Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-12-22
2001-08-21
Lintz, Paul R. (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000, C707S793000
Reexamination Certificate
active
06279004
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the design and use of database management systems, and in particular to a method and system for configuring a database management system to operate with multiple key versions.
2. Description of the Related Art
Large-scale integrated database management systems provide an efficient, consistent, and secure means for storing and retrieving vast amounts of data. This ability to manage massive amounts of information has become a virtual necessity in business today. Relational databases, which store retrieve data from tables having a number of rows and columns, are especially widespread.
Key values and indexes are useful features found in most database management systems. Key values are comprised of a single column or multiple columns of a record. Typical key values are account numbers, product codes, and customer names. An index is a structure within the database that can be used to quickly locate data based upon a key value because the key values are ordered. Each key value has at least one record identifier, or pointer, associated with it, which provides access to the entire record in the file. The use of key values and indexes can hasten the processing involved in performing database commands.
Another useful feature found in many relational database management systems is the ability to alter the columns or rows of the database tables after the tables have been defined. A typical such alteration might be to increase the length of the character column or to change the data type from a small two-byte integer field to a four-byte integer field.
Unfortunately, if the altered column is a key column or happens to contain a key field, the format of the index key that referenced the table will have changed. As a result, the index will be inaccessible until it is rebuilt to match the new key format stored in the catalog and control structures describing the index. This rebuild may take a considerable amount of time depending on the size of the table.
What is needed is a device and method that allows key columns to be altered, yet avoids the need to rebuild the index after the key columns have been altered. The present invention satisfies that need.
SUMMARY OF THE INVENTION
To address the requirements described above, the present invention discloses a method, apparatus, article of manufacture, and a memory structure for configuring a database management system to operate with multiple key versions.
The method comprises the steps of storing first key information comprising a first key format and an associated version indicator when a command altering the key format is accepted, storing altered key information comprising the altered key format and the incremented version indicator in the index page set, and storing altered key information in an index catalog. The apparatus comprises a means for performing the above-entitled operations, and the article of manufacture comprises a program storage device tangibly embodying instructions for performing the operations.
The foregoing uses an index versioning technique to avoid the need to rebuild the index after the key columns have been altered, and allows immediate access to the index. This is made possible because multiple older versions of the key formats are stored inside the index space itself while only the new key format resulting from the alteration is stored in the catalog and the control structures describing the index. Because the index space contains definitions of the older versions of the key formats, the need to maintain multiple versions of the key formats in the catalog is eliminated. Also, because the definitions of all the key formats can be accessed, a key in one format can be converted or compared to a key in a different format. As a result, keys in the new format resulting from the alteration can be inserted into existing indexes that still contain keys in the older formats. In addition, delete and select processing can handle keys in either the old or the new formats. This feature provides immediate availability to the index after the table-altering operation is completed.
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Lee Christina Marie
Lyle Robert William
Schmandt Stephen J.
Wang Hsiao Ming
Wang Yufen
Gates & Cooper LLP
International Business Machines - Corporation
Lintz Paul R.
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