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  1. Qpid Dispatch
  2. DISPATCH-1481

Multicast producers should block on credit until consumers are present



    • Bug
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 1.8.0, 1.9.0
    • 1.10.0
    • Router Node
    • None


      For all anycast forwarding treatments (balanced, closest, etc.)  the router does not provide capacity (credit) to the publisher until the router is aware of at least one consumer for that address. This allows the application to avoid sending messages that the router will simply RELEASE due to lack of consumers.

      This is not the case for multicast producers (specifically, ingress links with a multicast target address).  In fact, the router's behavior has varied over several releases (both intentionally and unintentionally):

      • pre 1.0: mcast credit was consistent with anycast - block until consumers present
      • at 1.0 mcast credit was change to always be provided regardless of the presence of consumers (DISPATCH-779)
      • at some point after 1.2 the router began returning RELEASED outcome for unsettled multicast.  This appears to be unintentional (and reveals a hole in the system test suite) as it can force an infinite loop as credit will automatically be replenished (per DISPATCH-779).
      • in 1.9.0 the router's handling of unsettled multicast outcomes was corrected and brought in line with the handling of anycast unsettled messages DISPATCH-1266. This change ended up codifying the RELEASED on no-consumer behavior as intentional, but did not address the infinite credit loop issue.

      The router should be consistent in the way it manages credit regardless of the forwarding treatment. Providing an unlimited credit supply can result in an infinite transmit->RELEASE->retransmit loop.


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              kgiusti Ken Giusti
              kgiusti Ken Giusti
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