In a database sharing (DB-Sharing) system, multiple loosely or closely coupled
processors share access to a single set of databases. Such systems aim at
high availability and high performance as demanded by large transaction processing
systems. To achieve high transaction rates and short response times an efficient
concurrency control is required for synchronizing access to the shared database.
This paper gives an overview of concurrency control algorithms for
DB-Sharing. We distinguish between locking and optimistic methods and between
centralized and distributed solutions. Five protocols are described
in some detail and compared with each other.