diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 76f77cb0fcf2f7e63d0d0d3419690db79d71178e..91fa4ca3b7c948d1014d77993639074fb71ac28a 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -14805,6 +14805,12 @@ SELECT * FROM pg_ls_dir('.') WITH ORDINALITY AS t(ls,n);
<entry>channel names that the session is currently listening on</entry>
</row>
+ <row>
+ <entry><literal><function>pg_notification_queue_usage()</function></literal></entry>
+ <entry><type>double</type></entry>
+ <entry>fraction of the asynchronous notification queue currently occupied (0-1)</entry>
+ </row>
+
<row>
<entry><literal><function>pg_my_temp_schema()</function></literal></entry>
<entry><type>oid</type></entry>
@@ -14945,10 +14951,19 @@ SET search_path TO <replaceable>schema</> <optional>, <replaceable>schema</>, ..
<primary>pg_listening_channels</primary>
</indexterm>
+ <indexterm>
+ <primary>pg_notification_queue_usage</primary>
+ </indexterm>
+
<para>
<function>pg_listening_channels</function> returns a set of names of
- channels that the current session is listening to. See <xref
- linkend="sql-listen"> for more information.
+ asynchronous notification channels that the current session is listening
+ to. <function>pg_notification_queue_usage</function> returns the
+ fraction of the total available space for notifications currently
+ occupied by notifications that are waiting to be processed, as a
+ <type>double</type> in the range 0-1.
+ See <xref linkend="sql-listen"> and <xref linkend="sql-notify">
+ for more information.
</para>
<indexterm>
diff --git a/doc/src/sgml/ref/notify.sgml b/doc/src/sgml/ref/notify.sgml
index ad574e9ea03228f74ef7bc25bc3ccf1846d60c0f..4dd560838b19111bdc48975fa0665f7941b63ee3 100644
--- a/doc/src/sgml/ref/notify.sgml
+++ b/doc/src/sgml/ref/notify.sgml
@@ -165,6 +165,11 @@ NOTIFY <replaceable class="PARAMETER">channel</replaceable> [ , <replaceable cla
cleanup. In this case you should make sure that this session ends its
current transaction so that cleanup can proceed.
</para>
+ <para>
+ The function <function>pg_notification_queue_usage</function> returns the
+ fraction of the queue that is currently occupied by pending notifications.
+ See <xref linkend="functions-info"> for more information.
+ </para>
<para>
A transaction that has executed <command>NOTIFY</command> cannot be
prepared for two-phase commit.
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 2826b7e43c446c13497490a7b629735758a84dcf..3b71174b82640a9118ced2d771a083e59f9603f6 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -371,6 +371,7 @@ static bool asyncQueueIsFull(void);
static bool asyncQueueAdvance(volatile QueuePosition *position, int entryLength);
static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe);
static ListCell *asyncQueueAddEntries(ListCell *nextNotify);
+static double asyncQueueUsage(void);
static void asyncQueueFillWarning(void);
static bool SignalBackends(void);
static void asyncQueueReadAllNotifications(void);
@@ -1362,26 +1363,37 @@ asyncQueueAddEntries(ListCell *nextNotify)
}
/*
- * Check whether the queue is at least half full, and emit a warning if so.
- *
- * This is unlikely given the size of the queue, but possible.
- * The warnings show up at most once every QUEUE_FULL_WARN_INTERVAL.
+ * SQL function to return the fraction of the notification queue currently
+ * occupied.
+ */
+Datum
+pg_notification_queue_usage(PG_FUNCTION_ARGS)
+{
+ double usage;
+
+ LWLockAcquire(AsyncQueueLock, LW_SHARED);
+ usage = asyncQueueUsage();
+ LWLockRelease(AsyncQueueLock);
+
+ PG_RETURN_FLOAT8(usage);
+}
+
+/*
+ * Return the fraction of the queue that is currently occupied.
*
- * Caller must hold exclusive AsyncQueueLock.
+ * The caller must hold AysncQueueLock in (at least) shared mode.
*/
-static void
-asyncQueueFillWarning(void)
+static double
+asyncQueueUsage(void)
{
int headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
int tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
int occupied;
- double fillDegree;
- TimestampTz t;
occupied = headPage - tailPage;
if (occupied == 0)
- return; /* fast exit for common case */
+ return (double) 0; /* fast exit for common case */
if (occupied < 0)
{
@@ -1389,8 +1401,24 @@ asyncQueueFillWarning(void)
occupied += QUEUE_MAX_PAGE + 1;
}
- fillDegree = (double) occupied / (double) ((QUEUE_MAX_PAGE + 1) / 2);
+ 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 AsyncQueueLock.
+ */
+static void
+asyncQueueFillWarning(void)
+{
+ double fillDegree;
+ TimestampTz t;
+ fillDegree = asyncQueueUsage();
if (fillDegree < 0.5)
return;
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 44ce2b3a6200689085a69e1bd19972f0530f0c6d..8f6685fd0cce89d8060dd8468b7575bd85bb412d 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
*/
/* yyyymmddN */
-#define CATALOG_VERSION_NO 201507021
+#define CATALOG_VERSION_NO 201507171
#endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 6fd1278d1b2448a3ab120f25a81f801a61f5a962..1d68ad7209e1c65333491a4a646945dfc525f2ab 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -4046,10 +4046,14 @@ DATA(insert OID = 2856 ( pg_timezone_names PGNSP PGUID 12 1 1000 0 0 f f f f t
DESCR("get the available time zone names");
DATA(insert OID = 2730 ( pg_get_triggerdef PGNSP PGUID 12 1 0 0 0 f f f f t f s 2 0 25 "26 16" _null_ _null_ _null_ _null_ _null_ pg_get_triggerdef_ext _null_ _null_ _null_ ));
DESCR("trigger description with pretty-print option");
+
+/* asynchronous notifications */
DATA(insert OID = 3035 ( pg_listening_channels PGNSP PGUID 12 1 10 0 0 f f f f t t s 0 0 25 "" _null_ _null_ _null_ _null_ _null_ pg_listening_channels _null_ _null_ _null_ ));
DESCR("get the channels that the current backend listens to");
DATA(insert OID = 3036 ( pg_notify PGNSP PGUID 12 1 0 0 0 f f f f f f v 2 0 2278 "25 25" _null_ _null_ _null_ _null_ _null_ pg_notify _null_ _null_ _null_ ));
DESCR("send a notification event");
+DATA(insert OID = 3296 ( pg_notification_queue_usage PGNSP PGUID 12 1 0 0 0 f f f f t f v 0 0 701 "" _null_ _null_ _null_ _null_ _null_ pg_notification_queue_usage _null_ _null_ _null_ ));
+DESCR("get the fraction of the asynchronous notification queue currently in use");
/* non-persistent series generator */
DATA(insert OID = 1066 ( generate_series PGNSP PGUID 12 1 1000 0 0 f f f f t t i 3 0 23 "23 23 23" _null_ _null_ _null_ _null_ _null_ generate_series_step_int4 _null_ _null_ _null_ ));
diff --git a/src/include/commands/async.h b/src/include/commands/async.h
index 8491f4736f701004666e684d4f1966bf545ebaa8..677dcaa3d0332e36fd989e5f783d6e164e82d7a7 100644
--- a/src/include/commands/async.h
+++ b/src/include/commands/async.h
@@ -37,6 +37,7 @@ extern void Async_UnlistenAll(void);
/* notify-related SQL functions */
extern Datum pg_listening_channels(PG_FUNCTION_ARGS);
extern Datum pg_notify(PG_FUNCTION_ARGS);
+extern Datum pg_notification_queue_usage(PG_FUNCTION_ARGS);
/* perform (or cancel) outbound notify processing at transaction commit */
extern void PreCommit_Notify(void);
diff --git a/src/test/isolation/expected/async-notify.out b/src/test/isolation/expected/async-notify.out
new file mode 100644
index 0000000000000000000000000000000000000000..92d281a7d1f3cd6192120c15dd777af39610b7a1
--- /dev/null
+++ b/src/test/isolation/expected/async-notify.out
@@ -0,0 +1,17 @@
+Parsed test spec with 2 sessions
+
+starting permutation: listen begin check notify check
+step listen: LISTEN a;
+step begin: BEGIN;
+step check: SELECT pg_notification_queue_usage() > 0 AS nonzero;
+nonzero
+
+f
+step notify: SELECT count(pg_notify('a', s::text)) FROM generate_series(1, 1000) s;
+count
+
+1000
+step check: SELECT pg_notification_queue_usage() > 0 AS nonzero;
+nonzero
+
+t
diff --git a/src/test/isolation/specs/async-notify.spec b/src/test/isolation/specs/async-notify.spec
new file mode 100644
index 0000000000000000000000000000000000000000..7f451b18a1579e808abb36ba6ed127c3571a12f5
--- /dev/null
+++ b/src/test/isolation/specs/async-notify.spec
@@ -0,0 +1,14 @@
+# Verify that pg_notification_queue_usage correctly reports a non-zero result,
+# after submitting notifications while another connection is listening for
+# those notifications and waiting inside an active transaction.
+
+session "listener"
+step "listen" { LISTEN a; }
+step "begin" { BEGIN; }
+teardown { ROLLBACK; }
+
+session "notifier"
+step "check" { SELECT pg_notification_queue_usage() > 0 AS nonzero; }
+step "notify" { SELECT count(pg_notify('a', s::text)) FROM generate_series(1, 1000) s; }
+
+permutation "listen" "begin" "check" "notify" "check"
diff --git a/src/test/regress/expected/async.out b/src/test/regress/expected/async.out
index ae0d5df3b7825f3cd8c1c8d0fda5a95a729b5a75..19cbe38e636d092b0677c3fba9f1ff273edab81f 100644
--- a/src/test/regress/expected/async.out
+++ b/src/test/regress/expected/async.out
@@ -32,3 +32,11 @@ NOTIFY notify_async2;
LISTEN notify_async2;
UNLISTEN notify_async2;
UNLISTEN *;
+-- Should return zero while there are no pending notifications.
+-- src/test/isolation/specs/async-notify.spec tests for actual usage.
+SELECT pg_notification_queue_usage();
+ pg_notification_queue_usage
+-----------------------------
+ 0
+(1 row)
+
diff --git a/src/test/regress/sql/async.sql b/src/test/regress/sql/async.sql
index af3a904e0f56f29267c95cbf5e7eada8e4b0df31..40f6e015387b5254cfbddcd55b0c67e964d65e3b 100644
--- a/src/test/regress/sql/async.sql
+++ b/src/test/regress/sql/async.sql
@@ -17,3 +17,7 @@ NOTIFY notify_async2;
LISTEN notify_async2;
UNLISTEN notify_async2;
UNLISTEN *;
+
+-- Should return zero while there are no pending notifications.
+-- src/test/isolation/specs/async-notify.spec tests for actual usage.
+SELECT pg_notification_queue_usage();