Report Number: CS-TR-87-1177
Institution: Stanford University, Department of Computer Science
Title: Log Files: An Extended File Service Exploiting Write-Once Storage
Author: Finlayson, R. S.
Author: Cheriton, D. R.
Date: August 1987
Abstract: A log service provides efficient storage and retrieval of data that is written sequentially (append-only) and not subsequently modified. Application programs an subsystems use log services for recovery, to record security audit trails, and for perforrnance monitoring. Ideally, a log service should accomodate very large, long-lived logs, and provlde efficient retrieval and low space overhead. In this paper, we describe the design and implementation of the Clio log service. Clio provides the abstraction of log files: readable, append-only files that are accessed in the same way as conventional files. The underlying storage medium is required only to be append-only; more general types of write access are not necessary. We show how log files can be implemented efficiently and robustly on top of such storage media - in particular, write-once. optical disk. In addition, we describe a general application software storage architecture that makes use of log files.