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From Celso Pinto <cpi...@7syntax.com>
Subject activemq stops dispatching messages aborting transaction (STOMP)
Date Tue, 17 Jun 2008 21:28:58 GMT
Hi all,

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.

TIA,
Celso



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