[AMQ-4148] Static subscriptions from network bridges do not respect TTL (off by one in calculation), resulting in duplicate consumers.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.8.0
• Fix Version/s: 5.8.0
• Patch Info: Patch Available
• Assignee: Unassigned
• Reporter: Stirling Chow
• Created: 31/Oct/12 06:22
• Updated: 24/Jan/13 18:41
• Resolved: 24/Jan/13 18:41

Description

Symptom
=======
The remote broker path is not set on network consumers that result from static subscriptions; as a result, they are forwarded to other bridges even when the network TTL on the bridges is 1. In an n+1 hub-and-spoke network, the next broker to join receives n subscriptions instead of 1.

Cause
=====
A consumer for a static subscriptions is created by the following code:

DemandForwardingBridgeSupport.java

private void startLocalBridge() throws Throwable {
...
    if (!disposed.get()) {
            setupStaticDestinations();
        } else {
            LOG.warn("Network connection between " + localBroker + " and " + remoteBroker + "(" + remoteBrokerName + ") was interrupted during establishment.");
        }
    }
}

/**
 * Subscriptions for these destinations are always created
 */
protected void setupStaticDestinations() {
...
            DemandSubscription sub = createDemandSubscription(dest);
            try {
                addSubscription(sub);
            } catch (IOException e) {
                LOG.error("Failed to add static destination " + dest, e);
            }
            if (LOG.isTraceEnabled()) {
                LOG.trace("bridging messages for static destination: " + dest);
            }
        }
    }
}

final protected DemandSubscription createDemandSubscription(ActiveMQDestination destination) {
    ConsumerInfo info = new ConsumerInfo();
    info.setDestination(destination);

    // the remote info held by the DemandSubscription holds the original consumerId,
    // the local info get's overwritten
    info.setConsumerId(new ConsumerId(localSessionInfo.getSessionId(), consumerIdGenerator.getNextSequenceId()));
    DemandSubscription result = null;
    try {
        result = createDemandSubscription(info);
    } catch (IOException e) {
        LOG.error("Failed to create DemandSubscription ", e);
    }
    return result;
}

Note how the broker path is not set on the ConsumerInfo that is used for the subscription.

In contrast, a consumer for a dynamic subscription does have its broker path updated to indicate that it is from a remote broker:

DemandForwardingBridgeSupport.java

protected void serviceRemoteCommand(Command command) {
    if (!disposed.get()) {
        try {
            if (command.isMessageDispatch()) {
                safeWaitUntilStarted();
                MessageDispatch md = (MessageDispatch) command;
                serviceRemoteConsumerAdvisory(md.getMessage().getDataStructure());
                ackAdvisory(md.getMessage());
...

private void serviceRemoteConsumerAdvisory(DataStructure data) throws IOException {
...
        if (addConsumerInfo(info)) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug(configuration.getBrokerName() + " bridged sub on " + localBroker + " from " + remoteBrokerName + " : " + info);
                }
            } else {
                if (LOG.isDebugEnabled()) {
                    LOG.debug(configuration.getBrokerName() + " Ignoring sub from " + remoteBrokerName + " as already subscribed to matching destination : " + info);
                }
            }
        }
...

protected boolean addConsumerInfo(final ConsumerInfo consumerInfo) throws IOException {
    boolean consumerAdded = false;
    ConsumerInfo info = consumerInfo.copy();
    addRemoteBrokerToBrokerPath(info);
...

Because of this difference, a static subscription will be forwarded to new bridges with a null brokerPath while a dynamic subscription to the same queue will be forwarded with a singleton brokerPath. As a result, static subscriptions will be propagated one further hop than their dynamic counterparts. In the case of a network TTL of 1, the static subscription consumers from existing bridges are unexpectedly propagated to new bridges, while the dynamic subscription consumers are correctly suppressed.

Solution
========
There should be no logical difference between a network consumer created for a static subscription vs. a dynamic subscription. In either case, the bridge creates a consumer on behalf of the remote broker. As such, the consumer for a static subscription should have the remote broker in its broker path because it represents a subscription from that remote broker (even if there is no consumer).