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 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.

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:

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.

Pausing a connection service has the following effects:

The admin connection service can never be paused; to pause and resume any other service, use the subcommands imqcmd pause svc and imqcmd resume svc. The syntax of the imqcmd pause svc subcommand is as follows:

For example, the following command pauses the httpjms service running on the default broker (host localhost at port 7676):

The imqcmd resume svc subcommand resumes operation of a connection service following a pause:

You can use the imqcmd update svc subcommand to change the value of one or more of the service properties listed in Table 6-2. See Connection Properties for a description of these properties.

Table 6-2 Connection Service Properties Updated by Command Utility

The imqcmd update svc subcommand has the following syntax:

For example, the following command changes the minimum number of threads assigned to the jms connection service on the default broker (host localhost at port 7676) to 20:

To list the connection services available on a broker, use the imqcmd list svc subcommand:

For example, the following command lists all services on the default broker (host localhost at port 7676):

Example 6-1 shows an example of the resulting output.

Example 6-1 Connection Services Listing

The imqcmd query svc subcommand displays information about a single connection service:

For example, the following command displays information about the jms connection service on the default broker (host localhost at port 7676):

Example 6-2 shows an example of the resulting output.

Example 6-2 Connection Service Information Listing

To display metrics information about a connection service, use the imqcmd metrics svc subcommand:

The -m option specifies the type of metric information to display:

The -int and -msp options specify, respectively, the interval (in seconds) at which to display the metrics and the number of samples to display in the output. The default values are 5 seconds and an unlimited number of samples.

For example, the following command displays cumulative totals for messages and packets handled by the default broker (host localhost at port 7676) by way of the jms connection service:

Example 6-3 shows an example of the resulting output.

Example 6-3 Connection Service Metrics Listing

For a more detailed description of the use of the Command utility to report connection service metrics, see Connection Service Metrics.