A survey of techniques and tools used in filing systems, database systems, and operating systems for recovery, backing out, restart, the mamtenance of consistency, and for the provismn of crash resistance is given. A particular view on the use of recovery techmques in a database system and a

Inexpensive storage and more powerful processors have resulted in a proliferation of data that needs to be reliably backed up. Network resource limitations make it increasingly difficult to backup a distributed file system on a nightly or even weekly basis. By using delta compression algorithms, which minimally encode a version of a file using only the bytes that have changed, a backup system can compress the data sent to a server. With the delta backup technique, we can achieve significant savings in network transmission time over previous techniques. Our measurements indicate that file system data may, on average, be compressed to within 10% of its original size with this method and that approximately 45% of all changed files have also been backed up in the previous week. Based on our measurements, we conclude that a small file store on the client that contains copies of previously backed up files can be used to retain versions in order to generate delta files. To reduce the load on ...

Redundant disk arrays are a popular method of improving the dependability and performance of disk storage and an ever-increasing number of array architectures are being proposed to balance cost, performance, and dependability. Despite their differences, there is a great deal of commonality between these architectures; unfortunately, it appears that current implementations are not able to effectively exploit this commonality due to their ad hoc approach to error recovery. Such techniques rely upon a case-by-case analysis of errors, a manual process that is tedious and prone to mistakes. For each distinct error scenario, a unique procedure is implemented to remove the effects of the error and complete the affected operation. Unfortunately, this form of recovery is not easily extended because the analysis must be repeated as new array operations and architectures are introduced. Transaction-processing systems utilize logging techniques to mechanize the process of recovering from errors. However, the expense of guaranteeing that all operations can be undone from any point in their execution is too expensive to satisfy the performance and resource requirements of redundant disk arrays. This dissertation describes a novel programming abstraction and execution mechanism based upon transactions that simplifies implementation. Disk array algorithms are modeled as directed acyclic graphs: the nodes are actions such as "XOR" and the arcs represent data and control dependencies between them. Using this abstraction, we implemented eight array architectures in RAIDframe, a framework for prototyping disk arrays. Code reuse was consistently above 90%. The additional layers of abstraction did not affect the response time and throughput characteristics of RAIDframe; however, RAIDframe co...

Increasingly, for extensibility and performance, specialpurpose application code is being integrated with database system code. Such application code has direct access to database system buffers, and as a result, the danger of data being corrupted due to inadvertent application writes is increased. Previously proposed hardware techniques to protect from corruption require system calls, and their performance depends on details of the hardware architecture. We investigate an alternative approach which uses codewords associated with regions of data to detect corruption and to prevent corrupted data from being used by subsequent transactions. We develop several such techniques which vary in the level of protection, space overhead, performance, and impact on concurrency. These techniques are implemented in the Dalí main-memory storage manager, and the performance impact of each on normal processing is evaluated. Novel techniques are developed to recover when a transaction had read corrupted data caused by a bad write, and gone on to write other data in the database. These techniques use limited and relatively low-cost logging of transaction reads to trace the corruption, and may also prove useful when resolving problems caused by incorrect data entry and other logical errors. 1.