To make a server UAP process a transaction branch, specify that the UAP have the transaction attribute. The transaction attribute is specified by the following method:

• TP1/Server Base:
  Specify Y for atomic_update in the user service definition.
  
• TP1/LiNK:
  Specify for the user server that the transaction facility will be used.
  

Processing of a UAP with the transaction attribute works as a transaction when:

• The UAP with the transaction attribute normally returns by using the function dc_trn_begin() to start a transaction.
• The UAP is requested for service via the function dc_rpc_call() by another UAP which is working as a transaction.

The nontransaction attribute (atomic_update=N or the specification that the transaction facility be not used) must be specified for server UAPs which perform only operation and other server UAPs which do not require that transactions be guaranteed. Server UAPs with the nontransaction attribute can always offer service to not only the present, but also other client UAPs independent of global transaction processing. Even if the server UAP is requested for service by multiple client UAPs, it can start handling these service requests without waiting until synchronization point acquisition processing is completed. This helps reduce the overhead involved in service request waits.

The figure below shows the relationship between RPCs and the transaction attribute.

Figure 2-31 Relationship between RPCs and transaction attribute

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The contents of a resource accessed by global transaction B are returned to the status immediately before global transaction B is started. The function for acquiring a synchronization point (the function dc_trn_unchained_commit() in the figure) returns an error to report that global transaction B has rolled back.

(a) Using nontransactional RPC from transaction process

If a transaction process requests a UAP for service and the requested UAP has the transaction attribute, the service request is handled by a transaction process. It is possible to make such service requests not handled by a transaction process. For this purpose, specify the argument to the function dc_rpc_call() to indicate that the RPC is nontransactional.