International Business Machines Corporation

William S Davidson

Gary Ross Ricard

Mark John Anderson

Richard Lee Cole

Larry William Youngren

Wilson D Lee

Robert W Collins

James S Effle

Peter M Wottreng

Steven Michael Dickes

Peter B Passe

Kurt W Eggerling

Russell J Weinschenk

Carle J Larson

The data dictionary manager takes advantage of the computer system's journaling capability enhanced to allow users and application programs to manipulate system objects without the use of the data dictionary's built-in utilities. As used here, journaling capability is an internal tracking facility which exists in a somewhat limited form on many computer systems. Typical journaling mechanisms maintain a repository of information about some of the activities that have taken place on the computer system. The information is usually stored in a record called an audit journal. Since many computer systems have limited journaling mechanisms already in place, these mechanisms can be enhanced to add the ability to record information about changes to system objects. Examples of system object changes included in the audit journal are deletes, creates, renames, and moves. Once the information has been logged in the audit journal, the data dictionary manager retrieves the information from the audit journal and ensures that the changes are accurately reflected in the data dictionary. Since the audit journal can be made accessible to several processes, it is possible to have different instances of the data dictionary manager responsible for different data dictionaries. Alternatively, it is possible to have a single data dictionary manager that is responsible for all of the computer system's data dictionaries.

Data dictionary manager for maintaining an active data dictionary

A recovery mechanism restarts jobs following correction of a system failure and automatically marks the jobs for interruption at a logical boundary. The logical boundary is above logical file updating functions such that logical files are in a known state when jobs reach the boundary. When a system failure is detected which has not yet resulted in lost data, an image of working memory, including hardware status is saved on nonvolatile storage. After the failure has been resolved, the system is initially loaded with operating programs (IPL) and working memory is reloaded from the nonvolatile storage. All jobs which were reloaded are marked for interrupt at a machine instruction boundary, and processing is started. After all jobs have reached the boundary, or a predetermined time has elapsed, processing is stopped and the system is re-IPLed. There are few system index recoveries to be performed, since most jobs reached a point where logical files were synchronized with corresponding data.

Job interrupt at predetermined boundary for enhanced recovery

A key estimator estimates the number of keys over a key range defined by key endpoints in an index to a data space. The number of keys in the key range required to be processed for a particular operation is estimated as a function of the number of pages referenced during a range level limited search. Two keys defining range endpoint keys are searched down to their lowest level in the tree. The level limit is then calculated as a function of desired granularity or accuracy of the estimate. The entire range of keys in the desired key range is then searched down to the level limit and the number of pages referenced during the search is counted and multiplied by an average key density per page to calculate the number of keys in the range.

Index key range estimator

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Oronoco, MN, United States of America

William S Davidson