Lehrgebiet Informationssysteme

FB Informatik

LG IS

AG DBIS

(C) AG DBIS

Recovery on the Basis of Objects

Fernando de Ferreira Rezende

University of Kaiserslautern
P.O. Box 3049, 67653 Kaiserslautern, Germany
e-mail: haerder@informatik.uni-kl.de

Full paper (postscript version compressed by gzip)

Abstract:

We present a recovery strategy working on the basis of objects, and supporting partial rollbacks of transactions and object-granularity locking, called WALORS (WAL-based and Object-oriented Recovery Strategy). As the name suggests, WALORS uses the principle of Write-Ahead Logging (WAL). In contrast to other recovery strategies, WALORS stores a Log Sequence Number (LSN) in every object of the database (DB) to correlate the state of the object with logged updates to the object. Due to this feature, WALORS does not need to employ a repeating history (redo all) paradigm. Instead, it supports selective undo as well as selective redo passes. To avoid the problems of supporting fine-granularity locking in the context of WAL, WALORS employs special control structures which enable it not having to write compensation log records (CLRs) from CLRs and guaranteeing its idempotence even in the face of repeated failures or of nested rollbacks. WALORS does operation logging of all updates, including the ones performed during rollbacks, works with fuzzy checkpoints, supports also media recovery, and is flexible enough with respect to the kinds of cache management policies being implemented.

Published in JBCS - Journal of the Brazilian Computer Society, Vol. 3, No. 2, Brazil, Nov. 1996.