diff options
Diffstat (limited to 'src/backend/commands/async.c')
| -rw-r--r-- | src/backend/commands/async.c | 1939 |
1 files changed, 1507 insertions, 432 deletions
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c index afc5e5fabc1..f5863480f5e 100644 --- a/src/backend/commands/async.c +++ b/src/backend/commands/async.c @@ -7,109 +7,280 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.150 2010/01/02 16:57:36 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/commands/async.c,v 1.151 2010/02/16 22:34:43 tgl Exp $ * *------------------------------------------------------------------------- */ /*------------------------------------------------------------------------- - * New Async Notification Model: - * 1. Multiple backends on same machine. Multiple backends listening on - * one relation. (Note: "listening on a relation" is not really the - * right way to think about it, since the notify names need not have - * anything to do with the names of relations actually in the database. - * But this terminology is all over the code and docs, and I don't feel - * like trying to replace it.) - * - * 2. There is a tuple in relation "pg_listener" for each active LISTEN, - * ie, each relname/listenerPID pair. The "notification" field of the - * tuple is zero when no NOTIFY is pending for that listener, or the PID - * of the originating backend when a cross-backend NOTIFY is pending. - * (We skip writing to pg_listener when doing a self-NOTIFY, so the - * notification field should never be equal to the listenerPID field.) - * - * 3. The NOTIFY statement itself (routine Async_Notify) just adds the target - * relname to a list of outstanding NOTIFY requests. Actual processing - * happens if and only if we reach transaction commit. At that time (in - * routine AtCommit_Notify) we scan pg_listener for matching relnames. - * If the listenerPID in a matching tuple is ours, we just send a notify - * message to our own front end. If it is not ours, and "notification" - * is not already nonzero, we set notification to our own PID and send a - * PROCSIG_NOTIFY_INTERRUPT signal to the receiving process (indicated by - * listenerPID). - * BTW: if the signal operation fails, we presume that the listener backend - * crashed without removing this tuple, and remove the tuple for it. - * - * 4. Upon receipt of a PROCSIG_NOTIFY_INTERRUPT signal, the signal handler + * Async Notification Model as of 9.0: + * + * 1. Multiple backends on same machine. Multiple backends listening on + * several channels. (Channels are also called "conditions" in other + * parts of the code.) + * + * 2. There is one central queue in disk-based storage (directory pg_notify/), + * with actively-used pages mapped into shared memory by the slru.c module. + * All notification messages are placed in the queue and later read out + * by listening backends. + * + * There is no central knowledge of which backend listens on which channel; + * every backend has its own list of interesting channels. + * + * Although there is only one queue, notifications are treated as being + * database-local; this is done by including the sender's database OID + * in each notification message. Listening backends ignore messages + * that don't match their database OID. This is important because it + * ensures senders and receivers have the same database encoding and won't + * misinterpret non-ASCII text in the channel name or payload string. + * + * Since notifications are not expected to survive database crashes, + * we can simply clean out the pg_notify data at any reboot, and there + * is no need for WAL support or fsync'ing. + * + * 3. Every backend that is listening on at least one channel registers by + * entering its PID into the array in AsyncQueueControl. It then scans all + * incoming notifications in the central queue and first compares the + * database OID of the notification with its own database OID and then + * compares the notified channel with the list of channels that it listens + * to. In case there is a match it delivers the notification event to its + * frontend. Non-matching events are simply skipped. + * + * 4. The NOTIFY statement (routine Async_Notify) stores the notification in + * a backend-local list which will not be processed until transaction end. + * + * Duplicate notifications from the same transaction are sent out as one + * notification only. This is done to save work when for example a trigger + * on a 2 million row table fires a notification for each row that has been + * changed. If the application needs to receive every single notification + * that has been sent, it can easily add some unique string into the extra + * payload parameter. + * + * When the transaction is ready to commit, PreCommit_Notify() adds the + * pending notifications to the head of the queue. The head pointer of the + * queue always points to the next free position and a position is just a + * page number and the offset in that page. This is done before marking the + * transaction as committed in clog. If we run into problems writing the + * notifications, we can still call elog(ERROR, ...) and the transaction + * will roll back. + * + * Once we have put all of the notifications into the queue, we return to + * CommitTransaction() which will then do the actual transaction commit. + * + * After commit we are called another time (AtCommit_Notify()). Here we + * make the actual updates to the effective listen state (listenChannels). + * + * Finally, after we are out of the transaction altogether, we check if + * we need to signal listening backends. In SignalBackends() we scan the + * list of listening backends and send a PROCSIG_NOTIFY_INTERRUPT signal + * to every listening backend (we don't know which backend is listening on + * which channel so we must signal them all). We can exclude backends that + * are already up to date, though. We don't bother with a self-signal + * either, but just process the queue directly. + * + * 5. Upon receipt of a PROCSIG_NOTIFY_INTERRUPT signal, the signal handler * can call inbound-notify processing immediately if this backend is idle * (ie, it is waiting for a frontend command and is not within a transaction * block). Otherwise the handler may only set a flag, which will cause the * processing to occur just before we next go idle. * - * 5. Inbound-notify processing consists of scanning pg_listener for tuples - * matching our own listenerPID and having nonzero notification fields. - * For each such tuple, we send a message to our frontend and clear the - * notification field. BTW: this routine has to start/commit its own - * transaction, since by assumption it is only called from outside any - * transaction. - * - * Like NOTIFY, LISTEN and UNLISTEN just add the desired action to a list - * of pending actions. If we reach transaction commit, the changes are - * applied to pg_listener just before executing any pending NOTIFYs. This - * method is necessary because to avoid race conditions, we must hold lock - * on pg_listener from when we insert a new listener tuple until we commit. - * To do that and not create undue hazard of deadlock, we don't want to - * touch pg_listener until we are otherwise done with the transaction; - * in particular it'd be uncool to still be taking user-commanded locks - * while holding the pg_listener lock. - * - * Although we grab ExclusiveLock on pg_listener for any operation, - * the lock is never held very long, so it shouldn't cause too much of - * a performance problem. (Previously we used AccessExclusiveLock, but - * there's no real reason to forbid concurrent reads.) - * - * An application that listens on the same relname it notifies will get + * Inbound-notify processing consists of reading all of the notifications + * that have arrived since scanning last time. We read every notification + * until we reach either a notification from an uncommitted transaction or + * the head pointer's position. Then we check if we were the laziest + * backend: if our pointer is set to the same position as the global tail + * pointer is set, then we move the global tail pointer ahead to where the + * second-laziest backend is (in general, we take the MIN of the current + * head position and all active backends' new tail pointers). Whenever we + * move the global tail pointer we also truncate now-unused pages (i.e., + * delete files in pg_notify/ that are no longer used). + * + * An application that listens on the same channel it notifies will get * NOTIFY messages for its own NOTIFYs. These can be ignored, if not useful, * by comparing be_pid in the NOTIFY message to the application's own backend's * PID. (As of FE/BE protocol 2.0, the backend's PID is provided to the * frontend during startup.) The above design guarantees that notifies from - * other backends will never be missed by ignoring self-notifies. Note, - * however, that we do *not* guarantee that a separate frontend message will - * be sent for every outside NOTIFY. Since there is only room for one - * originating PID in pg_listener, outside notifies occurring at about the - * same time may be collapsed into a single message bearing the PID of the - * first outside backend to perform the NOTIFY. + * other backends will never be missed by ignoring self-notifies. + * + * The amount of shared memory used for notify management (NUM_ASYNC_BUFFERS) + * can be varied without affecting anything but performance. The maximum + * amount of notification data that can be queued at one time is determined + * by slru.c's wraparound limit; see QUEUE_MAX_PAGE below. *------------------------------------------------------------------------- */ #include "postgres.h" +#include <limits.h> #include <unistd.h> #include <signal.h> -#include "access/heapam.h" -#include "access/twophase_rmgr.h" +#include "access/slru.h" +#include "access/transam.h" #include "access/xact.h" -#include "catalog/pg_listener.h" +#include "catalog/pg_database.h" #include "commands/async.h" +#include "funcapi.h" #include "libpq/libpq.h" #include "libpq/pqformat.h" #include "miscadmin.h" #include "storage/ipc.h" +#include "storage/lmgr.h" #include "storage/procsignal.h" #include "storage/sinval.h" #include "tcop/tcopprot.h" #include "utils/builtins.h" -#include "utils/fmgroids.h" #include "utils/memutils.h" #include "utils/ps_status.h" -#include "utils/tqual.h" /* + * Maximum size of a NOTIFY payload, including terminating NULL. This + * must be kept small enough so that a notification message fits on one + * SLRU page. + */ +#define NOTIFY_PAYLOAD_MAX_LENGTH 8000 + +/* + * Struct representing an entry in the global notify queue + * + * This struct declaration has the maximal length, but in a real queue entry + * the data area is only big enough for the actual channel and payload strings + * (each null-terminated). AsyncQueueEntryEmptySize is the minimum possible + * entry size, if both channel and payload strings are empty (but note it + * doesn't include alignment padding). + * + * The "length" field should always be rounded up to the next QUEUEALIGN + * multiple so that all fields are properly aligned. + */ +typedef struct AsyncQueueEntry +{ + int length; /* total allocated length of entry */ + Oid dboid; /* sender's database OID */ + TransactionId xid; /* sender's XID */ + int32 srcPid; /* sender's PID */ + char data[NAMEDATALEN + NOTIFY_PAYLOAD_MAX_LENGTH]; +} AsyncQueueEntry; + +/* Currently, no field of AsyncQueueEntry requires more than int alignment */ +#define QUEUEALIGN(len) INTALIGN(len) + +#define AsyncQueueEntryEmptySize (offsetof(AsyncQueueEntry, data) + 2) + +/* + * Struct describing a queue position, and assorted macros for working with it + */ +typedef struct QueuePosition +{ + int page; /* SLRU page number */ + int offset; /* byte offset within page */ +} QueuePosition; + +#define QUEUE_POS_PAGE(x) ((x).page) +#define QUEUE_POS_OFFSET(x) ((x).offset) + +#define SET_QUEUE_POS(x,y,z) \ + do { \ + (x).page = (y); \ + (x).offset = (z); \ + } while (0) + +#define QUEUE_POS_EQUAL(x,y) \ + ((x).page == (y).page && (x).offset == (y).offset) + +/* choose logically smaller QueuePosition */ +#define QUEUE_POS_MIN(x,y) \ + (asyncQueuePagePrecedesLogically((x).page, (y).page) ? (x) : \ + (x).page != (y).page ? (y) : \ + (x).offset < (y).offset ? (x) : (y)) + +/* + * Struct describing a listening backend's status + */ +typedef struct QueueBackendStatus +{ + int32 pid; /* either a PID or InvalidPid */ + QueuePosition pos; /* backend has read queue up to here */ +} QueueBackendStatus; + +#define InvalidPid (-1) + +/* + * Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff) + * + * The AsyncQueueControl structure is protected by the AsyncQueueLock. + * + * When holding the lock in SHARED mode, backends may only inspect their own + * entries as well as the head and tail pointers. Consequently we can allow a + * backend to update its own record while holding only SHARED lock (since no + * other backend will inspect it). + * + * When holding the lock in EXCLUSIVE mode, backends can inspect the entries + * of other backends and also change the head and tail pointers. + * + * In order to avoid deadlocks, whenever we need both locks, we always first + * get AsyncQueueLock and then AsyncCtlLock. + * + * Each backend uses the backend[] array entry with index equal to its + * BackendId (which can range from 1 to MaxBackends). We rely on this to make + * SendProcSignal fast. + */ +typedef struct AsyncQueueControl +{ + QueuePosition head; /* head points to the next free location */ + QueuePosition tail; /* the global tail is equivalent to the + tail of the "slowest" backend */ + TimestampTz lastQueueFillWarn; /* time of last queue-full msg */ + QueueBackendStatus backend[1]; /* actually of length MaxBackends+1 */ + /* DO NOT ADD FURTHER STRUCT MEMBERS HERE */ +} AsyncQueueControl; + +static AsyncQueueControl *asyncQueueControl; + +#define QUEUE_HEAD (asyncQueueControl->head) +#define QUEUE_TAIL (asyncQueueControl->tail) +#define QUEUE_BACKEND_PID(i) (asyncQueueControl->backend[i].pid) +#define QUEUE_BACKEND_POS(i) (asyncQueueControl->backend[i].pos) + +/* + * The SLRU buffer area through which we access the notification queue + */ +static SlruCtlData AsyncCtlData; + +#define AsyncCtl (&AsyncCtlData) +#define QUEUE_PAGESIZE BLCKSZ +#define QUEUE_FULL_WARN_INTERVAL 5000 /* warn at most once every 5s */ + +/* + * slru.c currently assumes that all filenames are four characters of hex + * digits. That means that we can use segments 0000 through FFFF. + * Each segment contains SLRU_PAGES_PER_SEGMENT pages which gives us + * the pages from 0 to SLRU_PAGES_PER_SEGMENT * 0x10000 - 1. + * + * It's of course possible to enhance slru.c, but this gives us so much + * space already that it doesn't seem worth the trouble. + * + * The most data we can have in the queue at a time is QUEUE_MAX_PAGE/2 + * pages, because more than that would confuse slru.c into thinking there + * was a wraparound condition. With the default BLCKSZ this means there + * can be up to 8GB of queued-and-not-read data. + * + * Note: it's possible to redefine QUEUE_MAX_PAGE with a smaller multiple of + * SLRU_PAGES_PER_SEGMENT, for easier testing of queue-full behaviour. + */ +#define QUEUE_MAX_PAGE (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1) + +/* + * listenChannels identifies the channels we are actually listening to + * (ie, have committed a LISTEN on). It is a simple list of channel names, + * allocated in TopMemoryContext. + */ +static List *listenChannels = NIL; /* list of C strings */ + +/* * State for pending LISTEN/UNLISTEN actions consists of an ordered list of * all actions requested in the current transaction. As explained above, - * we don't actually modify pg_listener until we reach transaction commit. + * we don't actually change listenChannels until we reach transaction commit. * * The list is kept in CurTransactionContext. In subtransactions, each * subtransaction has its own list in its own CurTransactionContext, but @@ -126,7 +297,7 @@ typedef enum typedef struct { ListenActionKind action; - char condname[1]; /* actually, as long as needed */ + char channel[1]; /* actually, as long as needed */ } ListenAction; static List *pendingActions = NIL; /* list of ListenAction */ @@ -134,9 +305,9 @@ static List *pendingActions = NIL; /* list of ListenAction */ static List *upperPendingActions = NIL; /* list of upper-xact lists */ /* - * State for outbound notifies consists of a list of all relnames NOTIFYed - * in the current transaction. We do not actually perform a NOTIFY until - * and unless the transaction commits. pendingNotifies is NIL if no + * State for outbound notifies consists of a list of all channels+payloads + * NOTIFYed in the current transaction. We do not actually perform a NOTIFY + * until and unless the transaction commits. pendingNotifies is NIL if no * NOTIFYs have been done in the current transaction. * * The list is kept in CurTransactionContext. In subtransactions, each @@ -149,12 +320,18 @@ static List *upperPendingActions = NIL; /* list of upper-xact lists */ * condition name, it will get a self-notify at commit. This is a bit odd * but is consistent with our historical behavior. */ -static List *pendingNotifies = NIL; /* list of C strings */ +typedef struct Notification +{ + char *channel; /* channel name */ + char *payload; /* payload string (can be empty) */ +} Notification; + +static List *pendingNotifies = NIL; /* list of Notifications */ static List *upperPendingNotifies = NIL; /* list of upper-xact lists */ /* - * State for inbound notifies consists of two flags: one saying whether + * State for inbound notifications consists of two flags: one saying whether * the signal handler is currently allowed to call ProcessIncomingNotify * directly, and one saying whether the signal has occurred but the handler * was not allowed to call ProcessIncomingNotify at the time. @@ -168,57 +345,259 @@ static volatile sig_atomic_t notifyInterruptOccurred = 0; /* True if we've registered an on_shmem_exit cleanup */ static bool unlistenExitRegistered = false; +/* has this backend sent notifications in the current transaction? */ +static bool backendHasSentNotifications = false; +/* has this backend executed its first LISTEN in the current transaction? */ +static bool backendHasExecutedInitialListen = false; +/* GUC parameter */ bool Trace_notify = false; - -static void queue_listen(ListenActionKind action, const char *condname); +/* local function prototypes */ +static bool asyncQueuePagePrecedesPhysically(int p, int q); +static bool asyncQueuePagePrecedesLogically(int p, int q); +static void queue_listen(ListenActionKind action, const char *channel); static void Async_UnlistenOnExit(int code, Datum arg); -static void Exec_Listen(Relation lRel, const char *relname); -static void Exec_Unlisten(Relation lRel, const char *relname); -static void Exec_UnlistenAll(Relation lRel); -static void Send_Notify(Relation lRel); +static void Exec_ListenPreCommit(void); +static void Exec_ListenCommit(const char *channel); +static void Exec_UnlistenCommit(const char *channel); +static void Exec_UnlistenAllCommit(void); +static bool IsListeningOn(const char *channel); +static void asyncQueueUnregister(void); +static bool asyncQueueIsFull(void); +static bool asyncQueueAdvance(QueuePosition *position, int entryLength); +static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe); +static ListCell *asyncQueueAddEntries(ListCell *nextNotify); +static void asyncQueueFillWarning(void); +static bool SignalBackends(void); +static void asyncQueueReadAllNotifications(void); +static bool asyncQueueProcessPageEntries(QueuePosition *current, + QueuePosition stop, + char *page_buffer); +static void asyncQueueAdvanceTail(void); static void ProcessIncomingNotify(void); -static void NotifyMyFrontEnd(char *relname, int32 listenerPID); -static bool AsyncExistsPendingNotify(const char *relname); +static void NotifyMyFrontEnd(const char *channel, + const char *payload, + int32 srcPid); +static bool AsyncExistsPendingNotify(const char *channel, const char *payload); static void ClearPendingActionsAndNotifies(void); /* + * We will work on the page range of 0..QUEUE_MAX_PAGE. + * + * asyncQueuePagePrecedesPhysically just checks numerically without any magic + * if one page precedes another one. This is wrong for normal operation but + * is helpful when clearing pg_notify/ during startup. + * + * asyncQueuePagePrecedesLogically compares using wraparound logic, as is + * required by slru.c. + */ +static bool +asyncQueuePagePrecedesPhysically(int p, int q) +{ + return p < q; +} + +static bool +asyncQueuePagePrecedesLogically(int p, int q) +{ + int diff; + + /* + * We have to compare modulo (QUEUE_MAX_PAGE+1)/2. Both inputs should + * be in the range 0..QUEUE_MAX_PAGE. + */ + Assert(p >= 0 && p <= QUEUE_MAX_PAGE); + Assert(q >= 0 && q <= QUEUE_MAX_PAGE); + + diff = p - q; + if (diff >= ((QUEUE_MAX_PAGE+1)/2)) + diff -= QUEUE_MAX_PAGE+1; + else if (diff < -((QUEUE_MAX_PAGE+1)/2)) + diff += QUEUE_MAX_PAGE+1; + return diff < 0; +} + +/* + * Report space needed for our shared memory area + */ +Size +AsyncShmemSize(void) +{ + Size size; + + /* This had better match AsyncShmemInit */ + size = mul_size(MaxBackends, sizeof(QueueBackendStatus)); + size = add_size(size, sizeof(AsyncQueueControl)); + + size = add_size(size, SimpleLruShmemSize(NUM_ASYNC_BUFFERS, 0)); + + return size; +} + +/* + * Initialize our shared memory area + */ +void +AsyncShmemInit(void) +{ + bool found; + int slotno; + Size size; + + /* + * Create or attach to the AsyncQueueControl structure. + * + * The used entries in the backend[] array run from 1 to MaxBackends. + * sizeof(AsyncQueueControl) already includes space for the unused zero'th + * entry, but we need to add on space for the used entries. + */ + size = mul_size(MaxBackends, sizeof(QueueBackendStatus)); + size = add_size(size, sizeof(AsyncQueueControl)); + + asyncQueueControl = (AsyncQueueControl *) + ShmemInitStruct("Async Queue Control", size, &found); + + if (!asyncQueueControl) + elog(ERROR, "out of shared memory"); + + if (!found) + { + /* First time through, so initialize it */ + int i; + + SET_QUEUE_POS(QUEUE_HEAD, 0, 0); + SET_QUEUE_POS(QUEUE_TAIL, 0, 0); + asyncQueueControl->lastQueueFillWarn = 0; + /* zero'th entry won't be used, but let's initialize it anyway */ + for (i = 0; i <= MaxBackends; i++) + { + QUEUE_BACKEND_PID(i) = InvalidPid; + SET_QUEUE_POS(QUEUE_BACKEND_POS(i), 0, 0); + } + } + + /* + * Set up SLRU management of the pg_notify data. + */ + AsyncCtl->PagePrecedes = asyncQueuePagePrecedesLogically; + SimpleLruInit(AsyncCtl, "Async Ctl", NUM_ASYNC_BUFFERS, 0, + AsyncCtlLock, "pg_notify"); + /* Override default assumption that writes should be fsync'd */ + AsyncCtl->do_fsync = false; + + if (!found) + { + /* + * During start or reboot, clean out the pg_notify directory. + * + * Since we want to remove every file, we temporarily use + * asyncQueuePagePrecedesPhysically() and pass INT_MAX as the + * comparison value; every file in the directory should therefore + * appear to be less than that. + */ + AsyncCtl->PagePrecedes = asyncQueuePagePrecedesPhysically; + (void) SlruScanDirectory(AsyncCtl, INT_MAX, true); + AsyncCtl->PagePrecedes = asyncQueuePagePrecedesLogically; + + /* Now initialize page zero to empty */ + LWLockAcquire(AsyncCtlLock, LW_EXCLUSIVE); + slotno = SimpleLruZeroPage(AsyncCtl, QUEUE_POS_PAGE(QUEUE_HEAD)); + /* This write is just to verify that pg_notify/ is writable */ + SimpleLruWritePage(AsyncCtl, slotno, NULL); + LWLockRelease(AsyncCtlLock); + } +} + + +/* + * pg_notify - + * SQL function to send a notification event + */ +Datum +pg_notify(PG_FUNCTION_ARGS) +{ + const char *channel; + const char *payload; + + if (PG_ARGISNULL(0)) + channel = ""; + else + channel = text_to_cstring(PG_GETARG_TEXT_PP(0)); + + if (PG_ARGISNULL(1)) + payload = ""; + else + payload = text_to_cstring(PG_GETARG_TEXT_PP(1)); + + Async_Notify(channel, payload); + + PG_RETURN_VOID(); +} + + +/* * Async_Notify * * This is executed by the SQL notify command. * - * Adds the relation to the list of pending notifies. + * Adds the message to the list of pending notifies. * Actual notification happens during transaction commit. * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ */ void -Async_Notify(const char *relname) +Async_Notify(const char *channel, const char *payload) { + Notification *n; + MemoryContext oldcontext; + if (Trace_notify) - elog(DEBUG1, "Async_Notify(%s)", relname); + elog(DEBUG1, "Async_Notify(%s)", channel); - /* no point in making duplicate entries in the list ... */ - if (!AsyncExistsPendingNotify(relname)) + /* a channel name must be specified */ + if (!channel || !strlen(channel)) + ereport(ERROR, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("channel name cannot be empty"))); + + if (strlen(channel) >= NAMEDATALEN) + ereport(ERROR, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("channel name too long"))); + + if (payload) { - /* - * The name list needs to live until end of transaction, so store it - * in the transaction context. - */ - MemoryContext oldcontext; + if (strlen(payload) >= NOTIFY_PAYLOAD_MAX_LENGTH) + ereport(ERROR, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("payload string too long"))); + } - oldcontext = MemoryContextSwitchTo(CurTransactionContext); + /* no point in making duplicate entries in the list ... */ + if (AsyncExistsPendingNotify(channel, payload)) + return; - /* - * Ordering of the list isn't important. We choose to put new entries - * on the front, as this might make duplicate-elimination a tad faster - * when the same condition is signaled many times in a row. - */ - pendingNotifies = lcons(pstrdup(relname), pendingNotifies); + /* + * The notification list needs to live until end of transaction, so store + * it in the transaction context. + */ + oldcontext = MemoryContextSwitchTo(CurTransactionContext); - MemoryContextSwitchTo(oldcontext); - } + n = (Notification *) palloc(sizeof(Notification)); + n->channel = pstrdup(channel); + if (payload) + n->payload = pstrdup(payload); + else + n->payload = ""; + + /* + * We want to preserve the order so we need to append every + * notification. See comments at AsyncExistsPendingNotify(). + */ + pendingNotifies = lappend(pendingNotifies, n); + + MemoryContextSwitchTo(oldcontext); } /* @@ -226,11 +605,11 @@ Async_Notify(const char *relname) * Common code for listen, unlisten, unlisten all commands. * * Adds the request to the list of pending actions. - * Actual update of pg_listener happens during transaction commit. - * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + * Actual update of the listenChannels list happens during transaction + * commit. */ static void -queue_listen(ListenActionKind action, const char *condname) +queue_listen(ListenActionKind action, const char *channel) { MemoryContext oldcontext; ListenAction *actrec; @@ -244,9 +623,9 @@ queue_listen(ListenActionKind action, const char *condname) oldcontext = MemoryContextSwitchTo(CurTransactionContext); /* space for terminating null is included in sizeof(ListenAction) */ - actrec = (ListenAction *) palloc(sizeof(ListenAction) + strlen(condname)); + actrec = (ListenAction *) palloc(sizeof(ListenAction) + strlen(channel)); actrec->action = action; - strcpy(actrec->condname, condname); + strcpy(actrec->channel, channel); pendingActions = lappend(pendingActions, actrec); @@ -259,12 +638,12 @@ queue_listen(ListenActionKind action, const char *condname) * This is executed by the SQL listen command. */ void -Async_Listen(const char *relname) +Async_Listen(const char *channel) { if (Trace_notify) - elog(DEBUG1, "Async_Listen(%s,%d)", relname, MyProcPid); + elog(DEBUG1, "Async_Listen(%s,%d)", channel, MyProcPid); - queue_listen(LISTEN_LISTEN, relname); + queue_listen(LISTEN_LISTEN, channel); } /* @@ -273,16 +652,16 @@ Async_Listen(const char *relname) * This is executed by the SQL unlisten command. */ void -Async_Unlisten(const char *relname) +Async_Unlisten(const char *channel) { if (Trace_notify) - elog(DEBUG1, "Async_Unlisten(%s,%d)", relname, MyProcPid); + elog(DEBUG1, "Async_Unlisten(%s,%d)", channel, MyProcPid); /* If we couldn't possibly be listening, no need to queue anything */ if (pendingActions == NIL && !unlistenExitRegistered) return; - queue_listen(LISTEN_UNLISTEN, relname); + queue_listen(LISTEN_UNLISTEN, channel); } /* @@ -304,28 +683,63 @@ Async_UnlistenAll(void) } /* - * Async_UnlistenOnExit + * SQL function: return a set of the channel names this backend is actively + * listening to. * - * Clean up the pg_listener table at backend exit. + * Note: this coding relies on the fact that the listenChannels list cannot + * change within a transaction. + */ +Datum +pg_listening_channels(PG_FUNCTION_ARGS) +{ + FuncCallContext *funcctx; + ListCell **lcp; + + /* stuff done only on the first call of the function */ + if (SRF_IS_FIRSTCALL()) + { + MemoryContext oldcontext; + + /* create a function context for cross-call persistence */ + funcctx = SRF_FIRSTCALL_INIT(); + + /* switch to memory context appropriate for multiple function calls */ + oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx); + + /* allocate memory for user context */ + lcp = (ListCell **) palloc(sizeof(ListCell *)); + *lcp = list_head(listenChannels); + funcctx->user_fctx = (void *) lcp; + + MemoryContextSwitchTo(oldcontext); + } + + /* stuff done on every call of the function */ + funcctx = SRF_PERCALL_SETUP(); + lcp = (ListCell **) funcctx->user_fctx; + + while (*lcp != NULL) + { + char *channel = (char *) lfirst(*lcp); + + *lcp = lnext(*lcp); + SRF_RETURN_NEXT(funcctx, CStringGetTextDatum(channel)); + } + + SRF_RETURN_DONE(funcctx); +} + +/* + * Async_UnlistenOnExit * - * This is executed if we have done any LISTENs in this backend. - * It might not be necessary anymore, if the user UNLISTENed everything, - * but we don't try to detect that case. + * This is executed at backend exit if we have done any LISTENs in this + * backend. It might not be necessary anymore, if the user UNLISTENed + * everything, but we don't try to detect that case. */ static void Async_UnlistenOnExit(int code, Datum arg) { - /* - * We need to start/commit a transaction for the unlisten, but if there is - * already an active transaction we had better abort that one first. - * Otherwise we'd end up committing changes that probably ought to be - * discarded. - */ - AbortOutOfAnyTransaction(); - /* Now we can do the unlisten */ - StartTransactionCommand(); - Async_UnlistenAll(); - CommitTransactionCommand(); + Exec_UnlistenAllCommit(); } /* @@ -337,72 +751,42 @@ Async_UnlistenOnExit(int code, Datum arg) void AtPrepare_Notify(void) { - ListCell *p; - - /* It's not sensible to have any pending LISTEN/UNLISTEN actions */ - if (pendingActions) + /* It's not allowed to have any pending LISTEN/UNLISTEN/NOTIFY actions */ + if (pendingActions || pendingNotifies) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), - errmsg("cannot PREPARE a transaction that has executed LISTEN or UNLISTEN"))); - - /* We can deal with pending NOTIFY though */ - foreach(p, pendingNotifies) - { - const char *relname = (const char *) lfirst(p); - - RegisterTwoPhaseRecord(TWOPHASE_RM_NOTIFY_ID, 0, - relname, strlen(relname) + 1); - } - - /* - * We can clear the state immediately, rather than needing a separate - * PostPrepare call, because if the transaction fails we'd just discard - * the state anyway. - */ - ClearPendingActionsAndNotifies(); + errmsg("cannot PREPARE a transaction that has executed LISTEN, UNLISTEN or NOTIFY"))); } /* - * AtCommit_Notify + * PreCommit_Notify * - * This is called at transaction commit. + * This is called at transaction commit, before actually committing to + * clog. * - * If there are pending LISTEN/UNLISTEN actions, insert or delete - * tuples in pg_listener accordingly. + * If there are pending LISTEN actions, make sure we are listed in the + * shared-memory listener array. This must happen before commit to + * ensure we don't miss any notifies from transactions that commit + * just after ours. * * If there are outbound notify requests in the pendingNotifies list, - * scan pg_listener for matching tuples, and either signal the other - * backend or send a message to our own frontend. - * - * NOTE: we are still inside the current transaction, therefore can - * piggyback on its committing of changes. + * add them to the global queue. We do that before commit so that + * we can still throw error if we run out of queue space. */ void -AtCommit_Notify(void) +PreCommit_Notify(void) { - Relation lRel; ListCell *p; if (pendingActions == NIL && pendingNotifies == NIL) return; /* no relevant statements in this xact */ - /* - * NOTIFY is disabled if not normal processing mode. This test used to be - * in xact.c, but it seems cleaner to do it here. - */ - if (!IsNormalProcessingMode()) - { - ClearPendingActionsAndNotifies(); - return; - } - if (Trace_notify) - elog(DEBUG1, "AtCommit_Notify"); + elog(DEBUG1, "PreCommit_Notify"); - /* Acquire ExclusiveLock on pg_listener */ - lRel = heap_open(ListenerRelationId, ExclusiveLock); + Assert(backendHasExecutedInitialListen == false); - /* Perform any pending listen/unlisten actions */ + /* Preflight for any pending listen/unlisten actions */ foreach(p, pendingActions) { ListenAction *actrec = (ListenAction *) lfirst(p); @@ -410,281 +794,743 @@ AtCommit_Notify(void) switch (actrec->action) { case LISTEN_LISTEN: - Exec_Listen(lRel, actrec->condname); + Exec_ListenPreCommit(); break; case LISTEN_UNLISTEN: - Exec_Unlisten(lRel, actrec->condname); + /* there is no Exec_UnlistenPreCommit() */ break; case LISTEN_UNLISTEN_ALL: - Exec_UnlistenAll(lRel); + /* there is no Exec_UnlistenAllPreCommit() */ break; } - - /* We must CCI after each action in case of conflicting actions */ - CommandCounterIncrement(); } - /* Perform any pending notifies */ + /* Queue any pending notifies */ if (pendingNotifies) - Send_Notify(lRel); + { + ListCell *nextNotify; - /* - * We do NOT release the lock on pg_listener here; we need to hold it - * until end of transaction (which is about to happen, anyway) to ensure - * that notified backends see our tuple updates when they look. Else they - * might disregard the signal, which would make the application programmer - * very unhappy. Also, this prevents race conditions when we have just - * inserted a listening tuple. - */ - heap_close(lRel, NoLock); + /* + * Make sure that we have an XID assigned to the current transaction. + * GetCurrentTransactionId is cheap if we already have an XID, but + * not so cheap if we don't, and we'd prefer not to do that work + * while holding AsyncQueueLock. + */ + (void) GetCurrentTransactionId(); - ClearPendingActionsAndNotifies(); + /* + * Serialize writers by acquiring a special lock that we hold till + * after commit. This ensures that queue entries appear in commit + * order, and in particular that there are never uncommitted queue + * entries ahead of committed ones, so an uncommitted transaction + * can't block delivery of deliverable notifications. + * + * We use a heavyweight lock so that it'll automatically be released + * after either commit or abort. This also allows deadlocks to be + * detected, though really a deadlock shouldn't be possible here. + * + * The lock is on "database 0", which is pretty ugly but it doesn't + * seem worth inventing a special locktag category just for this. + * (Historical note: before PG 9.0, a similar lock on "database 0" was + * used by the flatfiles mechanism.) + */ + LockSharedObject(DatabaseRelationId, InvalidOid, 0, + AccessExclusiveLock); - if (Trace_notify) - elog(DEBUG1, "AtCommit_Notify: done"); + /* Now push the notifications into the queue */ + backendHasSentNotifications = true; + + nextNotify = list_head(pendingNotifies); + while (nextNotify != NULL) + { + /* + * Add the pending notifications to the queue. We acquire and + * release AsyncQueueLock once per page, which might be overkill + * but it does allow readers to get in while we're doing this. + * + * A full queue is very uncommon and should really not happen, + * given that we have so much space available in the SLRU pages. + * Nevertheless we need to deal with this possibility. Note that + * when we get here we are in the process of committing our + * transaction, but we have not yet committed to clog, so at this + * point in time we can still roll the transaction back. + */ + LWLockAcquire(AsyncQueueLock, LW_EXCLUSIVE); + asyncQueueFillWarning(); + if (asyncQueueIsFull()) + ereport(ERROR, + (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), + errmsg("too many notifications in the NOTIFY queue"))); + nextNotify = asyncQueueAddEntries(nextNotify); + LWLockRelease(AsyncQueueLock); + } + } } /* - * Exec_Listen --- subroutine for AtCommit_Notify + * AtCommit_Notify + * + * This is called at transaction commit, after committing to clog. * - * Register the current backend as listening on the specified relation. + * Update listenChannels and clear transaction-local state. */ -static void -Exec_Listen(Relation lRel, const char *relname) +void +AtCommit_Notify(void) { - HeapScanDesc scan; - HeapTuple tuple; - Datum values[Natts_pg_listener]; - bool nulls[Natts_pg_listener]; - NameData condname; - bool alreadyListener = false; + ListCell *p; + + /* + * Allow transactions that have not executed LISTEN/UNLISTEN/NOTIFY to + * return as soon as possible + */ + if (!pendingActions && !pendingNotifies) + return; if (Trace_notify) - elog(DEBUG1, "Exec_Listen(%s,%d)", relname, MyProcPid); + elog(DEBUG1, "AtCommit_Notify"); - /* Detect whether we are already listening on this relname */ - scan = heap_beginscan(lRel, SnapshotNow, 0, NULL); - while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL) + /* Perform any pending listen/unlisten actions */ + foreach(p, pendingActions) { - Form_pg_listener listener = (Form_pg_listener) GETSTRUCT(tuple); + ListenAction *actrec = (ListenAction *) lfirst(p); - if (listener->listenerpid == MyProcPid && - strncmp(NameStr(listener->relname), relname, NAMEDATALEN) == 0) + switch (actrec->action) { - alreadyListener = true; - /* No need to scan the rest of the table */ - break; + case LISTEN_LISTEN: + Exec_ListenCommit(actrec->channel); + break; + case LISTEN_UNLISTEN: + Exec_UnlistenCommit(actrec->channel); + break; + case LISTEN_UNLISTEN_ALL: + Exec_UnlistenAllCommit(); + break; } } - heap_endscan(scan); - - if (alreadyListener) - return; /* - * OK to insert a new tuple + * If we did an initial LISTEN, listenChannels now has the entry, so + * we no longer need or want the flag to be set. */ - memset(nulls, false, sizeof(nulls)); - - namestrcpy(&condname, relname); - values[Anum_pg_listener_relname - 1] = NameGetDatum(&condname); - values[Anum_pg_listener_listenerpid - 1] = Int32GetDatum(MyProcPid); - values[Anum_pg_listener_notification - 1] = Int32GetDatum(0); /* no notifies pending */ + backendHasExecutedInitialListen = false; - tuple = heap_form_tuple(RelationGetDescr(lRel), values, nulls); + /* And clean up */ + ClearPendingActionsAndNotifies(); +} - simple_heap_insert(lRel, tuple); +/* + * Exec_ListenPreCommit --- subroutine for PreCommit_Notify + * + * This function must make sure we are ready to catch any incoming messages. + */ +static void +Exec_ListenPreCommit(void) +{ + /* + * Nothing to do if we are already listening to something, nor if we + * already ran this routine in this transaction. + */ + if (listenChannels != NIL || backendHasExecutedInitialListen) + return; -#ifdef NOT_USED /* currently there are no indexes */ - CatalogUpdateIndexes(lRel, tuple); -#endif + if (Trace_notify) + elog(DEBUG1, "Exec_ListenPreCommit(%d)", MyProcPid); - heap_freetuple(tuple); + /* + * We need this variable to detect an aborted initial LISTEN. + * In that case we would set up our pointer but not listen on any channel. + * This flag gets cleared in AtCommit_Notify or AtAbort_Notify(). + */ + backendHasExecutedInitialListen = true; /* - * now that we are listening, make sure we will unlisten before dying. + * Before registering, make sure we will unlisten before dying. + * (Note: this action does not get undone if we abort later.) */ if (!unlistenExitRegistered) { on_shmem_exit(Async_UnlistenOnExit, 0); unlistenExitRegistered = true; } + + /* + * This is our first LISTEN, so establish our pointer. + * + * We set our pointer to the global tail pointer and then move it forward + * over already-committed notifications. This ensures we cannot miss any + * not-yet-committed notifications. We might get a few more but that + * doesn't hurt. + */ + LWLockAcquire(AsyncQueueLock, LW_SHARED); + QUEUE_BACKEND_POS(MyBackendId) = QUEUE_TAIL; + QUEUE_BACKEND_PID(MyBackendId) = MyProcPid; + LWLockRelease(AsyncQueueLock); + + /* + * Try to move our pointer forward as far as possible. This will skip over + * already-committed notifications. Still, we could get notifications that + * have already committed before we started to LISTEN. + * + * Note that we are not yet listening on anything, so we won't deliver + * any notification to the frontend. + * + * This will also advance the global tail pointer if possible. + */ + asyncQueueReadAllNotifications(); } /* - * Exec_Unlisten --- subroutine for AtCommit_Notify + * Exec_ListenCommit --- subroutine for AtCommit_Notify * - * Remove the current backend from the list of listening backends - * for the specified relation. + * Add the channel to the list of channels we are listening on. */ static void -Exec_Unlisten(Relation lRel, const char *relname) +Exec_ListenCommit(const char *channel) { - HeapScanDesc scan; - HeapTuple tuple; + MemoryContext oldcontext; + + /* Do nothing if we are already listening on this channel */ + if (IsListeningOn(channel)) + return; + + /* + * Add the new channel name to listenChannels. + * + * XXX It is theoretically possible to get an out-of-memory failure here, + * which would be bad because we already committed. For the moment it + * doesn't seem worth trying to guard against that, but maybe improve this + * later. + */ + oldcontext = MemoryContextSwitchTo(TopMemoryContext); + listenChannels = lappend(listenChannels, pstrdup(channel)); + MemoryContextSwitchTo(oldcontext); +} + +/* + * Exec_UnlistenCommit --- subroutine for AtCommit_Notify + * + * Remove the specified channel name from listenChannels. + */ +static void +Exec_UnlistenCommit(const char *channel) +{ + ListCell *q; + ListCell *prev; if (Trace_notify) - elog(DEBUG1, "Exec_Unlisten(%s,%d)", relname, MyProcPid); + elog(DEBUG1, "Exec_UnlistenCommit(%s,%d)", channel, MyProcPid); - scan = heap_beginscan(lRel, SnapshotNow, 0, NULL); - while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL) + prev = NULL; + foreach(q, listenChannels) { - Form_pg_listener listener = (Form_pg_listener) GETSTRUCT(tuple); + char *lchan = (char *) lfirst(q); - if (listener->listenerpid == MyProcPid && - strncmp(NameStr(listener->relname), relname, NAMEDATALEN) == 0) + if (strcmp(lchan, channel) == 0) { - /* Found the matching tuple, delete it */ - simple_heap_delete(lRel, &tuple->t_self); - - /* - * We assume there can be only one match, so no need to scan the - * rest of the table - */ + listenChannels = list_delete_cell(listenChannels, q, prev); + pfree(lchan); break; } + prev = q; } - heap_endscan(scan); /* * We do not complain about unlistening something not being listened; * should we? */ + + /* If no longer listening to anything, get out of listener array */ + if (listenChannels == NIL) + asyncQueueUnregister(); } /* - * Exec_UnlistenAll --- subroutine for AtCommit_Notify + * Exec_UnlistenAllCommit --- subroutine for AtCommit_Notify * - * Update pg_listener to unlisten all relations for this backend. + * Unlisten on all channels for this backend. */ static void -Exec_UnlistenAll(Relation lRel) +Exec_UnlistenAllCommit(void) +{ + if (Trace_notify) + elog(DEBUG1, "Exec_UnlistenAllCommit(%d)", MyProcPid); + + list_free_deep(listenChannels); + listenChannels = NIL; + + asyncQueueUnregister(); +} + +/* + * ProcessCompletedNotifies --- send out signals and self-notifies + * + * This is called from postgres.c just before going idle at the completion + * of a transaction. If we issued any notifications in the just-completed + * transaction, send signals to other backends to process them, and also + * process the queue ourselves to send messages to our own frontend. + * + * The reason that this is not done in AtCommit_Notify is that there is + * a nonzero chance of errors here (for example, encoding conversion errors + * while trying to format messages to our frontend). An error during + * AtCommit_Notify would be a PANIC condition. The timing is also arranged + * to ensure that a transaction's self-notifies are delivered to the frontend + * before it gets the terminating ReadyForQuery message. + * + * Note that we send signals and process the queue even if the transaction + * eventually aborted. This is because we need to clean out whatever got + * added to the queue. + * + * NOTE: we are outside of any transaction here. + */ +void +ProcessCompletedNotifies(void) { - HeapScanDesc scan; - HeapTuple lTuple; - ScanKeyData key[1]; + bool signalled; + + /* Nothing to do if we didn't send any notifications */ + if (!backendHasSentNotifications) + return; + + /* + * We reset the flag immediately; otherwise, if any sort of error + * occurs below, we'd be locked up in an infinite loop, because + * control will come right back here after error cleanup. + */ + backendHasSentNotifications = false; if (Trace_notify) - elog(DEBUG1, "Exec_UnlistenAll"); + elog(DEBUG1, "ProcessCompletedNotifies"); + + /* + * We must run asyncQueueReadAllNotifications inside a transaction, + * else bad things happen if it gets an error. + */ + StartTransactionCommand(); + + /* Send signals to other backends */ + signalled = SignalBackends(); - /* Find and delete all entries with my listenerPID */ - ScanKeyInit(&key[0], - Anum_pg_listener_listenerpid, - BTEqualStrategyNumber, F_INT4EQ, - Int32GetDatum(MyProcPid)); - scan = heap_beginscan(lRel, SnapshotNow, 1, key); + if (listenChannels != NIL) + { + /* Read the queue ourselves, and send relevant stuff to the frontend */ + asyncQueueReadAllNotifications(); + } + else if (!signalled) + { + /* + * If we found no other listening backends, and we aren't listening + * ourselves, then we must execute asyncQueueAdvanceTail to flush + * the queue, because ain't nobody else gonna do it. This prevents + * queue overflow when we're sending useless notifies to nobody. + * (A new listener could have joined since we looked, but if so this + * is harmless.) + */ + asyncQueueAdvanceTail(); + } - while ((lTuple = heap_getnext(scan, ForwardScanDirection)) != NULL) - simple_heap_delete(lRel, &lTuple->t_self); + CommitTransactionCommand(); - heap_endscan(scan); + /* We don't need pq_flush() here since postgres.c will do one shortly */ } /* - * Send_Notify --- subroutine for AtCommit_Notify + * Test whether we are actively listening on the given channel name. * - * Scan pg_listener for tuples matching our pending notifies, and - * either signal the other backend or send a message to our own frontend. + * Note: this function is executed for every notification found in the queue. + * Perhaps it is worth further optimization, eg convert the list to a sorted + * array so we can binary-search it. In practice the list is likely to be + * fairly short, though. + */ +static bool +IsListeningOn(const char *channel) +{ + ListCell *p; + + foreach(p, listenChannels) + { + char *lchan = (char *) lfirst(p); + + if (strcmp(lchan, channel) == 0) + return true; + } + return false; +} + +/* + * Remove our entry from the listeners array when we are no longer listening + * on any channel. NB: must not fail if we're already not listening. */ static void -Send_Notify(Relation lRel) +asyncQueueUnregister(void) +{ + bool advanceTail; + + Assert(listenChannels == NIL); /* else caller error */ + + LWLockAcquire(AsyncQueueLock, LW_SHARED); + /* check if entry is valid and oldest ... */ + advanceTail = (MyProcPid == QUEUE_BACKEND_PID(MyBackendId)) && + QUEUE_POS_EQUAL(QUEUE_BACKEND_POS(MyBackendId), QUEUE_TAIL); + /* ... then mark it invalid */ + QUEUE_BACKEND_PID(MyBackendId) = InvalidPid; + LWLockRelease(AsyncQueueLock); + + /* If we were the laziest backend, try to advance the tail pointer */ + if (advanceTail) + asyncQueueAdvanceTail(); +} + +/* + * Test whether there is room to insert more notification messages. + * + * Caller must hold at least shared AsyncQueueLock. + */ +static bool +asyncQueueIsFull(void) +{ + int nexthead; + int boundary; + + /* + * The queue is full if creating a new head page would create a page that + * logically precedes the current global tail pointer, ie, the head + * pointer would wrap around compared to the tail. We cannot create such + * a head page for fear of confusing slru.c. For safety we round the tail + * pointer back to a segment boundary (compare the truncation logic in + * asyncQueueAdvanceTail). + * + * Note that this test is *not* dependent on how much space there is on + * the current head page. This is necessary because asyncQueueAddEntries + * might try to create the next head page in any case. + */ + nexthead = QUEUE_POS_PAGE(QUEUE_HEAD) + 1; + if (nexthead > QUEUE_MAX_PAGE) + nexthead = 0; /* wrap around */ + boundary = QUEUE_POS_PAGE(QUEUE_TAIL); + boundary -= boundary % SLRU_PAGES_PER_SEGMENT; + return asyncQueuePagePrecedesLogically(nexthead, boundary); +} + +/* + * Advance the QueuePosition to the next entry, assuming that the current + * entry is of length entryLength. If we jump to a new page the function + * returns true, else false. + */ +static bool +asyncQueueAdvance(QueuePosition *position, int entryLength) { - TupleDesc tdesc = RelationGetDescr(lRel); - HeapScanDesc scan; - HeapTuple lTuple, - rTuple; - Datum value[Natts_pg_listener]; - bool repl[Natts_pg_listener], - nulls[Natts_pg_listener]; - - /* preset data to update notify column to MyProcPid */ - memset(nulls, false, sizeof(nulls)); - memset(repl, false, sizeof(repl)); - repl[Anum_pg_listener_notification - 1] = true; - memset(value, 0, sizeof(value)); - value[Anum_pg_listener_notification - 1] = Int32GetDatum(MyProcPid); - - scan = heap_beginscan(lRel, SnapshotNow, 0, NULL); - - while ((lTuple = heap_getnext(scan, ForwardScanDirection)) != NULL) + int pageno = QUEUE_POS_PAGE(*position); + int offset = QUEUE_POS_OFFSET(*position); + bool pageJump = false; + + /* + * Move to the next writing position: First jump over what we have just + * written or read. + */ + offset += entryLength; + Assert(offset <= QUEUE_PAGESIZE); + + /* + * In a second step check if another entry can possibly be written to the + * page. If so, stay here, we have reached the next position. If not, then + * we need to move on to the next page. + */ + if (offset + QUEUEALIGN(AsyncQueueEntryEmptySize) > QUEUE_PAGESIZE) { - Form_pg_listener listener = (Form_pg_listener) GETSTRUCT(lTuple); - char *relname = NameStr(listener->relname); - int32 listenerPID = listener->listenerpid; + pageno++; + if (pageno > QUEUE_MAX_PAGE) + pageno = 0; /* wrap around */ + offset = 0; + pageJump = true; + } - if (!AsyncExistsPendingNotify(relname)) - continue; + SET_QUEUE_POS(*position, pageno, offset); + return pageJump; +} - if (listenerPID == MyProcPid) - { - /* - * Self-notify: no need to bother with table update. Indeed, we - * *must not* clear the notification field in this path, or we - * could lose an outside notify, which'd be bad for applications - * that ignore self-notify messages. - */ - if (Trace_notify) - elog(DEBUG1, "AtCommit_Notify: notifying self"); +/* + * Fill the AsyncQueueEntry at *qe with an outbound notification message. + */ +static void +asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe) +{ + size_t channellen = strlen(n->channel); + size_t payloadlen = strlen(n->payload); + int entryLength; + + Assert(channellen < NAMEDATALEN); + Assert(payloadlen < NOTIFY_PAYLOAD_MAX_LENGTH); + + /* The terminators are already included in AsyncQueueEntryEmptySize */ + entryLength = AsyncQueueEntryEmptySize + payloadlen + channellen; + entryLength = QUEUEALIGN(entryLength); + qe->length = entryLength; + qe->dboid = MyDatabaseId; + qe->xid = GetCurrentTransactionId(); + qe->srcPid = MyProcPid; + memcpy(qe->data, n->channel, channellen + 1); + memcpy(qe->data + channellen + 1, n->payload, payloadlen + 1); +} + +/* + * Add pending notifications to the queue. + * + * We go page by page here, i.e. we stop once we have to go to a new page but + * we will be called again and then fill that next page. If an entry does not + * fit into the current page, we write a dummy entry with an InvalidOid as the + * database OID in order to fill the page. So every page is always used up to + * the last byte which simplifies reading the page later. + * + * We are passed the list cell containing the next notification to write + * and return the first still-unwritten cell back. Eventually we will return + * NULL indicating all is done. + * + * We are holding AsyncQueueLock already from the caller and grab AsyncCtlLock + * locally in this function. + */ +static ListCell * +asyncQueueAddEntries(ListCell *nextNotify) +{ + AsyncQueueEntry qe; + int pageno; + int offset; + int slotno; + + /* We hold both AsyncQueueLock and AsyncCtlLock during this operation */ + LWLockAcquire(AsyncCtlLock, LW_EXCLUSIVE); + + /* Fetch the current page */ + pageno = QUEUE_POS_PAGE(QUEUE_HEAD); + slotno = SimpleLruReadPage(AsyncCtl, pageno, true, InvalidTransactionId); + /* Note we mark the page dirty before writing in it */ + AsyncCtl->shared->page_dirty[slotno] = true; + + while (nextNotify != NULL) + { + Notification *n = (Notification *) lfirst(nextNotify); - NotifyMyFrontEnd(relname, listenerPID); + /* Construct a valid queue entry in local variable qe */ + asyncQueueNotificationToEntry(n, &qe); + + offset = QUEUE_POS_OFFSET(QUEUE_HEAD); + + /* Check whether the entry really fits on the current page */ + if (offset + qe.length <= QUEUE_PAGESIZE) + { + /* OK, so advance nextNotify past this item */ + nextNotify = lnext(nextNotify); } else { - if (Trace_notify) - elog(DEBUG1, "AtCommit_Notify: notifying pid %d", - listenerPID); + /* + * Write a dummy entry to fill up the page. Actually readers will + * only check dboid and since it won't match any reader's database + * OID, they will ignore this entry and move on. + */ + qe.length = QUEUE_PAGESIZE - offset; + qe.dboid = InvalidOid; + qe.data[0] = '\0'; /* empty channel */ + qe.data[1] = '\0'; /* empty payload */ + } + /* Now copy qe into the shared buffer page */ + memcpy(AsyncCtl->shared->page_buffer[slotno] + offset, + &qe, + qe.length); + + /* Advance QUEUE_HEAD appropriately, and note if page is full */ + if (asyncQueueAdvance(&(QUEUE_HEAD), qe.length)) + { /* - * If someone has already notified this listener, we don't bother - * modifying the table, but we do still send a NOTIFY_INTERRUPT - * signal, just in case that backend missed the earlier signal for - * some reason. It's OK to send the signal first, because the - * other guy can't read pg_listener until we unlock it. - * - * Note: we don't have the other guy's BackendId available, so - * this will incur a search of the ProcSignal table. That's - * probably not worth worrying about. + * Page is full, so we're done here, but first fill the next + * page with zeroes. The reason to do this is to ensure that + * slru.c's idea of the head page is always the same as ours, + * which avoids boundary problems in SimpleLruTruncate. The + * test in asyncQueueIsFull() ensured that there is room to + * create this page without overrunning the queue. */ - if (SendProcSignal(listenerPID, PROCSIG_NOTIFY_INTERRUPT, - InvalidBackendId) < 0) + slotno = SimpleLruZeroPage(AsyncCtl, QUEUE_POS_PAGE(QUEUE_HEAD)); + /* And exit the loop */ + break; + } + } + + LWLockRelease(AsyncCtlLock); + + return nextNotify; +} + +/* + * Check whether the queue is at least half full, and emit a warning if so. + * + * This is unlikely given the size of the queue, but possible. + * The warnings show up at most once every QUEUE_FULL_WARN_INTERVAL. + * + * Caller must hold exclusive AsyncQueueLock. + */ +static void +asyncQueueFillWarning(void) +{ + int headPage = QUEUE_POS_PAGE(QUEUE_HEAD); + int tailPage = QUEUE_POS_PAGE(QUEUE_TAIL); + int occupied; + double fillDegree; + TimestampTz t; + + occupied = headPage - tailPage; + + if (occupied == 0) + return; /* fast exit for common case */ + + if (occupied < 0) + { + /* head has wrapped around, tail not yet */ + occupied += QUEUE_MAX_PAGE+1; + } + + fillDegree = (double) occupied / (double) ((QUEUE_MAX_PAGE+1)/2); + + if (fillDegree < 0.5) + return; + + t = GetCurrentTimestamp(); + + if (TimestampDifferenceExceeds(asyncQueueControl->lastQueueFillWarn, + t, QUEUE_FULL_WARN_INTERVAL)) + { + QueuePosition min = QUEUE_HEAD; + int32 minPid = InvalidPid; + int i; + + for (i = 1; i <= MaxBackends; i++) + { + if (QUEUE_BACKEND_PID(i) != InvalidPid) { - /* - * Get rid of pg_listener entry if it refers to a PID that no - * longer exists. Presumably, that backend crashed without - * deleting its pg_listener entries. This code used to only - * delete the entry if errno==ESRCH, but as far as I can see - * we should just do it for any failure (certainly at least - * for EPERM too...) - */ - simple_heap_delete(lRel, &lTuple->t_self); + min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i)); + if (QUEUE_POS_EQUAL(min, QUEUE_BACKEND_POS(i))) + minPid = QUEUE_BACKEND_PID(i); } - else if (listener->notification == 0) - { - /* Rewrite the tuple with my PID in notification column */ - rTuple = heap_modify_tuple(lTuple, tdesc, value, nulls, repl); - simple_heap_update(lRel, &lTuple->t_self, rTuple); + } + + ereport(WARNING, + (errmsg("pg_notify queue is %.0f%% full", fillDegree * 100), + (minPid != InvalidPid ? + errdetail("PID %d is among the slowest backends.", minPid) + : 0), + (minPid != InvalidPid ? + errhint("Cleanup can only proceed if this backend ends its current transaction.") + : 0))); + + asyncQueueControl->lastQueueFillWarn = t; + } +} + +/* + * Send signals to all listening backends (except our own). + * + * Returns true if we sent at least one signal. + * + * Since we need EXCLUSIVE lock anyway we also check the position of the other + * backends and in case one is already up-to-date we don't signal it. + * This can happen if concurrent notifying transactions have sent a signal and + * the signaled backend has read the other notifications and ours in the same + * step. + * + * Since we know the BackendId and the Pid the signalling is quite cheap. + */ +static bool +SignalBackends(void) +{ + bool signalled = false; + int32 *pids; + BackendId *ids; + int count; + int i; + int32 pid; -#ifdef NOT_USED /* currently there are no indexes */ - CatalogUpdateIndexes(lRel, rTuple); -#endif + /* + * Identify all backends that are listening and not already up-to-date. + * We don't want to send signals while holding the AsyncQueueLock, so + * we just build a list of target PIDs. + * + * XXX in principle these pallocs could fail, which would be bad. + * Maybe preallocate the arrays? But in practice this is only run + * in trivial transactions, so there should surely be space available. + */ + pids = (int32 *) palloc(MaxBackends * sizeof(int32)); + ids = (BackendId *) palloc(MaxBackends * sizeof(BackendId)); + count = 0; + + LWLockAcquire(AsyncQueueLock, LW_EXCLUSIVE); + for (i = 1; i <= MaxBackends; i++) + { + pid = QUEUE_BACKEND_PID(i); + if (pid != InvalidPid && pid != MyProcPid) + { + QueuePosition pos = QUEUE_BACKEND_POS(i); + + if (!QUEUE_POS_EQUAL(pos, QUEUE_HEAD)) + { + pids[count] = pid; + ids[count] = i; + count++; } } } + LWLockRelease(AsyncQueueLock); - heap_endscan(scan); + /* Now send signals */ + for (i = 0; i < count; i++) + { + pid = pids[i]; + + /* + * Note: assuming things aren't broken, a signal failure here could + * only occur if the target backend exited since we released + * AsyncQueueLock; which is unlikely but certainly possible. + * So we just log a low-level debug message if it happens. + */ + if (SendProcSignal(pid, PROCSIG_NOTIFY_INTERRUPT, ids[i]) < 0) + elog(DEBUG3, "could not signal backend with PID %d: %m", pid); + else + signalled = true; + } + + pfree(pids); + pfree(ids); + + return signalled; } /* * AtAbort_Notify * - * This is called at transaction abort. + * This is called at transaction abort. * - * Gets rid of pending actions and outbound notifies that we would have - * executed if the transaction got committed. + * Gets rid of pending actions and outbound notifies that we would have + * executed if the transaction got committed. */ void AtAbort_Notify(void) { + /* + * If we LISTEN but then roll back the transaction we have set our pointer + * but have not made any entry in listenChannels. In that case, remove + * our pointer again. + */ + if (backendHasExecutedInitialListen) + { + /* + * Checking listenChannels should be redundant but it can't hurt doing + * it for safety reasons. + */ + if (listenChannels == NIL) + asyncQueueUnregister(); + + backendHasExecutedInitialListen = false; + } + + /* And clean up */ ClearPendingActionsAndNotifies(); } @@ -940,30 +1786,298 @@ DisableNotifyInterrupt(void) } /* + * Read all pending notifications from the queue, and deliver appropriate + * ones to my frontend. Stop when we reach queue head or an uncommitted + * notification. + */ +static void +asyncQueueReadAllNotifications(void) +{ + QueuePosition pos; + QueuePosition oldpos; + QueuePosition head; + bool advanceTail; + /* page_buffer must be adequately aligned, so use a union */ + union { + char buf[QUEUE_PAGESIZE]; + AsyncQueueEntry align; + } page_buffer; + + /* Fetch current state */ + LWLockAcquire(AsyncQueueLock, LW_SHARED); + /* Assert checks that we have a valid state entry */ + Assert(MyProcPid == QUEUE_BACKEND_PID(MyBackendId)); + pos = oldpos = QUEUE_BACKEND_POS(MyBackendId); + head = QUEUE_HEAD; + LWLockRelease(AsyncQueueLock); + + if (QUEUE_POS_EQUAL(pos, head)) + { + /* Nothing to do, we have read all notifications already. */ + return; + } + + /*---------- + * Note that we deliver everything that we see in the queue and that + * matches our _current_ listening state. + * Especially we do not take into account different commit times. + * Consider the following example: + * + * Backend 1: Backend 2: + * + * transaction starts + * NOTIFY foo; + * commit starts + * transaction starts + * LISTEN foo; + * commit starts + * commit to clog + * commit to clog + * + * It could happen that backend 2 sees the notification from backend 1 in + * the queue. Even though the notifying transaction committed before + * the listening transaction, we still deliver the notification. + * + * The idea is that an additional notification does not do any harm, we + * just need to make sure that we do not miss a notification. + * + * It is possible that we fail while trying to send a message to our + * frontend (for example, because of encoding conversion failure). + * If that happens it is critical that we not try to send the same + * message over and over again. Therefore, we place a PG_TRY block + * here that will forcibly advance our backend position before we lose + * control to an error. (We could alternatively retake AsyncQueueLock + * and move the position before handling each individual message, but + * that seems like too much lock traffic.) + *---------- + */ + PG_TRY(); + { + bool reachedStop; + + do + { + int curpage = QUEUE_POS_PAGE(pos); + int curoffset = QUEUE_POS_OFFSET(pos); + int slotno; + int copysize; + + /* + * We copy the data from SLRU into a local buffer, so as to avoid + * holding the AsyncCtlLock while we are examining the entries and + * possibly transmitting them to our frontend. Copy only the part + * of the page we will actually inspect. + */ + slotno = SimpleLruReadPage_ReadOnly(AsyncCtl, curpage, + InvalidTransactionId); + if (curpage == QUEUE_POS_PAGE(head)) + { + /* we only want to read as far as head */ + copysize = QUEUE_POS_OFFSET(head) - curoffset; + if (copysize < 0) + copysize = 0; /* just for safety */ + } + else + { + /* fetch all the rest of the page */ + copysize = QUEUE_PAGESIZE - curoffset; + } + memcpy(page_buffer.buf + curoffset, + AsyncCtl->shared->page_buffer[slotno] + curoffset, + copysize); + /* Release lock that we got from SimpleLruReadPage_ReadOnly() */ + LWLockRelease(AsyncCtlLock); + + /* + * Process messages up to the stop position, end of page, or an + * uncommitted message. + * + * Our stop position is what we found to be the head's position + * when we entered this function. It might have changed + * already. But if it has, we will receive (or have already + * received and queued) another signal and come here again. + * + * We are not holding AsyncQueueLock here! The queue can only + * extend beyond the head pointer (see above) and we leave our + * backend's pointer where it is so nobody will truncate or + * rewrite pages under us. Especially we don't want to hold a lock + * while sending the notifications to the frontend. + */ + reachedStop = asyncQueueProcessPageEntries(&pos, head, + page_buffer.buf); + } while (!reachedStop); + } + PG_CATCH(); + { + /* Update shared state */ + LWLockAcquire(AsyncQueueLock, LW_SHARED); + QUEUE_BACKEND_POS(MyBackendId) = pos; + advanceTail = QUEUE_POS_EQUAL(oldpos, QUEUE_TAIL); + LWLockRelease(AsyncQueueLock); + + /* If we were the laziest backend, try to advance the tail pointer */ + if (advanceTail) + asyncQueueAdvanceTail(); + + PG_RE_THROW(); + } + PG_END_TRY(); + + /* Update shared state */ + LWLockAcquire(AsyncQueueLock, LW_SHARED); + QUEUE_BACKEND_POS(MyBackendId) = pos; + advanceTail = QUEUE_POS_EQUAL(oldpos, QUEUE_TAIL); + LWLockRelease(AsyncQueueLock); + + /* If we were the laziest backend, try to advance the tail pointer */ + if (advanceTail) + asyncQueueAdvanceTail(); +} + +/* + * Fetch notifications from the shared queue, beginning at position current, + * and deliver relevant ones to my frontend. + * + * The current page must have been fetched into page_buffer from shared + * memory. (We could access the page right in shared memory, but that + * would imply holding the AsyncCtlLock throughout this routine.) + * + * We stop if we reach the "stop" position, or reach a notification from an + * uncommitted transaction, or reach the end of the page. + * + * The function returns true once we have reached the stop position or an + * uncommitted notification, and false if we have finished with the page. + * In other words: once it returns true there is no need to look further. + */ +static bool +asyncQueueProcessPageEntries(QueuePosition *current, + QueuePosition stop, + char *page_buffer) +{ + bool reachedStop = false; + bool reachedEndOfPage; + AsyncQueueEntry *qe; + + do + { + if (QUEUE_POS_EQUAL(*current, stop)) + break; + + qe = (AsyncQueueEntry *) (page_buffer + QUEUE_POS_OFFSET(*current)); + + /* + * Advance *current over this message, possibly to the next page. + * As noted in the comments for asyncQueueReadAllNotifications, we + * must do this before possibly failing while processing the message. + */ + reachedEndOfPage = asyncQueueAdvance(current, qe->length); + + /* Ignore messages destined for other databases */ + if (qe->dboid == MyDatabaseId) + { + if (TransactionIdDidCommit(qe->xid)) + { + /* qe->data is the null-terminated channel name */ + char *channel = qe->data; + + if (IsListeningOn(channel)) + { + /* payload follows channel name */ + char *payload = qe->data + strlen(channel) + 1; + + NotifyMyFrontEnd(channel, payload, qe->srcPid); + } + } + else if (TransactionIdDidAbort(qe->xid)) + { + /* + * If the source transaction aborted, we just ignore its + * notifications. + */ + } + else + { + /* + * The transaction has neither committed nor aborted so far, + * so we can't process its message yet. Break out of the loop. + */ + reachedStop = true; + break; + } + } + + /* Loop back if we're not at end of page */ + } while (!reachedEndOfPage); + + if (QUEUE_POS_EQUAL(*current, stop)) + reachedStop = true; + + return reachedStop; +} + +/* + * Advance the shared queue tail variable to the minimum of all the + * per-backend tail pointers. Truncate pg_notify space if possible. + */ +static void +asyncQueueAdvanceTail(void) +{ + QueuePosition min; + int i; + int oldtailpage; + int newtailpage; + int boundary; + + LWLockAcquire(AsyncQueueLock, LW_EXCLUSIVE); + min = QUEUE_HEAD; + for (i = 1; i <= MaxBackends; i++) + { + if (QUEUE_BACKEND_PID(i) != InvalidPid) + min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i)); + } + oldtailpage = QUEUE_POS_PAGE(QUEUE_TAIL); + QUEUE_TAIL = min; + LWLockRelease(AsyncQueueLock); + + /* + * We can truncate something if the global tail advanced across an SLRU + * segment boundary. + * + * XXX it might be better to truncate only once every several segments, + * to reduce the number of directory scans. + */ + newtailpage = QUEUE_POS_PAGE(min); + boundary = newtailpage - (newtailpage % SLRU_PAGES_PER_SEGMENT); + if (asyncQueuePagePrecedesLogically(oldtailpage, boundary)) + { + /* + * SimpleLruTruncate() will ask for AsyncCtlLock but will also + * release the lock again. + */ + SimpleLruTruncate(AsyncCtl, newtailpage); + } +} + +/* * ProcessIncomingNotify * * Deal with arriving NOTIFYs from other backends. * This is called either directly from the PROCSIG_NOTIFY_INTERRUPT * signal handler, or the next time control reaches the outer idle loop. - * Scan pg_listener for arriving notifies, report them to my front end, - * and clear the notification field in pg_listener until next time. + * Scan the queue for arriving notifications and report them to my front + * end. * * NOTE: since we are outside any transaction, we must create our own. */ static void ProcessIncomingNotify(void) { - Relation lRel; - TupleDesc tdesc; - ScanKeyData key[1]; - HeapScanDesc scan; - HeapTuple lTuple, - rTuple; - Datum value[Natts_pg_listener]; - bool repl[Natts_pg_listener], - nulls[Natts_pg_listener]; bool catchup_enabled; + /* Do nothing if we aren't actively listening */ + if (listenChannels == NIL) + return; + /* Must prevent catchup interrupt while I am running */ catchup_enabled = DisableCatchupInterrupt(); @@ -974,62 +2088,13 @@ ProcessIncomingNotify(void) notifyInterruptOccurred = 0; - StartTransactionCommand(); - - lRel = heap_open(ListenerRelationId, ExclusiveLock); - tdesc = RelationGetDescr(lRel); - - /* Scan only entries with my listenerPID */ - ScanKeyInit(&key[0], - Anum_pg_listener_listenerpid, - BTEqualStrategyNumber, F_INT4EQ, - Int32GetDatum(MyProcPid)); - scan = heap_beginscan(lRel, SnapshotNow, 1, key); - - /* Prepare data for rewriting 0 into notification field */ - memset(nulls, false, sizeof(nulls)); - memset(repl, false, sizeof(repl)); - repl[Anum_pg_listener_notification - 1] = true; - memset(value, 0, sizeof(value)); - value[Anum_pg_listener_notification - 1] = Int32GetDatum(0); - - while ((lTuple = heap_getnext(scan, ForwardScanDirection)) != NULL) - { - Form_pg_listener listener = (Form_pg_listener) GETSTRUCT(lTuple); - char *relname = NameStr(listener->relname); - int32 sourcePID = listener->notification; - - if (sourcePID != 0) - { - /* Notify the frontend */ - - if (Trace_notify) - elog(DEBUG1, "ProcessIncomingNotify: received %s from %d", - relname, (int) sourcePID); - - NotifyMyFrontEnd(relname, sourcePID); - - /* - * Rewrite the tuple with 0 in notification column. - */ - rTuple = heap_modify_tuple(lTuple, tdesc, value, nulls, repl); - simple_heap_update(lRel, &lTuple->t_self, rTuple); - -#ifdef NOT_USED /* currently there are no indexes */ - CatalogUpdateIndexes(lRel, rTuple); -#endif - } - } - heap_endscan(scan); - /* - * We do NOT release the lock on pg_listener here; we need to hold it - * until end of transaction (which is about to happen, anyway) to ensure - * that other backends see our tuple updates when they look. Otherwise, a - * transaction started after this one might mistakenly think it doesn't - * need to send this backend a new NOTIFY. + * We must run asyncQueueReadAllNotifications inside a transaction, + * else bad things happen if it gets an error. */ - heap_close(lRel, NoLock); + StartTransactionCommand(); + + asyncQueueReadAllNotifications(); CommitTransactionCommand(); @@ -1051,20 +2116,17 @@ ProcessIncomingNotify(void) * Send NOTIFY message to my front end. */ static void -NotifyMyFrontEnd(char *relname, int32 listenerPID) +NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid) { if (whereToSendOutput == DestRemote) { StringInfoData buf; pq_beginmessage(&buf, 'A'); - pq_sendint(&buf, listenerPID, sizeof(int32)); - pq_sendstring(&buf, relname); + pq_sendint(&buf, srcPid, sizeof(int32)); + pq_sendstring(&buf, channel); if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3) - { - /* XXX Add parameter string here later */ - pq_sendstring(&buf, ""); - } + pq_sendstring(&buf, payload); pq_endmessage(&buf); /* @@ -1074,20 +2136,51 @@ NotifyMyFrontEnd(char *relname, int32 listenerPID) */ } else - elog(INFO, "NOTIFY for %s", relname); + elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload); } -/* Does pendingNotifies include the given relname? */ +/* Does pendingNotifies include the given channel/payload? */ static bool -AsyncExistsPendingNotify(const char *relname) +AsyncExistsPendingNotify(const char *channel, const char *payload) { ListCell *p; + Notification *n; + + if (pendingNotifies == NIL) + return false; + + if (payload == NULL) + payload = ""; + + /*---------- + * We need to append new elements to the end of the list in order to keep + * the order. However, on the other hand we'd like to check the list + * backwards in order to make duplicate-elimination a tad faster when the + * same condition is signaled many times in a row. So as a compromise we + * check the tail element first which we can access directly. If this + * doesn't match, we check the whole list. + * + * As we are not checking our parents' lists, we can still get duplicates + * in combination with subtransactions, like in: + * + * begin; + * notify foo '1'; + * savepoint foo; + * notify foo '1'; + * commit; + *---------- + */ + n = (Notification *) llast(pendingNotifies); + if (strcmp(n->channel, channel) == 0 && + strcmp(n->payload, payload) == 0) + return true; foreach(p, pendingNotifies) { - const char *prelname = (const char *) lfirst(p); + n = (Notification *) lfirst(p); - if (strcmp(prelname, relname) == 0) + if (strcmp(n->channel, channel) == 0 && + strcmp(n->payload, payload) == 0) return true; } @@ -1108,21 +2201,3 @@ ClearPendingActionsAndNotifies(void) pendingActions = NIL; pendingNotifies = NIL; } - -/* - * 2PC processing routine for COMMIT PREPARED case. - * - * (We don't have to do anything for ROLLBACK PREPARED.) - */ -void -notify_twophase_postcommit(TransactionId xid, uint16 info, - void *recdata, uint32 len) -{ - /* - * Set up to issue the NOTIFY at the end of my own current transaction. - * (XXX this has some issues if my own transaction later rolls back, or if - * there is any significant delay before I commit. OK for now because we - * disallow COMMIT PREPARED inside a transaction block.) - */ - Async_Notify((char *) recdata); -} |