Concurrency Control for Global Transaction Management in MDBSs

The objectives of global transaction management in mul-tidatabase systems(MDBS) are to avoid the inconsistent retrievals and guarantee the global serializability under the existence of indirect connict which is unknown to to the global transaction manager(GTM). Many researches have shown that it is diicult to design the global concur-rency control method because of local autonomy. In these method global transactions have a few opportunities to be executed concurrently. We concentrate our attention on 1) investigation into the more accurate indirect connict situation and 2) supporting the higher concurrency degree by using the concept of global integrity constraints. We deene the mul-tidatabase transaction model and then propose the concurrency control protocols. In our method the more global transaction can be concurrently executed, since the reened boundary of possibility of indirect connict is ooered. 1 Introduction The GTM has the responsibility for maintaining the global consistency of MDBS. The GTM however cannot take any kind of helpful information from local database systems to adjust the global serialization order. Many techniques in managing transactions for MDBS environments have been researched. These vary in degree to which they violate local autonomy and also in the degree of concurrency that they provide to users. The major diiculties addressed in these researches are to serialize the global transaction under the existence of indirect connicts which is unknown to the GTM. Traditional concurrency control methods are not directly applicable in MDBS because of these indirect connict. We brieey examine the deenition of indirect connict. Deenition 1. The global transaction G i and G j are in indirect connict in global schedule S if and only if there is a local transaction sequence L 1 ; L 2