Instant recovery improves system availability by reducing the mean time to repair, i.e., the interval during which a database is not available for queries and updates due to recovery activities. Variants of instant recovery pertain to system failures, media failures, node failures, and combinations of multiple failures. After a system failure, instant restart permits new transactions immediately after log analysis, before and concurrent to “redo” and “undo” recovery actions. After a media failure, instant restore permits new transactions immediately after allocation of a replacement device, before and concurrent to restoring backups and replaying the recovery log.
Write-ahead logging is already ubiquitous in data management software. The recent definition of single-page failures and techniques for log-based single-page recovery enable immediate, lossless repair after a localized wear-out in novel or traditional storage hardware. In addition, they form the backbone of on-demand “redo” in instant restart, instant restore, and eventually instant failover. Thus, they complement on-demand invocation of traditional single-transaction “undo” or rollback.
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.
Datenbank-Spektrum ist das offizielle Organ der Fachgruppe Datenbanken und Information Retrieval der Gesellschaft für Informatik (GI) e.V. Die Zeitschrift widmet sich den Themen Datenbanken, Datenbankanwendungen und Information Retrieval.
We use the term “instant” not in an absolute meaning but a relative one, i.e., in comparison to prior techniques. This is like instant coffee, which is not absolutely instantaneous but only relative to traditional techniques of coffee preparation. The reader’s taste and opinion must decide whether instant coffee actually is coffee. Instant recovery, however, is true and reliable recovery from system and media failures, with guarantees as strong as those of traditional recovery techniques.