Message throttling from a solace queue

@smpapas, you state "Most of the messages". Just confirming that there are messages getting to the 2nd instance of the application. Can you confirm that the Queue setting for Access Type is set to Non-Exclusive (Exclusive is set by default). Also confirm that you have 6 client connections from the web admin console.

@smpapas You can scale the ThreadPoolTaskExecutor to ensure you have an appropriate amount of threads to handle the incoming message rate. You can define a publish-subscribe channel that uses the thread pool and has a queue capacity. If that queue capacity is reached, the consumer thread will receive an exception attempting to put the message into that pubsub channel (from Spring Integration). You can issue a sleep or other logic to delay delivery of that message until the ThreadPool can catch up. The rejectedExecutionHandler is a handler for such logic. I simply tried to put the message back onto the channel for processing.

Here is an example of what I've done in the past and has worked for me.

   <int:publish-subscribe-channel id="msg.service" task-executor="taskExecutor"/>
   <beans:bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
        <beans:property name="corePoolSize" value="1" />
        <beans:property name="maxPoolSize" value="${service.max-thread-count}" />
        <beans:property name="queueCapacity" value="100" />
        <beans:property name="rejectedExecutionHandler" ref="blockCallerExecutionPolicy" />
    </beans:bean>

If I remember correctly, the executor is the same thread as the consumer thread. You may want to verify that.

public class BlockCallerExecutionPolicy implements RejectedExecutionHandler {
    private static final Logger logger = LoggerFactory.getLogger(BlockCallerExecutionPolicy.class);

    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        try {
            logger.info("Putting message back on queue for processing.");
            executor.getQueue().put(r);
        }
        catch (InterruptedException e) {
            throw new RejectedExecutionException("Unexpected InterruptedException while waiting to add Runnable to ThreadPoolExecutor queue...", e);
        }
    }
}