Configuring Connection Services

Broker configuration properties related to connection services are listed under Connection Properties.

Figure 6-1 shows the connection services provided by the Message Queue broker.

Figure 6-1 Message Queue Connection Services

These connection services are distinguished by two characteristics, as shown in Table 6-1:

• The service type specifies whether the service provides JMS message delivery (NORMAL) or Message Queue administration services ( ADMIN).

• The protocol type specifies the underlying transport protocol.

Table 6-1 Message Queue Connection Service Characteristics

By setting a broker’s imq.service.activelist property, you can configure it to run any or all of these connection services. The value of this property is a list of connection services to be activated when the broker is started up; if the property is not specified explicitly, the jms and admin services will be activated by default.

Each connection service also supports specific authentication and authorization features; see Introduction to Security Services for more information.

Port Mapper

Each connection service is available at a particular port, specified by host name (or IP address) and port number. You can explicitly specify a static port number for a service or have the broker’s Port Mapper assign one dynamically. The Port Mapper itself resides at the broker’s primary port, which is normally located at the standard port number 7676. (If necessary, you can use the broker configuration property imq.portmapper.port to override this with a different port number.) By default, each connection service registers itself with the Port Mapper when it starts up. When a client creates a connection to the broker, the Message Queue client runtime first contacts the Port Mapper, requesting a port number for the desired connection service.

Alternatively, you can override the Port Mapper and explicitly assign a static port number to a connection service, using the imq.serviceName.protocolType. port configuration property (where serviceName and protocolType identify the specific connection service, as shown in Table 6-1). (Only the jms, ssljms, admin, and ssladmin connection services can be configured this way; the httpjms and httpsjms services use different configuration properties, described in Appendix C, HTTP/HTTPS Support). Static ports are generally used only in special situations, however, such as in making connections through a firewall (see Connecting Through a Firewall), and are not recommended for general use.

When multiple Port Mapper requests are received concurrently, they are stored in an operating system backlog while awaiting action. The imq.portmapper.backlog property specifies the maximum number of such backlogged requests. When this limit is exceeded, any further requests will be rejected until the backlog is reduced.

Thread Pool Management

Each connection service is multithreaded, supporting multiple connections. The threads needed for these connections are maintained by the broker in a separate thread pool for each service. As threads are needed by a connection, they are added to the thread pool for the service supporting that connection.

The threading model you choose specifies whether threads are dedicated to a single connection or shared by multiple connections:

• In the dedicated model, each connection to the broker requires two threads: one for incoming and one for outgoing messages. This limits the number of connections that can be supported, but provides higher performance.

• In the shared model, connections are processed by a shared thread when sending or receiving messages. Because each connection does not require dedicated threads, this model increases the number of possible connections, but at the cost of lower performance because of the additional overhead needed for thread management.

The broker’s imq.serviceName. threadpool_model property specifies which of the two models to use for a given connection service. This property takes either of two string values: dedicated or shared. If you don’t set the property explicitly, dedicated is assumed by default.

You can also set the broker properties imq.serviceName. min_threads and imq.serviceName. max_threads to specify a minimum and maximum number of threads in a service’s thread pool. When the number of available threads exceeds the specified minimum threshold, Message Queue will shut down threads as they become free until the minimum is reached again, thereby saving on memory resources. Under heavy loads, the number of threads might increase until the pool’s maximum number is reached; at this point, new connections are rejected until a thread becomes available.

The shared threading model uses distributor threads to assign threads to active connections. The broker property imq.shared.connectionMonitor_limit specifies the maximum number of connections that can be monitored by a single distributor thread. The smaller the value of this property, the faster threads can be assigned to connections. The imq.ping.interval property specifies the time interval, in seconds, at which the broker will periodically test (“ping”) a connection to verify that it is still active, allowing connection failures to be detected preemptively before an attempted message transmission fails.