Simulations of the implementation of primary copy two-phase locking in distributed database systems

This paper considers algorithms for concurrency control in Distributed database (DDB) systems. Below are the simulating models of the implementation of two-phase locking (2PL) in DDB. From four types 2PL in DDB (Centralized 2PL, Primary copy 2PL, Distributed 2PL and voting 2PL) is viewed Primary copy 2PL, as this protocol is a "transitional" protocol of Centralized 2PL to the Distributed 2PL. The paper describes specifically the simulations of two-version 2PL and 2PL with integrated timestamp ordering mechanism. In concurrency control method 2PL may take place deadlocks of the transactions. Therefore, in the modelling algorithms described here are integrated algorithms for deadlock avoiding: two-version architecture of database and timestamp ordering strategy “wait-die”. There are also presented, the results of the simulations of these two variants of the 2PL method at different scales of the networks for the transmission of data and at different intensities of inflow transactions. Modelling algorithms are developed by means of the system for simulation modelling GPSS World Personal Version.