0002-better-notification-structure-1.patch

diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 3f5f054..6cb2d44 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -351,8 +351,10 @@ static List *upperPendingActions = NIL; /* list of upper-xact lists */
  */
 typedef struct Notification
 {
-	char	   *channel;		/* channel name */
-	char	   *payload;		/* payload string (can be empty) */
+	uint16		channel_len;	/* length of channel-name string */
+	uint16		payload_len;	/* length of payload string */
+	/* null-terminated channel name, then null-terminated payload follow */
+	char		data[FLEXIBLE_ARRAY_MEMBER];
 } Notification;
 
 typedef struct NotificationList
@@ -417,7 +419,7 @@ static bool asyncQueueProcessPageEntries(volatile QueuePosition *current,
 										 Snapshot snapshot);
 static void asyncQueueAdvanceTail(void);
 static void ProcessIncomingNotify(void);
-static bool AsyncExistsPendingNotify(const char *channel, const char *payload);
+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);
@@ -569,6 +571,8 @@ pg_notify(PG_FUNCTION_ARGS)
 void
 Async_Notify(const char *channel, const char *payload)
 {
+	size_t		channel_len;
+	size_t		payload_len;
 	Notification *n;
 	MemoryContext oldcontext;
 
@@ -578,41 +582,53 @@ Async_Notify(const char *channel, const char *payload)
 	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 || !strlen(channel))
+	if (channel_len == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("channel name cannot be empty")));
 
-	if (strlen(channel) >= NAMEDATALEN)
+	/* enforce length limits */
+	if (channel_len >= NAMEDATALEN)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("channel name too long")));
 
-	if (payload)
-	{
-		if (strlen(payload) >= NOTIFY_PAYLOAD_MAX_LENGTH)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("payload string too long")));
-	}
-
-	/* no point in making duplicate entries in the list ... */
-	if (AsyncExistsPendingNotify(channel, payload))
-		return;
+	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(sizeof(Notification));
-	n->channel = pstrdup(channel);
+	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)
-		n->payload = pstrdup(payload);
+		strcpy(n->data + channel_len + 1, payload);
 	else
-		n->payload = "";
+		n->data[channel_len + 1] = '\0';
+
+	/* Now check for duplicates */
+	if (AsyncExistsPendingNotify(n))
+	{
+		/* It's a dup, so forget it */
+		pfree(n);
+		MemoryContextSwitchTo(oldcontext);
+		return;
+	}
 
 	if (pendingNotifies == NULL)
 	{
@@ -1303,8 +1319,8 @@ asyncQueueAdvance(volatile QueuePosition *position, int entryLength)
 static void
 asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
 {
-	size_t		channellen = strlen(n->channel);
-	size_t		payloadlen = strlen(n->payload);
+	size_t		channellen = n->channel_len;
+	size_t		payloadlen = n->payload_len;
 	int			entryLength;
 
 	Assert(channellen < NAMEDATALEN);
@@ -1317,8 +1333,7 @@ asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
 	qe->dboid = MyDatabaseId;
 	qe->xid = GetCurrentTransactionId();
 	qe->srcPid = MyProcPid;
-	memcpy(qe->data, n->channel, channellen + 1);
-	memcpy(qe->data + channellen + 1, n->payload, payloadlen + 1);
+	memcpy(qe->data, n->data, channellen + payloadlen + 2);
 }
 
 /*
@@ -1701,7 +1716,7 @@ AtSubCommit_Notify(void)
 		{
 			Notification *childn = (Notification *) lfirst(l);
 
-			if (!AsyncExistsPendingNotify(childn->channel, childn->payload))
+			if (!AsyncExistsPendingNotify(childn))
 				AddEventToPendingNotifies(childn);
 		}
 	}
@@ -2159,29 +2174,18 @@ NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
 		elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload);
 }
 
-/* Does pendingNotifies include the given channel/payload? */
+/* Does pendingNotifies include a match for the given event? */
 static bool
-AsyncExistsPendingNotify(const char *channel, const char *payload)
+AsyncExistsPendingNotify(Notification *n)
 {
 	if (pendingNotifies == NULL)
 		return false;
 
-	if (payload == NULL)
-		payload = "";
-
 	if (pendingNotifies->hashtab != NULL)
 	{
 		/* Use the hash table to probe for a match */
-		Notification n;
-		Notification *k;
-
-		/* set up a dummy Notification struct */
-		n.channel = unconstify(char *, channel);
-		n.payload = unconstify(char *, payload);
-		k = &n;
-		/* ... and probe */
 		if (hash_search(pendingNotifies->hashtab,
-						&k,
+						&n,
 						HASH_FIND,
 						NULL))
 			return true;
@@ -2193,10 +2197,12 @@ AsyncExistsPendingNotify(const char *channel, const char *payload)
 
 		foreach(l, pendingNotifies->events)
 		{
-			Notification *n = (Notification *) lfirst(l);
+			Notification *oldn = (Notification *) lfirst(l);
 
-			if (strcmp(n->channel, channel) == 0 &&
-				strcmp(n->payload, payload) == 0)
+			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;
 		}
 	}
@@ -2278,16 +2284,11 @@ static uint32
 notification_hash(const void *key, Size keysize)
 {
 	const Notification *k = *(const Notification *const *) key;
-	uint32		hashc;
-	uint32		hashp;
 
 	Assert(keysize == sizeof(Notification *));
-	/* We just XOR the hashes for the two strings */
-	hashc = DatumGetUInt32(hash_any((const unsigned char *) k->channel,
-									(int) strlen((const char *) k->channel)));
-	hashp = DatumGetUInt32(hash_any((const unsigned char *) k->payload,
-									(int) strlen((const char *) k->payload)));
-	return hashc ^ hashp;
+	/* 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));
 }
 
 /*
@@ -2300,8 +2301,10 @@ notification_match(const void *key1, const void *key2, Size keysize)
 	const Notification *k2 = *(const Notification *const *) key2;
 
 	Assert(keysize == sizeof(Notification *));
-	if (strcmp(k1->channel, k2->channel) == 0 &&
-		strcmp(k1->payload, k2->payload) == 0)
+	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 */
 }