Details
Critical Description
As requested by Dejan Bosanac, I'm adding this ticket. I'm willing to help fix it, ie. I can get my hands dirty, but I must have some pointers on where to look because (unfortunately) I don't have much time to learn ActiveMQ's internals and architecture.
A copy of the email I sent to the users mailing-list:
=============================================
I'm currently struggling to understand the reason behind that's causing the behaviour described in the subject: I'm connecting to activemq via stomp on a python app. Because I need to have the messages rolled back in case of some processing failure I'm wrapping the message processing in the following way:
message received -> start transaction -> ack message in transaction ->
process message -> if no exception commit tx, else rollback transaction
AFAIK, this is the only way of making message unacknowledgement possible with stomp. Also, this is a single client connection, ie. I'm using a
single client connection to create a message processing daemon, all messages are sent and received via this single connection to the MQ server.
Here's a telnet session that can be used to reproduce the problem (open jconsole and send 5 text messages to the queue):
% telnet localhost 61613
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
CONNECT
^@
CONNECTED
session:ID:starfish-53281-1213736462979-2:2
SUBSCRIBE
destination: /queue/testq
ack: client
activemq.prefetchSize: 1
^@
MESSAGE
message-id:ID:starfish-53281-1213736462979-3:3:1:1:1
destination:/queue/testq
timestamp:1213736837743
expires:0
priority:0
1
BEGIN
transaction: 1
^@
ACK
message-id:ID:starfish-53281-1213736462979-3:3:1:1:1
transaction: 1
^@
MESSAGE
message-id:ID:starfish-53281-1213736462979-3:4:1:1:1
destination:/queue/testq
timestamp:1213736840224
expires:0
priority:0
2
MESSAGE
message-id:ID:starfish-53281-1213736462979-3:5:1:1:1
destination:/queue/testq
timestamp:1213736842611
expires:0
priority:0
3
ABORT
transaction: 1
^@
BEGIN
transaction:2
^@
ACK
message-id:ID:starfish-53281-1213736462979-3:4:1:1:1
transaction:2
^@
ABORT
transaction:2
^@
ACK
message-id:ID:starfish-53281-1213736462979-3:5:1:1:1
^@
I see a couple of issues here:
#1) even though I specified activemq.prefetchSize to 1 in the subscription command, the connector dispatches two messages in a row
#2) no more messages are dispatched after aborting the transaction/acknowledging the last received message. Even if the second message isn't wrapped in a transaction, message dispatch stops there.
To add to the confusion, if I don't use transactions at all, my client keeps getting messages, one by one, ie. no two messages are sent together, I only get a new message after ACK'ing the previous one.
I think I may be stepping into the realms of a buggy STOMP connector. Please tell me if I'm missing something obvious that fixes this issue
(hence making it a non-issue) or if indeed the STOMP connector has problems.