659 120 : notifies->upper = pendingNotifies;
660 120 : pendingNotifies = notifies;
661 : }
662 : else
663 : {
664 : /* Now check for duplicates */
665 2088 : if (AsyncExistsPendingNotify(n))
666 : {
667 : /* It's a dup, so forget it */
668 24 : pfree(n);
669 24 : MemoryContextSwitchTo(oldcontext);
670 24 : return;
671 : }
672 :
673 : /* Append more events to existing list */
674 2064 : AddEventToPendingNotifies(n);
675 : }
676 :
677 2184 : MemoryContextSwitchTo(oldcontext);
678 : }
679 :
680 : /*
681 : * queue_listen
682 : * Common code for listen, unlisten, unlisten all commands.
683 : *
684 : * Adds the request to the list of pending actions.
685 : * Actual update of the listenChannels list happens during transaction
686 : * commit.
687 : */
688 : static void
689 114 : queue_listen(ListenActionKind action, const char *channel)
690 : {
691 : MemoryContext oldcontext;
692 : ListenAction *actrec;
693 114 : int my_level = GetCurrentTransactionNestLevel();
694 :
695 : /*
696 : * Unlike Async_Notify, we don't try to collapse out duplicates. It would
697 : * be too complicated to ensure we get the right interactions of
698 : * conflicting LISTEN/UNLISTEN/UNLISTEN_ALL, and it's unlikely that there
699 : * would be any performance benefit anyway in sane applications.
700 : */
701 114 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
702 :
703 : /* space for terminating null is included in sizeof(ListenAction) */
704 114 : actrec = (ListenAction *) palloc(offsetof(ListenAction, channel) +
705 114 : strlen(channel) + 1);
706 114 : actrec->action = action;
707 114 : strcpy(actrec->channel, channel);
708 :
709 114 : if (pendingActions == NULL || my_level > pendingActions->nestingLevel)
710 100 : {
711 : ActionList *actions;
712 :
713 : /*
714 : * First action in current sub(xact). Note that we allocate the
715 : * ActionList in TopTransactionContext; the nestingLevel might get
716 : * changed later by AtSubCommit_Notify.
717 : */
718 : actions = (ActionList *)
719 100 : MemoryContextAlloc(TopTransactionContext, sizeof(ActionList));
720 100 : actions->nestingLevel = my_level;
721 100 : actions->actions = list_make1(actrec);
722 100 : actions->upper = pendingActions;
723 100 : pendingActions = actions;
724 : }
725 : else
726 14 : pendingActions->actions = lappend(pendingActions->actions, actrec);
727 :
728 114 : MemoryContextSwitchTo(oldcontext);
729 114 : }
730 :
731 : /*
732 : * Async_Listen
733 : *
734 : * This is executed by the SQL listen command.
735 : */
736 : void
737 74 : Async_Listen(const char *channel)
738 : {
739 74 : if (Trace_notify)
740 0 : elog(DEBUG1, "Async_Listen(%s,%d)", channel, MyProcPid);
741 :
742 74 : queue_listen(LISTEN_LISTEN, channel);
743 74 : }
744 :
745 : /*
746 : * Async_Unlisten
747 : *
748 : * This is executed by the SQL unlisten command.
749 : */
750 : void
751 6 : Async_Unlisten(const char *channel)
752 : {
753 6 : if (Trace_notify)
754 0 : elog(DEBUG1, "Async_Unlisten(%s,%d)", channel, MyProcPid);
755 :
756 : /* If we couldn't possibly be listening, no need to queue anything */
757 6 : if (pendingActions == NULL && !unlistenExitRegistered)
758 0 : return;
759 :
760 6 : queue_listen(LISTEN_UNLISTEN, channel);
761 : }
762 :
763 : /*
764 : * Async_UnlistenAll
765 : *
766 : * This is invoked by UNLISTEN * command, and also at backend exit.
767 : */
768 : void
769 38 : Async_UnlistenAll(void)
770 : {
771 38 : if (Trace_notify)
772 0 : elog(DEBUG1, "Async_UnlistenAll(%d)", MyProcPid);
773 :
774 : /* If we couldn't possibly be listening, no need to queue anything */
775 38 : if (pendingActions == NULL && !unlistenExitRegistered)
776 4 : return;
777 :
778 34 : queue_listen(LISTEN_UNLISTEN_ALL, "");
779 : }
780 :
781 : /*
782 : * SQL function: return a set of the channel names this backend is actively
783 : * listening to.
784 : *
785 : * Note: this coding relies on the fact that the listenChannels list cannot
786 : * change within a transaction.
787 : */
788 : Datum
789 18 : pg_listening_channels(PG_FUNCTION_ARGS)
790 : {
791 : FuncCallContext *funcctx;
792 :
793 : /* stuff done only on the first call of the function */
794 18 : if (SRF_IS_FIRSTCALL())
795 : {
796 : /* create a function context for cross-call persistence */
797 12 : funcctx = SRF_FIRSTCALL_INIT();
798 : }
799 :
800 : /* stuff done on every call of the function */
801 18 : funcctx = SRF_PERCALL_SETUP();
802 :
803 18 : if (funcctx->call_cntr < list_length(listenChannels))
804 : {
805 6 : char *channel = (char *) list_nth(listenChannels,
806 6 : funcctx->call_cntr);
807 :
808 6 : SRF_RETURN_NEXT(funcctx, CStringGetTextDatum(channel));
809 : }
810 :
811 12 : SRF_RETURN_DONE(funcctx);
812 : }
813 :
814 : /*
815 : * Async_UnlistenOnExit
816 : *
817 : * This is executed at backend exit if we have done any LISTENs in this
818 : * backend. It might not be necessary anymore, if the user UNLISTENed
819 : * everything, but we don't try to detect that case.
820 : */
821 : static void
822 28 : Async_UnlistenOnExit(int code, Datum arg)
823 : {
824 28 : Exec_UnlistenAllCommit();
825 28 : asyncQueueUnregister();
826 28 : }
827 :
828 : /*
829 : * AtPrepare_Notify
830 : *
831 : * This is called at the prepare phase of a two-phase
832 : * transaction. Save the state for possible commit later.
833 : */
834 : void
835 622 : AtPrepare_Notify(void)
836 : {
837 : /* It's not allowed to have any pending LISTEN/UNLISTEN/NOTIFY actions */
838 622 : if (pendingActions || pendingNotifies)
839 0 : ereport(ERROR,
840 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
841 : errmsg("cannot PREPARE a transaction that has executed LISTEN, UNLISTEN, or NOTIFY")));
842 622 : }
843 :
844 : /*
845 : * PreCommit_Notify
846 : *
847 : * This is called at transaction commit, before actually committing to
848 : * clog.
849 : *
850 : * If there are pending LISTEN actions, make sure we are listed in the
851 : * shared-memory listener array. This must happen before commit to
852 : * ensure we don't miss any notifies from transactions that commit
853 : * just after ours.
854 : *
855 : * If there are outbound notify requests in the pendingNotifies list,
856 : * add them to the global queue. We do that before commit so that
857 : * we can still throw error if we run out of queue space.
858 : */
859 : void
860 1025684 : PreCommit_Notify(void)
861 : {
862 : ListCell *p;
863 :
864 1025684 : if (!pendingActions && !pendingNotifies)
865 1025470 : return; /* no relevant statements in this xact */
866 :
867 214 : if (Trace_notify)
868 0 : elog(DEBUG1, "PreCommit_Notify");
869 :
870 : /* Preflight for any pending listen/unlisten actions */
871 214 : if (pendingActions != NULL)
872 : {
873 210 : foreach(p, pendingActions->actions)
874 : {
875 112 : ListenAction *actrec = (ListenAction *) lfirst(p);
876 :
877 112 : switch (actrec->action)
878 : {
879 74 : case LISTEN_LISTEN:
880 74 : Exec_ListenPreCommit();
881 74 : break;
882 6 : case LISTEN_UNLISTEN:
883 : /* there is no Exec_UnlistenPreCommit() */
884 6 : break;
885 32 : case LISTEN_UNLISTEN_ALL:
886 : /* there is no Exec_UnlistenAllPreCommit() */
887 32 : break;
888 : }
889 : }
890 : }
891 :
892 : /* Queue any pending notifies (must happen after the above) */
893 214 : if (pendingNotifies)
894 : {
895 : ListCell *nextNotify;
896 :
897 : /*
898 : * Make sure that we have an XID assigned to the current transaction.
899 : * GetCurrentTransactionId is cheap if we already have an XID, but not
900 : * so cheap if we don't, and we'd prefer not to do that work while
901 : * holding NotifyQueueLock.
902 : */
903 116 : (void) GetCurrentTransactionId();
904 :
905 : /*
906 : * Serialize writers by acquiring a special lock that we hold till
907 : * after commit. This ensures that queue entries appear in commit
908 : * order, and in particular that there are never uncommitted queue
909 : * entries ahead of committed ones, so an uncommitted transaction
910 : * can't block delivery of deliverable notifications.
911 : *
912 : * We use a heavyweight lock so that it'll automatically be released
913 : * after either commit or abort. This also allows deadlocks to be
914 : * detected, though really a deadlock shouldn't be possible here.
915 : *
916 : * The lock is on "database 0", which is pretty ugly but it doesn't
917 : * seem worth inventing a special locktag category just for this.
918 : * (Historical note: before PG 9.0, a similar lock on "database 0" was
919 : * used by the flatfiles mechanism.)
920 : */
921 116 : LockSharedObject(DatabaseRelationId, InvalidOid, 0,
922 : AccessExclusiveLock);
923 :
924 : /* Now push the notifications into the queue */
925 116 : nextNotify = list_head(pendingNotifies->events);
926 302 : while (nextNotify != NULL)
927 : {
928 : /*
929 : * Add the pending notifications to the queue. We acquire and
930 : * release NotifyQueueLock once per page, which might be overkill
931 : * but it does allow readers to get in while we're doing this.
932 : *
933 : * A full queue is very uncommon and should really not happen,
934 : * given that we have so much space available in the SLRU pages.
935 : * Nevertheless we need to deal with this possibility. Note that
936 : * when we get here we are in the process of committing our
937 : * transaction, but we have not yet committed to clog, so at this
938 : * point in time we can still roll the transaction back.
939 : */
940 186 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
941 186 : asyncQueueFillWarning();
942 186 : if (asyncQueueIsFull())
943 0 : ereport(ERROR,
944 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
945 : errmsg("too many notifications in the NOTIFY queue")));
946 186 : nextNotify = asyncQueueAddEntries(nextNotify);
947 186 : LWLockRelease(NotifyQueueLock);
948 : }
949 :
950 : /* Note that we don't clear pendingNotifies; AtCommit_Notify will. */
951 : }
952 : }
953 :
954 : /*
955 : * AtCommit_Notify
956 : *
957 : * This is called at transaction commit, after committing to clog.
958 : *
959 : * Update listenChannels and clear transaction-local state.
960 : *
961 : * If we issued any notifications in the transaction, send signals to
962 : * listening backends (possibly including ourselves) to process them.
963 : * Also, if we filled enough queue pages with new notifies, try to
964 : * advance the queue tail pointer.
965 : */
966 : void
967 1025374 : AtCommit_Notify(void)
968 : {
969 : ListCell *p;
970 :
971 : /*
972 : * Allow transactions that have not executed LISTEN/UNLISTEN/NOTIFY to
973 : * return as soon as possible
974 : */
975 1025374 : if (!pendingActions && !pendingNotifies)
976 1025160 : return;
977 :
978 214 : if (Trace_notify)
979 0 : elog(DEBUG1, "AtCommit_Notify");
980 :
981 : /* Perform any pending listen/unlisten actions */
982 214 : if (pendingActions != NULL)
983 : {
984 210 : foreach(p, pendingActions->actions)
985 : {
986 112 : ListenAction *actrec = (ListenAction *) lfirst(p);
987 :
988 112 : switch (actrec->action)
989 : {
990 74 : case LISTEN_LISTEN:
991 74 : Exec_ListenCommit(actrec->channel);
992 74 : break;
993 6 : case LISTEN_UNLISTEN:
994 6 : Exec_UnlistenCommit(actrec->channel);
995 6 : break;
996 32 : case LISTEN_UNLISTEN_ALL:
997 32 : Exec_UnlistenAllCommit();
998 32 : break;
999 : }
1000 : }
1001 : }
1002 :
1003 : /* If no longer listening to anything, get out of listener array */
1004 214 : if (amRegisteredListener && listenChannels == NIL)
1005 26 : asyncQueueUnregister();
1006 :
1007 : /*
1008 : * Send signals to listening backends. We need do this only if there are
1009 : * pending notifies, which were previously added to the shared queue by
1010 : * PreCommit_Notify().
1011 : */
1012 214 : if (pendingNotifies != NULL)
1013 116 : SignalBackends();
1014 :
1015 : /*
1016 : * If it's time to try to advance the global tail pointer, do that.
1017 : *
1018 : * (It might seem odd to do this in the sender, when more than likely the
1019 : * listeners won't yet have read the messages we just sent. However,
1020 : * there's less contention if only the sender does it, and there is little
1021 : * need for urgency in advancing the global tail. So this typically will
1022 : * be clearing out messages that were sent some time ago.)
1023 : */
1024 214 : if (tryAdvanceTail)
1025 : {
1026 16 : tryAdvanceTail = false;
1027 16 : asyncQueueAdvanceTail();
1028 : }
1029 :
1030 : /* And clean up */
1031 214 : ClearPendingActionsAndNotifies();
1032 : }
1033 :
1034 : /*
1035 : * Exec_ListenPreCommit --- subroutine for PreCommit_Notify
1036 : *
1037 : * This function must make sure we are ready to catch any incoming messages.
1038 : */
1039 : static void
1040 74 : Exec_ListenPreCommit(void)
1041 : {
1042 : QueuePosition head;
1043 : QueuePosition max;
1044 : ProcNumber prevListener;
1045 :
1046 : /*
1047 : * Nothing to do if we are already listening to something, nor if we
1048 : * already ran this routine in this transaction.
1049 : */
1050 74 : if (amRegisteredListener)
1051 36 : return;
1052 :
1053 38 : if (Trace_notify)
1054 0 : elog(DEBUG1, "Exec_ListenPreCommit(%d)", MyProcPid);
1055 :
1056 : /*
1057 : * Before registering, make sure we will unlisten before dying. (Note:
1058 : * this action does not get undone if we abort later.)
1059 : */
1060 38 : if (!unlistenExitRegistered)
1061 : {
1062 28 : before_shmem_exit(Async_UnlistenOnExit, 0);
1063 28 : unlistenExitRegistered = true;
1064 : }
1065 :
1066 : /*
1067 : * This is our first LISTEN, so establish our pointer.
1068 : *
1069 : * We set our pointer to the global tail pointer and then move it forward
1070 : * over already-committed notifications. This ensures we cannot miss any
1071 : * not-yet-committed notifications. We might get a few more but that
1072 : * doesn't hurt.
1073 : *
1074 : * In some scenarios there might be a lot of committed notifications that
1075 : * have not yet been pruned away (because some backend is being lazy about
1076 : * reading them). To reduce our startup time, we can look at other
1077 : * backends and adopt the maximum "pos" pointer of any backend that's in
1078 : * our database; any notifications it's already advanced over are surely
1079 : * committed and need not be re-examined by us. (We must consider only
1080 : * backends connected to our DB, because others will not have bothered to
1081 : * check committed-ness of notifications in our DB.)
1082 : *
1083 : * We need exclusive lock here so we can look at other backends' entries
1084 : * and manipulate the list links.
1085 : */
1086 38 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1087 38 : head = QUEUE_HEAD;
1088 38 : max = QUEUE_TAIL;
1089 38 : prevListener = INVALID_PROC_NUMBER;
1090 42 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1091 : {
1092 4 : if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
1093 4 : max = QUEUE_POS_MAX(max, QUEUE_BACKEND_POS(i));
1094 : /* Also find last listening backend before this one */
1095 4 : if (i < MyProcNumber)
1096 4 : prevListener = i;
1097 : }
1098 38 : QUEUE_BACKEND_POS(MyProcNumber) = max;
1099 38 : QUEUE_BACKEND_PID(MyProcNumber) = MyProcPid;
1100 38 : QUEUE_BACKEND_DBOID(MyProcNumber) = MyDatabaseId;
1101 : /* Insert backend into list of listeners at correct position */
1102 38 : if (prevListener != INVALID_PROC_NUMBER)
1103 : {
1104 4 : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_NEXT_LISTENER(prevListener);
1105 4 : QUEUE_NEXT_LISTENER(prevListener) = MyProcNumber;
1106 : }
1107 : else
1108 : {
1109 34 : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_FIRST_LISTENER;
1110 34 : QUEUE_FIRST_LISTENER = MyProcNumber;
1111 : }
1112 38 : LWLockRelease(NotifyQueueLock);
1113 :
1114 : /* Now we are listed in the global array, so remember we're listening */
1115 38 : amRegisteredListener = true;
1116 :
1117 : /*
1118 : * Try to move our pointer forward as far as possible. This will skip
1119 : * over already-committed notifications, which we want to do because they
1120 : * might be quite stale. Note that we are not yet listening on anything,
1121 : * so we won't deliver such notifications to our frontend. Also, although
1122 : * our transaction might have executed NOTIFY, those message(s) aren't
1123 : * queued yet so we won't skip them here.
1124 : */
1125 38 : if (!QUEUE_POS_EQUAL(max, head))
1126 22 : asyncQueueReadAllNotifications();
1127 : }
1128 :
1129 : /*
1130 : * Exec_ListenCommit --- subroutine for AtCommit_Notify
1131 : *
1132 : * Add the channel to the list of channels we are listening on.
1133 : */
1134 : static void
1135 74 : Exec_ListenCommit(const char *channel)
1136 : {
1137 : MemoryContext oldcontext;
1138 :
1139 : /* Do nothing if we are already listening on this channel */
1140 74 : if (IsListeningOn(channel))
1141 20 : return;
1142 :
1143 : /*
1144 : * Add the new channel name to listenChannels.
1145 : *
1146 : * XXX It is theoretically possible to get an out-of-memory failure here,
1147 : * which would be bad because we already committed. For the moment it
1148 : * doesn't seem worth trying to guard against that, but maybe improve this
1149 : * later.
1150 : */
1151 54 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
1152 54 : listenChannels = lappend(listenChannels, pstrdup(channel));
1153 54 : MemoryContextSwitchTo(oldcontext);
1154 : }
1155 :
1156 : /*
1157 : * Exec_UnlistenCommit --- subroutine for AtCommit_Notify
1158 : *
1159 : * Remove the specified channel name from listenChannels.
1160 : */
1161 : static void
1162 6 : Exec_UnlistenCommit(const char *channel)
1163 : {
1164 : ListCell *q;
1165 :
1166 6 : if (Trace_notify)
1167 0 : elog(DEBUG1, "Exec_UnlistenCommit(%s,%d)", channel, MyProcPid);
1168 :
1169 6 : foreach(q, listenChannels)
1170 : {
1171 6 : char *lchan = (char *) lfirst(q);
1172 :
1173 6 : if (strcmp(lchan, channel) == 0)
1174 : {
1175 6 : listenChannels = foreach_delete_current(listenChannels, q);
1176 6 : pfree(lchan);
1177 6 : break;
1178 : }
1179 : }
1180 :
1181 : /*
1182 : * We do not complain about unlistening something not being listened;
1183 : * should we?
1184 : */
1185 6 : }
1186 :
1187 : /*
1188 : * Exec_UnlistenAllCommit --- subroutine for AtCommit_Notify
1189 : *
1190 : * Unlisten on all channels for this backend.
1191 : */
1192 : static void
1193 60 : Exec_UnlistenAllCommit(void)
1194 : {
1195 60 : if (Trace_notify)
1196 0 : elog(DEBUG1, "Exec_UnlistenAllCommit(%d)", MyProcPid);
1197 :
1198 60 : list_free_deep(listenChannels);
1199 60 : listenChannels = NIL;
1200 60 : }
1201 :
1202 : /*
1203 : * Test whether we are actively listening on the given channel name.
1204 : *
1205 : * Note: this function is executed for every notification found in the queue.
1206 : * Perhaps it is worth further optimization, eg convert the list to a sorted
1207 : * array so we can binary-search it. In practice the list is likely to be
1208 : * fairly short, though.
1209 : */
1210 : static bool
1211 210 : IsListeningOn(const char *channel)
1212 : {
1213 : ListCell *p;
1214 :
1215 332 : foreach(p, listenChannels)
1216 : {
1217 204 : char *lchan = (char *) lfirst(p);
1218 :
1219 204 : if (strcmp(lchan, channel) == 0)
1220 82 : return true;
1221 : }
1222 128 : return false;
1223 : }
1224 :
1225 : /*
1226 : * Remove our entry from the listeners array when we are no longer listening
1227 : * on any channel. NB: must not fail if we're already not listening.
1228 : */
1229 : static void
1230 54 : asyncQueueUnregister(void)
1231 : {
1232 : Assert(listenChannels == NIL); /* else caller error */
1233 :
1234 54 : if (!amRegisteredListener) /* nothing to do */
1235 16 : return;
1236 :
1237 : /*
1238 : * Need exclusive lock here to manipulate list links.
1239 : */
1240 38 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1241 : /* Mark our entry as invalid */
1242 38 : QUEUE_BACKEND_PID(MyProcNumber) = InvalidPid;
1243 38 : QUEUE_BACKEND_DBOID(MyProcNumber) = InvalidOid;
1244 : /* and remove it from the list */
1245 38 : if (QUEUE_FIRST_LISTENER == MyProcNumber)
1246 38 : QUEUE_FIRST_LISTENER = QUEUE_NEXT_LISTENER(MyProcNumber);
1247 : else
1248 : {
1249 0 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1250 : {
1251 0 : if (QUEUE_NEXT_LISTENER(i) == MyProcNumber)
1252 : {
1253 0 : QUEUE_NEXT_LISTENER(i) = QUEUE_NEXT_LISTENER(MyProcNumber);
1254 0 : break;
1255 : }
1256 : }
1257 : }
1258 38 : QUEUE_NEXT_LISTENER(MyProcNumber) = INVALID_PROC_NUMBER;
1259 38 : LWLockRelease(NotifyQueueLock);
1260 :
1261 : /* mark ourselves as no longer listed in the global array */
1262 38 : amRegisteredListener = false;
1263 : }
1264 :
1265 : /*
1266 : * Test whether there is room to insert more notification messages.
1267 : *
1268 : * Caller must hold at least shared NotifyQueueLock.
1269 : */
1270 : static bool
1271 186 : asyncQueueIsFull(void)
1272 : {
1273 186 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
1274 186 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
1275 186 : int64 occupied = headPage - tailPage;
1276 :
1277 186 : return occupied >= max_notify_queue_pages;
1278 : }
1279 :
1280 : /*
1281 : * Advance the QueuePosition to the next entry, assuming that the current
1282 : * entry is of length entryLength. If we jump to a new page the function
1283 : * returns true, else false.
1284 : */
1285 : static bool
1286 4662 : asyncQueueAdvance(volatile QueuePosition *position, int entryLength)
1287 : {
1288 4662 : int64 pageno = QUEUE_POS_PAGE(*position);
1289 4662 : int offset = QUEUE_POS_OFFSET(*position);
1290 4662 : bool pageJump = false;
1291 :
1292 : /*
1293 : * Move to the next writing position: First jump over what we have just
1294 : * written or read.
1295 : */
1296 4662 : offset += entryLength;
1297 : Assert(offset <= QUEUE_PAGESIZE);
1298 :
1299 : /*
1300 : * In a second step check if another entry can possibly be written to the
1301 : * page. If so, stay here, we have reached the next position. If not, then
1302 : * we need to move on to the next page.
1303 : */
1304 4662 : if (offset + QUEUEALIGN(AsyncQueueEntryEmptySize) > QUEUE_PAGESIZE)
1305 : {
1306 140 : pageno++;
1307 140 : offset = 0;
1308 140 : pageJump = true;
1309 : }
1310 :
1311 4662 : SET_QUEUE_POS(*position, pageno, offset);
1312 4662 : return pageJump;
1313 : }
1314 :
1315 : /*
1316 : * Fill the AsyncQueueEntry at *qe with an outbound notification message.
1317 : */
1318 : static void
1319 2238 : asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
1320 : {
1321 2238 : size_t channellen = n->channel_len;
1322 2238 : size_t payloadlen = n->payload_len;
1323 : int entryLength;
1324 :
1325 : Assert(channellen < NAMEDATALEN);
1326 : Assert(payloadlen < NOTIFY_PAYLOAD_MAX_LENGTH);
1327 :
1328 : /* The terminators are already included in AsyncQueueEntryEmptySize */
1329 2238 : entryLength = AsyncQueueEntryEmptySize + payloadlen + channellen;
1330 2238 : entryLength = QUEUEALIGN(entryLength);
1331 2238 : qe->length = entryLength;
1332 2238 : qe->dboid = MyDatabaseId;
1333 2238 : qe->xid = GetCurrentTransactionId();
1334 2238 : qe->srcPid = MyProcPid;
1335 2238 : memcpy(qe->data, n->data, channellen + payloadlen + 2);
1336 2238 : }
1337 :
1338 : /*
1339 : * Add pending notifications to the queue.
1340 : *
1341 : * We go page by page here, i.e. we stop once we have to go to a new page but
1342 : * we will be called again and then fill that next page. If an entry does not
1343 : * fit into the current page, we write a dummy entry with an InvalidOid as the
1344 : * database OID in order to fill the page. So every page is always used up to
1345 : * the last byte which simplifies reading the page later.
1346 : *
1347 : * We are passed the list cell (in pendingNotifies->events) containing the next
1348 : * notification to write and return the first still-unwritten cell back.
1349 : * Eventually we will return NULL indicating all is done.
1350 : *
1351 : * We are holding NotifyQueueLock already from the caller and grab
1352 : * page specific SLRU bank lock locally in this function.
1353 : */
1354 : static ListCell *
1355 186 : asyncQueueAddEntries(ListCell *nextNotify)
1356 : {
1357 : AsyncQueueEntry qe;
1358 : QueuePosition queue_head;
1359 : int64 pageno;
1360 : int offset;
1361 : int slotno;
1362 : LWLock *prevlock;
1363 :
1364 : /*
1365 : * We work with a local copy of QUEUE_HEAD, which we write back to shared
1366 : * memory upon exiting. The reason for this is that if we have to advance
1367 : * to a new page, SimpleLruZeroPage might fail (out of disk space, for
1368 : * instance), and we must not advance QUEUE_HEAD if it does. (Otherwise,
1369 : * subsequent insertions would try to put entries into a page that slru.c
1370 : * thinks doesn't exist yet.) So, use a local position variable. Note
1371 : * that if we do fail, any already-inserted queue entries are forgotten;
1372 : * this is okay, since they'd be useless anyway after our transaction
1373 : * rolls back.
1374 : */
1375 186 : queue_head = QUEUE_HEAD;
1376 :
1377 : /*
1378 : * If this is the first write since the postmaster started, we need to
1379 : * initialize the first page of the async SLRU. Otherwise, the current
1380 : * page should be initialized already, so just fetch it.
1381 : */
1382 186 : pageno = QUEUE_POS_PAGE(queue_head);
1383 186 : prevlock = SimpleLruGetBankLock(NotifyCtl, pageno);
1384 :
1385 : /* We hold both NotifyQueueLock and SLRU bank lock during this operation */
1386 186 : LWLockAcquire(prevlock, LW_EXCLUSIVE);
1387 :
1388 186 : if (QUEUE_POS_IS_ZERO(queue_head))
1389 16 : slotno = SimpleLruZeroPage(NotifyCtl, pageno);
1390 : else
1391 170 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
1392 : InvalidTransactionId);
1393 :
1394 : /* Note we mark the page dirty before writing in it */
1395 186 : NotifyCtl->shared->page_dirty[slotno] = true;
1396 :
1397 2354 : while (nextNotify != NULL)
1398 : {
1399 2238 : Notification *n = (Notification *) lfirst(nextNotify);
1400 :
1401 : /* Construct a valid queue entry in local variable qe */
1402 2238 : asyncQueueNotificationToEntry(n, &qe);
1403 :
1404 2238 : offset = QUEUE_POS_OFFSET(queue_head);
1405 :
1406 : /* Check whether the entry really fits on the current page */
1407 2238 : if (offset + qe.length <= QUEUE_PAGESIZE)
1408 : {
1409 : /* OK, so advance nextNotify past this item */
1410 2172 : nextNotify = lnext(pendingNotifies->events, nextNotify);
1411 : }
1412 : else
1413 : {
1414 : /*
1415 : * Write a dummy entry to fill up the page. Actually readers will
1416 : * only check dboid and since it won't match any reader's database
1417 : * OID, they will ignore this entry and move on.
1418 : */
1419 66 : qe.length = QUEUE_PAGESIZE - offset;
1420 66 : qe.dboid = InvalidOid;
1421 66 : qe.xid = InvalidTransactionId;
1422 66 : qe.data[0] = '\0'; /* empty channel */
1423 66 : qe.data[1] = '\0'; /* empty payload */
1424 : }
1425 :
1426 : /* Now copy qe into the shared buffer page */
1427 2238 : memcpy(NotifyCtl->shared->page_buffer[slotno] + offset,
1428 : &qe,
1429 2238 : qe.length);
1430 :
1431 : /* Advance queue_head appropriately, and detect if page is full */
1432 2238 : if (asyncQueueAdvance(&(queue_head), qe.length))
1433 : {
1434 : LWLock *lock;
1435 :
1436 70 : pageno = QUEUE_POS_PAGE(queue_head);
1437 70 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
1438 70 : if (lock != prevlock)
1439 : {
1440 0 : LWLockRelease(prevlock);
1441 0 : LWLockAcquire(lock, LW_EXCLUSIVE);
1442 0 : prevlock = lock;
1443 : }
1444 :
1445 : /*
1446 : * Page is full, so we're done here, but first fill the next page
1447 : * with zeroes. The reason to do this is to ensure that slru.c's
1448 : * idea of the head page is always the same as ours, which avoids
1449 : * boundary problems in SimpleLruTruncate. The test in
1450 : * asyncQueueIsFull() ensured that there is room to create this
1451 : * page without overrunning the queue.
1452 : */
1453 70 : slotno = SimpleLruZeroPage(NotifyCtl, QUEUE_POS_PAGE(queue_head));
1454 :
1455 : /*
1456 : * If the new page address is a multiple of QUEUE_CLEANUP_DELAY,
1457 : * set flag to remember that we should try to advance the tail
1458 : * pointer (we don't want to actually do that right here).
1459 : */
1460 70 : if (QUEUE_POS_PAGE(queue_head) % QUEUE_CLEANUP_DELAY == 0)
1461 16 : tryAdvanceTail = true;
1462 :
1463 : /* And exit the loop */
1464 70 : break;
1465 : }
1466 : }
1467 :
1468 : /* Success, so update the global QUEUE_HEAD */
1469 186 : QUEUE_HEAD = queue_head;
1470 :
1471 186 : LWLockRelease(prevlock);
1472 :
1473 186 : return nextNotify;
1474 : }
1475 :
1476 : /*
1477 : * SQL function to return the fraction of the notification queue currently
1478 : * occupied.
1479 : */
1480 : Datum
1481 10 : pg_notification_queue_usage(PG_FUNCTION_ARGS)
1482 : {
1483 : double usage;
1484 :
1485 : /* Advance the queue tail so we don't report a too-large result */
1486 10 : asyncQueueAdvanceTail();
1487 :
1488 10 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
1489 10 : usage = asyncQueueUsage();
1490 10 : LWLockRelease(NotifyQueueLock);
1491 :
1492 10 : PG_RETURN_FLOAT8(usage);
1493 : }
1494 :
1495 : /*
1496 : * Return the fraction of the queue that is currently occupied.
1497 : *
1498 : * The caller must hold NotifyQueueLock in (at least) shared mode.
1499 : *
1500 : * Note: we measure the distance to the logical tail page, not the physical
1501 : * tail page. In some sense that's wrong, but the relative position of the
1502 : * physical tail is affected by details such as SLRU segment boundaries,
1503 : * so that a result based on that is unpleasantly unstable.
1504 : */
1505 : static double
1506 196 : asyncQueueUsage(void)
1507 : {
1508 196 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
1509 196 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
1510 196 : int64 occupied = headPage - tailPage;
1511 :
1512 196 : if (occupied == 0)
1513 102 : return (double) 0; /* fast exit for common case */
1514 :
1515 94 : return (double) occupied / (double) max_notify_queue_pages;
1516 : }
1517 :
1518 : /*
1519 : * Check whether the queue is at least half full, and emit a warning if so.
1520 : *
1521 : * This is unlikely given the size of the queue, but possible.
1522 : * The warnings show up at most once every QUEUE_FULL_WARN_INTERVAL.
1523 : *
1524 : * Caller must hold exclusive NotifyQueueLock.
1525 : */
1526 : static void
1527 186 : asyncQueueFillWarning(void)
1528 : {
1529 : double fillDegree;
1530 : TimestampTz t;
1531 :
1532 186 : fillDegree = asyncQueueUsage();
1533 186 : if (fillDegree < 0.5)
1534 186 : return;
1535 :
1536 0 : t = GetCurrentTimestamp();
1537 :
1538 0 : if (TimestampDifferenceExceeds(asyncQueueControl->lastQueueFillWarn,
1539 : t, QUEUE_FULL_WARN_INTERVAL))
1540 : {
1541 0 : QueuePosition min = QUEUE_HEAD;
1542 0 : int32 minPid = InvalidPid;
1543 :
1544 0 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1545 : {
1546 : Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
1547 0 : min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
1548 0 : if (QUEUE_POS_EQUAL(min, QUEUE_BACKEND_POS(i)))
1549 0 : minPid = QUEUE_BACKEND_PID(i);
1550 : }
1551 :
1552 0 : ereport(WARNING,
1553 : (errmsg("NOTIFY queue is %.0f%% full", fillDegree * 100),
1554 : (minPid != InvalidPid ?
1555 : errdetail("The server process with PID %d is among those with the oldest transactions.", minPid)
1556 : : 0),
1557 : (minPid != InvalidPid ?
1558 : errhint("The NOTIFY queue cannot be emptied until that process ends its current transaction.")
1559 : : 0)));
1560 :
1561 0 : asyncQueueControl->lastQueueFillWarn = t;
1562 : }
1563 : }
1564 :
1565 : /*
1566 : * Send signals to listening backends.
1567 : *
1568 : * Normally we signal only backends in our own database, since only those
1569 : * backends could be interested in notifies we send. However, if there's
1570 : * notify traffic in our database but no traffic in another database that
1571 : * does have listener(s), those listeners will fall further and further
1572 : * behind. Waken them anyway if they're far enough behind, so that they'll
1573 : * advance their queue position pointers, allowing the global tail to advance.
1574 : *
1575 : * Since we know the ProcNumber and the Pid the signaling is quite cheap.
1576 : *
1577 : * This is called during CommitTransaction(), so it's important for it
1578 : * to have very low probability of failure.
1579 : */
1580 : static void
1581 116 : SignalBackends(void)
1582 : {
1583 : int32 *pids;
1584 : ProcNumber *procnos;
1585 : int count;
1586 :
1587 : /*
1588 : * Identify backends that we need to signal. We don't want to send
1589 : * signals while holding the NotifyQueueLock, so this loop just builds a
1590 : * list of target PIDs.
1591 : *
1592 : * XXX in principle these pallocs could fail, which would be bad. Maybe
1593 : * preallocate the arrays? They're not that large, though.
1594 : */
1595 116 : pids = (int32 *) palloc(MaxBackends * sizeof(int32));
1596 116 : procnos = (ProcNumber *) palloc(MaxBackends * sizeof(ProcNumber));
1597 116 : count = 0;
1598 :
1599 116 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1600 216 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1601 : {
1602 100 : int32 pid = QUEUE_BACKEND_PID(i);
1603 : QueuePosition pos;
1604 :
1605 : Assert(pid != InvalidPid);
1606 100 : pos = QUEUE_BACKEND_POS(i);
1607 100 : if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
1608 : {
1609 : /*
1610 : * Always signal listeners in our own database, unless they're
1611 : * already caught up (unlikely, but possible).
1612 : */
1613 100 : if (QUEUE_POS_EQUAL(pos, QUEUE_HEAD))
1614 0 : continue;
1615 : }
1616 : else
1617 : {
1618 : /*
1619 : * Listeners in other databases should be signaled only if they
1620 : * are far behind.
1621 : */
1622 0 : if (asyncQueuePageDiff(QUEUE_POS_PAGE(QUEUE_HEAD),
1623 : QUEUE_POS_PAGE(pos)) < QUEUE_CLEANUP_DELAY)
1624 0 : continue;
1625 : }
1626 : /* OK, need to signal this one */
1627 100 : pids[count] = pid;
1628 100 : procnos[count] = i;
1629 100 : count++;
1630 : }
1631 116 : LWLockRelease(NotifyQueueLock);
1632 :
1633 : /* Now send signals */
1634 216 : for (int i = 0; i < count; i++)
1635 : {
1636 100 : int32 pid = pids[i];
1637 :
1638 : /*
1639 : * If we are signaling our own process, no need to involve the kernel;
1640 : * just set the flag directly.
1641 : */
1642 100 : if (pid == MyProcPid)
1643 : {
1644 40 : notifyInterruptPending = true;
1645 40 : continue;
1646 : }
1647 :
1648 : /*
1649 : * Note: assuming things aren't broken, a signal failure here could
1650 : * only occur if the target backend exited since we released
1651 : * NotifyQueueLock; which is unlikely but certainly possible. So we
1652 : * just log a low-level debug message if it happens.
1653 : */
1654 60 : if (SendProcSignal(pid, PROCSIG_NOTIFY_INTERRUPT, procnos[i]) < 0)
1655 0 : elog(DEBUG3, "could not signal backend with PID %d: %m", pid);
1656 : }
1657 :
1658 116 : pfree(pids);
1659 116 : pfree(procnos);
1660 116 : }
1661 :
1662 : /*
1663 : * AtAbort_Notify
1664 : *
1665 : * This is called at transaction abort.
1666 : *
1667 : * Gets rid of pending actions and outbound notifies that we would have
1668 : * executed if the transaction got committed.
1669 : */
1670 : void
1671 50420 : AtAbort_Notify(void)
1672 : {
1673 : /*
1674 : * If we LISTEN but then roll back the transaction after PreCommit_Notify,
1675 : * we have registered as a listener but have not made any entry in
1676 : * listenChannels. In that case, deregister again.
1677 : */
1678 50420 : if (amRegisteredListener && listenChannels == NIL)
1679 0 : asyncQueueUnregister();
1680 :
1681 : /* And clean up */
1682 50420 : ClearPendingActionsAndNotifies();
1683 50420 : }
1684 :
1685 : /*
1686 : * AtSubCommit_Notify() --- Take care of subtransaction commit.
1687 : *
1688 : * Reassign all items in the pending lists to the parent transaction.
1689 : */
1690 : void
1691 10748 : AtSubCommit_Notify(void)
1692 : {
1693 10748 : int my_level = GetCurrentTransactionNestLevel();
1694 :
1695 : /* If there are actions at our nesting level, we must reparent them. */
1696 10748 : if (pendingActions != NULL &&
1697 0 : pendingActions->nestingLevel >= my_level)
1698 : {
1699 0 : if (pendingActions->upper == NULL ||
1700 0 : pendingActions->upper->nestingLevel < my_level - 1)
1701 : {
1702 : /* nothing to merge; give the whole thing to the parent */
1703 0 : --pendingActions->nestingLevel;
1704 : }
1705 : else
1706 : {
1707 0 : ActionList *childPendingActions = pendingActions;
1708 :
1709 0 : pendingActions = pendingActions->upper;
1710 :
1711 : /*
1712 : * Mustn't try to eliminate duplicates here --- see queue_listen()
1713 : */
1714 0 : pendingActions->actions =
1715 0 : list_concat(pendingActions->actions,
1716 0 : childPendingActions->actions);
1717 0 : pfree(childPendingActions);
1718 : }
1719 : }
1720 :
1721 : /* If there are notifies at our nesting level, we must reparent them. */
1722 10748 : if (pendingNotifies != NULL &&
1723 4 : pendingNotifies->nestingLevel >= my_level)
1724 : {
1725 : Assert(pendingNotifies->nestingLevel == my_level);
1726 :
1727 2 : if (pendingNotifies->upper == NULL ||
1728 2 : pendingNotifies->upper->nestingLevel < my_level - 1)
1729 : {
1730 : /* nothing to merge; give the whole thing to the parent */
1731 0 : --pendingNotifies->nestingLevel;
1732 : }
1733 : else
1734 : {
1735 : /*
1736 : * Formerly, we didn't bother to eliminate duplicates here, but
1737 : * now we must, else we fall foul of "Assert(!found)", either here
1738 : * or during a later attempt to build the parent-level hashtable.
1739 : */
1740 2 : NotificationList *childPendingNotifies = pendingNotifies;
1741 : ListCell *l;
1742 :
1743 2 : pendingNotifies = pendingNotifies->upper;
1744 : /* Insert all the subxact's events into parent, except for dups */
1745 10 : foreach(l, childPendingNotifies->events)
1746 : {
1747 8 : Notification *childn = (Notification *) lfirst(l);
1748 :
1749 8 : if (!AsyncExistsPendingNotify(childn))
1750 4 : AddEventToPendingNotifies(childn);
1751 : }
1752 2 : pfree(childPendingNotifies);
1753 : }
1754 : }
1755 10748 : }
1756 :
1757 : /*
1758 : * AtSubAbort_Notify() --- Take care of subtransaction abort.
1759 : */
1760 : void
1761 9380 : AtSubAbort_Notify(void)
1762 : {
1763 9380 : int my_level = GetCurrentTransactionNestLevel();
1764 :
1765 : /*
1766 : * All we have to do is pop the stack --- the actions/notifies made in
1767 : * this subxact are no longer interesting, and the space will be freed
1768 : * when CurTransactionContext is recycled. We still have to free the
1769 : * ActionList and NotificationList objects themselves, though, because
1770 : * those are allocated in TopTransactionContext.
1771 : *
1772 : * Note that there might be no entries at all, or no entries for the
1773 : * current subtransaction level, either because none were ever created, or
1774 : * because we reentered this routine due to trouble during subxact abort.
1775 : */
1776 9380 : while (pendingActions != NULL &&
1777 0 : pendingActions->nestingLevel >= my_level)
1778 : {
1779 0 : ActionList *childPendingActions = pendingActions;
1780 :
1781 0 : pendingActions = pendingActions->upper;
1782 0 : pfree(childPendingActions);
1783 : }
1784 :
1785 9382 : while (pendingNotifies != NULL &&
1786 4 : pendingNotifies->nestingLevel >= my_level)
1787 : {
1788 2 : NotificationList *childPendingNotifies = pendingNotifies;
1789 :
1790 2 : pendingNotifies = pendingNotifies->upper;
1791 2 : pfree(childPendingNotifies);
1792 : }
1793 9380 : }
1794 :
1795 : /*
1796 : * HandleNotifyInterrupt
1797 : *
1798 : * Signal handler portion of interrupt handling. Let the backend know
1799 : * that there's a pending notify interrupt. If we're currently reading
1800 : * from the client, this will interrupt the read and
1801 : * ProcessClientReadInterrupt() will call ProcessNotifyInterrupt().
1802 : */
1803 : void
1804 40 : HandleNotifyInterrupt(void)
1805 : {
1806 : /*
1807 : * Note: this is called by a SIGNAL HANDLER. You must be very wary what
1808 : * you do here.
1809 : */
1810 :
1811 : /* signal that work needs to be done */
1812 40 : notifyInterruptPending = true;
1813 :
1814 : /* make sure the event is processed in due course */
1815 40 : SetLatch(MyLatch);
1816 40 : }
1817 :
1818 : /*
1819 : * ProcessNotifyInterrupt
1820 : *
1821 : * This is called if we see notifyInterruptPending set, just before
1822 : * transmitting ReadyForQuery at the end of a frontend command, and
1823 : * also if a notify signal occurs while reading from the frontend.
1824 : * HandleNotifyInterrupt() will cause the read to be interrupted
1825 : * via the process's latch, and this routine will get called.
1826 : * If we are truly idle (ie, *not* inside a transaction block),
1827 : * process the incoming notifies.
1828 : *
1829 : * If "flush" is true, force any frontend messages out immediately.
1830 : * This can be false when being called at the end of a frontend command,
1831 : * since we'll flush after sending ReadyForQuery.
1832 : */
1833 : void
1834 190 : ProcessNotifyInterrupt(bool flush)
1835 : {
1836 190 : if (IsTransactionOrTransactionBlock())
1837 112 : return; /* not really idle */
1838 :
1839 : /* Loop in case another signal arrives while sending messages */
1840 156 : while (notifyInterruptPending)
1841 78 : ProcessIncomingNotify(flush);
1842 : }
1843 :
1844 :
1845 : /*
1846 : * Read all pending notifications from the queue, and deliver appropriate
1847 : * ones to my frontend. Stop when we reach queue head or an uncommitted
1848 : * notification.
1849 : */
1850 : static void
1851 100 : asyncQueueReadAllNotifications(void)
1852 : {
1853 : QueuePosition pos;
1854 : QueuePosition head;
1855 : Snapshot snapshot;
1856 :
1857 : /* Fetch current state */
1858 100 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
1859 : /* Assert checks that we have a valid state entry */
1860 : Assert(MyProcPid == QUEUE_BACKEND_PID(MyProcNumber));
1861 100 : pos = QUEUE_BACKEND_POS(MyProcNumber);
1862 100 : head = QUEUE_HEAD;
1863 100 : LWLockRelease(NotifyQueueLock);
1864 :
1865 100 : if (QUEUE_POS_EQUAL(pos, head))
1866 : {
1867 : /* Nothing to do, we have read all notifications already. */
1868 0 : return;
1869 : }
1870 :
1871 : /*----------
1872 : * Get snapshot we'll use to decide which xacts are still in progress.
1873 : * This is trickier than it might seem, because of race conditions.
1874 : * Consider the following example:
1875 : *
1876 : * Backend 1: Backend 2:
1877 : *
1878 : * transaction starts
1879 : * UPDATE foo SET ...;
1880 : * NOTIFY foo;
1881 : * commit starts
1882 : * queue the notify message
1883 : * transaction starts
1884 : * LISTEN foo; -- first LISTEN in session
1885 : * SELECT * FROM foo WHERE ...;
1886 : * commit to clog
1887 : * commit starts
1888 : * add backend 2 to array of listeners
1889 : * advance to queue head (this code)
1890 : * commit to clog
1891 : *
1892 : * Transaction 2's SELECT has not seen the UPDATE's effects, since that
1893 : * wasn't committed yet. Ideally we'd ensure that client 2 would
1894 : * eventually get transaction 1's notify message, but there's no way
1895 : * to do that; until we're in the listener array, there's no guarantee
1896 : * that the notify message doesn't get removed from the queue.
1897 : *
1898 : * Therefore the coding technique transaction 2 is using is unsafe:
1899 : * applications must commit a LISTEN before inspecting database state,
1900 : * if they want to ensure they will see notifications about subsequent
1901 : * changes to that state.
1902 : *
1903 : * What we do guarantee is that we'll see all notifications from
1904 : * transactions committing after the snapshot we take here.
1905 : * Exec_ListenPreCommit has already added us to the listener array,
1906 : * so no not-yet-committed messages can be removed from the queue
1907 : * before we see them.
1908 : *----------
1909 : */
1910 100 : snapshot = RegisterSnapshot(GetLatestSnapshot());
1911 :
1912 : /*
1913 : * It is possible that we fail while trying to send a message to our
1914 : * frontend (for example, because of encoding conversion failure). If
1915 : * that happens it is critical that we not try to send the same message
1916 : * over and over again. Therefore, we set ExitOnAnyError to upgrade any
1917 : * ERRORs to FATAL, causing the client connection to be closed on error.
1918 : *
1919 : * We used to only skip over the offending message and try to soldier on,
1920 : * but it was somewhat questionable to lose a notification and give the
1921 : * client an ERROR instead. A client application is not be prepared for
1922 : * that and can't tell that a notification was missed. It was also not
1923 : * very useful in practice because notifications are often processed while
1924 : * a connection is idle and reading a message from the client, and in that
1925 : * state, any error is upgraded to FATAL anyway. Closing the connection
1926 : * is a clear signal to the application that it might have missed
1927 : * notifications.
1928 : */
1929 : {
1930 100 : bool save_ExitOnAnyError = ExitOnAnyError;
1931 : bool reachedStop;
1932 :
1933 100 : ExitOnAnyError = true;
1934 :
1935 : do
1936 : {
1937 : /*
1938 : * Process messages up to the stop position, end of page, or an
1939 : * uncommitted message.
1940 : *
1941 : * Our stop position is what we found to be the head's position
1942 : * when we entered this function. It might have changed already.
1943 : * But if it has, we will receive (or have already received and
1944 : * queued) another signal and come here again.
1945 : *
1946 : * We are not holding NotifyQueueLock here! The queue can only
1947 : * extend beyond the head pointer (see above) and we leave our
1948 : * backend's pointer where it is so nobody will truncate or
1949 : * rewrite pages under us. Especially we don't want to hold a lock
1950 : * while sending the notifications to the frontend.
1951 : */
1952 170 : reachedStop = asyncQueueProcessPageEntries(&pos, head, snapshot);
1953 170 : } while (!reachedStop);
1954 :
1955 : /* Update shared state */
1956 100 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
1957 100 : QUEUE_BACKEND_POS(MyProcNumber) = pos;
1958 100 : LWLockRelease(NotifyQueueLock);
1959 :
1960 100 : ExitOnAnyError = save_ExitOnAnyError;
1961 : }
1962 :
1963 : /* Done with snapshot */
1964 100 : UnregisterSnapshot(snapshot);
1965 : }
1966 :
1967 : /*
1968 : * Fetch notifications from the shared queue, beginning at position current,
1969 : * and deliver relevant ones to my frontend.
1970 : *
1971 : * The function returns true once we have reached the stop position or an
1972 : * uncommitted notification, and false if we have finished with the page.
1973 : * In other words: once it returns true there is no need to look further.
1974 : * The QueuePosition *current is advanced past all processed messages.
1975 : */
1976 : static bool
1977 170 : asyncQueueProcessPageEntries(QueuePosition *current,
1978 : QueuePosition stop,
1979 : Snapshot snapshot)
1980 : {
1981 170 : int64 curpage = QUEUE_POS_PAGE(*current);
1982 : int slotno;
1983 : char *page_buffer;
1984 170 : bool reachedStop = false;
1985 : bool reachedEndOfPage;
1986 :
1987 : /*
1988 : * We copy the entries into a local buffer to avoid holding the SLRU lock
1989 : * while we transmit them to our frontend. The local buffer must be
1990 : * adequately aligned, so use a union.
1991 : */
1992 : union
1993 : {
1994 : char buf[QUEUE_PAGESIZE];
1995 : AsyncQueueEntry align;
1996 : } local_buf;
1997 170 : char *local_buf_end = local_buf.buf;
1998 :
1999 170 : slotno = SimpleLruReadPage_ReadOnly(NotifyCtl, curpage,
2000 : InvalidTransactionId);
2001 170 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
2002 :
2003 : do
2004 : {
2005 2484 : QueuePosition thisentry = *current;
2006 : AsyncQueueEntry *qe;
2007 :
2008 2484 : if (QUEUE_POS_EQUAL(thisentry, stop))
2009 100 : break;
2010 :
2011 2384 : qe = (AsyncQueueEntry *) (page_buffer + QUEUE_POS_OFFSET(thisentry));
2012 :
2013 : /*
2014 : * Advance *current over this message, possibly to the next page. As
2015 : * noted in the comments for asyncQueueReadAllNotifications, we must
2016 : * do this before possibly failing while processing the message.
2017 : */
2018 2384 : reachedEndOfPage = asyncQueueAdvance(current, qe->length);
2019 :
2020 : /* Ignore messages destined for other databases */
2021 2384 : if (qe->dboid == MyDatabaseId)
2022 : {
2023 2318 : if (XidInMVCCSnapshot(qe->xid, snapshot))
2024 : {
2025 : /*
2026 : * The source transaction is still in progress, so we can't
2027 : * process this message yet. Break out of the loop, but first
2028 : * back up *current so we will reprocess the message next
2029 : * time. (Note: it is unlikely but not impossible for
2030 : * TransactionIdDidCommit to fail, so we can't really avoid
2031 : * this advance-then-back-up behavior when dealing with an
2032 : * uncommitted message.)
2033 : *
2034 : * Note that we must test XidInMVCCSnapshot before we test
2035 : * TransactionIdDidCommit, else we might return a message from
2036 : * a transaction that is not yet visible to snapshots; compare
2037 : * the comments at the head of heapam_visibility.c.
2038 : *
2039 : * Also, while our own xact won't be listed in the snapshot,
2040 : * we need not check for TransactionIdIsCurrentTransactionId
2041 : * because our transaction cannot (yet) have queued any
2042 : * messages.
2043 : */
2044 0 : *current = thisentry;
2045 0 : reachedStop = true;
2046 0 : break;
2047 : }
2048 :
2049 : /*
2050 : * Quick check for the case that we're not listening on any
2051 : * channels, before calling TransactionIdDidCommit(). This makes
2052 : * that case a little faster, but more importantly, it ensures
2053 : * that if there's a bad entry in the queue for which
2054 : * TransactionIdDidCommit() fails for some reason, we can skip
2055 : * over it on the first LISTEN in a session, and not get stuck on
2056 : * it indefinitely.
2057 : */
2058 2318 : if (listenChannels == NIL)
2059 2182 : continue;
2060 :
2061 136 : if (TransactionIdDidCommit(qe->xid))
2062 : {
2063 136 : memcpy(local_buf_end, qe, qe->length);
2064 136 : local_buf_end += qe->length;
2065 : }
2066 : else
2067 : {
2068 : /*
2069 : * The source transaction aborted or crashed, so we just
2070 : * ignore its notifications.
2071 : */
2072 : }
2073 : }
2074 :
2075 : /* Loop back if we're not at end of page */
2076 2384 : } while (!reachedEndOfPage);
2077 :
2078 : /* Release lock that we got from SimpleLruReadPage_ReadOnly() */
2079 170 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2080 :
2081 : /*
2082 : * Now that we have let go of the SLRU bank lock, send the notifications
2083 : * to our backend
2084 : */
2085 : Assert(local_buf_end - local_buf.buf <= BLCKSZ);
2086 306 : for (char *p = local_buf.buf; p < local_buf_end;)
2087 : {
2088 136 : AsyncQueueEntry *qe = (AsyncQueueEntry *) p;
2089 :
2090 : /* qe->data is the null-terminated channel name */
2091 136 : char *channel = qe->data;
2092 :
2093 136 : if (IsListeningOn(channel))
2094 : {
2095 : /* payload follows channel name */
2096 62 : char *payload = qe->data + strlen(channel) + 1;
2097 :
2098 62 : NotifyMyFrontEnd(channel, payload, qe->srcPid);
2099 : }
2100 :
2101 136 : p += qe->length;
2102 : }
2103 :
2104 170 : if (QUEUE_POS_EQUAL(*current, stop))
2105 100 : reachedStop = true;
2106 :
2107 170 : return reachedStop;
2108 : }
2109 :
2110 : /*
2111 : * Advance the shared queue tail variable to the minimum of all the
2112 : * per-backend tail pointers. Truncate pg_notify space if possible.
2113 : *
2114 : * This is (usually) called during CommitTransaction(), so it's important for
2115 : * it to have very low probability of failure.
2116 : */
2117 : static void
2118 26 : asyncQueueAdvanceTail(void)
2119 : {
2120 : QueuePosition min;
2121 : int64 oldtailpage;
2122 : int64 newtailpage;
2123 : int64 boundary;
2124 :
2125 : /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
2126 26 : LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE);
2127 :
2128 : /*
2129 : * Compute the new tail. Pre-v13, it's essential that QUEUE_TAIL be exact
2130 : * (ie, exactly match at least one backend's queue position), so it must
2131 : * be updated atomically with the actual computation. Since v13, we could
2132 : * get away with not doing it like that, but it seems prudent to keep it
2133 : * so.
2134 : *
2135 : * Also, because incoming backends will scan forward from QUEUE_TAIL, that
2136 : * must be advanced before we can truncate any data. Thus, QUEUE_TAIL is
2137 : * the logical tail, while QUEUE_STOP_PAGE is the physical tail, or oldest
2138 : * un-truncated page. When QUEUE_STOP_PAGE != QUEUE_POS_PAGE(QUEUE_TAIL),
2139 : * there are pages we can truncate but haven't yet finished doing so.
2140 : *
2141 : * For concurrency's sake, we don't want to hold NotifyQueueLock while
2142 : * performing SimpleLruTruncate. This is OK because no backend will try
2143 : * to access the pages we are in the midst of truncating.
2144 : */
2145 26 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2146 26 : min = QUEUE_HEAD;
2147 46 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
2148 : {
2149 : Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
2150 20 : min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
2151 : }
2152 26 : QUEUE_TAIL = min;
2153 26 : oldtailpage = QUEUE_STOP_PAGE;
2154 26 : LWLockRelease(NotifyQueueLock);
2155 :
2156 : /*
2157 : * We can truncate something if the global tail advanced across an SLRU
2158 : * segment boundary.
2159 : *
2160 : * XXX it might be better to truncate only once every several segments, to
2161 : * reduce the number of directory scans.
2162 : */
2163 26 : newtailpage = QUEUE_POS_PAGE(min);
2164 26 : boundary = newtailpage - (newtailpage % SLRU_PAGES_PER_SEGMENT);
2165 26 : if (asyncQueuePagePrecedes(oldtailpage, boundary))
2166 : {
2167 : /*
2168 : * SimpleLruTruncate() will ask for SLRU bank locks but will also
2169 : * release the lock again.
2170 : */
2171 0 : SimpleLruTruncate(NotifyCtl, newtailpage);
2172 :
2173 0 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2174 0 : QUEUE_STOP_PAGE = newtailpage;
2175 0 : LWLockRelease(NotifyQueueLock);
2176 : }
2177 :
2178 26 : LWLockRelease(NotifyQueueTailLock);
2179 26 : }
2180 :
2181 : /*
2182 : * AsyncNotifyFreezeXids
2183 : *
2184 : * Prepare the async notification queue for CLOG truncation by freezing
2185 : * transaction IDs that are about to become inaccessible.
2186 : *
2187 : * This function is called by VACUUM before advancing datfrozenxid. It scans
2188 : * the notification queue and replaces XIDs that would become inaccessible
2189 : * after CLOG truncation with special markers:
2190 : * - Committed transactions are set to FrozenTransactionId
2191 : * - Aborted/crashed transactions are set to InvalidTransactionId
2192 : *
2193 : * Only XIDs < newFrozenXid are processed, as those are the ones whose CLOG
2194 : * pages will be truncated. If XID < newFrozenXid, it cannot still be running
2195 : * (or it would have held back newFrozenXid through ProcArray).
2196 : * Therefore, if TransactionIdDidCommit returns false, we know the transaction
2197 : * either aborted explicitly or crashed, and we can safely mark it invalid.
2198 : */
2199 : void
2200 2190 : AsyncNotifyFreezeXids(TransactionId newFrozenXid)
2201 : {
2202 : QueuePosition pos;
2203 : QueuePosition head;
2204 2190 : int64 curpage = -1;
2205 2190 : int slotno = -1;
2206 2190 : char *page_buffer = NULL;
2207 2190 : bool page_dirty = false;
2208 :
2209 : /*
2210 : * Acquire locks in the correct order to avoid deadlocks. As per the
2211 : * locking protocol: NotifyQueueTailLock, then NotifyQueueLock, then SLRU
2212 : * bank locks.
2213 : *
2214 : * We only need SHARED mode since we're just reading the head/tail
2215 : * positions, not modifying them.
2216 : */
2217 2190 : LWLockAcquire(NotifyQueueTailLock, LW_SHARED);
2218 2190 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2219 :
2220 2190 : pos = QUEUE_TAIL;
2221 2190 : head = QUEUE_HEAD;
2222 :
2223 : /* Release NotifyQueueLock early, we only needed to read the positions */
2224 2190 : LWLockRelease(NotifyQueueLock);
2225 :
2226 : /*
2227 : * Scan the queue from tail to head, freezing XIDs as needed. We hold
2228 : * NotifyQueueTailLock throughout to ensure the tail doesn't move while
2229 : * we're working.
2230 : */
2231 2230 : while (!QUEUE_POS_EQUAL(pos, head))
2232 : {
2233 : AsyncQueueEntry *qe;
2234 : TransactionId xid;
2235 40 : int64 pageno = QUEUE_POS_PAGE(pos);
2236 40 : int offset = QUEUE_POS_OFFSET(pos);
2237 :
2238 : /* If we need a different page, release old lock and get new one */
2239 40 : if (pageno != curpage)
2240 : {
2241 : LWLock *lock;
2242 :
2243 : /* Release previous page if any */
2244 4 : if (slotno >= 0)
2245 : {
2246 0 : if (page_dirty)
2247 : {
2248 0 : NotifyCtl->shared->page_dirty[slotno] = true;
2249 0 : page_dirty = false;
2250 : }
2251 0 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2252 : }
2253 :
2254 4 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
2255 4 : LWLockAcquire(lock, LW_EXCLUSIVE);
2256 4 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
2257 : InvalidTransactionId);
2258 4 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
2259 4 : curpage = pageno;
2260 : }
2261 :
2262 40 : qe = (AsyncQueueEntry *) (page_buffer + offset);
2263 40 : xid = qe->xid;
2264 :
2265 80 : if (TransactionIdIsNormal(xid) &&
2266 40 : TransactionIdPrecedes(xid, newFrozenXid))
2267 : {
2268 0 : if (TransactionIdDidCommit(xid))
2269 : {
2270 0 : qe->xid = FrozenTransactionId;
2271 0 : page_dirty = true;
2272 : }
2273 : else
2274 : {
2275 0 : qe->xid = InvalidTransactionId;
2276 0 : page_dirty = true;
2277 : }
2278 : }
2279 :
2280 : /* Advance to next entry */
2281 40 : asyncQueueAdvance(&pos, qe->length);
2282 : }
2283 :
2284 : /* Release final page lock if we acquired one */
2285 2190 : if (slotno >= 0)
2286 : {
2287 4 : if (page_dirty)
2288 0 : NotifyCtl->shared->page_dirty[slotno] = true;
2289 4 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2290 : }
2291 :
2292 2190 : LWLockRelease(NotifyQueueTailLock);
2293 2190 : }
2294 :
2295 : /*
2296 : * ProcessIncomingNotify
2297 : *
2298 : * Scan the queue for arriving notifications and report them to the front
2299 : * end. The notifications might be from other sessions, or our own;
2300 : * there's no need to distinguish here.
2301 : *
2302 : * If "flush" is true, force any frontend messages out immediately.
2303 : *
2304 : * NOTE: since we are outside any transaction, we must create our own.
2305 : */
2306 : static void
2307 78 : ProcessIncomingNotify(bool flush)
2308 : {
2309 : /* We *must* reset the flag */
2310 78 : notifyInterruptPending = false;
2311 :
2312 : /* Do nothing else if we aren't actively listening */
2313 78 : if (listenChannels == NIL)
2314 0 : return;
2315 :
2316 78 : if (Trace_notify)
2317 0 : elog(DEBUG1, "ProcessIncomingNotify");
2318 :
2319 78 : set_ps_display("notify interrupt");
2320 :
2321 : /*
2322 : * We must run asyncQueueReadAllNotifications inside a transaction, else
2323 : * bad things happen if it gets an error.
2324 : */
2325 78 : StartTransactionCommand();
2326 :
2327 78 : asyncQueueReadAllNotifications();
2328 :
2329 78 : CommitTransactionCommand();
2330 :
2331 : /*
2332 : * If this isn't an end-of-command case, we must flush the notify messages
2333 : * to ensure frontend gets them promptly.
2334 : */
2335 78 : if (flush)
2336 20 : pq_flush();
2337 :
2338 78 : set_ps_display("idle");
2339 :
2340 78 : if (Trace_notify)
2341 0 : elog(DEBUG1, "ProcessIncomingNotify: done");
2342 : }
2343 :
2344 : /*
2345 : * Send NOTIFY message to my front end.
2346 : */
2347 : void
2348 62 : NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
2349 : {
2350 62 : if (whereToSendOutput == DestRemote)
2351 : {
2352 : StringInfoData buf;
2353 :
2354 62 : pq_beginmessage(&buf, PqMsg_NotificationResponse);
2355 62 : pq_sendint32(&buf, srcPid);
2356 62 : pq_sendstring(&buf, channel);
2357 62 : pq_sendstring(&buf, payload);
2358 62 : pq_endmessage(&buf);
2359 :
2360 : /*
2361 : * NOTE: we do not do pq_flush() here. Some level of caller will
2362 : * handle it later, allowing this message to be combined into a packet
2363 : * with other ones.
2364 : */
2365 : }
2366 : else
2367 0 : elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload);
2368 62 : }
2369 :
2370 : /* Does pendingNotifies include a match for the given event? */
2371 : static bool
2372 2096 : AsyncExistsPendingNotify(Notification *n)
2373 : {
2374 2096 : if (pendingNotifies == NULL)
2375 0 : return false;
2376 :
2377 2096 : if (pendingNotifies->hashtab != NULL)
2378 : {
2379 : /* Use the hash table to probe for a match */
2380 1966 : if (hash_search(pendingNotifies->hashtab,
2381 : &n,
2382 : HASH_FIND,
2383 : NULL))
2384 0 : return true;
2385 : }
2386 : else
2387 : {
2388 : /* Must scan the event list */
2389 : ListCell *l;
2390 :
2391 542 : foreach(l, pendingNotifies->events)
2392 : {
2393 440 : Notification *oldn = (Notification *) lfirst(l);
2394 :
2395 440 : if (n->channel_len == oldn->channel_len &&
2396 440 : n->payload_len == oldn->payload_len &&
2397 250 : memcmp(n->data, oldn->data,
2398 250 : n->channel_len + n->payload_len + 2) == 0)
2399 28 : return true;
2400 : }
2401 : }
2402 :
2403 2068 : return false;
2404 : }
2405 :
2406 : /*
2407 : * Add a notification event to a pre-existing pendingNotifies list.
2408 : *
2409 : * Because pendingNotifies->events is already nonempty, this works
2410 : * correctly no matter what CurrentMemoryContext is.
2411 : */
2412 : static void
2413 2068 : AddEventToPendingNotifies(Notification *n)
2414 : {
2415 : Assert(pendingNotifies->events != NIL);
2416 :
2417 : /* Create the hash table if it's time to */
2418 2068 : if (list_length(pendingNotifies->events) >= MIN_HASHABLE_NOTIFIES &&
2419 1968 : pendingNotifies->hashtab == NULL)
2420 : {
2421 : HASHCTL hash_ctl;
2422 : ListCell *l;
2423 :
2424 : /* Create the hash table */
2425 2 : hash_ctl.keysize = sizeof(Notification *);
2426 2 : hash_ctl.entrysize = sizeof(struct NotificationHash);
2427 2 : hash_ctl.hash = notification_hash;
2428 2 : hash_ctl.match = notification_match;
2429 2 : hash_ctl.hcxt = CurTransactionContext;
2430 4 : pendingNotifies->hashtab =
2431 2 : hash_create("Pending Notifies",
2432 : 256L,
2433 : &hash_ctl,
2434 : HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
2435 :
2436 : /* Insert all the already-existing events */
2437 34 : foreach(l, pendingNotifies->events)
2438 : {
2439 32 : Notification *oldn = (Notification *) lfirst(l);
2440 : bool found;
2441 :
2442 32 : (void) hash_search(pendingNotifies->hashtab,
2443 : &oldn,
2444 : HASH_ENTER,
2445 : &found);
2446 : Assert(!found);
2447 : }
2448 : }
2449 :
2450 : /* Add new event to the list, in order */
2451 2068 : pendingNotifies->events = lappend(pendingNotifies->events, n);
2452 :
2453 : /* Add event to the hash table if needed */
2454 2068 : if (pendingNotifies->hashtab != NULL)
2455 : {
2456 : bool found;
2457 :
2458 1968 : (void) hash_search(pendingNotifies->hashtab,
2459 : &n,
2460 : HASH_ENTER,
2461 : &found);
2462 : Assert(!found);
2463 : }
2464 2068 : }
2465 :
2466 : /*
2467 : * notification_hash: hash function for notification hash table
2468 : *
2469 : * The hash "keys" are pointers to Notification structs.
2470 : */
2471 : static uint32
2472 3966 : notification_hash(const void *key, Size keysize)
2473 : {
2474 3966 : const Notification *k = *(const Notification *const *) key;
2475 :
2476 : Assert(keysize == sizeof(Notification *));
2477 : /* We don't bother to include the payload's trailing null in the hash */
2478 3966 : return DatumGetUInt32(hash_any((const unsigned char *) k->data,
2479 3966 : k->channel_len + k->payload_len + 1));
2480 : }
2481 :
2482 : /*
2483 : * notification_match: match function to use with notification_hash
2484 : */
2485 : static int
2486 0 : notification_match(const void *key1, const void *key2, Size keysize)
2487 : {
2488 0 : const Notification *k1 = *(const Notification *const *) key1;
2489 0 : const Notification *k2 = *(const Notification *const *) key2;
2490 :
2491 : Assert(keysize == sizeof(Notification *));
2492 0 : if (k1->channel_len == k2->channel_len &&
2493 0 : k1->payload_len == k2->payload_len &&
2494 0 : memcmp(k1->data, k2->data,
2495 0 : k1->channel_len + k1->payload_len + 2) == 0)
2496 0 : return 0; /* equal */
2497 0 : return 1; /* not equal */
2498 : }
2499 :
2500 : /* Clear the pendingActions and pendingNotifies lists. */
2501 : static void
2502 50634 : ClearPendingActionsAndNotifies(void)
2503 : {
2504 : /*
2505 : * Everything's allocated in either TopTransactionContext or the context
2506 : * for the subtransaction to which it corresponds. So, there's nothing to
2507 : * do here except reset the pointers; the space will be reclaimed when the
2508 : * contexts are deleted.
2509 : */
2510 50634 : pendingActions = NULL;
2511 50634 : pendingNotifies = NULL;
2512 50634 : }
2513 :
2514 : /*
2515 : * GUC check_hook for notify_buffers
2516 : */
2517 : bool
2518 2276 : check_notify_buffers(int *newval, void **extra, GucSource source)
2519 : {
2520 2276 : return check_slru_buffers("notify_buffers", newval);
2521 : }
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