[jboss-jira] [JBoss JIRA] (WFLY-9688) Messaging - default max client threads

[Kabir Khan (JIRA)]

Kabir Khan created WFLY-9688:
--------------------------------

             Summary: Messaging - default max client threads
                 Key: WFLY-9688
                 URL: https://issues.jboss.org/browse/WFLY-9688
             Project: WildFly
          Issue Type: Enhancement
          Components: JMS
    Affects Versions: 11.0.0.Final
            Reporter: Martin Styk
            Assignee: Jeff Mesnil


By default, size of client thread pool is configured as 8 * number of CPU cores.

On 1 CPU machine, with default configuration and MDB deployed on server, resource starvation is possible
On one CPU there are by default
* 8 ActiveMQ client threads (8 * CPU count)
* 4 MDB instances (mdb-strict-max-pool = 4 * CPU count)
* 15 JCA RA sessions consuming messages from queue (default value of maxSession)

Consuming of messages by MDB gets stuck because all 8 client threads are awaiting large message completion and there is no other thread to handle other tasks.

{code:title=Client thread waiting for large message completion}
"Thread-7 (ActiveMQ-client-global-threads)" #475 daemon prio=5 os_prio=0
tid=0x000000000590f000 nid=0x7c7a in Object.wait() [0x00007fda43413000]
      java.lang.Thread.State: TIMED_WAITING (on object monitor)
           at java.lang.Object.wait(Native Method)
           at
           org.apache.activemq.artemis.core.client.impl.LargeMessageControllerImpl.waitCompletion(LargeMessageControllerImpl.java:302)
           - locked <0x00000000b0083e88> (a
           org.apache.activemq.artemis.core.client.impl.LargeMessageControllerImpl)
           at
           org.apache.activemq.artemis.core.client.impl.LargeMessageControllerImpl.saveBuffer(LargeMessageControllerImpl.java:276)
           - locked <0x00000000b0083e88> (a
           org.apache.activemq.artemis.core.client.impl.LargeMessageControllerImpl)
           at
           org.apache.activemq.artemis.core.client.impl.ClientLargeMessageImpl.checkBuffer(ClientLargeMessageImpl.java:159)
           at
           org.apache.activemq.artemis.core.client.impl.ClientLargeMessageImpl.checkCompletion(ClientLargeMessageImpl.java:84)
           at
           org.apache.activemq.artemis.jms.client.ActiveMQMessage.doBeforeReceive(ActiveMQMessage.java:786)
           at
           org.apache.activemq.artemis.jms.client.ActiveMQTextMessage.doBeforeReceive(ActiveMQTextMessage.java:110)
           at
           org.apache.activemq.artemis.ra.inflow.ActiveMQMessageHandler.onMessage(ActiveMQMessageHandler.java:295)
           at
           org.apache.activemq.artemis.core.client.impl.ClientConsumerImpl.callOnMessage(ClientConsumerImpl.java:1001)
           at
           org.apache.activemq.artemis.core.client.impl.ClientConsumerImpl.access$400(ClientConsumerImpl.java:49)
           at
           org.apache.activemq.artemis.core.client.impl.ClientConsumerImpl$Runner.run(ClientConsumerImpl.java:1124)
           at
           org.apache.activemq.artemis.utils.OrderedExecutorFactory$OrderedExecutor$ExecutorTask.run(OrderedExecutorFactory.java:122)
           at
           java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
           at
           java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
           at java.lang.Thread.run(Thread.java:748)
{code}


This can be fixed by adjusting default values for these parameters.
In this case, we need more client threads than JCA RA sessions (maxSession). 

To avoid resource starvation, number of client threads must be greater than sum of {{maxSession}} for each MDB deployed on server.
We should check number of client threads required by deployments (MDBs), and at least print warning message that size of client thread pool may be insufficient.




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