Heterogeneous multilevel transaction management with multiple subtransactions

Abstract

Heterogeneous transaction management has been an active research field for a few years. Based on the degree of local transaction autonomy we distinguish between update autonomous, semi-autonomous, and non-autonomous multidatabase systems. In the semi-autonomous environments one problem is the inter-site correctness problem, i.e. that a mix of pre-existing local and global transactions might not enforce any unique global consistency or might violate local consistency. Independently of this, it is not possible to dynamically detect exactly those global subtransactions that have local RW conflicts, without considerably restricting at least some aspect of local autonomy. No optimal global syntactical conflict detection mechanism is practical and even a syntactically correct mechanism is difficult to achieve, without restricting autonomy. Semantically oriented multilevel transaction management scheme with multiple subtransactions per site is therefore favourable. The binary valued concept of consistency should also be replaced. Locally serializable schedules (LSR) seems to contain all reasonable RW schedules in the environment.