MLR: a recovery method for multi-level systems

  • Authors:

  • David B. Lomet

  • Affiliations:

  • Digital Equipment Corp., Cambridge Research Lab, One Kendall Sq., Bldg. 700, Cambridge, MA

  • Venue:
  • SIGMOD '92 Proceedings of the 1992 ACM SIGMOD international conference on Management of data
  • Year:
  • 1992

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Abstract

To achieve high concurrency in a database system has meant building a system that copes well with important special cases. Recent work on multi-level systems suggest a systematic path to high concurrency. A multi-level system using locks permits restrictive low level locks of a subtransaction to be replaced with less restrictive high level locks when sub-transactions commit, enhancing concurrency. This is possible because sub-transactions can be undone via high level compensation actions rather than by restoring a prior lower level state. We describe a recovery scheme, called Multi-Level Recovery (MLR) that logs this high level undo operation with the commit record for the subtransaction that it compensates, posting log records to only a single log. A variant of the method copes with nested transactions, and both nested and multi-level transactions can be treated in a unified fashion.