The members of a service integration bus can be application servers, WebSphere MQ servers, or server clusters. Bus members that are application servers or server clusters contain messaging engines, which are the application server components that provide asynchronous messaging services.
To use a service integration bus, you must add at least one member that is an application server or server cluster.
You can also add bus members that are WebSphere MQ servers; service integration uses these bus members to write messages to, and read messages from, WebSphere MQ queues.
Adding a bus member automatically creates a messaging engine for that bus member. Each messaging engine has its own message store, used for example to store persistent messages and maintain durable subscriptions. Refer to Message stores for more details.
When the bus member is an application server, it can have only one messaging engine. If the bus member is a server cluster, it can have additional messaging engines to provide high availability or workload sharing characteristics. If the bus member is a WebSphere MQ server, it does not have a messaging engine, but it provides the ability to access WebSphere MQ queues directly from WebSphere MQ queue managers and queue-sharing groups.
To host queue-type destinations, the messaging engine can hold messages until consuming applications are ready to receive them. Each messaging engine also has a file store or a data store where it can hold messages so that if the messaging engine fails, messages are not lost.
When you define a queue-type destination, you assign it to a bus member. When that bus member is an application server or a server cluster, the messaging engine (or engines) in that bus member holds the messages. When that bus member is a WebSphere MQ server, service integration uses WebSphere MQ queues, which you specify when you define the destination, to hold messages.
If required, you can remove members from a bus. However, this action deletes any messaging engines that are associated with a bus member, including knowledge of any messages held by the message store for those messaging engines. Therefore, you must plan this action carefully.
When a bus member is deleted, the data source associated with this bus member is not automatically deleted, because users often associate their own data source with a bus member. This also applies to bus members created using the default data source: the data source is not automatically deleted and you must remove it manually.
It is not essential to remove the default data sources because they use a universal unique identifier (UUID) in the name of the Cloudscape Version 10.1.x (Derby) database. However, it is advisable to delete the data source to avoid wasting disk space.