On 6/20/06, Thomas Swindells <[EMAIL PROTECTED]> wrote:
James.Strachan wrote:
>
> On 6/19/06, Sanjiv Jivan <[EMAIL PROTECTED]> wrote:
>> > 2. Is there a way to detach a message group affinity to a particular
>> broker.
>>
>> >Just set JMSXGroupSeq to zero on the last message which 'closes' the
>> >message group so if another message is sent in the future with the
>> >same group ID it will be reassigned to a new consumer.
>>
>> >message.setIntProperty("JMSXGroupSeq", 0);
>>
>> This would reset all the affinity of all the message groups, right?
>
> No - just the message group for the JMSXGroupId setting.
> I should have been more clear... to clear message group FOO use
>
> message.setStringProperty("JMSXGroupID", "FOO");
> message.setIntProperty("JMSXGroupSeq", 0);
>
Reading the Message group page
(http://activemq.org/site/message-groups.html) there is probably a minor bug
here in that it would close all messsage groups with the same Hash as "FOO",
although in practice for a well designed system expecting that msg groups
could change this shouldn't be a problem. Of course the chances of a hash
clash for relatively short group id's is pretty tiny.
Yeah - hashing collisions should be fairly unlikely - though its a RAM
v risk tradeoff - the larger the number of hash buckets, the more RAM
used but the less likely a collision.
Though worse case a message group is closed and reopened - which just
rebalances the association of message groups to consumers so it
doesn't cause much harm (*).
(*) if there are lots of in-fight messages in-process and more
messages are sent after the close, then there's a small window where
ordering could break. So its generally easier to kill the consumer
who's consuming a message group to ensure that no overlap occurs.
--
James
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