CONCURRENCY-CONTROL FOR A MIX OF UNIVERSIONED AND MULTIVERSIONED ENTITIES IN DISTRIBUTED DATABASES

In this paper, we present a concurrency control protocol applicable to distributed databases with any mix of universioned and multiversioned entities. The protocol has performance merits at high workloads at which even pessimistic protocols do not perform well. These merits exist at the expense of poorer performance at lower workloads. This protocol is based on two features. The first feature is concerned with predecessors of transactions and can be described as follows for a transaction. Order between transactions is chosen at run time based on the actual conflict or transitive order; each transaction explicitly carries state information about predecessor transactions which is sufficient to ensure serializability; at an entity, a transaction executes logically after all predecessor transactions carried in the state by the transaction to the entity. The second feature facilitates and reduces the work required for the collection of state information sufficient to ensure serializability and is the following. Entities are preordered and whenever possible each transaction accesses these entities in this order with possible skips; random or out-of-order accesses are permitted at additional costs. © 1990.