2445 lines
74 KiB
C
2445 lines
74 KiB
C
/*-------------------------------------------------------------------------
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*
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* async.c
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* Asynchronous notification: NOTIFY, LISTEN, UNLISTEN
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* src/backend/commands/async.c
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*
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*-------------------------------------------------------------------------
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*/
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/*-------------------------------------------------------------------------
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* Async Notification Model as of 9.0:
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*
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* 1. Multiple backends on same machine. Multiple backends listening on
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* several channels. (Channels are also called "conditions" in other
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* parts of the code.)
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*
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* 2. There is one central queue in disk-based storage (directory pg_notify/),
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* with actively-used pages mapped into shared memory by the slru.c module.
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* All notification messages are placed in the queue and later read out
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* by listening backends.
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*
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* There is no central knowledge of which backend listens on which channel;
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* every backend has its own list of interesting channels.
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*
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* Although there is only one queue, notifications are treated as being
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* database-local; this is done by including the sender's database OID
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* in each notification message. Listening backends ignore messages
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* that don't match their database OID. This is important because it
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* ensures senders and receivers have the same database encoding and won't
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* misinterpret non-ASCII text in the channel name or payload string.
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*
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* Since notifications are not expected to survive database crashes,
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* we can simply clean out the pg_notify data at any reboot, and there
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* is no need for WAL support or fsync'ing.
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*
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* 3. Every backend that is listening on at least one channel registers by
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* entering its PID into the array in AsyncQueueControl. It then scans all
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* incoming notifications in the central queue and first compares the
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* database OID of the notification with its own database OID and then
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* compares the notified channel with the list of channels that it listens
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* to. In case there is a match it delivers the notification event to its
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* frontend. Non-matching events are simply skipped.
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*
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* 4. The NOTIFY statement (routine Async_Notify) stores the notification in
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* a backend-local list which will not be processed until transaction end.
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*
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* Duplicate notifications from the same transaction are sent out as one
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* notification only. This is done to save work when for example a trigger
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* on a 2 million row table fires a notification for each row that has been
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* changed. If the application needs to receive every single notification
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* that has been sent, it can easily add some unique string into the extra
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* payload parameter.
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*
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* When the transaction is ready to commit, PreCommit_Notify() adds the
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* pending notifications to the head of the queue. The head pointer of the
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* queue always points to the next free position and a position is just a
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* page number and the offset in that page. This is done before marking the
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* transaction as committed in clog. If we run into problems writing the
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* notifications, we can still call elog(ERROR, ...) and the transaction
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* will roll back.
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*
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* Once we have put all of the notifications into the queue, we return to
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* CommitTransaction() which will then do the actual transaction commit.
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*
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* After commit we are called another time (AtCommit_Notify()). Here we
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* make the actual updates to the effective listen state (listenChannels).
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*
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* Finally, after we are out of the transaction altogether, we check if
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* we need to signal listening backends. In SignalBackends() we scan the
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* list of listening backends and send a PROCSIG_NOTIFY_INTERRUPT signal
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* to every listening backend (we don't know which backend is listening on
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* which channel so we must signal them all). We can exclude backends that
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* are already up to date, though, and we can also exclude backends that
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* are in other databases (unless they are way behind and should be kicked
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* to make them advance their pointers). We don't bother with a
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* self-signal either, but just process the queue directly.
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*
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* 5. Upon receipt of a PROCSIG_NOTIFY_INTERRUPT signal, the signal handler
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* sets the process's latch, which triggers the event to be processed
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* immediately if this backend is idle (i.e., it is waiting for a frontend
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* command and is not within a transaction block. C.f.
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* ProcessClientReadInterrupt()). Otherwise the handler may only set a
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* flag, which will cause the processing to occur just before we next go
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* idle.
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*
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* Inbound-notify processing consists of reading all of the notifications
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* that have arrived since scanning last time. We read every notification
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* until we reach either a notification from an uncommitted transaction or
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* the head pointer's position.
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*
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* 6. To avoid SLRU wraparound and limit disk space consumption, the tail
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* pointer needs to be advanced so that old pages can be truncated.
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* This is relatively expensive (notably, it requires an exclusive lock),
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* so we don't want to do it often. We make sending backends do this work
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* if they advanced the queue head into a new page, but only once every
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* QUEUE_CLEANUP_DELAY pages.
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*
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* An application that listens on the same channel it notifies will get
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* NOTIFY messages for its own NOTIFYs. These can be ignored, if not useful,
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* by comparing be_pid in the NOTIFY message to the application's own backend's
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* PID. (As of FE/BE protocol 2.0, the backend's PID is provided to the
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* frontend during startup.) The above design guarantees that notifies from
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* other backends will never be missed by ignoring self-notifies.
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*
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* The amount of shared memory used for notify management (NUM_NOTIFY_BUFFERS)
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* can be varied without affecting anything but performance. The maximum
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* amount of notification data that can be queued at one time is determined
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* by slru.c's wraparound limit; see QUEUE_MAX_PAGE below.
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <limits.h>
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#include <unistd.h>
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#include <signal.h>
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#include "access/parallel.h"
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#include "access/slru.h"
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#include "access/transam.h"
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#include "access/xact.h"
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#include "catalog/pg_database.h"
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#include "commands/async.h"
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#include "common/hashfn.h"
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#include "funcapi.h"
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#include "libpq/libpq.h"
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#include "libpq/pqformat.h"
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#include "miscadmin.h"
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#include "storage/ipc.h"
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#include "storage/lmgr.h"
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#include "storage/proc.h"
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#include "storage/procarray.h"
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#include "storage/procsignal.h"
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#include "storage/sinval.h"
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#include "tcop/tcopprot.h"
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#include "utils/builtins.h"
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#include "utils/memutils.h"
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#include "utils/ps_status.h"
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#include "utils/snapmgr.h"
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#include "utils/timestamp.h"
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/*
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* Maximum size of a NOTIFY payload, including terminating NULL. This
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* must be kept small enough so that a notification message fits on one
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* SLRU page. The magic fudge factor here is noncritical as long as it's
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* more than AsyncQueueEntryEmptySize --- we make it significantly bigger
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* than that, so changes in that data structure won't affect user-visible
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* restrictions.
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*/
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#define NOTIFY_PAYLOAD_MAX_LENGTH (BLCKSZ - NAMEDATALEN - 128)
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/*
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* Struct representing an entry in the global notify queue
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*
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* This struct declaration has the maximal length, but in a real queue entry
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* the data area is only big enough for the actual channel and payload strings
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* (each null-terminated). AsyncQueueEntryEmptySize is the minimum possible
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* entry size, if both channel and payload strings are empty (but note it
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* doesn't include alignment padding).
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*
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* The "length" field should always be rounded up to the next QUEUEALIGN
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* multiple so that all fields are properly aligned.
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*/
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typedef struct AsyncQueueEntry
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{
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int length; /* total allocated length of entry */
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Oid dboid; /* sender's database OID */
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TransactionId xid; /* sender's XID */
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int32 srcPid; /* sender's PID */
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char data[NAMEDATALEN + NOTIFY_PAYLOAD_MAX_LENGTH];
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} AsyncQueueEntry;
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/* Currently, no field of AsyncQueueEntry requires more than int alignment */
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#define QUEUEALIGN(len) INTALIGN(len)
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#define AsyncQueueEntryEmptySize (offsetof(AsyncQueueEntry, data) + 2)
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/*
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* Struct describing a queue position, and assorted macros for working with it
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*/
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typedef struct QueuePosition
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{
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int page; /* SLRU page number */
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int offset; /* byte offset within page */
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} QueuePosition;
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#define QUEUE_POS_PAGE(x) ((x).page)
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#define QUEUE_POS_OFFSET(x) ((x).offset)
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#define SET_QUEUE_POS(x,y,z) \
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do { \
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(x).page = (y); \
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(x).offset = (z); \
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} while (0)
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#define QUEUE_POS_EQUAL(x,y) \
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((x).page == (y).page && (x).offset == (y).offset)
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#define QUEUE_POS_IS_ZERO(x) \
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((x).page == 0 && (x).offset == 0)
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/* choose logically smaller QueuePosition */
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#define QUEUE_POS_MIN(x,y) \
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(asyncQueuePagePrecedes((x).page, (y).page) ? (x) : \
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(x).page != (y).page ? (y) : \
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(x).offset < (y).offset ? (x) : (y))
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/* choose logically larger QueuePosition */
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#define QUEUE_POS_MAX(x,y) \
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(asyncQueuePagePrecedes((x).page, (y).page) ? (y) : \
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(x).page != (y).page ? (x) : \
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(x).offset > (y).offset ? (x) : (y))
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/*
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* Parameter determining how often we try to advance the tail pointer:
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* we do that after every QUEUE_CLEANUP_DELAY pages of NOTIFY data. This is
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* also the distance by which a backend in another database needs to be
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* behind before we'll decide we need to wake it up to advance its pointer.
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*
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* Resist the temptation to make this really large. While that would save
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* work in some places, it would add cost in others. In particular, this
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* should likely be less than NUM_NOTIFY_BUFFERS, to ensure that backends
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* catch up before the pages they'll need to read fall out of SLRU cache.
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*/
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#define QUEUE_CLEANUP_DELAY 4
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/*
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* Struct describing a listening backend's status
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*/
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typedef struct QueueBackendStatus
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{
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int32 pid; /* either a PID or InvalidPid */
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Oid dboid; /* backend's database OID, or InvalidOid */
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BackendId nextListener; /* id of next listener, or InvalidBackendId */
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QueuePosition pos; /* backend has read queue up to here */
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} QueueBackendStatus;
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/*
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* Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff)
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*
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* The AsyncQueueControl structure is protected by the NotifyQueueLock and
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* NotifyQueueTailLock.
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*
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* When holding NotifyQueueLock in SHARED mode, backends may only inspect
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* their own entries as well as the head and tail pointers. Consequently we
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* can allow a backend to update its own record while holding only SHARED lock
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* (since no other backend will inspect it).
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*
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* When holding NotifyQueueLock in EXCLUSIVE mode, backends can inspect the
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* entries of other backends and also change the head pointer. When holding
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* both NotifyQueueLock and NotifyQueueTailLock in EXCLUSIVE mode, backends
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* can change the tail pointer.
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*
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* NotifySLRULock is used as the control lock for the pg_notify SLRU buffers.
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* In order to avoid deadlocks, whenever we need multiple locks, we first get
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* NotifyQueueTailLock, then NotifyQueueLock, and lastly NotifySLRULock.
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*
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* Each backend uses the backend[] array entry with index equal to its
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* BackendId (which can range from 1 to MaxBackends). We rely on this to make
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* SendProcSignal fast.
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*
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* The backend[] array entries for actively-listening backends are threaded
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* together using firstListener and the nextListener links, so that we can
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* scan them without having to iterate over inactive entries. We keep this
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* list in order by BackendId so that the scan is cache-friendly when there
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* are many active entries.
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*/
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typedef struct AsyncQueueControl
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{
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QueuePosition head; /* head points to the next free location */
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QueuePosition tail; /* tail must be <= the queue position of every
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* listening backend */
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BackendId firstListener; /* id of first listener, or InvalidBackendId */
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TimestampTz lastQueueFillWarn; /* time of last queue-full msg */
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QueueBackendStatus backend[FLEXIBLE_ARRAY_MEMBER];
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/* backend[0] is not used; used entries are from [1] to [MaxBackends] */
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} AsyncQueueControl;
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static AsyncQueueControl *asyncQueueControl;
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#define QUEUE_HEAD (asyncQueueControl->head)
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#define QUEUE_TAIL (asyncQueueControl->tail)
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#define QUEUE_FIRST_LISTENER (asyncQueueControl->firstListener)
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#define QUEUE_BACKEND_PID(i) (asyncQueueControl->backend[i].pid)
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#define QUEUE_BACKEND_DBOID(i) (asyncQueueControl->backend[i].dboid)
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#define QUEUE_NEXT_LISTENER(i) (asyncQueueControl->backend[i].nextListener)
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#define QUEUE_BACKEND_POS(i) (asyncQueueControl->backend[i].pos)
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/*
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* The SLRU buffer area through which we access the notification queue
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*/
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static SlruCtlData NotifyCtlData;
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#define NotifyCtl (&NotifyCtlData)
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#define QUEUE_PAGESIZE BLCKSZ
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#define QUEUE_FULL_WARN_INTERVAL 5000 /* warn at most once every 5s */
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/*
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* Use segments 0000 through FFFF. Each contains SLRU_PAGES_PER_SEGMENT pages
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* which gives us the pages from 0 to SLRU_PAGES_PER_SEGMENT * 0x10000 - 1.
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* We could use as many segments as SlruScanDirectory() allows, but this gives
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* us so much space already that it doesn't seem worth the trouble.
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*
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* The most data we can have in the queue at a time is QUEUE_MAX_PAGE/2
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* pages, because more than that would confuse slru.c into thinking there
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* was a wraparound condition. With the default BLCKSZ this means there
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* can be up to 8GB of queued-and-not-read data.
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*
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* Note: it's possible to redefine QUEUE_MAX_PAGE with a smaller multiple of
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* SLRU_PAGES_PER_SEGMENT, for easier testing of queue-full behaviour.
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*/
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#define QUEUE_MAX_PAGE (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1)
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/*
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* listenChannels identifies the channels we are actually listening to
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* (ie, have committed a LISTEN on). It is a simple list of channel names,
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* allocated in TopMemoryContext.
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*/
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static List *listenChannels = NIL; /* list of C strings */
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/*
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* State for pending LISTEN/UNLISTEN actions consists of an ordered list of
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* all actions requested in the current transaction. As explained above,
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* we don't actually change listenChannels until we reach transaction commit.
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*
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* The list is kept in CurTransactionContext. In subtransactions, each
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* subtransaction has its own list in its own CurTransactionContext, but
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* successful subtransactions attach their lists to their parent's list.
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* Failed subtransactions simply discard their lists.
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*/
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typedef enum
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{
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LISTEN_LISTEN,
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LISTEN_UNLISTEN,
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LISTEN_UNLISTEN_ALL
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} ListenActionKind;
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typedef struct
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{
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ListenActionKind action;
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char channel[FLEXIBLE_ARRAY_MEMBER]; /* nul-terminated string */
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} ListenAction;
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typedef struct ActionList
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{
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int nestingLevel; /* current transaction nesting depth */
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List *actions; /* list of ListenAction structs */
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struct ActionList *upper; /* details for upper transaction levels */
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} ActionList;
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static ActionList *pendingActions = NULL;
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/*
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* State for outbound notifies consists of a list of all channels+payloads
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* NOTIFYed in the current transaction. We do not actually perform a NOTIFY
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* until and unless the transaction commits. pendingNotifies is NULL if no
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* NOTIFYs have been done in the current (sub) transaction.
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*
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* We discard duplicate notify events issued in the same transaction.
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* Hence, in addition to the list proper (which we need to track the order
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* of the events, since we guarantee to deliver them in order), we build a
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* hash table which we can probe to detect duplicates. Since building the
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* hash table is somewhat expensive, we do so only once we have at least
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* MIN_HASHABLE_NOTIFIES events queued in the current (sub) transaction;
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* before that we just scan the events linearly.
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*
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* The list is kept in CurTransactionContext. In subtransactions, each
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* subtransaction has its own list in its own CurTransactionContext, but
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* successful subtransactions add their entries to their parent's list.
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* Failed subtransactions simply discard their lists. Since these lists
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* are independent, there may be notify events in a subtransaction's list
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* that duplicate events in some ancestor (sub) transaction; we get rid of
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* the dups when merging the subtransaction's list into its parent's.
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*
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* Note: the action and notify lists do not interact within a transaction.
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* In particular, if a transaction does NOTIFY and then LISTEN on the same
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* condition name, it will get a self-notify at commit. This is a bit odd
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* but is consistent with our historical behavior.
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*/
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typedef struct Notification
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{
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uint16 channel_len; /* length of channel-name string */
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uint16 payload_len; /* length of payload string */
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/* null-terminated channel name, then null-terminated payload follow */
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char data[FLEXIBLE_ARRAY_MEMBER];
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} Notification;
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typedef struct NotificationList
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{
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int nestingLevel; /* current transaction nesting depth */
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List *events; /* list of Notification structs */
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HTAB *hashtab; /* hash of NotificationHash structs, or NULL */
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struct NotificationList *upper; /* details for upper transaction levels */
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} NotificationList;
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#define MIN_HASHABLE_NOTIFIES 16 /* threshold to build hashtab */
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typedef struct NotificationHash
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{
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Notification *event; /* => the actual Notification struct */
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} NotificationHash;
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static NotificationList *pendingNotifies = NULL;
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/*
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* Inbound notifications are initially processed by HandleNotifyInterrupt(),
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* called from inside a signal handler. That just sets the
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* notifyInterruptPending flag and sets the process
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* latch. ProcessNotifyInterrupt() will then be called whenever it's safe to
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* actually deal with the interrupt.
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*/
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volatile sig_atomic_t notifyInterruptPending = false;
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/* True if we've registered an on_shmem_exit cleanup */
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static bool unlistenExitRegistered = false;
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/* True if we're currently registered as a listener in asyncQueueControl */
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static bool amRegisteredListener = false;
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/* has this backend sent notifications in the current transaction? */
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static bool backendHasSentNotifications = false;
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/* have we advanced to a page that's a multiple of QUEUE_CLEANUP_DELAY? */
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static bool backendTryAdvanceTail = false;
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/* GUC parameter */
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bool Trace_notify = false;
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/* local function prototypes */
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static int asyncQueuePageDiff(int p, int q);
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static bool asyncQueuePagePrecedes(int p, int q);
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static void queue_listen(ListenActionKind action, const char *channel);
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static void Async_UnlistenOnExit(int code, Datum arg);
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static void Exec_ListenPreCommit(void);
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static void Exec_ListenCommit(const char *channel);
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static void Exec_UnlistenCommit(const char *channel);
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static void Exec_UnlistenAllCommit(void);
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static bool IsListeningOn(const char *channel);
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static void asyncQueueUnregister(void);
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static bool asyncQueueIsFull(void);
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static bool asyncQueueAdvance(volatile QueuePosition *position, int entryLength);
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static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe);
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static ListCell *asyncQueueAddEntries(ListCell *nextNotify);
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static double asyncQueueUsage(void);
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static void asyncQueueFillWarning(void);
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static void SignalBackends(void);
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static void asyncQueueReadAllNotifications(void);
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static bool asyncQueueProcessPageEntries(volatile QueuePosition *current,
|
|
QueuePosition stop,
|
|
char *page_buffer,
|
|
Snapshot snapshot);
|
|
static void asyncQueueAdvanceTail(void);
|
|
static void ProcessIncomingNotify(void);
|
|
static bool AsyncExistsPendingNotify(Notification *n);
|
|
static void AddEventToPendingNotifies(Notification *n);
|
|
static uint32 notification_hash(const void *key, Size keysize);
|
|
static int notification_match(const void *key1, const void *key2, Size keysize);
|
|
static void ClearPendingActionsAndNotifies(void);
|
|
|
|
/*
|
|
* Compute the difference between two queue page numbers (i.e., p - q),
|
|
* accounting for wraparound.
|
|
*/
|
|
static int
|
|
asyncQueuePageDiff(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;
|
|
}
|
|
|
|
/* Is p < q, accounting for wraparound? */
|
|
static bool
|
|
asyncQueuePagePrecedes(int p, int q)
|
|
{
|
|
return asyncQueuePageDiff(p, q) < 0;
|
|
}
|
|
|
|
/*
|
|
* Report space needed for our shared memory area
|
|
*/
|
|
Size
|
|
AsyncShmemSize(void)
|
|
{
|
|
Size size;
|
|
|
|
/* This had better match AsyncShmemInit */
|
|
size = mul_size(MaxBackends + 1, sizeof(QueueBackendStatus));
|
|
size = add_size(size, offsetof(AsyncQueueControl, backend));
|
|
|
|
size = add_size(size, SimpleLruShmemSize(NUM_NOTIFY_BUFFERS, 0));
|
|
|
|
return size;
|
|
}
|
|
|
|
/*
|
|
* Initialize our shared memory area
|
|
*/
|
|
void
|
|
AsyncShmemInit(void)
|
|
{
|
|
bool found;
|
|
Size size;
|
|
|
|
/*
|
|
* Create or attach to the AsyncQueueControl structure.
|
|
*
|
|
* The used entries in the backend[] array run from 1 to MaxBackends; the
|
|
* zero'th entry is unused but must be allocated.
|
|
*/
|
|
size = mul_size(MaxBackends + 1, sizeof(QueueBackendStatus));
|
|
size = add_size(size, offsetof(AsyncQueueControl, backend));
|
|
|
|
asyncQueueControl = (AsyncQueueControl *)
|
|
ShmemInitStruct("Async Queue Control", size, &found);
|
|
|
|
if (!found)
|
|
{
|
|
/* First time through, so initialize it */
|
|
SET_QUEUE_POS(QUEUE_HEAD, 0, 0);
|
|
SET_QUEUE_POS(QUEUE_TAIL, 0, 0);
|
|
QUEUE_FIRST_LISTENER = InvalidBackendId;
|
|
asyncQueueControl->lastQueueFillWarn = 0;
|
|
/* zero'th entry won't be used, but let's initialize it anyway */
|
|
for (int i = 0; i <= MaxBackends; i++)
|
|
{
|
|
QUEUE_BACKEND_PID(i) = InvalidPid;
|
|
QUEUE_BACKEND_DBOID(i) = InvalidOid;
|
|
QUEUE_NEXT_LISTENER(i) = InvalidBackendId;
|
|
SET_QUEUE_POS(QUEUE_BACKEND_POS(i), 0, 0);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Set up SLRU management of the pg_notify data.
|
|
*/
|
|
NotifyCtl->PagePrecedes = asyncQueuePagePrecedes;
|
|
SimpleLruInit(NotifyCtl, "Notify", NUM_NOTIFY_BUFFERS, 0,
|
|
NotifySLRULock, "pg_notify", LWTRANCHE_NOTIFY_BUFFER,
|
|
SYNC_HANDLER_NONE);
|
|
|
|
if (!found)
|
|
{
|
|
/*
|
|
* During start or reboot, clean out the pg_notify directory.
|
|
*/
|
|
(void) SlruScanDirectory(NotifyCtl, SlruScanDirCbDeleteAll, NULL);
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* 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));
|
|
|
|
/* For NOTIFY as a statement, this is checked in ProcessUtility */
|
|
PreventCommandDuringRecovery("NOTIFY");
|
|
|
|
Async_Notify(channel, payload);
|
|
|
|
PG_RETURN_VOID();
|
|
}
|
|
|
|
|
|
/*
|
|
* Async_Notify
|
|
*
|
|
* This is executed by the SQL notify command.
|
|
*
|
|
* Adds the message to the list of pending notifies.
|
|
* Actual notification happens during transaction commit.
|
|
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
*/
|
|
void
|
|
Async_Notify(const char *channel, const char *payload)
|
|
{
|
|
int my_level = GetCurrentTransactionNestLevel();
|
|
size_t channel_len;
|
|
size_t payload_len;
|
|
Notification *n;
|
|
MemoryContext oldcontext;
|
|
|
|
if (IsParallelWorker())
|
|
elog(ERROR, "cannot send notifications from a parallel worker");
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Async_Notify(%s)", channel);
|
|
|
|
channel_len = channel ? strlen(channel) : 0;
|
|
payload_len = payload ? strlen(payload) : 0;
|
|
|
|
/* a channel name must be specified */
|
|
if (channel_len == 0)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
|
|
errmsg("channel name cannot be empty")));
|
|
|
|
/* enforce length limits */
|
|
if (channel_len >= NAMEDATALEN)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
|
|
errmsg("channel name too long")));
|
|
|
|
if (payload_len >= NOTIFY_PAYLOAD_MAX_LENGTH)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
|
|
errmsg("payload string too long")));
|
|
|
|
/*
|
|
* We must construct the Notification entry, even if we end up not using
|
|
* it, in order to compare it cheaply to existing list entries.
|
|
*
|
|
* The notification list needs to live until end of transaction, so store
|
|
* it in the transaction context.
|
|
*/
|
|
oldcontext = MemoryContextSwitchTo(CurTransactionContext);
|
|
|
|
n = (Notification *) palloc(offsetof(Notification, data) +
|
|
channel_len + payload_len + 2);
|
|
n->channel_len = channel_len;
|
|
n->payload_len = payload_len;
|
|
strcpy(n->data, channel);
|
|
if (payload)
|
|
strcpy(n->data + channel_len + 1, payload);
|
|
else
|
|
n->data[channel_len + 1] = '\0';
|
|
|
|
if (pendingNotifies == NULL || my_level > pendingNotifies->nestingLevel)
|
|
{
|
|
NotificationList *notifies;
|
|
|
|
/*
|
|
* First notify event in current (sub)xact. Note that we allocate the
|
|
* NotificationList in TopTransactionContext; the nestingLevel might
|
|
* get changed later by AtSubCommit_Notify.
|
|
*/
|
|
notifies = (NotificationList *)
|
|
MemoryContextAlloc(TopTransactionContext,
|
|
sizeof(NotificationList));
|
|
notifies->nestingLevel = my_level;
|
|
notifies->events = list_make1(n);
|
|
/* We certainly don't need a hashtable yet */
|
|
notifies->hashtab = NULL;
|
|
notifies->upper = pendingNotifies;
|
|
pendingNotifies = notifies;
|
|
}
|
|
else
|
|
{
|
|
/* Now check for duplicates */
|
|
if (AsyncExistsPendingNotify(n))
|
|
{
|
|
/* It's a dup, so forget it */
|
|
pfree(n);
|
|
MemoryContextSwitchTo(oldcontext);
|
|
return;
|
|
}
|
|
|
|
/* Append more events to existing list */
|
|
AddEventToPendingNotifies(n);
|
|
}
|
|
|
|
MemoryContextSwitchTo(oldcontext);
|
|
}
|
|
|
|
/*
|
|
* queue_listen
|
|
* Common code for listen, unlisten, unlisten all commands.
|
|
*
|
|
* Adds the request to the list of pending actions.
|
|
* Actual update of the listenChannels list happens during transaction
|
|
* commit.
|
|
*/
|
|
static void
|
|
queue_listen(ListenActionKind action, const char *channel)
|
|
{
|
|
MemoryContext oldcontext;
|
|
ListenAction *actrec;
|
|
int my_level = GetCurrentTransactionNestLevel();
|
|
|
|
/*
|
|
* Unlike Async_Notify, we don't try to collapse out duplicates. It would
|
|
* be too complicated to ensure we get the right interactions of
|
|
* conflicting LISTEN/UNLISTEN/UNLISTEN_ALL, and it's unlikely that there
|
|
* would be any performance benefit anyway in sane applications.
|
|
*/
|
|
oldcontext = MemoryContextSwitchTo(CurTransactionContext);
|
|
|
|
/* space for terminating null is included in sizeof(ListenAction) */
|
|
actrec = (ListenAction *) palloc(offsetof(ListenAction, channel) +
|
|
strlen(channel) + 1);
|
|
actrec->action = action;
|
|
strcpy(actrec->channel, channel);
|
|
|
|
if (pendingActions == NULL || my_level > pendingActions->nestingLevel)
|
|
{
|
|
ActionList *actions;
|
|
|
|
/*
|
|
* First action in current sub(xact). Note that we allocate the
|
|
* ActionList in TopTransactionContext; the nestingLevel might get
|
|
* changed later by AtSubCommit_Notify.
|
|
*/
|
|
actions = (ActionList *)
|
|
MemoryContextAlloc(TopTransactionContext, sizeof(ActionList));
|
|
actions->nestingLevel = my_level;
|
|
actions->actions = list_make1(actrec);
|
|
actions->upper = pendingActions;
|
|
pendingActions = actions;
|
|
}
|
|
else
|
|
pendingActions->actions = lappend(pendingActions->actions, actrec);
|
|
|
|
MemoryContextSwitchTo(oldcontext);
|
|
}
|
|
|
|
/*
|
|
* Async_Listen
|
|
*
|
|
* This is executed by the SQL listen command.
|
|
*/
|
|
void
|
|
Async_Listen(const char *channel)
|
|
{
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Async_Listen(%s,%d)", channel, MyProcPid);
|
|
|
|
queue_listen(LISTEN_LISTEN, channel);
|
|
}
|
|
|
|
/*
|
|
* Async_Unlisten
|
|
*
|
|
* This is executed by the SQL unlisten command.
|
|
*/
|
|
void
|
|
Async_Unlisten(const char *channel)
|
|
{
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Async_Unlisten(%s,%d)", channel, MyProcPid);
|
|
|
|
/* If we couldn't possibly be listening, no need to queue anything */
|
|
if (pendingActions == NULL && !unlistenExitRegistered)
|
|
return;
|
|
|
|
queue_listen(LISTEN_UNLISTEN, channel);
|
|
}
|
|
|
|
/*
|
|
* Async_UnlistenAll
|
|
*
|
|
* This is invoked by UNLISTEN * command, and also at backend exit.
|
|
*/
|
|
void
|
|
Async_UnlistenAll(void)
|
|
{
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Async_UnlistenAll(%d)", MyProcPid);
|
|
|
|
/* If we couldn't possibly be listening, no need to queue anything */
|
|
if (pendingActions == NULL && !unlistenExitRegistered)
|
|
return;
|
|
|
|
queue_listen(LISTEN_UNLISTEN_ALL, "");
|
|
}
|
|
|
|
/*
|
|
* SQL function: return a set of the channel names this backend is actively
|
|
* listening to.
|
|
*
|
|
* 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;
|
|
|
|
/* stuff done only on the first call of the function */
|
|
if (SRF_IS_FIRSTCALL())
|
|
{
|
|
/* create a function context for cross-call persistence */
|
|
funcctx = SRF_FIRSTCALL_INIT();
|
|
}
|
|
|
|
/* stuff done on every call of the function */
|
|
funcctx = SRF_PERCALL_SETUP();
|
|
|
|
if (funcctx->call_cntr < list_length(listenChannels))
|
|
{
|
|
char *channel = (char *) list_nth(listenChannels,
|
|
funcctx->call_cntr);
|
|
|
|
SRF_RETURN_NEXT(funcctx, CStringGetTextDatum(channel));
|
|
}
|
|
|
|
SRF_RETURN_DONE(funcctx);
|
|
}
|
|
|
|
/*
|
|
* Async_UnlistenOnExit
|
|
*
|
|
* 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)
|
|
{
|
|
Exec_UnlistenAllCommit();
|
|
asyncQueueUnregister();
|
|
}
|
|
|
|
/*
|
|
* AtPrepare_Notify
|
|
*
|
|
* This is called at the prepare phase of a two-phase
|
|
* transaction. Save the state for possible commit later.
|
|
*/
|
|
void
|
|
AtPrepare_Notify(void)
|
|
{
|
|
/* 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, UNLISTEN, or NOTIFY")));
|
|
}
|
|
|
|
/*
|
|
* PreCommit_Notify
|
|
*
|
|
* This is called at transaction commit, before actually committing to
|
|
* clog.
|
|
*
|
|
* 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,
|
|
* 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
|
|
PreCommit_Notify(void)
|
|
{
|
|
ListCell *p;
|
|
|
|
if (!pendingActions && !pendingNotifies)
|
|
return; /* no relevant statements in this xact */
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "PreCommit_Notify");
|
|
|
|
/* Preflight for any pending listen/unlisten actions */
|
|
if (pendingActions != NULL)
|
|
{
|
|
foreach(p, pendingActions->actions)
|
|
{
|
|
ListenAction *actrec = (ListenAction *) lfirst(p);
|
|
|
|
switch (actrec->action)
|
|
{
|
|
case LISTEN_LISTEN:
|
|
Exec_ListenPreCommit();
|
|
break;
|
|
case LISTEN_UNLISTEN:
|
|
/* there is no Exec_UnlistenPreCommit() */
|
|
break;
|
|
case LISTEN_UNLISTEN_ALL:
|
|
/* there is no Exec_UnlistenAllPreCommit() */
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Queue any pending notifies (must happen after the above) */
|
|
if (pendingNotifies)
|
|
{
|
|
ListCell *nextNotify;
|
|
|
|
/*
|
|
* 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 NotifyQueueLock.
|
|
*/
|
|
(void) GetCurrentTransactionId();
|
|
|
|
/*
|
|
* 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);
|
|
|
|
/* Now push the notifications into the queue */
|
|
backendHasSentNotifications = true;
|
|
|
|
nextNotify = list_head(pendingNotifies->events);
|
|
while (nextNotify != NULL)
|
|
{
|
|
/*
|
|
* Add the pending notifications to the queue. We acquire and
|
|
* release NotifyQueueLock 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(NotifyQueueLock, LW_EXCLUSIVE);
|
|
asyncQueueFillWarning();
|
|
if (asyncQueueIsFull())
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("too many notifications in the NOTIFY queue")));
|
|
nextNotify = asyncQueueAddEntries(nextNotify);
|
|
LWLockRelease(NotifyQueueLock);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* AtCommit_Notify
|
|
*
|
|
* This is called at transaction commit, after committing to clog.
|
|
*
|
|
* Update listenChannels and clear transaction-local state.
|
|
*/
|
|
void
|
|
AtCommit_Notify(void)
|
|
{
|
|
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, "AtCommit_Notify");
|
|
|
|
/* Perform any pending listen/unlisten actions */
|
|
if (pendingActions != NULL)
|
|
{
|
|
foreach(p, pendingActions->actions)
|
|
{
|
|
ListenAction *actrec = (ListenAction *) lfirst(p);
|
|
|
|
switch (actrec->action)
|
|
{
|
|
case LISTEN_LISTEN:
|
|
Exec_ListenCommit(actrec->channel);
|
|
break;
|
|
case LISTEN_UNLISTEN:
|
|
Exec_UnlistenCommit(actrec->channel);
|
|
break;
|
|
case LISTEN_UNLISTEN_ALL:
|
|
Exec_UnlistenAllCommit();
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* If no longer listening to anything, get out of listener array */
|
|
if (amRegisteredListener && listenChannels == NIL)
|
|
asyncQueueUnregister();
|
|
|
|
/* And clean up */
|
|
ClearPendingActionsAndNotifies();
|
|
}
|
|
|
|
/*
|
|
* Exec_ListenPreCommit --- subroutine for PreCommit_Notify
|
|
*
|
|
* This function must make sure we are ready to catch any incoming messages.
|
|
*/
|
|
static void
|
|
Exec_ListenPreCommit(void)
|
|
{
|
|
QueuePosition head;
|
|
QueuePosition max;
|
|
BackendId prevListener;
|
|
|
|
/*
|
|
* Nothing to do if we are already listening to something, nor if we
|
|
* already ran this routine in this transaction.
|
|
*/
|
|
if (amRegisteredListener)
|
|
return;
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Exec_ListenPreCommit(%d)", MyProcPid);
|
|
|
|
/*
|
|
* Before registering, make sure we will unlisten before dying. (Note:
|
|
* this action does not get undone if we abort later.)
|
|
*/
|
|
if (!unlistenExitRegistered)
|
|
{
|
|
before_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.
|
|
*
|
|
* In some scenarios there might be a lot of committed notifications that
|
|
* have not yet been pruned away (because some backend is being lazy about
|
|
* reading them). To reduce our startup time, we can look at other
|
|
* backends and adopt the maximum "pos" pointer of any backend that's in
|
|
* our database; any notifications it's already advanced over are surely
|
|
* committed and need not be re-examined by us. (We must consider only
|
|
* backends connected to our DB, because others will not have bothered to
|
|
* check committed-ness of notifications in our DB.)
|
|
*
|
|
* We need exclusive lock here so we can look at other backends' entries
|
|
* and manipulate the list links.
|
|
*/
|
|
LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
|
|
head = QUEUE_HEAD;
|
|
max = QUEUE_TAIL;
|
|
prevListener = InvalidBackendId;
|
|
for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i))
|
|
{
|
|
if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
|
|
max = QUEUE_POS_MAX(max, QUEUE_BACKEND_POS(i));
|
|
/* Also find last listening backend before this one */
|
|
if (i < MyBackendId)
|
|
prevListener = i;
|
|
}
|
|
QUEUE_BACKEND_POS(MyBackendId) = max;
|
|
QUEUE_BACKEND_PID(MyBackendId) = MyProcPid;
|
|
QUEUE_BACKEND_DBOID(MyBackendId) = MyDatabaseId;
|
|
/* Insert backend into list of listeners at correct position */
|
|
if (prevListener > 0)
|
|
{
|
|
QUEUE_NEXT_LISTENER(MyBackendId) = QUEUE_NEXT_LISTENER(prevListener);
|
|
QUEUE_NEXT_LISTENER(prevListener) = MyBackendId;
|
|
}
|
|
else
|
|
{
|
|
QUEUE_NEXT_LISTENER(MyBackendId) = QUEUE_FIRST_LISTENER;
|
|
QUEUE_FIRST_LISTENER = MyBackendId;
|
|
}
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
/* Now we are listed in the global array, so remember we're listening */
|
|
amRegisteredListener = true;
|
|
|
|
/*
|
|
* Try to move our pointer forward as far as possible. This will skip
|
|
* over already-committed notifications, which we want to do because they
|
|
* might be quite stale. Note that we are not yet listening on anything,
|
|
* so we won't deliver such notifications to our frontend. Also, although
|
|
* our transaction might have executed NOTIFY, those message(s) aren't
|
|
* queued yet so we won't skip them here.
|
|
*/
|
|
if (!QUEUE_POS_EQUAL(max, head))
|
|
asyncQueueReadAllNotifications();
|
|
}
|
|
|
|
/*
|
|
* Exec_ListenCommit --- subroutine for AtCommit_Notify
|
|
*
|
|
* Add the channel to the list of channels we are listening on.
|
|
*/
|
|
static void
|
|
Exec_ListenCommit(const char *channel)
|
|
{
|
|
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;
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Exec_UnlistenCommit(%s,%d)", channel, MyProcPid);
|
|
|
|
foreach(q, listenChannels)
|
|
{
|
|
char *lchan = (char *) lfirst(q);
|
|
|
|
if (strcmp(lchan, channel) == 0)
|
|
{
|
|
listenChannels = foreach_delete_current(listenChannels, q);
|
|
pfree(lchan);
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* We do not complain about unlistening something not being listened;
|
|
* should we?
|
|
*/
|
|
}
|
|
|
|
/*
|
|
* Exec_UnlistenAllCommit --- subroutine for AtCommit_Notify
|
|
*
|
|
* Unlisten on all channels for this backend.
|
|
*/
|
|
static void
|
|
Exec_UnlistenAllCommit(void)
|
|
{
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "Exec_UnlistenAllCommit(%d)", MyProcPid);
|
|
|
|
list_free_deep(listenChannels);
|
|
listenChannels = NIL;
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
* Also, if we filled enough queue pages with new notifies, try to advance
|
|
* the queue tail pointer.
|
|
*
|
|
* 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)
|
|
{
|
|
MemoryContext caller_context;
|
|
|
|
/* 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;
|
|
|
|
/*
|
|
* We must preserve the caller's memory context (probably MessageContext)
|
|
* across the transaction we do here.
|
|
*/
|
|
caller_context = CurrentMemoryContext;
|
|
|
|
if (Trace_notify)
|
|
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 */
|
|
SignalBackends();
|
|
|
|
if (listenChannels != NIL)
|
|
{
|
|
/* Read the queue ourselves, and send relevant stuff to the frontend */
|
|
asyncQueueReadAllNotifications();
|
|
}
|
|
|
|
/*
|
|
* If it's time to try to advance the global tail pointer, do that.
|
|
*/
|
|
if (backendTryAdvanceTail)
|
|
{
|
|
backendTryAdvanceTail = false;
|
|
asyncQueueAdvanceTail();
|
|
}
|
|
|
|
CommitTransactionCommand();
|
|
|
|
MemoryContextSwitchTo(caller_context);
|
|
|
|
/* We don't need pq_flush() here since postgres.c will do one shortly */
|
|
}
|
|
|
|
/*
|
|
* Test whether we are actively listening on the given channel name.
|
|
*
|
|
* 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
|
|
asyncQueueUnregister(void)
|
|
{
|
|
Assert(listenChannels == NIL); /* else caller error */
|
|
|
|
if (!amRegisteredListener) /* nothing to do */
|
|
return;
|
|
|
|
/*
|
|
* Need exclusive lock here to manipulate list links.
|
|
*/
|
|
LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
|
|
/* Mark our entry as invalid */
|
|
QUEUE_BACKEND_PID(MyBackendId) = InvalidPid;
|
|
QUEUE_BACKEND_DBOID(MyBackendId) = InvalidOid;
|
|
/* and remove it from the list */
|
|
if (QUEUE_FIRST_LISTENER == MyBackendId)
|
|
QUEUE_FIRST_LISTENER = QUEUE_NEXT_LISTENER(MyBackendId);
|
|
else
|
|
{
|
|
for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i))
|
|
{
|
|
if (QUEUE_NEXT_LISTENER(i) == MyBackendId)
|
|
{
|
|
QUEUE_NEXT_LISTENER(i) = QUEUE_NEXT_LISTENER(MyBackendId);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
QUEUE_NEXT_LISTENER(MyBackendId) = InvalidBackendId;
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
/* mark ourselves as no longer listed in the global array */
|
|
amRegisteredListener = false;
|
|
}
|
|
|
|
/*
|
|
* Test whether there is room to insert more notification messages.
|
|
*
|
|
* Caller must hold at least shared NotifyQueueLock.
|
|
*/
|
|
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 asyncQueuePagePrecedes(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(volatile QueuePosition *position, int entryLength)
|
|
{
|
|
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)
|
|
{
|
|
pageno++;
|
|
if (pageno > QUEUE_MAX_PAGE)
|
|
pageno = 0; /* wrap around */
|
|
offset = 0;
|
|
pageJump = true;
|
|
}
|
|
|
|
SET_QUEUE_POS(*position, pageno, offset);
|
|
return pageJump;
|
|
}
|
|
|
|
/*
|
|
* Fill the AsyncQueueEntry at *qe with an outbound notification message.
|
|
*/
|
|
static void
|
|
asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
|
|
{
|
|
size_t channellen = n->channel_len;
|
|
size_t payloadlen = n->payload_len;
|
|
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->data, channellen + payloadlen + 2);
|
|
}
|
|
|
|
/*
|
|
* 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 (in pendingNotifies->events) 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 NotifyQueueLock already from the caller and grab
|
|
* NotifySLRULock locally in this function.
|
|
*/
|
|
static ListCell *
|
|
asyncQueueAddEntries(ListCell *nextNotify)
|
|
{
|
|
AsyncQueueEntry qe;
|
|
QueuePosition queue_head;
|
|
int pageno;
|
|
int offset;
|
|
int slotno;
|
|
|
|
/* We hold both NotifyQueueLock and NotifySLRULock during this operation */
|
|
LWLockAcquire(NotifySLRULock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* We work with a local copy of QUEUE_HEAD, which we write back to shared
|
|
* memory upon exiting. The reason for this is that if we have to advance
|
|
* to a new page, SimpleLruZeroPage might fail (out of disk space, for
|
|
* instance), and we must not advance QUEUE_HEAD if it does. (Otherwise,
|
|
* subsequent insertions would try to put entries into a page that slru.c
|
|
* thinks doesn't exist yet.) So, use a local position variable. Note
|
|
* that if we do fail, any already-inserted queue entries are forgotten;
|
|
* this is okay, since they'd be useless anyway after our transaction
|
|
* rolls back.
|
|
*/
|
|
queue_head = QUEUE_HEAD;
|
|
|
|
/*
|
|
* If this is the first write since the postmaster started, we need to
|
|
* initialize the first page of the async SLRU. Otherwise, the current
|
|
* page should be initialized already, so just fetch it.
|
|
*
|
|
* (We could also take the first path when the SLRU position has just
|
|
* wrapped around, but re-zeroing the page is harmless in that case.)
|
|
*/
|
|
pageno = QUEUE_POS_PAGE(queue_head);
|
|
if (QUEUE_POS_IS_ZERO(queue_head))
|
|
slotno = SimpleLruZeroPage(NotifyCtl, pageno);
|
|
else
|
|
slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
|
|
InvalidTransactionId);
|
|
|
|
/* Note we mark the page dirty before writing in it */
|
|
NotifyCtl->shared->page_dirty[slotno] = true;
|
|
|
|
while (nextNotify != NULL)
|
|
{
|
|
Notification *n = (Notification *) lfirst(nextNotify);
|
|
|
|
/* 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(pendingNotifies->events, nextNotify);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* 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(NotifyCtl->shared->page_buffer[slotno] + offset,
|
|
&qe,
|
|
qe.length);
|
|
|
|
/* Advance queue_head appropriately, and detect if page is full */
|
|
if (asyncQueueAdvance(&(queue_head), qe.length))
|
|
{
|
|
/*
|
|
* 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.
|
|
*/
|
|
slotno = SimpleLruZeroPage(NotifyCtl, QUEUE_POS_PAGE(queue_head));
|
|
|
|
/*
|
|
* If the new page address is a multiple of QUEUE_CLEANUP_DELAY,
|
|
* set flag to remember that we should try to advance the tail
|
|
* pointer (we don't want to actually do that right here).
|
|
*/
|
|
if (QUEUE_POS_PAGE(queue_head) % QUEUE_CLEANUP_DELAY == 0)
|
|
backendTryAdvanceTail = true;
|
|
|
|
/* And exit the loop */
|
|
break;
|
|
}
|
|
}
|
|
|
|
/* Success, so update the global QUEUE_HEAD */
|
|
QUEUE_HEAD = queue_head;
|
|
|
|
LWLockRelease(NotifySLRULock);
|
|
|
|
return nextNotify;
|
|
}
|
|
|
|
/*
|
|
* SQL function to return the fraction of the notification queue currently
|
|
* occupied.
|
|
*/
|
|
Datum
|
|
pg_notification_queue_usage(PG_FUNCTION_ARGS)
|
|
{
|
|
double usage;
|
|
|
|
/* Advance the queue tail so we don't report a too-large result */
|
|
asyncQueueAdvanceTail();
|
|
|
|
LWLockAcquire(NotifyQueueLock, LW_SHARED);
|
|
usage = asyncQueueUsage();
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
PG_RETURN_FLOAT8(usage);
|
|
}
|
|
|
|
/*
|
|
* Return the fraction of the queue that is currently occupied.
|
|
*
|
|
* The caller must hold NotifyQueueLock in (at least) shared mode.
|
|
*/
|
|
static double
|
|
asyncQueueUsage(void)
|
|
{
|
|
int headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
|
|
int tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
|
|
int occupied;
|
|
|
|
occupied = headPage - tailPage;
|
|
|
|
if (occupied == 0)
|
|
return (double) 0; /* fast exit for common case */
|
|
|
|
if (occupied < 0)
|
|
{
|
|
/* head has wrapped around, tail not yet */
|
|
occupied += QUEUE_MAX_PAGE + 1;
|
|
}
|
|
|
|
return (double) occupied / (double) ((QUEUE_MAX_PAGE + 1) / 2);
|
|
}
|
|
|
|
/*
|
|
* 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 NotifyQueueLock.
|
|
*/
|
|
static void
|
|
asyncQueueFillWarning(void)
|
|
{
|
|
double fillDegree;
|
|
TimestampTz t;
|
|
|
|
fillDegree = asyncQueueUsage();
|
|
if (fillDegree < 0.5)
|
|
return;
|
|
|
|
t = GetCurrentTimestamp();
|
|
|
|
if (TimestampDifferenceExceeds(asyncQueueControl->lastQueueFillWarn,
|
|
t, QUEUE_FULL_WARN_INTERVAL))
|
|
{
|
|
QueuePosition min = QUEUE_HEAD;
|
|
int32 minPid = InvalidPid;
|
|
|
|
for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i))
|
|
{
|
|
Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
|
|
min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
|
|
if (QUEUE_POS_EQUAL(min, QUEUE_BACKEND_POS(i)))
|
|
minPid = QUEUE_BACKEND_PID(i);
|
|
}
|
|
|
|
ereport(WARNING,
|
|
(errmsg("NOTIFY queue is %.0f%% full", fillDegree * 100),
|
|
(minPid != InvalidPid ?
|
|
errdetail("The server process with PID %d is among those with the oldest transactions.", minPid)
|
|
: 0),
|
|
(minPid != InvalidPid ?
|
|
errhint("The NOTIFY queue cannot be emptied until that process ends its current transaction.")
|
|
: 0)));
|
|
|
|
asyncQueueControl->lastQueueFillWarn = t;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Send signals to listening backends.
|
|
*
|
|
* We never signal our own process; that should be handled by our caller.
|
|
*
|
|
* Normally we signal only backends in our own database, since only those
|
|
* backends could be interested in notifies we send. However, if there's
|
|
* notify traffic in our database but no traffic in another database that
|
|
* does have listener(s), those listeners will fall further and further
|
|
* behind. Waken them anyway if they're far enough behind, so that they'll
|
|
* advance their queue position pointers, allowing the global tail to advance.
|
|
*
|
|
* Since we know the BackendId and the Pid the signaling is quite cheap.
|
|
*/
|
|
static void
|
|
SignalBackends(void)
|
|
{
|
|
int32 *pids;
|
|
BackendId *ids;
|
|
int count;
|
|
|
|
/*
|
|
* Identify backends that we need to signal. We don't want to send
|
|
* signals while holding the NotifyQueueLock, so this loop just builds 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(NotifyQueueLock, LW_EXCLUSIVE);
|
|
for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i))
|
|
{
|
|
int32 pid = QUEUE_BACKEND_PID(i);
|
|
QueuePosition pos;
|
|
|
|
Assert(pid != InvalidPid);
|
|
if (pid == MyProcPid)
|
|
continue; /* never signal self */
|
|
pos = QUEUE_BACKEND_POS(i);
|
|
if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
|
|
{
|
|
/*
|
|
* Always signal listeners in our own database, unless they're
|
|
* already caught up (unlikely, but possible).
|
|
*/
|
|
if (QUEUE_POS_EQUAL(pos, QUEUE_HEAD))
|
|
continue;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Listeners in other databases should be signaled only if they
|
|
* are far behind.
|
|
*/
|
|
if (asyncQueuePageDiff(QUEUE_POS_PAGE(QUEUE_HEAD),
|
|
QUEUE_POS_PAGE(pos)) < QUEUE_CLEANUP_DELAY)
|
|
continue;
|
|
}
|
|
/* OK, need to signal this one */
|
|
pids[count] = pid;
|
|
ids[count] = i;
|
|
count++;
|
|
}
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
/* Now send signals */
|
|
for (int i = 0; i < count; i++)
|
|
{
|
|
int32 pid = pids[i];
|
|
|
|
/*
|
|
* Note: assuming things aren't broken, a signal failure here could
|
|
* only occur if the target backend exited since we released
|
|
* NotifyQueueLock; 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);
|
|
}
|
|
|
|
pfree(pids);
|
|
pfree(ids);
|
|
}
|
|
|
|
/*
|
|
* AtAbort_Notify
|
|
*
|
|
* This is called at transaction abort.
|
|
*
|
|
* 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 after PreCommit_Notify,
|
|
* we have registered as a listener but have not made any entry in
|
|
* listenChannels. In that case, deregister again.
|
|
*/
|
|
if (amRegisteredListener && listenChannels == NIL)
|
|
asyncQueueUnregister();
|
|
|
|
/* And clean up */
|
|
ClearPendingActionsAndNotifies();
|
|
}
|
|
|
|
/*
|
|
* AtSubCommit_Notify() --- Take care of subtransaction commit.
|
|
*
|
|
* Reassign all items in the pending lists to the parent transaction.
|
|
*/
|
|
void
|
|
AtSubCommit_Notify(void)
|
|
{
|
|
int my_level = GetCurrentTransactionNestLevel();
|
|
|
|
/* If there are actions at our nesting level, we must reparent them. */
|
|
if (pendingActions != NULL &&
|
|
pendingActions->nestingLevel >= my_level)
|
|
{
|
|
if (pendingActions->upper == NULL ||
|
|
pendingActions->upper->nestingLevel < my_level - 1)
|
|
{
|
|
/* nothing to merge; give the whole thing to the parent */
|
|
--pendingActions->nestingLevel;
|
|
}
|
|
else
|
|
{
|
|
ActionList *childPendingActions = pendingActions;
|
|
|
|
pendingActions = pendingActions->upper;
|
|
|
|
/*
|
|
* Mustn't try to eliminate duplicates here --- see queue_listen()
|
|
*/
|
|
pendingActions->actions =
|
|
list_concat(pendingActions->actions,
|
|
childPendingActions->actions);
|
|
pfree(childPendingActions);
|
|
}
|
|
}
|
|
|
|
/* If there are notifies at our nesting level, we must reparent them. */
|
|
if (pendingNotifies != NULL &&
|
|
pendingNotifies->nestingLevel >= my_level)
|
|
{
|
|
Assert(pendingNotifies->nestingLevel == my_level);
|
|
|
|
if (pendingNotifies->upper == NULL ||
|
|
pendingNotifies->upper->nestingLevel < my_level - 1)
|
|
{
|
|
/* nothing to merge; give the whole thing to the parent */
|
|
--pendingNotifies->nestingLevel;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Formerly, we didn't bother to eliminate duplicates here, but
|
|
* now we must, else we fall foul of "Assert(!found)", either here
|
|
* or during a later attempt to build the parent-level hashtable.
|
|
*/
|
|
NotificationList *childPendingNotifies = pendingNotifies;
|
|
ListCell *l;
|
|
|
|
pendingNotifies = pendingNotifies->upper;
|
|
/* Insert all the subxact's events into parent, except for dups */
|
|
foreach(l, childPendingNotifies->events)
|
|
{
|
|
Notification *childn = (Notification *) lfirst(l);
|
|
|
|
if (!AsyncExistsPendingNotify(childn))
|
|
AddEventToPendingNotifies(childn);
|
|
}
|
|
pfree(childPendingNotifies);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* AtSubAbort_Notify() --- Take care of subtransaction abort.
|
|
*/
|
|
void
|
|
AtSubAbort_Notify(void)
|
|
{
|
|
int my_level = GetCurrentTransactionNestLevel();
|
|
|
|
/*
|
|
* All we have to do is pop the stack --- the actions/notifies made in
|
|
* this subxact are no longer interesting, and the space will be freed
|
|
* when CurTransactionContext is recycled. We still have to free the
|
|
* ActionList and NotificationList objects themselves, though, because
|
|
* those are allocated in TopTransactionContext.
|
|
*
|
|
* Note that there might be no entries at all, or no entries for the
|
|
* current subtransaction level, either because none were ever created, or
|
|
* because we reentered this routine due to trouble during subxact abort.
|
|
*/
|
|
while (pendingActions != NULL &&
|
|
pendingActions->nestingLevel >= my_level)
|
|
{
|
|
ActionList *childPendingActions = pendingActions;
|
|
|
|
pendingActions = pendingActions->upper;
|
|
pfree(childPendingActions);
|
|
}
|
|
|
|
while (pendingNotifies != NULL &&
|
|
pendingNotifies->nestingLevel >= my_level)
|
|
{
|
|
NotificationList *childPendingNotifies = pendingNotifies;
|
|
|
|
pendingNotifies = pendingNotifies->upper;
|
|
pfree(childPendingNotifies);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* HandleNotifyInterrupt
|
|
*
|
|
* Signal handler portion of interrupt handling. Let the backend know
|
|
* that there's a pending notify interrupt. If we're currently reading
|
|
* from the client, this will interrupt the read and
|
|
* ProcessClientReadInterrupt() will call ProcessNotifyInterrupt().
|
|
*/
|
|
void
|
|
HandleNotifyInterrupt(void)
|
|
{
|
|
/*
|
|
* Note: this is called by a SIGNAL HANDLER. You must be very wary what
|
|
* you do here.
|
|
*/
|
|
|
|
/* signal that work needs to be done */
|
|
notifyInterruptPending = true;
|
|
|
|
/* make sure the event is processed in due course */
|
|
SetLatch(MyLatch);
|
|
}
|
|
|
|
/*
|
|
* ProcessNotifyInterrupt
|
|
*
|
|
* This is called if we see notifyInterruptPending set, just before
|
|
* transmitting ReadyForQuery at the end of a frontend command, and
|
|
* also if a notify signal occurs while reading from the frontend.
|
|
* HandleNotifyInterrupt() will cause the read to be interrupted
|
|
* via the process's latch, and this routine will get called.
|
|
* If we are truly idle (ie, *not* inside a transaction block),
|
|
* process the incoming notifies.
|
|
*/
|
|
void
|
|
ProcessNotifyInterrupt(void)
|
|
{
|
|
if (IsTransactionOrTransactionBlock())
|
|
return; /* not really idle */
|
|
|
|
while (notifyInterruptPending)
|
|
ProcessIncomingNotify();
|
|
}
|
|
|
|
|
|
/*
|
|
* 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)
|
|
{
|
|
volatile QueuePosition pos;
|
|
QueuePosition head;
|
|
Snapshot snapshot;
|
|
|
|
/* page_buffer must be adequately aligned, so use a union */
|
|
union
|
|
{
|
|
char buf[QUEUE_PAGESIZE];
|
|
AsyncQueueEntry align;
|
|
} page_buffer;
|
|
|
|
/* Fetch current state */
|
|
LWLockAcquire(NotifyQueueLock, LW_SHARED);
|
|
/* Assert checks that we have a valid state entry */
|
|
Assert(MyProcPid == QUEUE_BACKEND_PID(MyBackendId));
|
|
pos = QUEUE_BACKEND_POS(MyBackendId);
|
|
head = QUEUE_HEAD;
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
if (QUEUE_POS_EQUAL(pos, head))
|
|
{
|
|
/* Nothing to do, we have read all notifications already. */
|
|
return;
|
|
}
|
|
|
|
/*----------
|
|
* Get snapshot we'll use to decide which xacts are still in progress.
|
|
* This is trickier than it might seem, because of race conditions.
|
|
* Consider the following example:
|
|
*
|
|
* Backend 1: Backend 2:
|
|
*
|
|
* transaction starts
|
|
* UPDATE foo SET ...;
|
|
* NOTIFY foo;
|
|
* commit starts
|
|
* queue the notify message
|
|
* transaction starts
|
|
* LISTEN foo; -- first LISTEN in session
|
|
* SELECT * FROM foo WHERE ...;
|
|
* commit to clog
|
|
* commit starts
|
|
* add backend 2 to array of listeners
|
|
* advance to queue head (this code)
|
|
* commit to clog
|
|
*
|
|
* Transaction 2's SELECT has not seen the UPDATE's effects, since that
|
|
* wasn't committed yet. Ideally we'd ensure that client 2 would
|
|
* eventually get transaction 1's notify message, but there's no way
|
|
* to do that; until we're in the listener array, there's no guarantee
|
|
* that the notify message doesn't get removed from the queue.
|
|
*
|
|
* Therefore the coding technique transaction 2 is using is unsafe:
|
|
* applications must commit a LISTEN before inspecting database state,
|
|
* if they want to ensure they will see notifications about subsequent
|
|
* changes to that state.
|
|
*
|
|
* What we do guarantee is that we'll see all notifications from
|
|
* transactions committing after the snapshot we take here.
|
|
* Exec_ListenPreCommit has already added us to the listener array,
|
|
* so no not-yet-committed messages can be removed from the queue
|
|
* before we see them.
|
|
*----------
|
|
*/
|
|
snapshot = RegisterSnapshot(GetLatestSnapshot());
|
|
|
|
/*
|
|
* 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 queue position before we lose control to an error.
|
|
* (We could alternatively retake NotifyQueueLock 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 NotifySLRULock 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(NotifyCtl, 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,
|
|
NotifyCtl->shared->page_buffer[slotno] + curoffset,
|
|
copysize);
|
|
/* Release lock that we got from SimpleLruReadPage_ReadOnly() */
|
|
LWLockRelease(NotifySLRULock);
|
|
|
|
/*
|
|
* 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 NotifyQueueLock 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,
|
|
snapshot);
|
|
} while (!reachedStop);
|
|
}
|
|
PG_FINALLY();
|
|
{
|
|
/* Update shared state */
|
|
LWLockAcquire(NotifyQueueLock, LW_SHARED);
|
|
QUEUE_BACKEND_POS(MyBackendId) = pos;
|
|
LWLockRelease(NotifyQueueLock);
|
|
}
|
|
PG_END_TRY();
|
|
|
|
/* Done with snapshot */
|
|
UnregisterSnapshot(snapshot);
|
|
}
|
|
|
|
/*
|
|
* 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 NotifySLRULock 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.
|
|
* The QueuePosition *current is advanced past all processed messages.
|
|
*/
|
|
static bool
|
|
asyncQueueProcessPageEntries(volatile QueuePosition *current,
|
|
QueuePosition stop,
|
|
char *page_buffer,
|
|
Snapshot snapshot)
|
|
{
|
|
bool reachedStop = false;
|
|
bool reachedEndOfPage;
|
|
AsyncQueueEntry *qe;
|
|
|
|
do
|
|
{
|
|
QueuePosition thisentry = *current;
|
|
|
|
if (QUEUE_POS_EQUAL(thisentry, stop))
|
|
break;
|
|
|
|
qe = (AsyncQueueEntry *) (page_buffer + QUEUE_POS_OFFSET(thisentry));
|
|
|
|
/*
|
|
* 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 (XidInMVCCSnapshot(qe->xid, snapshot))
|
|
{
|
|
/*
|
|
* The source transaction is still in progress, so we can't
|
|
* process this message yet. Break out of the loop, but first
|
|
* back up *current so we will reprocess the message next
|
|
* time. (Note: it is unlikely but not impossible for
|
|
* TransactionIdDidCommit to fail, so we can't really avoid
|
|
* this advance-then-back-up behavior when dealing with an
|
|
* uncommitted message.)
|
|
*
|
|
* Note that we must test XidInMVCCSnapshot before we test
|
|
* TransactionIdDidCommit, else we might return a message from
|
|
* a transaction that is not yet visible to snapshots; compare
|
|
* the comments at the head of heapam_visibility.c.
|
|
*
|
|
* Also, while our own xact won't be listed in the snapshot,
|
|
* we need not check for TransactionIdIsCurrentTransactionId
|
|
* because our transaction cannot (yet) have queued any
|
|
* messages.
|
|
*/
|
|
*current = thisentry;
|
|
reachedStop = true;
|
|
break;
|
|
}
|
|
else 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
|
|
{
|
|
/*
|
|
* The source transaction aborted or crashed, so we just
|
|
* ignore its notifications.
|
|
*/
|
|
}
|
|
}
|
|
|
|
/* 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 oldtailpage;
|
|
int newtailpage;
|
|
int boundary;
|
|
|
|
/* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
|
|
LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE);
|
|
|
|
/* Compute the new tail. */
|
|
LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
|
|
min = QUEUE_HEAD;
|
|
for (BackendId i = QUEUE_FIRST_LISTENER; i > 0; i = QUEUE_NEXT_LISTENER(i))
|
|
{
|
|
Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
|
|
min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
|
|
}
|
|
oldtailpage = QUEUE_POS_PAGE(QUEUE_TAIL);
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
/*
|
|
* 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 (asyncQueuePagePrecedes(oldtailpage, boundary))
|
|
{
|
|
/*
|
|
* SimpleLruTruncate() will ask for NotifySLRULock but will also
|
|
* release the lock again.
|
|
*/
|
|
SimpleLruTruncate(NotifyCtl, newtailpage);
|
|
}
|
|
|
|
/*
|
|
* Advertise the new tail. This changes asyncQueueIsFull()'s verdict for
|
|
* the segment immediately prior to the new tail, allowing fresh data into
|
|
* that segment.
|
|
*/
|
|
LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
|
|
QUEUE_TAIL = min;
|
|
LWLockRelease(NotifyQueueLock);
|
|
|
|
LWLockRelease(NotifyQueueTailLock);
|
|
}
|
|
|
|
/*
|
|
* ProcessIncomingNotify
|
|
*
|
|
* Deal with arriving NOTIFYs from other backends as soon as it's safe to
|
|
* do so. This used to be called from the PROCSIG_NOTIFY_INTERRUPT
|
|
* signal handler, but isn't anymore.
|
|
*
|
|
* 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)
|
|
{
|
|
/* We *must* reset the flag */
|
|
notifyInterruptPending = false;
|
|
|
|
/* Do nothing else if we aren't actively listening */
|
|
if (listenChannels == NIL)
|
|
return;
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "ProcessIncomingNotify");
|
|
|
|
set_ps_display("notify interrupt");
|
|
|
|
/*
|
|
* We must run asyncQueueReadAllNotifications inside a transaction, else
|
|
* bad things happen if it gets an error.
|
|
*/
|
|
StartTransactionCommand();
|
|
|
|
asyncQueueReadAllNotifications();
|
|
|
|
CommitTransactionCommand();
|
|
|
|
/*
|
|
* Must flush the notify messages to ensure frontend gets them promptly.
|
|
*/
|
|
pq_flush();
|
|
|
|
set_ps_display("idle");
|
|
|
|
if (Trace_notify)
|
|
elog(DEBUG1, "ProcessIncomingNotify: done");
|
|
}
|
|
|
|
/*
|
|
* Send NOTIFY message to my front end.
|
|
*/
|
|
void
|
|
NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
|
|
{
|
|
if (whereToSendOutput == DestRemote)
|
|
{
|
|
StringInfoData buf;
|
|
|
|
pq_beginmessage(&buf, 'A');
|
|
pq_sendint32(&buf, srcPid);
|
|
pq_sendstring(&buf, channel);
|
|
if (PG_PROTOCOL_MAJOR(FrontendProtocol) >= 3)
|
|
pq_sendstring(&buf, payload);
|
|
pq_endmessage(&buf);
|
|
|
|
/*
|
|
* NOTE: we do not do pq_flush() here. For a self-notify, it will
|
|
* happen at the end of the transaction, and for incoming notifies
|
|
* ProcessIncomingNotify will do it after finding all the notifies.
|
|
*/
|
|
}
|
|
else
|
|
elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload);
|
|
}
|
|
|
|
/* Does pendingNotifies include a match for the given event? */
|
|
static bool
|
|
AsyncExistsPendingNotify(Notification *n)
|
|
{
|
|
if (pendingNotifies == NULL)
|
|
return false;
|
|
|
|
if (pendingNotifies->hashtab != NULL)
|
|
{
|
|
/* Use the hash table to probe for a match */
|
|
if (hash_search(pendingNotifies->hashtab,
|
|
&n,
|
|
HASH_FIND,
|
|
NULL))
|
|
return true;
|
|
}
|
|
else
|
|
{
|
|
/* Must scan the event list */
|
|
ListCell *l;
|
|
|
|
foreach(l, pendingNotifies->events)
|
|
{
|
|
Notification *oldn = (Notification *) lfirst(l);
|
|
|
|
if (n->channel_len == oldn->channel_len &&
|
|
n->payload_len == oldn->payload_len &&
|
|
memcmp(n->data, oldn->data,
|
|
n->channel_len + n->payload_len + 2) == 0)
|
|
return true;
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Add a notification event to a pre-existing pendingNotifies list.
|
|
*
|
|
* Because pendingNotifies->events is already nonempty, this works
|
|
* correctly no matter what CurrentMemoryContext is.
|
|
*/
|
|
static void
|
|
AddEventToPendingNotifies(Notification *n)
|
|
{
|
|
Assert(pendingNotifies->events != NIL);
|
|
|
|
/* Create the hash table if it's time to */
|
|
if (list_length(pendingNotifies->events) >= MIN_HASHABLE_NOTIFIES &&
|
|
pendingNotifies->hashtab == NULL)
|
|
{
|
|
HASHCTL hash_ctl;
|
|
ListCell *l;
|
|
|
|
/* Create the hash table */
|
|
MemSet(&hash_ctl, 0, sizeof(hash_ctl));
|
|
hash_ctl.keysize = sizeof(Notification *);
|
|
hash_ctl.entrysize = sizeof(NotificationHash);
|
|
hash_ctl.hash = notification_hash;
|
|
hash_ctl.match = notification_match;
|
|
hash_ctl.hcxt = CurTransactionContext;
|
|
pendingNotifies->hashtab =
|
|
hash_create("Pending Notifies",
|
|
256L,
|
|
&hash_ctl,
|
|
HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
|
|
|
|
/* Insert all the already-existing events */
|
|
foreach(l, pendingNotifies->events)
|
|
{
|
|
Notification *oldn = (Notification *) lfirst(l);
|
|
NotificationHash *hentry;
|
|
bool found;
|
|
|
|
hentry = (NotificationHash *) hash_search(pendingNotifies->hashtab,
|
|
&oldn,
|
|
HASH_ENTER,
|
|
&found);
|
|
Assert(!found);
|
|
hentry->event = oldn;
|
|
}
|
|
}
|
|
|
|
/* Add new event to the list, in order */
|
|
pendingNotifies->events = lappend(pendingNotifies->events, n);
|
|
|
|
/* Add event to the hash table if needed */
|
|
if (pendingNotifies->hashtab != NULL)
|
|
{
|
|
NotificationHash *hentry;
|
|
bool found;
|
|
|
|
hentry = (NotificationHash *) hash_search(pendingNotifies->hashtab,
|
|
&n,
|
|
HASH_ENTER,
|
|
&found);
|
|
Assert(!found);
|
|
hentry->event = n;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* notification_hash: hash function for notification hash table
|
|
*
|
|
* The hash "keys" are pointers to Notification structs.
|
|
*/
|
|
static uint32
|
|
notification_hash(const void *key, Size keysize)
|
|
{
|
|
const Notification *k = *(const Notification *const *) key;
|
|
|
|
Assert(keysize == sizeof(Notification *));
|
|
/* We don't bother to include the payload's trailing null in the hash */
|
|
return DatumGetUInt32(hash_any((const unsigned char *) k->data,
|
|
k->channel_len + k->payload_len + 1));
|
|
}
|
|
|
|
/*
|
|
* notification_match: match function to use with notification_hash
|
|
*/
|
|
static int
|
|
notification_match(const void *key1, const void *key2, Size keysize)
|
|
{
|
|
const Notification *k1 = *(const Notification *const *) key1;
|
|
const Notification *k2 = *(const Notification *const *) key2;
|
|
|
|
Assert(keysize == sizeof(Notification *));
|
|
if (k1->channel_len == k2->channel_len &&
|
|
k1->payload_len == k2->payload_len &&
|
|
memcmp(k1->data, k2->data,
|
|
k1->channel_len + k1->payload_len + 2) == 0)
|
|
return 0; /* equal */
|
|
return 1; /* not equal */
|
|
}
|
|
|
|
/* Clear the pendingActions and pendingNotifies lists. */
|
|
static void
|
|
ClearPendingActionsAndNotifies(void)
|
|
{
|
|
/*
|
|
* Everything's allocated in either TopTransactionContext or the context
|
|
* for the subtransaction to which it corresponds. So, there's nothing to
|
|
* do here except reset the pointers; the space will be reclaimed when the
|
|
* contexts are deleted.
|
|
*/
|
|
pendingActions = NULL;
|
|
pendingNotifies = NULL;
|
|
}
|