Stirling Chow created AMQ-4148:
----------------------------------
Summary: Static subscriptions from network bridges do not respect
TTL (off by one in calculation), resulting in duplicate consumers.
Key: AMQ-4148
URL: https://issues.apache.org/jira/browse/AMQ-4148
Project: ActiveMQ
Issue Type: Bug
Affects Versions: 5.8.0
Reporter: Stirling Chow
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:
{code:title=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;
}
{code}
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:
{code:title=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);
...
{code}
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 propagate one further hop than their dynamic
counterparts. In the case of a network TTL of 1, the static subscription
consumers are unexpected 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).
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