Browse Prior Art Database

Log Scopes of Interest

IP.com Disclosure Number: IPCOM000050716D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 50K

Publishing Venue

IBM

Related People

Jenner, EH: AUTHOR

Abstract

This article describes a method for operating a computing apparatus including a data base manager which provides for a sequential recovery log where each record in the log is identified by a continuous log data addressing range value assigned when the record is logically written to the log. During the process of restoring a data base to a consistent state from the contents of the log, those records are bypassed which exist outside of the bounds of both (1) the records of interest of all resource managers, and (2) the logged activity of all interrupted work units undergoing recovery processing.

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Log Scopes of Interest

This article describes a method for operating a computing apparatus including a data base manager which provides for a sequential recovery log where each record in the log is identified by a continuous log data addressing range value assigned when the record is logically written to the log. During the process of restoring a data base to a consistent state from the contents of the log, those records are bypassed which exist outside of the bounds of both (1) the records of interest of all resource managers, and (2) the logged activity of all interrupted work units undergoing recovery processing.

A data base management subsystem recovery log represents a chronological record of the events and actions of work units upon the resource collections managed by the subsystem. Its contents reflect events which alter the content of recoverable resources, and which change the states of resource collections. A continuous log data addressing range value, or relative byte address (RBA), is assigned to each recovery log record when it is logically written. Each record, therefore, has a unique, time-ordered identifier.

Restarting following an unplanned subsystem termination typically involves the restoration of resources left in a potentially inconsistent state due to work unit interruption. Resource managers which provided services to these interrupted work units may have recovery responsibilities associated with the work units during restart. The information needed to perform the recovery process is contained in log records contributed on behalf of each work unit. Each work unit is considered to have a different log activity scope.

In either a planned or unplanned subsystem termination situation, resource managers may need information from the log during restart which is not associated with interrupted work units. Each resource manager could potentially have a different log interest scope from which the records must be read. A subsystem Recovery Manager component is herein described which selectively reads the log records existing within the various log scopes. It uses the basic services provided by a log manager component for actual log record retrieval. Via Recovery Manager log record presentation broadcasts, resource managers receive the log records needed to perform their recovery responsibilities.

The phases of restart are structured around the time-ordered direction in which the log will be read and the records processed. The technique of managing log scopes of interest used by Recovery Manager attempts to minimize the number of log records accessed during the restart process. It does this by recognizing when the log can be bypassed because it; current position is of no interest to any restart or recovery process. In describing the technique the forward recovery phase of restart is used since it deals with multiple scope categories.

The method involves creating sort elements for the identified log scopes, sorting thes...