Browse Prior Art Database

Write Ahead Logging With Efficient Restart

IP.com Disclosure Number: IPCOM000044733D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Traiger, IL: AUTHOR

Abstract

This relates to a method for write ahead logging with efficient restart in a CPU system supporting any data base. The method comprises the steps of (a) modifying pages and logging of a description of said page modifications; and at the time of failure (b) identifying which transactions were incomplete (needing undo), identifying unforced pages modified in a buffer pool (needing redo) by scanning forward along the system log starting at the last checkpoint until a null or restart log record is encountered and building transactions and dirty page tables; (c) executing "undo processing"; and (d) executing "redo processing". This method may be used for both record level as well as page level locking.

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Write Ahead Logging With Efficient Restart

This relates to a method for write ahead logging with efficient restart in a CPU system supporting any data base. The method comprises the steps of (a) modifying pages and logging of a description of said page modifications; and at the time of failure (b) identifying which transactions were incomplete (needing undo), identifying unforced pages modified in a buffer pool (needing redo) by scanning forward along the system log starting at the last checkpoint until a null or restart log record is encountered and building transactions and dirty page tables; (c) executing "undo processing"; and (d) executing "redo processing". This method may be used for both record level as well as page level locking.

The method is based on using a write ahead logging protocol during normal operation, maintaining both undo and redo log sequence numbers associated with the modification of each data base page, and recording both a begin write and end write log record when the modified page is to be written into the data base system. The restart is a 3-phase method involving an initial analysis and table building phase, an undo phase and a redo phase. The restart uses the additional logged information to minimize the amount of actual undo and redo processing that must be performed in order to restore the data base to a consistent state without the requirement of logging individual actions during restart.

Anonymous

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