Maintaining Quasi Serializability in HDDBSs
Weimin Du, Ahmed K. Elmagarmid, Won Bae Kim · Purdue e-Pubs (Purdue University System) · 1990
conflicts between global transactions. It is also very difficult to resolve the conflicts[DEL089J.In this paper. we present a scheduler based on quasi serializability, a new correctness criterionfor concurrency control in HDDBSs [DE89]. Quasi serializability represents a weaker type ofHDDBS consistency because it is based primarily on the behaviour of global transactions. Quasiserializability is meaningful for HDDBSs because it can be effectively maintained at the globallevel without violating local autonomy. The aspects of HDDBS consistency that are maintainedhy serializable executions but not quasi serializable executions (e.g.• interference between localtransactions at different sites) can be easily maintained explicitly at the global level [DE90J.The scheduler guarantees quasi serializability of executions by controlling the submission andinterleaving of global transactions only. Therefore. it does not violate local autonomy.The rest of the paper is organized as follows. In Section 2, we review tlle basic quasi serioalizability theory. Then. we discuss. in Section 3, the feature of quasi serializability that makesit maintainable at the global level without violating local autonomy. The scheduler and its cor·rectness proof are given in Section 4. A detailed discussion of various features of the scheduler isgiven in Section 5. Fjnally, some concluding remarks are given in Section 6.