140.5. Transaction Support

The SAP Component supports the BAPI transaction model for outbound communication with SAP. A destination endpoint with a URL containing the transacted option set to true will, if necessary, initiate a stateful session on the outbound connection of the endpoint and register a Camel Synchronization object with the exchange. This synchronization object will call the BAPI service method BAPI_TRANSACTION_COMMIT and end the stateful session when the processing of the message exchange is complete. If the processing of the message exchange fails, the synchronization object will call the BAPI server method BAPI_TRANSACTION_ROLLBACK and end the stateful session.

The tRFC protocol accomplishes an AT-MOST-ONCE delivery and processing guarantee by identifying each transactional request with a unique transaction identifier (TID). A TID accompanies each request sent in the protocol. A sending application using the tRFC protocol must identify each instance of a request with a unique TID when sending the request. An application may send a request with a given TID multiple times, but the protocol ensures that the request is delivered and processed in the receiving system at most once. An application may choose to resend a request with a given TID when encountering a communication or system error when sending the request, and is thus in doubt as to whether that request was delivered and processed in the receiving system. By resending a request when encountering an communication error, a client application using the tRFC protocol can thus ensure EXACTLY-ONCE delivery and processing guarantees for its request.

A BAPI transaction is an application level transaction, in the sense that it imposes ACID guarantees on the persistent data changes performed by a BAPI method or RFC function in the SAP database. An RFC transaction is a communication transaction, in the sense that it imposes delivery guarantees (AT-MOST-ONCE, EXACTLY-ONCE, EXACTLY-ONCE-IN-ORDER) on requests to a BAPI method and/or RFC function.

The following destination endpoints support RFC transactions:

A single Camel route can include multiple transactional RFC destination endpoints, sending messages to multiple RFC destinations and even sending messages to the same RFC destination multiple times. This implies that the Camel SAP component potentially needs to keep track of many transaction IDs (TIDs) for each Exchange object passing along a route. Now if the route processing fails and must be retried, the situation gets quite complicated. The RFC transaction semantics demand that each RFC destination along the route must be invoked using the same TID that was used the first time around (and where the TIDs for each of the destinations are distinct from each other). In other words, the Camel SAP component must keep track of which TID was used at which point along the route, and remember this information, so that the TIDs can be replayed in the correct order.

By default, Camel does not provide a mechanism that enables an Exchange to know where it is in a route. To provide such a mechanism, it is necessary to install the CurrentProcessorDefinitionInterceptStrategy interceptor into the Camel runtime. This interceptor must be installed into the Camel runtime, in order for the Camel SAP component to keep track of the TIDs in a route. For details of how to configure the interceptor, see the section called “Interceptor for tRFC and qRFC destinations”.

The following server endpoints support RFC transactions:

When a Camel exchange processing a transactional request encounters a processing error, Camel handles the processing error through its standard error handling mechanisms. If the Camel route processing the exchange is configured to propagate the error back to the caller, the SAP server endpoint that initiated the exchange takes note of the failure and the sending SAP system is notified of the error. The sending SAP system can then respond by sending another transaction request with the same TID to process the request again.