Reconciling chained and unchained transactional support for distributed systems

Abstract Distributed transactions require transaction processing support either from their communications protocols or from protocols at some higher layer. One of the earliest “industrial-strength” distributed transactional support systems was provided by SNA (LUG.1 and LUG.2). As OSI began specifying the flows for transactional support, the notion of unchained transactional support as opposed to the chained nature of LU6.2 transactions gradually developed. OSI/TP supports both chained and unchained transactions. This makes the coexistence of applications requiring both kinds of transaction processing support on a platform that supports only chained transactions problematic and reduces the interoperability of communication protocols providing transactional support. This paper addresses the above problems by identifying the extra functionality provided by unchained transactions over chained transactions. It then shows how a protocol/platform (i.e., IBM's SNA) that provides only chained transactional support can provide the functionality of unchained transactions, and without using the notion of chained or unchained transactions at the API. The paper also describes an efficient way by which protocols providing only chained support can provide the functionality of unchained transactions using the X/Open TX API based on OSI TP's Chained and Unchained Functional Units.