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this setting does not influence transactional scope. Increase this value (for example, to 8) for
activation specs that are associated with SCA modules and long-running business processes
to improve performance and scalability, especially for large multi-core systems.
Configuring thread pool sizes
The sizes of thread pools have a direct impact on the ability of a server to run applications
concurrently. For maximum concurrency, you must set the thread pool sizes to optimal values.
Increasing the maxConcurrency parameter or Maximum sessions parameter only enables the
concurrent delivery of business objects from the JMS or WebSphere MQ queues. For a
Business Process Manager server to process multiple requests concurrently, you must
increase the corresponding thread pool sizes to allow higher concurrent execution of these
MDB threads.
MDB work is dispatched to threads allocated from the default thread pool. All MDBs in the
application server share this thread pool unless a different thread pool is specified. This
condition means that the default thread pool size needs to be larger, probably significantly
larger, than the maxConcurrency parameter of any individual MDB.
Threads in the WebContainer thread pool are used for handling incoming HTTP and web
services requests. This thread pool is shared by all applications deployed on the server, and
you must tune it, likely to a higher value than the default.
Object request broker (ORB) thread pool threads are employed for running ORB requests (for
example, remote EJB calls). The thread pool size needs to be large enough to handle
requests coming through the interface, such as certain human task manager APIs.
Configuring dedicated thread pools for message-driven beans
The default thread pool is shared by many WebSphere Application Server tasks. It is
sometimes preferable to separate the execution of JMS MDBs to a dedicated thread pool.
Complete the following steps to change the thread pool used for JMS MDB threads:
1. Create a thread pool (for example, MDBThreadPool) on the server by clicking Servers
Server Types WebSphere application servers server Thread pools. Then
click New.
2. Open the service integration bus (SIB) JMS Resource Adapter administrative console with
server scope by clicking Resources Resource Adapters Resource adapters. If
the adapter is not visible, go to Preferences, and select the Show built-in resources
check box.
3. Change the thread pool alias from Default to MDBThreadPool.
4. Repeat steps 2 and 3 for SIB JMS resource adapters at the node and cell scope.
5. Restart the server so that the changes become effective.
SCA Module MDBs for asynchronous SCA calls use a separate resource adapter, the
Platform Messaging Component SPI Resource Adapter. Follow the same steps to change the
thread pool to a different one if you want.
Even with a dedicated thread pool, all MDBs that are associated with the resource adapter
still share a thread pool. However, they do not have to compete with other WebSphere
Application Server tasks that also use the default thread pool.
Configuring JMS and JMS service queue connection factories
Multiple concurrently running threads might cause bottlenecks on resources such as JMS
and database connection pools if such resources are not tuned properly. The Maximum
Connections pool size parameter specifies the maximum number of physical connections
that can be created in this pool. These physical connections interface with back-end
Chapter 4. Performance tuning and configuration 65