Martin, message groups (by design) guarantee that only a single consumer will process messages for a group at a time. It preserves ordering of related/group messages by single threading their processing while still allowing concurrent processing of the queue as a whole (each group has it's own thread/consumer)...
Martin C. wrote: > > Hi, > > My issue is that in a dynamically load-balancing scenario with scaling > the number of consumers up/down, long-living consumers will tend to > gather all available message groups and newly created won't have > anything available. Even if a newly created consumer gets a new > message group, it will only receive this new message group and in case > messages within a group are rare, it is likely to be removed by > downscaling after some idle time, as all other messages went to the > older consumer, releasing the message group and making it more likely > that the long-living consumer will also get one of those messages and > gets this group assigned additionally to all the ones it already has. > > I was thinking about using JMSXGroupSeq as well, but as far as I > understand it (and the linked article), it wouldn't help me to reach > my goal: I want to consume messages within a group one at a time, > where I don't care which consumer consumes it, though. I want to > ensure the following: > > Producer produces Msg1, Msg2, Msg3 within Group1. > Consumer1: handles Msg1 > Consumer1: handles Msg2 > Consumer2: handles Msg3 > > All I care about is, that Msg1 and Msg2 and Msg3 are not consumed in > parallel. As far as I understood, setting JMSXGroupSeq to -1 on the > three messages wouldn't give me this guarantee, would it? It would > rather result in Msg1 being consumed by Consumer1 and Msg2 being > consumed by Consumer 2 in parallel, wouldn't it? > > Thanks for your input! > > Best regards, > Martin > > On Fri, Jul 1, 2011 at 6:21 AM, boday > <ben.o...@initekconsulting.com> wrote: >> Is your issue that certain consumers become too slow? If so, you can >> always >> set the JMSXGroupSeq header to -1 to force a new consumer (maybe set this >> periodically or after a certain number of messages)... >> >> here is a good article that discusses this a bit... >> >> http://scottcranton.blogspot.com/2010/09/activemq-message-groups.html >> >> Either way, I'd think this could be a feature of the message groups. >> Basically let you specify a frequency (either elapsed time or message >> count) >> to force a new consumer for a group. Would serve to better randomize the >> load across consumers to protect against slow consumers, etc... >> >> >> Martin C. wrote: >>> >>> Hi, >>> >>> we currently use message groups to ensure ordered delivery of messages >>> within a given group. As noted on the documentation for message >>> groups, this often does not scale very well with variable consumer >>> counts, as in this case the oldest consumers will hog all message >>> groups. >>> >>> In our use-case, and I suppose this might apply to others as well, we >>> simply don't care which consumer consumes which message, but only, >>> that the next message from the same message group is not consumed >>> before the first has been processed. So my idea would be to add a >>> configuration option, that a consumer will release the message group >>> directly after consuming its current message, releasing the message >>> group for re-distribution to other brokers. >>> >>> Would something like this be possible / do I overlook some downside of >>> this approach? >>> >>> Best regards, >>> Martin >>> >> >> >> -- >> View this message in context: >> http://activemq.2283324.n4.nabble.com/Fwd-Message-groups-enhancement-feature-request-tp3635293p3637432.html >> Sent from the ActiveMQ - User mailing list archive at Nabble.com. >> > -- View this message in context: http://activemq.2283324.n4.nabble.com/Fwd-Message-groups-enhancement-feature-request-tp3635293p3638261.html Sent from the ActiveMQ - User mailing list archive at Nabble.com.
