Achieving high degree of concurrency in multidatabase transaction scheduling: MTOS

A multidatabase system (MDBS), which is also called a heterogeneous distributed database system (HDDBS) or federated database system (FDBS), is a facility that allows users or applications to access data located in multiple local database systems (LDBSs), each of which is autonomously operated. Several practical MDBS concurrency control schemes have been proposed whilst maintaining global consistency without compromising local autonomy. However, they could degrade either local concurrency of local transactions or global concurrency of global transactions for the purpose of ensuring the global serializability. In this paper, we propose a new ticketbased global concurrency control scheme that employs multiple tickets at each site. The basic idea is that, with proper consideration of the potential cyclic global serialization orders, subtransactions with the possibility of the local indirect conflicts must access the same ticket at their sites, otherwise they are allowed to access the different tickets. This scheme alleviates the blockage on local resources, and, as a result, increases both global concurrency and local concurrency, whilst preserving the local autonomy.