[ https://issues.apache.org/activemq/browse/AMQ-855?page=comments#action_36716 ] james strachan commented on AMQ-855: ------------------------------------
Andrew I just commented on this thread on why a prefetch of 1 is the lowest possible value to have while still fully implementing the JMS spec... http://www.nabble.com/forum/ViewPost.jtp?post=5583273&framed=y A few further comments... > Now, you could in theory hack together a "pull" model by setting prefetch > size = 0, so that basically each ack is a request for the next message Thats a prefetch of 1. With a prefetch of zero no messages would be dispatched so there could be no ack :) > Systems like this need to be designed under the assumption that clients will > not behave themselves. > They will deadlock themselves, slow down arbitrarily, boxes will go up and > down, etc. > These things happen all the time in real life and shouldn't have adverse > effects on other, well-behaved consumers. This is a valid problem - a badly behaving consumer can hog a message. However changing from a push to pull model or having prefetch of 0 or 1 will not change this. A hogged message is a hogged message however the consumer manages to get the message (pull or push). e.g. if we did implement prefetch of zero - which means don't deliver a message to a consumer at all - unless they perform a consumer.receive() - even then, the consumer could then hang/deadlock and never actually acknowledge or process the message. The workaround to this is to just kill consumers if they take too long to process a message - see this JIRA which I think what you really need http://issues.apache.org/activemq/browse/AMQ-850 > Add support for prefetchSize = 0 > -------------------------------- > > Key: AMQ-855 > URL: https://issues.apache.org/activemq/browse/AMQ-855 > Project: ActiveMQ > Issue Type: New Feature > Components: Broker > Affects Versions: 4.0, 4.0.1, 4.0.2 > Environment: any > Reporter: Vadim Pesochinskiy > Priority: Critical > Fix For: 4.2 > > > This feature would enable to support following test case: > 2 servers are processing 3 submitted jobs with following processing times 10 > min, 1 min, 1 min. This sequence should finish in 10 minutes as one service > will pick up the 10 minutes job, meanwhile the other one should manage the > two 1 minute jobs. Since I cannot set prefetchSize=0, one of the 1 minute > jobs is sitting in prefetch buffer and the jobs are processed in 11 minutes > instead of 10. > This is simplification of the real scenario where I have about 30 consumers > submitting jobs to 20 consumers through AMQ 4.0.1. I have following problems: > Messages are sitting in prefetch buffer are not available to processors, > which results in a lot of idle time. > Order of processing is random. For some reason Job # 20 is processed after > Job # 1500. Since senders are synchronously blocked this can result in > time-outs. > Some requests are real-time, i.e. there is a user waiting, so the system > cannot wait, so AMQ-850 does not fix this issue. -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: https://issues.apache.org/activemq/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira
