Analysis of some optimistic concurrency control schemes based on certification

Abstract

Optimistic Concurrency Control-OCC schemes based on certification are analyzed in this paper. We allow two types of data access schemes referred to as static and dynamic. According to the first (second) scheme a transaction reads all the required data items at the beginning of its processing (on demand during its processing), respectively. After completing its processing, each transaction is checked aa to whether it has encountered a data conflict. Validated transactions commit; otherwise, they are restarted. A variant of the regular (silent) commit scheme where a committing transaction notifies conflicted transactions to restart immediately (broadcast commit scheme) is also considered. We use an iterative method to analyze the performance of OCC schemes in the framework of a system with a fiied number of transactions in multiple classes with given probabilities for their occurrence. The iterative method is validated against simulation and shown to be highly accurate even for high data contention. We present graphs/tables, which are used to determine how system performance is affected by: (i) various OCC schemes, (ii) transaction size, i.e., number of data items accessed, (iii) number of transactions, (iv) the distribution of transaction processing time requirements, (v) the throughput characteristic of the system, and (vi) granule placement.