And suddenly it works. Testing showed that removing the crude limit UNSENT_MESSAGE_LIMIT made performance better. This then made me wonder if the unblock and notify_sent messages weren't getting through fast enough, and sure enough, using pcast is much better there. Also, turning on dbg:tpl showed that the common path in mixed_queue was to call publish_delivered (i.e. the message has been delivered to a consumer, we just need to record this fact). Making sure everything in there for the non-persistent, non-durable but disk-only mode is asynchronous also helped performance massively.

3 files changed, 17 insertions, 14 deletions

diff --git a/src/rabbit_amqqueue.erl b/src/rabbit_amqqueue.erl
index a5c58f2358..01d40aa1a8 100644
--- a/src/rabbit_amqqueue.erl
+++ b/src/rabbit_amqqueue.erl
@@ -309,10 +309,10 @@ basic_cancel(#amqqueue{pid = QPid}, ChPid, ConsumerTag, OkMsg) ->
                           infinity).
 
 notify_sent(QPid, ChPid) ->
-    gen_server2:cast(QPid, {notify_sent, ChPid}).
+    gen_server2:pcast(QPid, 10, {notify_sent, ChPid}).
 
 unblock(QPid, ChPid) ->
-    gen_server2:cast(QPid, {unblock, ChPid}).
+    gen_server2:pcast(QPid, 10, {unblock, ChPid}).
 
 constrain_memory(QPid, Constrain) ->
     gen_server2:pcast(QPid, 10, {constrain, Constrain}).
diff --git a/src/rabbit_amqqueue_process.erl b/src/rabbit_amqqueue_process.erl
index 6ad4e4e6b7..d325346c9e 100644
--- a/src/rabbit_amqqueue_process.erl
+++ b/src/rabbit_amqqueue_process.erl
@@ -208,7 +208,7 @@ deliver_queue(Fun, FunAcc0,
                                true -> deliver_queue(Fun, FunAcc1, State3)
                             end
                     end;
-                %% if IsMsgReady then (AckRequired and we've hit the limiter)
+                %% if IsMsgReady then we've hit the limiter
                 false when IsMsgReady ->
                     store_ch_record(C#cr{is_limit_active = true}),
                     NewConsumers = block_consumers(ChPid, RoundRobinTail),
@@ -245,8 +245,8 @@ attempt_immediate_delivery(none, _ChPid, Msg, State) ->
             (AckRequired, false, State2) ->
                 {AckTag, State3} =
                     if AckRequired ->
-                            {ok, AckTag2, MS} = rabbit_mixed_queue:publish_delivered(Msg,
-                                                                                     State2 #q.mixed_state),
+                            {ok, AckTag2, MS} = rabbit_mixed_queue:publish_delivered(
+                                                  Msg, State2 #q.mixed_state),
                             {AckTag2, State2 #q { mixed_state = MS }};
                        true ->
                             {noack, State2}
diff --git a/src/rabbit_mixed_queue.erl b/src/rabbit_mixed_queue.erl
index 4dce52e70f..a950584a10 100644
--- a/src/rabbit_mixed_queue.erl
+++ b/src/rabbit_mixed_queue.erl
@@ -187,16 +187,19 @@ publish_delivered(Msg =
                   State = #mqstate { mode = Mode, is_durable = IsDurable,
                                      next_write_seq = NextSeq, queue = Q })
   when Mode =:= disk orelse (IsDurable andalso IsPersistent) ->
-    true = rabbit_disk_queue:is_empty(Q),
     rabbit_disk_queue:publish(Q, MsgId, msg_to_bin(Msg), false),
-    %% must call phantom_deliver otherwise the msg remains at the head
-    %% of the queue
-    {MsgId, false, AckTag, 0} = rabbit_disk_queue:phantom_deliver(Q),
-    State2 =
-	if Mode =:= mixed -> State #mqstate { next_write_seq = NextSeq + 1 };
-	   true -> State
-	end,
-    {ok, AckTag, State2};
+    if IsDurable andalso IsPersistent ->
+            %% must call phantom_deliver otherwise the msg remains at
+            %% the head of the queue. This is synchronous, but
+            %% unavoidable as we need the AckTag
+            {MsgId, false, AckTag, 0} = rabbit_disk_queue:phantom_deliver(Q),
+            {ok, AckTag, State};
+       true ->
+            %% in this case, we don't actually care about the ack, so
+            %% auto ack it (asynchronously).
+            ok = rabbit_disk_queue:auto_ack_next_message(Q),
+            {ok, noack, State #mqstate { next_write_seq = NextSeq + 1 }}
+    end;
 publish_delivered(_Msg, State = #mqstate { mode = mixed, msg_buf = MsgBuf }) ->
     true = queue:is_empty(MsgBuf),
     {ok, noack, State}.