Age Owner Branch data TLA 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
748 akorotkov@postgresql 465 :UBC 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
748 akorotkov@postgresql 475 :CBC 25 : asyncQueuePagePrecedes(int64 p, int64 q)
476 : : {
477 : 25 : return p < q;
478 : : }
479 : :
480 : : /*
481 : : * Report space needed for our shared memory area
482 : : */
483 : : Size
5782 tgl@sss.pgh.pa.us 484 : 1986 : AsyncShmemSize(void)
485 : : {
486 : : Size size;
487 : :
488 : : /* This had better match AsyncShmemInit */
653 heikki.linnakangas@i 489 : 1986 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
3951 tgl@sss.pgh.pa.us 490 : 1986 : size = add_size(size, offsetof(AsyncQueueControl, backend));
491 : :
657 alvherre@alvh.no-ip. 492 : 1986 : size = add_size(size, SimpleLruShmemSize(notify_buffers, 0));
493 : :
5782 tgl@sss.pgh.pa.us 494 : 1986 : return size;
495 : : }
496 : :
497 : : /*
498 : : * Initialize our shared memory area
499 : : */
500 : : void
501 : 1069 : AsyncShmemInit(void)
502 : : {
503 : : bool found;
504 : : Size size;
505 : :
506 : : /*
507 : : * Create or attach to the AsyncQueueControl structure.
508 : : */
653 heikki.linnakangas@i 509 : 1069 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
3951 tgl@sss.pgh.pa.us 510 : 1069 : size = add_size(size, offsetof(AsyncQueueControl, backend));
511 : :
5782 512 : 1069 : asyncQueueControl = (AsyncQueueControl *)
513 : 1069 : ShmemInitStruct("Async Queue Control", size, &found);
514 : :
515 [ + - ]: 1069 : if (!found)
516 : : {
517 : : /* First time through, so initialize it */
518 : 1069 : SET_QUEUE_POS(QUEUE_HEAD, 0, 0);
519 : 1069 : SET_QUEUE_POS(QUEUE_TAIL, 0, 0);
1844 520 : 1069 : QUEUE_STOP_PAGE = 0;
653 heikki.linnakangas@i 521 : 1069 : QUEUE_FIRST_LISTENER = INVALID_PROC_NUMBER;
5782 tgl@sss.pgh.pa.us 522 : 1069 : asyncQueueControl->lastQueueFillWarn = 0;
653 heikki.linnakangas@i 523 [ + + ]: 99982 : for (int i = 0; i < MaxBackends; i++)
524 : : {
5782 tgl@sss.pgh.pa.us 525 : 98913 : QUEUE_BACKEND_PID(i) = InvalidPid;
3730 526 : 98913 : QUEUE_BACKEND_DBOID(i) = InvalidOid;
653 heikki.linnakangas@i 527 : 98913 : QUEUE_NEXT_LISTENER(i) = INVALID_PROC_NUMBER;
5782 tgl@sss.pgh.pa.us 528 : 98913 : 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 : : */
2041 536 : 1069 : NotifyCtl->PagePrecedes = asyncQueuePagePrecedes;
657 alvherre@alvh.no-ip. 537 : 1069 : SimpleLruInit(NotifyCtl, "notify", notify_buffers, 0,
538 : : "pg_notify", LWTRANCHE_NOTIFY_BUFFER, LWTRANCHE_NOTIFY_SLRU,
539 : : SYNC_HANDLER_NONE, true);
540 : :
5782 tgl@sss.pgh.pa.us 541 [ + - ]: 1069 : if (!found)
542 : : {
543 : : /*
544 : : * During start or reboot, clean out the pg_notify directory.
545 : : */
2041 546 : 1069 : (void) SlruScanDirectory(NotifyCtl, SlruScanDirCbDeleteAll, NULL);
547 : : }
5782 548 : 1069 : }
549 : :
550 : :
551 : : /*
552 : : * pg_notify -
553 : : * SQL function to send a notification event
554 : : */
555 : : Datum
556 : 1054 : pg_notify(PG_FUNCTION_ARGS)
557 : : {
558 : : const char *channel;
559 : : const char *payload;
560 : :
561 [ + + ]: 1054 : if (PG_ARGISNULL(0))
562 : 3 : channel = "";
563 : : else
564 : 1051 : channel = text_to_cstring(PG_GETARG_TEXT_PP(0));
565 : :
566 [ + + ]: 1054 : if (PG_ARGISNULL(1))
567 : 6 : payload = "";
568 : : else
569 : 1048 : payload = text_to_cstring(PG_GETARG_TEXT_PP(1));
570 : :
571 : : /* For NOTIFY as a statement, this is checked in ProcessUtility */
5778 572 : 1054 : PreventCommandDuringRecovery("NOTIFY");
573 : :
5782 574 : 1054 : Async_Notify(channel, payload);
575 : :
576 : 1045 : 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 : 1103 : Async_Notify(const char *channel, const char *payload)
591 : : {
2265 rhaas@postgresql.org 592 : 1103 : int my_level = GetCurrentTransactionNestLevel();
593 : : size_t channel_len;
594 : : size_t payload_len;
595 : : Notification *n;
596 : : MemoryContext oldcontext;
597 : :
3708 598 [ - + ]: 1103 : if (IsParallelWorker())
3708 rhaas@postgresql.org 599 [ # # ]:UBC 0 : elog(ERROR, "cannot send notifications from a parallel worker");
600 : :
9330 peter_e@gmx.net 601 [ - + ]:CBC 1103 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 602 [ # # ]:UBC 0 : elog(DEBUG1, "Async_Notify(%s)", channel);
603 : :
2315 tgl@sss.pgh.pa.us 604 [ + - ]:CBC 1103 : channel_len = channel ? strlen(channel) : 0;
605 [ + + ]: 1103 : payload_len = payload ? strlen(payload) : 0;
606 : :
607 : : /* a channel name must be specified */
608 [ + + ]: 1103 : if (channel_len == 0)
5782 609 [ + - ]: 6 : ereport(ERROR,
610 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
611 : : errmsg("channel name cannot be empty")));
612 : :
613 : : /* enforce length limits */
2315 614 [ + + ]: 1097 : if (channel_len >= NAMEDATALEN)
5782 615 [ + - ]: 3 : ereport(ERROR,
616 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
617 : : errmsg("channel name too long")));
618 : :
2315 619 [ - + ]: 1094 : if (payload_len >= NOTIFY_PAYLOAD_MAX_LENGTH)
2315 tgl@sss.pgh.pa.us 620 [ # # ]:UBC 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 : : */
5782 tgl@sss.pgh.pa.us 631 :CBC 1094 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
632 : :
2315 633 : 1094 : n = (Notification *) palloc(offsetof(Notification, data) +
634 : 1094 : channel_len + payload_len + 2);
635 : 1094 : n->channel_len = channel_len;
636 : 1094 : n->payload_len = payload_len;
637 : 1094 : strcpy(n->data, channel);
5782 638 [ + + ]: 1094 : if (payload)
2315 639 : 1081 : strcpy(n->data + channel_len + 1, payload);
640 : : else
641 : 13 : n->data[channel_len + 1] = '\0';
642 : :
2265 rhaas@postgresql.org 643 [ + + + + ]: 1094 : if (pendingNotifies == NULL || my_level > pendingNotifies->nestingLevel)
2315 tgl@sss.pgh.pa.us 644 : 50 : {
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 *)
2265 rhaas@postgresql.org 653 : 50 : MemoryContextAlloc(TopTransactionContext,
654 : : sizeof(NotificationList));
655 : 50 : notifies->nestingLevel = my_level;
656 : 50 : notifies->events = list_make1(n);
657 : : /* We certainly don't need a hashtable yet */
658 : 50 : notifies->hashtab = NULL;
659 : 50 : notifies->upper = pendingNotifies;
660 : 50 : pendingNotifies = notifies;
661 : : }
662 : : else
663 : : {
664 : : /* Now check for duplicates */
665 [ + + ]: 1044 : if (AsyncExistsPendingNotify(n))
666 : : {
667 : : /* It's a dup, so forget it */
668 : 12 : pfree(n);
669 : 12 : MemoryContextSwitchTo(oldcontext);
670 : 12 : return;
671 : : }
672 : :
673 : : /* Append more events to existing list */
2315 tgl@sss.pgh.pa.us 674 : 1032 : AddEventToPendingNotifies(n);
675 : : }
676 : :
5782 677 : 1082 : 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 : 57 : queue_listen(ListenActionKind action, const char *channel)
690 : : {
691 : : MemoryContext oldcontext;
692 : : ListenAction *actrec;
2265 rhaas@postgresql.org 693 : 57 : 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 : : */
6488 tgl@sss.pgh.pa.us 701 : 57 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
702 : :
703 : : /* space for terminating null is included in sizeof(ListenAction) */
3951 704 : 57 : actrec = (ListenAction *) palloc(offsetof(ListenAction, channel) +
705 : 57 : strlen(channel) + 1);
6488 706 : 57 : actrec->action = action;
5782 707 : 57 : strcpy(actrec->channel, channel);
708 : :
2265 rhaas@postgresql.org 709 [ + + - + ]: 57 : if (pendingActions == NULL || my_level > pendingActions->nestingLevel)
710 : 50 : {
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 : 50 : MemoryContextAlloc(TopTransactionContext, sizeof(ActionList));
720 : 50 : actions->nestingLevel = my_level;
721 : 50 : actions->actions = list_make1(actrec);
722 : 50 : actions->upper = pendingActions;
723 : 50 : pendingActions = actions;
724 : : }
725 : : else
726 : 7 : pendingActions->actions = lappend(pendingActions->actions, actrec);
727 : :
6488 tgl@sss.pgh.pa.us 728 : 57 : MemoryContextSwitchTo(oldcontext);
729 : 57 : }
730 : :
731 : : /*
732 : : * Async_Listen
733 : : *
734 : : * This is executed by the SQL listen command.
735 : : */
736 : : void
5782 737 : 37 : Async_Listen(const char *channel)
738 : : {
6488 739 [ - + ]: 37 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 740 [ # # ]:UBC 0 : elog(DEBUG1, "Async_Listen(%s,%d)", channel, MyProcPid);
741 : :
5782 tgl@sss.pgh.pa.us 742 :CBC 37 : queue_listen(LISTEN_LISTEN, channel);
6488 743 : 37 : }
744 : :
745 : : /*
746 : : * Async_Unlisten
747 : : *
748 : : * This is executed by the SQL unlisten command.
749 : : */
750 : : void
5782 751 : 3 : Async_Unlisten(const char *channel)
752 : : {
6317 753 [ - + ]: 3 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 754 [ # # ]:UBC 0 : elog(DEBUG1, "Async_Unlisten(%s,%d)", channel, MyProcPid);
755 : :
756 : : /* If we couldn't possibly be listening, no need to queue anything */
2265 rhaas@postgresql.org 757 [ + - - + ]:CBC 3 : if (pendingActions == NULL && !unlistenExitRegistered)
6150 tgl@sss.pgh.pa.us 758 :UBC 0 : return;
759 : :
5782 tgl@sss.pgh.pa.us 760 :CBC 3 : 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
6488 769 : 19 : Async_UnlistenAll(void)
770 : : {
771 [ - + ]: 19 : if (Trace_notify)
6488 tgl@sss.pgh.pa.us 772 [ # # ]:UBC 0 : elog(DEBUG1, "Async_UnlistenAll(%d)", MyProcPid);
773 : :
774 : : /* If we couldn't possibly be listening, no need to queue anything */
2265 rhaas@postgresql.org 775 [ + - + + ]:CBC 19 : if (pendingActions == NULL && !unlistenExitRegistered)
6150 tgl@sss.pgh.pa.us 776 : 2 : return;
777 : :
6488 778 : 17 : 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
5782 789 : 9 : pg_listening_channels(PG_FUNCTION_ARGS)
790 : : {
791 : : FuncCallContext *funcctx;
792 : :
793 : : /* stuff done only on the first call of the function */
794 [ + + ]: 9 : if (SRF_IS_FIRSTCALL())
795 : : {
796 : : /* create a function context for cross-call persistence */
797 : 6 : funcctx = SRF_FIRSTCALL_INIT();
798 : : }
799 : :
800 : : /* stuff done on every call of the function */
801 : 9 : funcctx = SRF_PERCALL_SETUP();
802 : :
2346 803 [ + + ]: 9 : if (funcctx->call_cntr < list_length(listenChannels))
804 : : {
805 : 3 : char *channel = (char *) list_nth(listenChannels,
806 : 3 : funcctx->call_cntr);
807 : :
5782 808 : 3 : SRF_RETURN_NEXT(funcctx, CStringGetTextDatum(channel));
809 : : }
810 : :
811 : 6 : 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
6488 822 : 14 : Async_UnlistenOnExit(int code, Datum arg)
823 : : {
5782 824 : 14 : Exec_UnlistenAllCommit();
4689 825 : 14 : asyncQueueUnregister();
6488 826 : 14 : }
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 : 298 : AtPrepare_Notify(void)
836 : : {
837 : : /* It's not allowed to have any pending LISTEN/UNLISTEN/NOTIFY actions */
5782 838 [ + - - + ]: 298 : if (pendingActions || pendingNotifies)
6488 tgl@sss.pgh.pa.us 839 [ # # ]:UBC 0 : ereport(ERROR,
840 : : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
841 : : errmsg("cannot PREPARE a transaction that has executed LISTEN, UNLISTEN, or NOTIFY")));
5782 tgl@sss.pgh.pa.us 842 :CBC 298 : }
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 : 304341 : PreCommit_Notify(void)
861 : : {
862 : : ListCell *p;
863 : :
2315 864 [ + + + + ]: 304341 : if (!pendingActions && !pendingNotifies)
5782 865 : 304244 : return; /* no relevant statements in this xact */
866 : :
867 [ - + ]: 97 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 868 [ # # ]:UBC 0 : elog(DEBUG1, "PreCommit_Notify");
869 : :
870 : : /* Preflight for any pending listen/unlisten actions */
2265 rhaas@postgresql.org 871 [ + + ]:CBC 97 : if (pendingActions != NULL)
872 : : {
873 [ + - + + : 105 : foreach(p, pendingActions->actions)
+ + ]
874 : : {
875 : 56 : ListenAction *actrec = (ListenAction *) lfirst(p);
876 : :
877 [ + + + - ]: 56 : switch (actrec->action)
878 : : {
879 : 37 : case LISTEN_LISTEN:
880 : 37 : Exec_ListenPreCommit();
881 : 37 : break;
882 : 3 : case LISTEN_UNLISTEN:
883 : : /* there is no Exec_UnlistenPreCommit() */
884 : 3 : break;
885 : 16 : case LISTEN_UNLISTEN_ALL:
886 : : /* there is no Exec_UnlistenAllPreCommit() */
887 : 16 : break;
888 : : }
889 : : }
890 : : }
891 : :
892 : : /* Queue any pending notifies (must happen after the above) */
5782 tgl@sss.pgh.pa.us 893 [ + + ]: 97 : 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 : 48 : (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 : 48 : LockSharedObject(DatabaseRelationId, InvalidOid, 0,
922 : : AccessExclusiveLock);
923 : :
924 : : /* Now push the notifications into the queue */
2315 925 : 48 : nextNotify = list_head(pendingNotifies->events);
5782 926 [ + + ]: 131 : 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 : : */
2041 940 : 83 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
5782 941 : 83 : asyncQueueFillWarning();
942 [ - + ]: 83 : if (asyncQueueIsFull())
5782 tgl@sss.pgh.pa.us 943 [ # # ]:UBC 0 : ereport(ERROR,
944 : : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
945 : : errmsg("too many notifications in the NOTIFY queue")));
5782 tgl@sss.pgh.pa.us 946 :CBC 83 : nextNotify = asyncQueueAddEntries(nextNotify);
2041 947 : 83 : 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
6488 967 : 304186 : 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 : : */
5782 975 [ + + + + ]: 304186 : if (!pendingActions && !pendingNotifies)
6488 976 : 304089 : return;
977 : :
978 [ - + ]: 97 : if (Trace_notify)
6488 tgl@sss.pgh.pa.us 979 [ # # ]:UBC 0 : elog(DEBUG1, "AtCommit_Notify");
980 : :
981 : : /* Perform any pending listen/unlisten actions */
2265 rhaas@postgresql.org 982 [ + + ]:CBC 97 : if (pendingActions != NULL)
983 : : {
984 [ + - + + : 105 : foreach(p, pendingActions->actions)
+ + ]
985 : : {
986 : 56 : ListenAction *actrec = (ListenAction *) lfirst(p);
987 : :
988 [ + + + - ]: 56 : switch (actrec->action)
989 : : {
990 : 37 : case LISTEN_LISTEN:
991 : 37 : Exec_ListenCommit(actrec->channel);
992 : 37 : break;
993 : 3 : case LISTEN_UNLISTEN:
994 : 3 : Exec_UnlistenCommit(actrec->channel);
995 : 3 : break;
996 : 16 : case LISTEN_UNLISTEN_ALL:
997 : 16 : Exec_UnlistenAllCommit();
998 : 16 : break;
999 : : }
1000 : : }
1001 : : }
1002 : :
1003 : : /* If no longer listening to anything, get out of listener array */
4689 tgl@sss.pgh.pa.us 1004 [ + + + + ]: 97 : if (amRegisteredListener && listenChannels == NIL)
1005 : 13 : 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 : : */
1554 1012 [ + + ]: 97 : if (pendingNotifies != NULL)
1013 : 48 : 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 [ + + ]: 97 : if (tryAdvanceTail)
1025 : : {
1026 : 8 : tryAdvanceTail = false;
1027 : 8 : asyncQueueAdvanceTail();
1028 : : }
1029 : :
1030 : : /* And clean up */
5782 1031 : 97 : 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 : 37 : 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 : : */
4689 1050 [ + + ]: 37 : if (amRegisteredListener)
5782 1051 : 18 : return;
1052 : :
1053 [ - + ]: 19 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 1054 [ # # ]:UBC 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 : : */
5782 tgl@sss.pgh.pa.us 1060 [ + + ]:CBC 19 : if (!unlistenExitRegistered)
1061 : : {
4381 rhaas@postgresql.org 1062 : 14 : before_shmem_exit(Async_UnlistenOnExit, 0);
5782 tgl@sss.pgh.pa.us 1063 : 14 : 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 : : */
2041 1086 : 19 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
3730 1087 : 19 : head = QUEUE_HEAD;
1088 : 19 : max = QUEUE_TAIL;
653 heikki.linnakangas@i 1089 : 19 : prevListener = INVALID_PROC_NUMBER;
1090 [ + + ]: 21 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1091 : : {
2289 tgl@sss.pgh.pa.us 1092 [ + - ]: 2 : if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
1093 [ - + + - : 2 : max = QUEUE_POS_MAX(max, QUEUE_BACKEND_POS(i));
+ - ]
1094 : : /* Also find last listening backend before this one */
653 heikki.linnakangas@i 1095 [ - + ]: 2 : if (i < MyProcNumber)
2289 tgl@sss.pgh.pa.us 1096 :LBC (2) : prevListener = i;
1097 : : }
653 heikki.linnakangas@i 1098 :CBC 19 : QUEUE_BACKEND_POS(MyProcNumber) = max;
1099 : 19 : QUEUE_BACKEND_PID(MyProcNumber) = MyProcPid;
1100 : 19 : QUEUE_BACKEND_DBOID(MyProcNumber) = MyDatabaseId;
1101 : : /* Insert backend into list of listeners at correct position */
1102 [ - + ]: 19 : if (prevListener != INVALID_PROC_NUMBER)
1103 : : {
653 heikki.linnakangas@i 1104 :LBC (2) : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_NEXT_LISTENER(prevListener);
1105 : (2) : QUEUE_NEXT_LISTENER(prevListener) = MyProcNumber;
1106 : : }
1107 : : else
1108 : : {
653 heikki.linnakangas@i 1109 :CBC 19 : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_FIRST_LISTENER;
1110 : 19 : QUEUE_FIRST_LISTENER = MyProcNumber;
1111 : : }
2041 tgl@sss.pgh.pa.us 1112 : 19 : LWLockRelease(NotifyQueueLock);
1113 : :
1114 : : /* Now we are listed in the global array, so remember we're listening */
4689 1115 : 19 : 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 : : */
3730 1125 [ + + + + ]: 19 : if (!QUEUE_POS_EQUAL(max, head))
1126 : 11 : 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
5782 1135 : 37 : Exec_ListenCommit(const char *channel)
1136 : : {
1137 : : MemoryContext oldcontext;
1138 : :
1139 : : /* Do nothing if we are already listening on this channel */
1140 [ + + ]: 37 : if (IsListeningOn(channel))
1141 : 10 : 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 : 27 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
1152 : 27 : listenChannels = lappend(listenChannels, pstrdup(channel));
1153 : 27 : 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 : 3 : Exec_UnlistenCommit(const char *channel)
1163 : : {
1164 : : ListCell *q;
1165 : :
1166 [ - + ]: 3 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 1167 [ # # ]:UBC 0 : elog(DEBUG1, "Exec_UnlistenCommit(%s,%d)", channel, MyProcPid);
1168 : :
5782 tgl@sss.pgh.pa.us 1169 [ + - + - :CBC 3 : foreach(q, listenChannels)
+ - ]
1170 : : {
5772 bruce@momjian.us 1171 : 3 : char *lchan = (char *) lfirst(q);
1172 : :
5782 tgl@sss.pgh.pa.us 1173 [ + - ]: 3 : if (strcmp(lchan, channel) == 0)
1174 : : {
2346 1175 : 3 : listenChannels = foreach_delete_current(listenChannels, q);
5782 1176 : 3 : pfree(lchan);
1177 : 3 : break;
1178 : : }
1179 : : }
1180 : :
1181 : : /*
1182 : : * We do not complain about unlistening something not being listened;
1183 : : * should we?
1184 : : */
1185 : 3 : }
1186 : :
1187 : : /*
1188 : : * Exec_UnlistenAllCommit --- subroutine for AtCommit_Notify
1189 : : *
1190 : : * Unlisten on all channels for this backend.
1191 : : */
1192 : : static void
1193 : 30 : Exec_UnlistenAllCommit(void)
1194 : : {
1195 [ - + ]: 30 : if (Trace_notify)
5782 tgl@sss.pgh.pa.us 1196 [ # # ]:UBC 0 : elog(DEBUG1, "Exec_UnlistenAllCommit(%d)", MyProcPid);
1197 : :
5782 tgl@sss.pgh.pa.us 1198 :CBC 30 : list_free_deep(listenChannels);
1199 : 30 : listenChannels = NIL;
1200 : 30 : }
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 : 105 : IsListeningOn(const char *channel)
1212 : : {
1213 : : ListCell *p;
1214 : :
1215 [ + + + + : 166 : foreach(p, listenChannels)
+ + ]
1216 : : {
1217 : 102 : char *lchan = (char *) lfirst(p);
1218 : :
1219 [ + + ]: 102 : if (strcmp(lchan, channel) == 0)
1220 : 41 : return true;
1221 : : }
1222 : 64 : 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 : 27 : asyncQueueUnregister(void)
1231 : : {
3100 1232 [ - + ]: 27 : Assert(listenChannels == NIL); /* else caller error */
1233 : :
4584 bruce@momjian.us 1234 [ + + ]: 27 : if (!amRegisteredListener) /* nothing to do */
4689 tgl@sss.pgh.pa.us 1235 : 8 : return;
1236 : :
1237 : : /*
1238 : : * Need exclusive lock here to manipulate list links.
1239 : : */
2041 1240 : 19 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1241 : : /* Mark our entry as invalid */
653 heikki.linnakangas@i 1242 : 19 : QUEUE_BACKEND_PID(MyProcNumber) = InvalidPid;
1243 : 19 : QUEUE_BACKEND_DBOID(MyProcNumber) = InvalidOid;
1244 : : /* and remove it from the list */
1245 [ + + ]: 19 : if (QUEUE_FIRST_LISTENER == MyProcNumber)
1246 : 17 : QUEUE_FIRST_LISTENER = QUEUE_NEXT_LISTENER(MyProcNumber);
1247 : : else
1248 : : {
653 heikki.linnakangas@i 1249 [ + - ]:GBC 2 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1250 : : {
1251 [ + - ]: 2 : if (QUEUE_NEXT_LISTENER(i) == MyProcNumber)
1252 : : {
1253 : 2 : QUEUE_NEXT_LISTENER(i) = QUEUE_NEXT_LISTENER(MyProcNumber);
2289 tgl@sss.pgh.pa.us 1254 : 2 : break;
1255 : : }
1256 : : }
1257 : : }
653 heikki.linnakangas@i 1258 :CBC 19 : QUEUE_NEXT_LISTENER(MyProcNumber) = INVALID_PROC_NUMBER;
2041 tgl@sss.pgh.pa.us 1259 : 19 : LWLockRelease(NotifyQueueLock);
1260 : :
1261 : : /* mark ourselves as no longer listed in the global array */
4689 1262 : 19 : 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
5782 1271 : 83 : asyncQueueIsFull(void)
1272 : : {
511 michael@paquier.xyz 1273 : 83 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
1274 : 83 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
1275 : 83 : int64 occupied = headPage - tailPage;
1276 : :
748 akorotkov@postgresql 1277 : 83 : 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
3977 tgl@sss.pgh.pa.us 1286 : 2301 : asyncQueueAdvance(volatile QueuePosition *position, int entryLength)
1287 : : {
748 akorotkov@postgresql 1288 : 2301 : int64 pageno = QUEUE_POS_PAGE(*position);
5772 bruce@momjian.us 1289 : 2301 : int offset = QUEUE_POS_OFFSET(*position);
1290 : 2301 : bool pageJump = false;
1291 : :
1292 : : /*
1293 : : * Move to the next writing position: First jump over what we have just
1294 : : * written or read.
1295 : : */
5782 tgl@sss.pgh.pa.us 1296 : 2301 : offset += entryLength;
1297 [ - + ]: 2301 : 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 [ + + ]: 2301 : if (offset + QUEUEALIGN(AsyncQueueEntryEmptySize) > QUEUE_PAGESIZE)
1305 : : {
1306 : 70 : pageno++;
1307 : 70 : offset = 0;
1308 : 70 : pageJump = true;
1309 : : }
1310 : :
1311 : 2301 : SET_QUEUE_POS(*position, pageno, offset);
1312 : 2301 : return pageJump;
1313 : : }
1314 : :
1315 : : /*
1316 : : * Fill the AsyncQueueEntry at *qe with an outbound notification message.
1317 : : */
1318 : : static void
1319 : 1109 : asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
1320 : : {
2315 1321 : 1109 : size_t channellen = n->channel_len;
1322 : 1109 : size_t payloadlen = n->payload_len;
1323 : : int entryLength;
1324 : :
5782 1325 [ - + ]: 1109 : Assert(channellen < NAMEDATALEN);
1326 [ - + ]: 1109 : Assert(payloadlen < NOTIFY_PAYLOAD_MAX_LENGTH);
1327 : :
1328 : : /* The terminators are already included in AsyncQueueEntryEmptySize */
1329 : 1109 : entryLength = AsyncQueueEntryEmptySize + payloadlen + channellen;
1330 : 1109 : entryLength = QUEUEALIGN(entryLength);
1331 : 1109 : qe->length = entryLength;
1332 : 1109 : qe->dboid = MyDatabaseId;
1333 : 1109 : qe->xid = GetCurrentTransactionId();
1334 : 1109 : qe->srcPid = MyProcPid;
2315 1335 : 1109 : memcpy(qe->data, n->data, channellen + payloadlen + 2);
5782 1336 : 1109 : }
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 : 83 : 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 : : */
4918 1375 : 83 : 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 : 83 : pageno = QUEUE_POS_PAGE(queue_head);
657 alvherre@alvh.no-ip. 1383 : 83 : prevlock = SimpleLruGetBankLock(NotifyCtl, pageno);
1384 : :
1385 : : /* We hold both NotifyQueueLock and SLRU bank lock during this operation */
1386 : 83 : LWLockAcquire(prevlock, LW_EXCLUSIVE);
1387 : :
2043 tgl@sss.pgh.pa.us 1388 [ + + + + ]: 83 : if (QUEUE_POS_IS_ZERO(queue_head))
2041 1389 : 7 : slotno = SimpleLruZeroPage(NotifyCtl, pageno);
1390 : : else
1391 : 76 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
1392 : : InvalidTransactionId);
1393 : :
1394 : : /* Note we mark the page dirty before writing in it */
1395 : 83 : NotifyCtl->shared->page_dirty[slotno] = true;
1396 : :
5782 1397 [ + + ]: 1157 : while (nextNotify != NULL)
1398 : : {
5772 bruce@momjian.us 1399 : 1109 : Notification *n = (Notification *) lfirst(nextNotify);
1400 : :
1401 : : /* Construct a valid queue entry in local variable qe */
5782 tgl@sss.pgh.pa.us 1402 : 1109 : asyncQueueNotificationToEntry(n, &qe);
1403 : :
4918 1404 : 1109 : offset = QUEUE_POS_OFFSET(queue_head);
1405 : :
1406 : : /* Check whether the entry really fits on the current page */
5782 1407 [ + + ]: 1109 : if (offset + qe.length <= QUEUE_PAGESIZE)
1408 : : {
1409 : : /* OK, so advance nextNotify past this item */
2315 1410 : 1076 : 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 : : */
5782 1419 : 33 : qe.length = QUEUE_PAGESIZE - offset;
1420 : 33 : qe.dboid = InvalidOid;
34 heikki.linnakangas@i 1421 : 33 : qe.xid = InvalidTransactionId;
5772 bruce@momjian.us 1422 : 33 : qe.data[0] = '\0'; /* empty channel */
1423 : 33 : qe.data[1] = '\0'; /* empty payload */
1424 : : }
1425 : :
1426 : : /* Now copy qe into the shared buffer page */
2041 tgl@sss.pgh.pa.us 1427 : 1109 : memcpy(NotifyCtl->shared->page_buffer[slotno] + offset,
1428 : : &qe,
5782 1429 : 1109 : qe.length);
1430 : :
1431 : : /* Advance queue_head appropriately, and detect if page is full */
4918 1432 [ + + ]: 1109 : if (asyncQueueAdvance(&(queue_head), qe.length))
1433 : : {
1434 : : LWLock *lock;
1435 : :
657 alvherre@alvh.no-ip. 1436 : 35 : pageno = QUEUE_POS_PAGE(queue_head);
1437 : 35 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
1438 [ - + ]: 35 : if (lock != prevlock)
1439 : : {
657 alvherre@alvh.no-ip. 1440 :UBC 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 : : */
2041 tgl@sss.pgh.pa.us 1453 :CBC 35 : 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 : : */
2277 1460 [ + + ]: 35 : if (QUEUE_POS_PAGE(queue_head) % QUEUE_CLEANUP_DELAY == 0)
1554 1461 : 8 : tryAdvanceTail = true;
1462 : :
1463 : : /* And exit the loop */
8953 1464 : 35 : break;
1465 : : }
1466 : : }
1467 : :
1468 : : /* Success, so update the global QUEUE_HEAD */
4918 1469 : 83 : QUEUE_HEAD = queue_head;
1470 : :
657 alvherre@alvh.no-ip. 1471 : 83 : LWLockRelease(prevlock);
1472 : :
5782 tgl@sss.pgh.pa.us 1473 : 83 : return nextNotify;
1474 : : }
1475 : :
1476 : : /*
1477 : : * SQL function to return the fraction of the notification queue currently
1478 : : * occupied.
1479 : : */
1480 : : Datum
3805 rhaas@postgresql.org 1481 : 5 : 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 */
2214 tgl@sss.pgh.pa.us 1486 : 5 : asyncQueueAdvanceTail();
1487 : :
2041 1488 : 5 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
3805 rhaas@postgresql.org 1489 : 5 : usage = asyncQueueUsage();
2041 tgl@sss.pgh.pa.us 1490 : 5 : LWLockRelease(NotifyQueueLock);
1491 : :
3805 rhaas@postgresql.org 1492 : 5 : 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 : 88 : asyncQueueUsage(void)
1507 : : {
511 michael@paquier.xyz 1508 : 88 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
1509 : 88 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
1510 : 88 : int64 occupied = headPage - tailPage;
1511 : :
5782 tgl@sss.pgh.pa.us 1512 [ + + ]: 88 : if (occupied == 0)
3805 rhaas@postgresql.org 1513 : 42 : return (double) 0; /* fast exit for common case */
1514 : :
748 akorotkov@postgresql 1515 : 46 : 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
3805 rhaas@postgresql.org 1527 : 83 : asyncQueueFillWarning(void)
1528 : : {
1529 : : double fillDegree;
1530 : : TimestampTz t;
1531 : :
1532 : 83 : fillDegree = asyncQueueUsage();
5782 tgl@sss.pgh.pa.us 1533 [ + - ]: 83 : if (fillDegree < 0.5)
1534 : 83 : return;
1535 : :
5782 tgl@sss.pgh.pa.us 1536 :UBC 0 : t = GetCurrentTimestamp();
1537 : :
1538 [ # # ]: 0 : if (TimestampDifferenceExceeds(asyncQueueControl->lastQueueFillWarn,
1539 : : t, QUEUE_FULL_WARN_INTERVAL))
1540 : : {
5772 bruce@momjian.us 1541 : 0 : QueuePosition min = QUEUE_HEAD;
1542 : 0 : int32 minPid = InvalidPid;
1543 : :
653 heikki.linnakangas@i 1544 [ # # ]: 0 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1545 : : {
2289 tgl@sss.pgh.pa.us 1546 [ # # ]: 0 : 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 : :
5782 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
5782 tgl@sss.pgh.pa.us 1581 :CBC 48 : 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 : : */
1344 rhaas@postgresql.org 1595 : 48 : pids = (int32 *) palloc(MaxBackends * sizeof(int32));
653 heikki.linnakangas@i 1596 : 48 : procnos = (ProcNumber *) palloc(MaxBackends * sizeof(ProcNumber));
5782 tgl@sss.pgh.pa.us 1597 : 48 : count = 0;
1598 : :
2041 1599 : 48 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
653 heikki.linnakangas@i 1600 [ + + ]: 88 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1601 : : {
2277 tgl@sss.pgh.pa.us 1602 : 40 : int32 pid = QUEUE_BACKEND_PID(i);
1603 : : QueuePosition pos;
1604 : :
2289 1605 [ - + ]: 40 : Assert(pid != InvalidPid);
2277 1606 : 40 : pos = QUEUE_BACKEND_POS(i);
1607 [ + - ]: 40 : 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 [ + + - + ]: 40 : if (QUEUE_POS_EQUAL(pos, QUEUE_HEAD))
2277 tgl@sss.pgh.pa.us 1614 :UBC 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 */
2277 tgl@sss.pgh.pa.us 1627 :CBC 40 : pids[count] = pid;
653 heikki.linnakangas@i 1628 : 40 : procnos[count] = i;
2277 tgl@sss.pgh.pa.us 1629 : 40 : count++;
1630 : : }
2041 1631 : 48 : LWLockRelease(NotifyQueueLock);
1632 : :
1633 : : /* Now send signals */
2289 1634 [ + + ]: 88 : for (int i = 0; i < count; i++)
1635 : : {
2277 1636 : 40 : 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 : : */
1554 1642 [ + + ]: 40 : if (pid == MyProcPid)
1643 : : {
1644 : 20 : notifyInterruptPending = true;
1645 : 20 : 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 : : */
653 heikki.linnakangas@i 1654 [ - + ]: 20 : if (SendProcSignal(pid, PROCSIG_NOTIFY_INTERRUPT, procnos[i]) < 0)
5782 tgl@sss.pgh.pa.us 1655 [ # # ]:UBC 0 : elog(DEBUG3, "could not signal backend with PID %d: %m", pid);
1656 : : }
1657 : :
5782 tgl@sss.pgh.pa.us 1658 :CBC 48 : pfree(pids);
653 heikki.linnakangas@i 1659 : 48 : pfree(procnos);
9933 tgl@sss.pgh.pa.us 1660 : 48 : }
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
8948 1671 : 26098 : 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 : : */
4689 1678 [ - + - - ]: 26098 : if (amRegisteredListener && listenChannels == NIL)
4689 tgl@sss.pgh.pa.us 1679 :UBC 0 : asyncQueueUnregister();
1680 : :
1681 : : /* And clean up */
6488 tgl@sss.pgh.pa.us 1682 :CBC 26098 : ClearPendingActionsAndNotifies();
9933 1683 : 26098 : }
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
7838 1691 : 4419 : AtSubCommit_Notify(void)
1692 : : {
2265 rhaas@postgresql.org 1693 : 4419 : int my_level = GetCurrentTransactionNestLevel();
1694 : :
1695 : : /* If there are actions at our nesting level, we must reparent them. */
1696 [ - + ]: 4419 : if (pendingActions != NULL &&
2265 rhaas@postgresql.org 1697 [ # # ]:UBC 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. */
2265 rhaas@postgresql.org 1722 [ + + ]:CBC 4419 : if (pendingNotifies != NULL &&
1723 [ + + ]: 2 : pendingNotifies->nestingLevel >= my_level)
1724 : : {
1725 [ - + ]: 1 : Assert(pendingNotifies->nestingLevel == my_level);
1726 : :
1727 [ + - ]: 1 : if (pendingNotifies->upper == NULL ||
1728 [ - + ]: 1 : pendingNotifies->upper->nestingLevel < my_level - 1)
1729 : : {
1730 : : /* nothing to merge; give the whole thing to the parent */
2265 rhaas@postgresql.org 1731 :UBC 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 : : */
2265 rhaas@postgresql.org 1740 :CBC 1 : NotificationList *childPendingNotifies = pendingNotifies;
1741 : : ListCell *l;
1742 : :
1743 : 1 : pendingNotifies = pendingNotifies->upper;
1744 : : /* Insert all the subxact's events into parent, except for dups */
1745 [ + - + + : 5 : foreach(l, childPendingNotifies->events)
+ + ]
1746 : : {
1747 : 4 : Notification *childn = (Notification *) lfirst(l);
1748 : :
1749 [ + + ]: 4 : if (!AsyncExistsPendingNotify(childn))
1750 : 2 : AddEventToPendingNotifies(childn);
1751 : : }
1752 : 1 : pfree(childPendingNotifies);
1753 : : }
1754 : : }
7838 tgl@sss.pgh.pa.us 1755 : 4419 : }
1756 : :
1757 : : /*
1758 : : * AtSubAbort_Notify() --- Take care of subtransaction abort.
1759 : : */
1760 : : void
1761 : 4683 : AtSubAbort_Notify(void)
1762 : : {
7771 1763 : 4683 : 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 : : */
2265 rhaas@postgresql.org 1776 [ - + ]: 4683 : while (pendingActions != NULL &&
2265 rhaas@postgresql.org 1777 [ # # ]:UBC 0 : pendingActions->nestingLevel >= my_level)
1778 : : {
1779 : 0 : ActionList *childPendingActions = pendingActions;
1780 : :
1781 : 0 : pendingActions = pendingActions->upper;
1782 : 0 : pfree(childPendingActions);
1783 : : }
1784 : :
2265 rhaas@postgresql.org 1785 [ + + ]:CBC 4684 : while (pendingNotifies != NULL &&
1786 [ + + ]: 2 : pendingNotifies->nestingLevel >= my_level)
1787 : : {
1788 : 1 : NotificationList *childPendingNotifies = pendingNotifies;
1789 : :
1790 : 1 : pendingNotifies = pendingNotifies->upper;
1791 : 1 : pfree(childPendingNotifies);
1792 : : }
7838 tgl@sss.pgh.pa.us 1793 : 4683 : }
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
5982 1804 : 20 : 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 */
3969 andres@anarazel.de 1812 : 20 : notifyInterruptPending = true;
1813 : :
1814 : : /* make sure the event is processed in due course */
1815 : 20 : SetLatch(MyLatch);
9933 tgl@sss.pgh.pa.us 1816 : 20 : }
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
1554 1834 : 96 : ProcessNotifyInterrupt(bool flush)
1835 : : {
8097 1836 [ + + ]: 96 : if (IsTransactionOrTransactionBlock())
9933 1837 : 57 : return; /* not really idle */
1838 : :
1839 : : /* Loop in case another signal arrives while sending messages */
3969 andres@anarazel.de 1840 [ + + ]: 78 : while (notifyInterruptPending)
1554 tgl@sss.pgh.pa.us 1841 : 39 : 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
5782 1851 : 50 : asyncQueueReadAllNotifications(void)
1852 : : {
1853 : : QueuePosition pos;
1854 : : QueuePosition head;
1855 : : Snapshot snapshot;
1856 : :
1857 : : /* Fetch current state */
2041 1858 : 50 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
1859 : : /* Assert checks that we have a valid state entry */
653 heikki.linnakangas@i 1860 [ - + ]: 50 : Assert(MyProcPid == QUEUE_BACKEND_PID(MyProcNumber));
1861 : 50 : pos = QUEUE_BACKEND_POS(MyProcNumber);
5782 tgl@sss.pgh.pa.us 1862 : 50 : head = QUEUE_HEAD;
2041 1863 : 50 : LWLockRelease(NotifyQueueLock);
1864 : :
5782 1865 [ + + - + ]: 50 : if (QUEUE_POS_EQUAL(pos, head))
1866 : : {
1867 : : /* Nothing to do, we have read all notifications already. */
5782 tgl@sss.pgh.pa.us 1868 :UBC 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 : : */
2214 tgl@sss.pgh.pa.us 1910 :CBC 50 : 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 : : {
34 heikki.linnakangas@i 1930 : 50 : bool save_ExitOnAnyError = ExitOnAnyError;
1931 : : bool reachedStop;
1932 : :
1933 : 50 : 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 : 85 : reachedStop = asyncQueueProcessPageEntries(&pos, head, snapshot);
5782 tgl@sss.pgh.pa.us 1953 [ + + ]: 85 : } while (!reachedStop);
1954 : :
1955 : : /* Update shared state */
2041 1956 : 50 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
653 heikki.linnakangas@i 1957 : 50 : QUEUE_BACKEND_POS(MyProcNumber) = pos;
2041 tgl@sss.pgh.pa.us 1958 : 50 : LWLockRelease(NotifyQueueLock);
1959 : :
34 heikki.linnakangas@i 1960 : 50 : ExitOnAnyError = save_ExitOnAnyError;
1961 : : }
1962 : :
1963 : : /* Done with snapshot */
2988 tgl@sss.pgh.pa.us 1964 : 50 : 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
34 heikki.linnakangas@i 1977 : 85 : asyncQueueProcessPageEntries(QueuePosition *current,
1978 : : QueuePosition stop,
1979 : : Snapshot snapshot)
1980 : : {
1981 : 85 : int64 curpage = QUEUE_POS_PAGE(*current);
1982 : : int slotno;
1983 : : char *page_buffer;
5782 tgl@sss.pgh.pa.us 1984 : 85 : 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.
1991 : : */
1992 : : alignas(AsyncQueueEntry) char local_buf[QUEUE_PAGESIZE];
25 peter@eisentraut.org 1993 :GNC 85 : char *local_buf_end = local_buf;
1994 : :
34 heikki.linnakangas@i 1995 :CBC 85 : slotno = SimpleLruReadPage_ReadOnly(NotifyCtl, curpage,
1996 : : InvalidTransactionId);
1997 : 85 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
1998 : :
1999 : : do
2000 : : {
5772 bruce@momjian.us 2001 : 1242 : QueuePosition thisentry = *current;
2002 : : AsyncQueueEntry *qe;
2003 : :
5781 tgl@sss.pgh.pa.us 2004 [ + + + + ]: 1242 : if (QUEUE_POS_EQUAL(thisentry, stop))
5782 2005 : 50 : break;
2006 : :
5781 2007 : 1192 : qe = (AsyncQueueEntry *) (page_buffer + QUEUE_POS_OFFSET(thisentry));
2008 : :
2009 : : /*
2010 : : * Advance *current over this message, possibly to the next page. As
2011 : : * noted in the comments for asyncQueueReadAllNotifications, we must
2012 : : * do this before possibly failing while processing the message.
2013 : : */
5782 2014 : 1192 : reachedEndOfPage = asyncQueueAdvance(current, qe->length);
2015 : :
2016 : : /* Ignore messages destined for other databases */
2017 [ + + ]: 1192 : if (qe->dboid == MyDatabaseId)
2018 : : {
2988 2019 [ - + ]: 1159 : if (XidInMVCCSnapshot(qe->xid, snapshot))
2020 : : {
2021 : : /*
2022 : : * The source transaction is still in progress, so we can't
2023 : : * process this message yet. Break out of the loop, but first
2024 : : * back up *current so we will reprocess the message next
2025 : : * time. (Note: it is unlikely but not impossible for
2026 : : * TransactionIdDidCommit to fail, so we can't really avoid
2027 : : * this advance-then-back-up behavior when dealing with an
2028 : : * uncommitted message.)
2029 : : *
2030 : : * Note that we must test XidInMVCCSnapshot before we test
2031 : : * TransactionIdDidCommit, else we might return a message from
2032 : : * a transaction that is not yet visible to snapshots; compare
2033 : : * the comments at the head of heapam_visibility.c.
2034 : : *
2035 : : * Also, while our own xact won't be listed in the snapshot,
2036 : : * we need not check for TransactionIdIsCurrentTransactionId
2037 : : * because our transaction cannot (yet) have queued any
2038 : : * messages.
2039 : : */
4296 tgl@sss.pgh.pa.us 2040 :UBC 0 : *current = thisentry;
2041 : 0 : reachedStop = true;
2042 : 0 : break;
2043 : : }
2044 : :
2045 : : /*
2046 : : * Quick check for the case that we're not listening on any
2047 : : * channels, before calling TransactionIdDidCommit(). This makes
2048 : : * that case a little faster, but more importantly, it ensures
2049 : : * that if there's a bad entry in the queue for which
2050 : : * TransactionIdDidCommit() fails for some reason, we can skip
2051 : : * over it on the first LISTEN in a session, and not get stuck on
2052 : : * it indefinitely.
2053 : : */
34 heikki.linnakangas@i 2054 [ + + ]:CBC 1159 : if (listenChannels == NIL)
2055 : 1091 : continue;
2056 : :
2057 [ + - ]: 68 : if (TransactionIdDidCommit(qe->xid))
2058 : : {
2059 : 68 : memcpy(local_buf_end, qe, qe->length);
2060 : 68 : local_buf_end += qe->length;
2061 : : }
2062 : : else
2063 : : {
2064 : : /*
2065 : : * The source transaction aborted or crashed, so we just
2066 : : * ignore its notifications.
2067 : : */
2068 : : }
2069 : : }
2070 : :
2071 : : /* Loop back if we're not at end of page */
5782 tgl@sss.pgh.pa.us 2072 [ + + ]: 1192 : } while (!reachedEndOfPage);
2073 : :
2074 : : /* Release lock that we got from SimpleLruReadPage_ReadOnly() */
34 heikki.linnakangas@i 2075 : 85 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2076 : :
2077 : : /*
2078 : : * Now that we have let go of the SLRU bank lock, send the notifications
2079 : : * to our backend
2080 : : */
25 peter@eisentraut.org 2081 [ - + ]:GNC 85 : Assert(local_buf_end - local_buf <= BLCKSZ);
2082 [ + + ]: 153 : for (char *p = local_buf; p < local_buf_end;)
2083 : : {
34 heikki.linnakangas@i 2084 :CBC 68 : AsyncQueueEntry *qe = (AsyncQueueEntry *) p;
2085 : :
2086 : : /* qe->data is the null-terminated channel name */
2087 : 68 : char *channel = qe->data;
2088 : :
2089 [ + + ]: 68 : if (IsListeningOn(channel))
2090 : : {
2091 : : /* payload follows channel name */
2092 : 31 : char *payload = qe->data + strlen(channel) + 1;
2093 : :
2094 : 31 : NotifyMyFrontEnd(channel, payload, qe->srcPid);
2095 : : }
2096 : :
2097 : 68 : p += qe->length;
2098 : : }
2099 : :
5782 tgl@sss.pgh.pa.us 2100 [ + + + + ]: 85 : if (QUEUE_POS_EQUAL(*current, stop))
2101 : 50 : reachedStop = true;
2102 : :
2103 : 85 : return reachedStop;
2104 : : }
2105 : :
2106 : : /*
2107 : : * Advance the shared queue tail variable to the minimum of all the
2108 : : * per-backend tail pointers. Truncate pg_notify space if possible.
2109 : : *
2110 : : * This is (usually) called during CommitTransaction(), so it's important for
2111 : : * it to have very low probability of failure.
2112 : : */
2113 : : static void
2114 : 13 : asyncQueueAdvanceTail(void)
2115 : : {
2116 : : QueuePosition min;
2117 : : int64 oldtailpage;
2118 : : int64 newtailpage;
2119 : : int64 boundary;
2120 : :
2121 : : /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
1949 noah@leadboat.com 2122 : 13 : LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE);
2123 : :
2124 : : /*
2125 : : * Compute the new tail. Pre-v13, it's essential that QUEUE_TAIL be exact
2126 : : * (ie, exactly match at least one backend's queue position), so it must
2127 : : * be updated atomically with the actual computation. Since v13, we could
2128 : : * get away with not doing it like that, but it seems prudent to keep it
2129 : : * so.
2130 : : *
2131 : : * Also, because incoming backends will scan forward from QUEUE_TAIL, that
2132 : : * must be advanced before we can truncate any data. Thus, QUEUE_TAIL is
2133 : : * the logical tail, while QUEUE_STOP_PAGE is the physical tail, or oldest
2134 : : * un-truncated page. When QUEUE_STOP_PAGE != QUEUE_POS_PAGE(QUEUE_TAIL),
2135 : : * there are pages we can truncate but haven't yet finished doing so.
2136 : : *
2137 : : * For concurrency's sake, we don't want to hold NotifyQueueLock while
2138 : : * performing SimpleLruTruncate. This is OK because no backend will try
2139 : : * to access the pages we are in the midst of truncating.
2140 : : */
2041 tgl@sss.pgh.pa.us 2141 : 13 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
5782 2142 : 13 : min = QUEUE_HEAD;
653 heikki.linnakangas@i 2143 [ + + ]: 23 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
2144 : : {
2289 tgl@sss.pgh.pa.us 2145 [ - + ]: 10 : Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
2146 [ + - + + : 10 : min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
+ - ]
2147 : : }
1844 2148 : 13 : QUEUE_TAIL = min;
2149 : 13 : oldtailpage = QUEUE_STOP_PAGE;
2041 2150 : 13 : LWLockRelease(NotifyQueueLock);
2151 : :
2152 : : /*
2153 : : * We can truncate something if the global tail advanced across an SLRU
2154 : : * segment boundary.
2155 : : *
2156 : : * XXX it might be better to truncate only once every several segments, to
2157 : : * reduce the number of directory scans.
2158 : : */
5782 2159 : 13 : newtailpage = QUEUE_POS_PAGE(min);
2160 : 13 : boundary = newtailpage - (newtailpage % SLRU_PAGES_PER_SEGMENT);
5193 alvherre@alvh.no-ip. 2161 [ - + ]: 13 : if (asyncQueuePagePrecedes(oldtailpage, boundary))
2162 : : {
2163 : : /*
2164 : : * SimpleLruTruncate() will ask for SLRU bank locks but will also
2165 : : * release the lock again.
2166 : : */
2041 tgl@sss.pgh.pa.us 2167 :UBC 0 : SimpleLruTruncate(NotifyCtl, newtailpage);
2168 : :
1844 2169 : 0 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2170 : 0 : QUEUE_STOP_PAGE = newtailpage;
2171 : 0 : LWLockRelease(NotifyQueueLock);
2172 : : }
2173 : :
1949 noah@leadboat.com 2174 :CBC 13 : LWLockRelease(NotifyQueueTailLock);
5782 tgl@sss.pgh.pa.us 2175 : 13 : }
2176 : :
2177 : : /*
2178 : : * AsyncNotifyFreezeXids
2179 : : *
2180 : : * Prepare the async notification queue for CLOG truncation by freezing
2181 : : * transaction IDs that are about to become inaccessible.
2182 : : *
2183 : : * This function is called by VACUUM before advancing datfrozenxid. It scans
2184 : : * the notification queue and replaces XIDs that would become inaccessible
2185 : : * after CLOG truncation with special markers:
2186 : : * - Committed transactions are set to FrozenTransactionId
2187 : : * - Aborted/crashed transactions are set to InvalidTransactionId
2188 : : *
2189 : : * Only XIDs < newFrozenXid are processed, as those are the ones whose CLOG
2190 : : * pages will be truncated. If XID < newFrozenXid, it cannot still be running
2191 : : * (or it would have held back newFrozenXid through ProcArray).
2192 : : * Therefore, if TransactionIdDidCommit returns false, we know the transaction
2193 : : * either aborted explicitly or crashed, and we can safely mark it invalid.
2194 : : */
2195 : : void
34 heikki.linnakangas@i 2196 : 103 : AsyncNotifyFreezeXids(TransactionId newFrozenXid)
2197 : : {
2198 : : QueuePosition pos;
2199 : : QueuePosition head;
2200 : 103 : int64 curpage = -1;
2201 : 103 : int slotno = -1;
2202 : 103 : char *page_buffer = NULL;
2203 : 103 : bool page_dirty = false;
2204 : :
2205 : : /*
2206 : : * Acquire locks in the correct order to avoid deadlocks. As per the
2207 : : * locking protocol: NotifyQueueTailLock, then NotifyQueueLock, then SLRU
2208 : : * bank locks.
2209 : : *
2210 : : * We only need SHARED mode since we're just reading the head/tail
2211 : : * positions, not modifying them.
2212 : : */
2213 : 103 : LWLockAcquire(NotifyQueueTailLock, LW_SHARED);
2214 : 103 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2215 : :
2216 : 103 : pos = QUEUE_TAIL;
2217 : 103 : head = QUEUE_HEAD;
2218 : :
2219 : : /* Release NotifyQueueLock early, we only needed to read the positions */
2220 : 103 : LWLockRelease(NotifyQueueLock);
2221 : :
2222 : : /*
2223 : : * Scan the queue from tail to head, freezing XIDs as needed. We hold
2224 : : * NotifyQueueTailLock throughout to ensure the tail doesn't move while
2225 : : * we're working.
2226 : : */
2227 [ - + - + ]: 103 : while (!QUEUE_POS_EQUAL(pos, head))
2228 : : {
2229 : : AsyncQueueEntry *qe;
2230 : : TransactionId xid;
34 heikki.linnakangas@i 2231 :UBC 0 : int64 pageno = QUEUE_POS_PAGE(pos);
2232 : 0 : int offset = QUEUE_POS_OFFSET(pos);
2233 : :
2234 : : /* If we need a different page, release old lock and get new one */
2235 [ # # ]: 0 : if (pageno != curpage)
2236 : : {
2237 : : LWLock *lock;
2238 : :
2239 : : /* Release previous page if any */
2240 [ # # ]: 0 : if (slotno >= 0)
2241 : : {
2242 [ # # ]: 0 : if (page_dirty)
2243 : : {
2244 : 0 : NotifyCtl->shared->page_dirty[slotno] = true;
2245 : 0 : page_dirty = false;
2246 : : }
2247 : 0 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2248 : : }
2249 : :
2250 : 0 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
2251 : 0 : LWLockAcquire(lock, LW_EXCLUSIVE);
2252 : 0 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
2253 : : InvalidTransactionId);
2254 : 0 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
2255 : 0 : curpage = pageno;
2256 : : }
2257 : :
2258 : 0 : qe = (AsyncQueueEntry *) (page_buffer + offset);
2259 : 0 : xid = qe->xid;
2260 : :
2261 [ # # # # ]: 0 : if (TransactionIdIsNormal(xid) &&
2262 : 0 : TransactionIdPrecedes(xid, newFrozenXid))
2263 : : {
2264 [ # # ]: 0 : if (TransactionIdDidCommit(xid))
2265 : : {
2266 : 0 : qe->xid = FrozenTransactionId;
2267 : 0 : page_dirty = true;
2268 : : }
2269 : : else
2270 : : {
2271 : 0 : qe->xid = InvalidTransactionId;
2272 : 0 : page_dirty = true;
2273 : : }
2274 : : }
2275 : :
2276 : : /* Advance to next entry */
2277 : 0 : asyncQueueAdvance(&pos, qe->length);
2278 : : }
2279 : :
2280 : : /* Release final page lock if we acquired one */
34 heikki.linnakangas@i 2281 [ - + ]:CBC 103 : if (slotno >= 0)
2282 : : {
34 heikki.linnakangas@i 2283 [ # # ]:UBC 0 : if (page_dirty)
2284 : 0 : NotifyCtl->shared->page_dirty[slotno] = true;
2285 : 0 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2286 : : }
2287 : :
34 heikki.linnakangas@i 2288 :CBC 103 : LWLockRelease(NotifyQueueTailLock);
2289 : 103 : }
2290 : :
2291 : : /*
2292 : : * ProcessIncomingNotify
2293 : : *
2294 : : * Scan the queue for arriving notifications and report them to the front
2295 : : * end. The notifications might be from other sessions, or our own;
2296 : : * there's no need to distinguish here.
2297 : : *
2298 : : * If "flush" is true, force any frontend messages out immediately.
2299 : : *
2300 : : * NOTE: since we are outside any transaction, we must create our own.
2301 : : */
2302 : : static void
1554 tgl@sss.pgh.pa.us 2303 : 39 : ProcessIncomingNotify(bool flush)
2304 : : {
2305 : : /* We *must* reset the flag */
3969 andres@anarazel.de 2306 : 39 : notifyInterruptPending = false;
2307 : :
2308 : : /* Do nothing else if we aren't actively listening */
5782 tgl@sss.pgh.pa.us 2309 [ - + ]: 39 : if (listenChannels == NIL)
5782 tgl@sss.pgh.pa.us 2310 :UBC 0 : return;
2311 : :
9330 peter_e@gmx.net 2312 [ - + ]:CBC 39 : if (Trace_notify)
8239 bruce@momjian.us 2313 [ # # ]:UBC 0 : elog(DEBUG1, "ProcessIncomingNotify");
2314 : :
2106 peter@eisentraut.org 2315 :CBC 39 : set_ps_display("notify interrupt");
2316 : :
2317 : : /*
2318 : : * We must run asyncQueueReadAllNotifications inside a transaction, else
2319 : : * bad things happen if it gets an error.
2320 : : */
5782 tgl@sss.pgh.pa.us 2321 : 39 : StartTransactionCommand();
2322 : :
2323 : 39 : asyncQueueReadAllNotifications();
2324 : :
8252 2325 : 39 : CommitTransactionCommand();
2326 : :
2327 : : /*
2328 : : * If this isn't an end-of-command case, we must flush the notify messages
2329 : : * to ensure frontend gets them promptly.
2330 : : */
1554 2331 [ + + ]: 39 : if (flush)
2332 : 10 : pq_flush();
2333 : :
2106 peter@eisentraut.org 2334 : 39 : set_ps_display("idle");
2335 : :
9330 peter_e@gmx.net 2336 [ - + ]: 39 : if (Trace_notify)
8239 bruce@momjian.us 2337 [ # # ]:UBC 0 : elog(DEBUG1, "ProcessIncomingNotify: done");
2338 : : }
2339 : :
2340 : : /*
2341 : : * Send NOTIFY message to my front end.
2342 : : */
2343 : : void
5782 tgl@sss.pgh.pa.us 2344 :CBC 31 : NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
2345 : : {
7348 alvherre@alvh.no-ip. 2346 [ + - ]: 31 : if (whereToSendOutput == DestRemote)
2347 : : {
2348 : : StringInfoData buf;
2349 : :
847 nathan@postgresql.or 2350 : 31 : pq_beginmessage(&buf, PqMsg_NotificationResponse);
2988 andres@anarazel.de 2351 : 31 : pq_sendint32(&buf, srcPid);
5782 tgl@sss.pgh.pa.us 2352 : 31 : pq_sendstring(&buf, channel);
1748 heikki.linnakangas@i 2353 : 31 : pq_sendstring(&buf, payload);
9732 tgl@sss.pgh.pa.us 2354 : 31 : pq_endmessage(&buf);
2355 : :
2356 : : /*
2357 : : * NOTE: we do not do pq_flush() here. Some level of caller will
2358 : : * handle it later, allowing this message to be combined into a packet
2359 : : * with other ones.
2360 : : */
2361 : : }
2362 : : else
5782 tgl@sss.pgh.pa.us 2363 [ # # ]:UBC 0 : elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload);
9933 tgl@sss.pgh.pa.us 2364 :CBC 31 : }
2365 : :
2366 : : /* Does pendingNotifies include a match for the given event? */
2367 : : static bool
2315 2368 : 1048 : AsyncExistsPendingNotify(Notification *n)
2369 : : {
2370 [ - + ]: 1048 : if (pendingNotifies == NULL)
5782 tgl@sss.pgh.pa.us 2371 :UBC 0 : return false;
2372 : :
2315 tgl@sss.pgh.pa.us 2373 [ + + ]:CBC 1048 : if (pendingNotifies->hashtab != NULL)
2374 : : {
2375 : : /* Use the hash table to probe for a match */
2376 [ - + ]: 983 : if (hash_search(pendingNotifies->hashtab,
2377 : : &n,
2378 : : HASH_FIND,
2379 : : NULL))
2315 tgl@sss.pgh.pa.us 2380 :UBC 0 : return true;
2381 : : }
2382 : : else
2383 : : {
2384 : : /* Must scan the event list */
2385 : : ListCell *l;
2386 : :
2315 tgl@sss.pgh.pa.us 2387 [ + - + + :CBC 271 : foreach(l, pendingNotifies->events)
+ + ]
2388 : : {
2389 : 220 : Notification *oldn = (Notification *) lfirst(l);
2390 : :
2391 [ + - ]: 220 : if (n->channel_len == oldn->channel_len &&
2392 [ + + ]: 220 : n->payload_len == oldn->payload_len &&
2393 : 125 : memcmp(n->data, oldn->data,
2394 [ + + ]: 125 : n->channel_len + n->payload_len + 2) == 0)
2395 : 14 : return true;
2396 : : }
2397 : : }
2398 : :
2399 : 1034 : return false;
2400 : : }
2401 : :
2402 : : /*
2403 : : * Add a notification event to a pre-existing pendingNotifies list.
2404 : : *
2405 : : * Because pendingNotifies->events is already nonempty, this works
2406 : : * correctly no matter what CurrentMemoryContext is.
2407 : : */
2408 : : static void
2409 : 1034 : AddEventToPendingNotifies(Notification *n)
2410 : : {
2411 [ - + ]: 1034 : Assert(pendingNotifies->events != NIL);
2412 : :
2413 : : /* Create the hash table if it's time to */
2414 [ + + ]: 1034 : if (list_length(pendingNotifies->events) >= MIN_HASHABLE_NOTIFIES &&
2415 [ + + ]: 984 : pendingNotifies->hashtab == NULL)
2416 : : {
2417 : : HASHCTL hash_ctl;
2418 : : ListCell *l;
2419 : :
2420 : : /* Create the hash table */
2421 : 1 : hash_ctl.keysize = sizeof(Notification *);
578 peter@eisentraut.org 2422 : 1 : hash_ctl.entrysize = sizeof(struct NotificationHash);
2315 tgl@sss.pgh.pa.us 2423 : 1 : hash_ctl.hash = notification_hash;
2424 : 1 : hash_ctl.match = notification_match;
2425 : 1 : hash_ctl.hcxt = CurTransactionContext;
2426 : 2 : pendingNotifies->hashtab =
2427 : 1 : hash_create("Pending Notifies",
2428 : : 256L,
2429 : : &hash_ctl,
2430 : : HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
2431 : :
2432 : : /* Insert all the already-existing events */
2433 [ + - + + : 17 : foreach(l, pendingNotifies->events)
+ + ]
2434 : : {
2435 : 16 : Notification *oldn = (Notification *) lfirst(l);
2436 : : bool found;
2437 : :
747 john.naylor@postgres 2438 : 16 : (void) hash_search(pendingNotifies->hashtab,
2439 : : &oldn,
2440 : : HASH_ENTER,
2441 : : &found);
2315 tgl@sss.pgh.pa.us 2442 [ - + ]: 16 : Assert(!found);
2443 : : }
2444 : : }
2445 : :
2446 : : /* Add new event to the list, in order */
2447 : 1034 : pendingNotifies->events = lappend(pendingNotifies->events, n);
2448 : :
2449 : : /* Add event to the hash table if needed */
2450 [ + + ]: 1034 : if (pendingNotifies->hashtab != NULL)
2451 : : {
2452 : : bool found;
2453 : :
747 john.naylor@postgres 2454 : 984 : (void) hash_search(pendingNotifies->hashtab,
2455 : : &n,
2456 : : HASH_ENTER,
2457 : : &found);
2315 tgl@sss.pgh.pa.us 2458 [ - + ]: 984 : Assert(!found);
2459 : : }
2460 : 1034 : }
2461 : :
2462 : : /*
2463 : : * notification_hash: hash function for notification hash table
2464 : : *
2465 : : * The hash "keys" are pointers to Notification structs.
2466 : : */
2467 : : static uint32
2468 : 1983 : notification_hash(const void *key, Size keysize)
2469 : : {
2470 : 1983 : const Notification *k = *(const Notification *const *) key;
2471 : :
2472 [ - + ]: 1983 : Assert(keysize == sizeof(Notification *));
2473 : : /* We don't bother to include the payload's trailing null in the hash */
2474 : 1983 : return DatumGetUInt32(hash_any((const unsigned char *) k->data,
2475 : 1983 : k->channel_len + k->payload_len + 1));
2476 : : }
2477 : :
2478 : : /*
2479 : : * notification_match: match function to use with notification_hash
2480 : : */
2481 : : static int
2315 tgl@sss.pgh.pa.us 2482 :UBC 0 : notification_match(const void *key1, const void *key2, Size keysize)
2483 : : {
2484 : 0 : const Notification *k1 = *(const Notification *const *) key1;
2485 : 0 : const Notification *k2 = *(const Notification *const *) key2;
2486 : :
2487 [ # # ]: 0 : Assert(keysize == sizeof(Notification *));
2488 [ # # ]: 0 : if (k1->channel_len == k2->channel_len &&
2489 [ # # ]: 0 : k1->payload_len == k2->payload_len &&
2490 : 0 : memcmp(k1->data, k2->data,
2491 [ # # ]: 0 : k1->channel_len + k1->payload_len + 2) == 0)
2492 : 0 : return 0; /* equal */
2493 : 0 : return 1; /* not equal */
2494 : : }
2495 : :
2496 : : /* Clear the pendingActions and pendingNotifies lists. */
2497 : : static void
6488 tgl@sss.pgh.pa.us 2498 :CBC 26195 : ClearPendingActionsAndNotifies(void)
2499 : : {
2500 : : /*
2501 : : * Everything's allocated in either TopTransactionContext or the context
2502 : : * for the subtransaction to which it corresponds. So, there's nothing to
2503 : : * do here except reset the pointers; the space will be reclaimed when the
2504 : : * contexts are deleted.
2505 : : */
2265 rhaas@postgresql.org 2506 : 26195 : pendingActions = NULL;
2315 tgl@sss.pgh.pa.us 2507 : 26195 : pendingNotifies = NULL;
10327 bruce@momjian.us 2508 : 26195 : }
2509 : :
2510 : : /*
2511 : : * GUC check_hook for notify_buffers
2512 : : */
2513 : : bool
657 alvherre@alvh.no-ip. 2514 : 1107 : check_notify_buffers(int *newval, void **extra, GucSource source)
2515 : : {
2516 : 1107 : return check_slru_buffers("notify_buffers", newval);
2517 : : }
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