Comparing Publish, Routing and Service Callout actions in Oracle Service Bus

Publish Action
The Publish Action is best to use when you want to perform One-Way calls or Asynchronous Calls, but it can be used for synchronous calls too. You can use a Routing Options action to set the following properties to determing the Publich Action behaviour.

• When QoS is exactly-once, the publish action waits (blocking call) until the response from the target service is available, although the response itself is discarded. When the target is a business service, the publish action waits until the business service response is available. When the target is a proxy service, the publish action waits until the proxy service's response pipeline completes.

• When QoS is best-effort and the target service is a one-way proxy service or a one-way business service with retry count > 0, the publish action waits until the target service returns. With a one-way target service there is no response, but the publish action waits until the request is delivered.

• If the target proxy or business service is request-response or a one-way business service with retry count = 0, the publish action does not wait for the response (non-blocking call).

• If you are calling a Business service and you specify Best Effort for QoS (Quality of Service), then OSB will release the thread it is holding while the business service executes.

• If you are calling a Business service and you specify Exactly Once or At Least Once for QoS, then OSB will hold onto the thread while the business service executes.

• If you are calling a local Proxy service, then OSB will hold onto the thread until the Proxy service finishes executing.

Route Action
A Route Action is used when we want to perform a call to a Business Service. OSB picks a thread, creates a payload and transmits it to the destination. Then it releases the thread to execute other tasks, when the response arrives Weblogic assigns a different thread to continue the execution of work. In the meantime, the one who invoked OSB remains blocked, but OSB itself uses minimal threads for process execution.
When you add a Route action it must be the last node in the pipeline, JDeveloper does not permit the addition of another node after a Route Action.

Service Callout Action
The service callout action is to invoke multiple services within a single pipeline, in order to perform message enrichment, augmentation or validation, as part of a single orchestration. When performing service callouts OSB will hold a thread until a the response arrives. This can cause severe performance issues under heavy loads.