Details
Major Description
Symptom
========
An AMQ broker that is configured to join a statically-defined (i.e., using uri="static:(tcp://host1:61616,tcp://host2:61616,tcp://..) ) network of brokers can have an extremely long startup time (in the order of 5+ minutes), if many of the brokers in the network are not alive.
The following log entires show the startup of an AMQ Broker (http://192.168.170.112:50000) that is configured to join a network with three other brokers:
http://10.10.60.78:50000
http://10.9.62.135:50000
http://10.10.60.75:50000)
The three other have not yet started.
The log file shows that it takes nearly 4 minutes from BrokerService#start() to return control to the calling thread (AlarmPoint Node-main):
2009-12-18 15:24:46,783 [AlarmPoint Node-main] INFO - - ActiveMQ 5.3.0 JMS Message Broker (localhost) is starting
...
2009-12-18 15:24:47,158 [AlarmPoint Node-main] INFO - - Connector http://192.168.170.112:50000 Started
2009-12-18 15:24:47,158 [AlarmPoint Node-main] INFO - - Establishing network connection from vm://localhost to http://10.10.60.78:50000
...
2009-12-18 15:26:11,314 [AlarmPoint Node-main] WARN - - Could not start network bridge between: vm://localhost and: http://10.10.60.78:50000 due to: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:26:11,314 [AlarmPoint Node-main] DEBUG - - Start failure exception: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:26:11,314 [AlarmPoint Node-main] INFO - - Establishing network connection from vm://localhost to http://10.9.62.135:50000
...
2009-12-18 15:27:35,299 [AlarmPoint Node-main] WARN - - Could not start network bridge between: vm://localhost and: http://10.9.62.135:50000 due to: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:27:35,299 [AlarmPoint Node-main] DEBUG - - Start failure exception: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:27:35,299 [AlarmPoint Node-main] INFO - - Establishing network connection from vm://localhost to http://10.10.60.75:50000
...
2009-12-18 15:28:59,314 [AlarmPoint Node-main] WARN - - Could not start network bridge between: vm://localhost and: http://10.10.60.75:50000 due to: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:28:59,314 [AlarmPoint Node-main] DEBUG - - Start failure exception: java.net.ConnectException: Connection timed out: connect
2009-12-18 15:28:59,314 [AlarmPoint Node-main] INFO - - Network Connector bridge Started
2009-12-18 15:28:59,314 [AlarmPoint Node-main] INFO - - ActiveMQ JMS Message Broker (localhost, ID:vic-esx4-ns1-1280-1261178686846-0:0) started
Cause
=====
The broker's network connector is implemented by org.apache.activemq.network.DiscoveryNetworkConnector, which in turn uses org.apache.activemq.transport.discovery.simple.SimpleDiscoveryAgent to determine whether the URLs configured in uri="static:(tcp://host1:61616,tcp://host2:61616,tcp://..) " are active. SimpleDiscoveryAgent#start() has this loop:
public void start() throws Exception {
running.set(true);
for (int i = 0; i < services.length; i++)
}
"listener.onServiceAdd(...) " is called for each URL and is implemented by DiscoveryNetworkConnector#onServiceAdd(...). The main thread calls BrokerService#start() which calls DiscoveryNetworkConnector#start() which calls SimpleDiscoveryAgent#start(), which sequentially calls DiscoveryNetworkConnector#onServiceAdd(...). Since the URLs being "discovered" are inactive, DiscoveryNetworkConnector#onServiceAdd(...) blocks ~1m30s (this will depend on network configuration) for each URL. This blocks the main thread that is trying to start the broker. If there are several inactive URLs, then the blocking time becomes excessive.
Solution
=======
If you follow through the DiscoveryNetworkConnector#onServiceAdd(...) method, it eventially calls SimpleDiscoveryAgent#serviceFailed(...) for each inactive URL. In turn SimpleDiscoveryAgent#serviceFailed(...) launches an asynchronous task that pauses for the configured reconnect delay, and then retries the call to DiscoveryNetworkConnector#onServiceAdd(...). So it must be safe to call DiscoveryNetworkConnector#onServiceAdd(...) concurrently. Therefore, SimpleDiscoveryAgent#start()'s loop should be changed to launch asynchronous tasks to make the DiscoveryNetworkConnector#onServiceAdd(...) calls concurrently rather than synchronously.
This solution has the benefit of returning control immediately to the caller of SimpleDiscoveryAgent#start(...), thus starting the broker faster, and allows the network discovery to find "active" URLs much faster (i.e., with the sequential loop, if the "active" URL is the last one, its discovery is significantly delayed).