An emerging paradigm that handles multiple locii of control in a system allows multiple program threads to work on the same task, each thread to work on a different task, or a thread to work on multiple tasks for greater design flexibility or due to system constraints such as real-time demands and a high load on tasking. We use the definition of context to capture the notion of logical locus of control. The context of the work being currently executed must be identifiable uniquely by the application, the Resource Managers and the Transaction Manager because each context represents different work. In this paper we define context management by defining a local Context Manager and its user interface. We then show why the notion of context is required to solve the problems that arise in local and distributed transaction processing due to the emerging paradigm. We present solutions to these problems in transaction processing using the proposed context management.

Eleven two-phase commit (2PC) protocol variations that optimize towards the normal case are described and compared with a baseline 2PC protocol. Environments in which they are most effective are discussed. The variations are compared and contrasted in terms of number of message flows, number of log writes (both forced and non-forced), probability of heuristic damage, how damage is reported, and other tradeoffs.>