Logging Subsystem Performance: Model and Evaluation

• Main Author: Clark, Thomas K.
• Format: Others
• Published: PDXScholar 1994
• Subjects: Memory management (Computer science); Data recovery (Computer science); Computer algorithms; Computer Sciences
• Online Access: https://pdxscholar.library.pdx.edu/open_access_etds/4724; https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=5795&context=open_access_etds

Transaction logging is an integral part of ensuring proper transformation of data from one state to another in modern data management. Because of this, the throughput of the logging subsystem can be critical to the throughput of an application. The purpose of this research is to break the log bottleneck at minimum cost. We first present a model for evaluating a logging subsystem, where a logging subsystem is made up of a log device, a log backup device, and the interconnect algorithm between the two, which we term the log backup method. Included in the logging model is a set of criteria for evaluating a logging subsystem and a system for weighting the criteria in order to facilitate comparisons of two logging subsystem configurations to determine the better of the two. We then present an evaluation of each of the pieces of the logging subsystem in order to increase the bandwidth of both the log device and log backup device, while selecting the best log backup method, at minimum cost. We show that the use of striping and RAID is the best alternative for increasing log device bandwidth. Along with our discussion of RAID, we introduce a new RAID algorithm that is designed to overcome the performance problems of small writes in a RAID log. In order to increase the effective bandwidth of the log backup device, we suggest the use of inexpensive magnetic tape drives and striping in the log backup device, where the bandwidth of the log backup device is increased to the point that it matches the bandwidth of the log device. For the log backup interconnect algorithm, we present the novel approach of backing up the log synchronously, where the log backup device is essentially a mirror of the log device, as well as evaluating other log backup interconnect algorithms. Finally, we present a discussion of a prototype implementation of some of the ideas in the thesis. The prototype was implemented in a commercial database system, using a beta version of INFORMIX-OnLine Dynamic Server™ version 6.0.