Performance of an Adaptable Synchronization Method

03.12.2001

Abstract

A transaction in a database system, is the execution of a program that access the database. In order to reduce transaction response time and increase system throughput, transactions often access the database concurrently. However, uncontrolled execution of concurrent transactions may produce undesirable results to the database due to to lost updates or inconsistent retrievals. Therefore increasing the degree of concurrency in transaction processing and maintaining data consistency appear to be two conflicting goals in designing database systems. This problem becomes especially difficult if the database is serving long-lasting transactions.

Serializability and Two-phase locking are much used methods, to ensure a correct execution of concurrent transactions in traditional database systems. Transactions for these systems are generally short and atomic. However, there is broad consensus in the database research community that serializability can cause serious performance problems for a number of applications domains, specially where support for long-lasting transactions is necessary. Recently, a number of new methods and techniques has been introduces that addresses this problem.

One of these methods is Two-dimensional locking, developed here at the University of Tromsø department of computer science. Two-dimensional locking provides high degree of concurrency among transactions by allowing transactions to release their lock as early as possible. However, it is also subject to overhead due to the efforts needed to recover from failures.

In this thesis we conduct a series of simulation studies to compare the performance of Two-dimensional locking and Two-phase locking in environment with only short transactions loads, and in environment with both short and long-lasting transactions. We have varied the number of hardware resources (Disk and Cpu) in both environment. In environment where only short transactions are executed, the simulation results indicates that Two-dimensional locking perform as good as or slightly better than Two-phase locking. The simulation shows also that Two-dimensional locking outperforms Two-phase locking in all situations where long-lasting transactions are interleaved with short transactions.