Riassunto
Traditional theory and practice of write-ahead logging and of database recovery focus on three failure classes: transaction failures (typically due to deadlocks) resolved by transaction rollback; system failures (typically power or software faults) resolved by restart with log analysis, "redo," and "undo" phases; and media failures (typically hardware faults) resolved by restore operations that combine multiple types of backups and log replay. The recent addition of single-page failures and single-page recovery has opened new opportunities far beyond the original aim of immediate, lossless repair of single-page wear-out in novel or traditional storage hardware. In the contexts of system and media failures, efficient single-page recovery enables on-demand incremental "redo" and "undo" as part of system restart or media restore operations. This can give the illusion of practically instantaneous restart and restore: instant restart permits processing new queries and updates seconds aftersystem reboot and instant restore permits resuming queries and updates on empty replacement media as if those were already fully recovered. In the context of node and network failures, instant restart and instant restore combine to enable practically instant failover from a failing database node to one holding merely an out-of-date backup and a log archive, yet without loss of data, updates, or transactional integrity. In addition to these instant recovery techniques, the discussion introduces self-repairing indexes and much faster offline restore operations, which impose no slowdown in backup operations and hardly any slowdown in log archiving operations. The new restore techniques also render differential and incremental backups obsolete, complete backup commands on a database server practically instantly, and even permit taking full up-to-date backups without imposing any load on the database server. Compared to the first version of this book, this second edition adds sections on applications of single-page repair, instant restart, single-pass restore, and instant restore. Moreover, it adds sections on instant failover among nodes in a cluster, applications of instant failover, recovery for file systems and data files, and the performance of instant restart and instant restore.
Informazioni sull?autore
Goetz Graefe has been a professor, product architect, and industrial researcher since 1987. Like other database vendors, Microsoft SQL Server adopted his designs for query optimization and query execution. He has published tutorial surveys on query execution, sorting, b-tree indexing, concurrency control, logging and recovery, as well as numerous novel techniques and research results in query processing and transactional data storage.Wey Guy is an independent software engineer. She earned a Masters degree in computer science from the University of Iowa and spent 15 years with Microsofts SQL Server development team before she became an independent software developer in 2011. She has been working with Hewlett Packard Labs since 2012.Caetano Sauer is a doctoral candidate in computer science at the Technical University of Kaiserslautern, Germany. He earned his M.Sc. degree in 2012 at the same institution. While his interests and experience cover all components of transactional storage and indexing, his research focuses on logging and recovery algorithms. He is advised by Prof. Theo Harder and Dr. Goetz Graefe.
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