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LONG Field File Descriptive Parameters

IP.com Disclosure Number: IPCOM000035690D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Camp, LS: AUTHOR [+2]

Abstract

In a relational database, data in the database is stored in tables consisting of rows and columns. One of the datatypes supported in a table is the LONG VARYING CHARACTER, or long field, type. Because of the large size allowed for this data (larger than the maximum sized row allowed for a table), long field data is stored in a separate file from the rest of the data in the table. This file is called the long field file.

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LONG Field File Descriptive Parameters

In a relational database, data in the database is stored in tables consisting of rows and columns. One of the datatypes supported in a table is the LONG VARYING CHARACTER, or long field, type. Because of the large size allowed for this data (larger than the maximum sized row allowed for a table), long field data is stored in a separate file from the rest of the data in the table. This file is called the long field file.

The storage management scheme of this file is based on the "Buddy Space" concept [*]. Within the long field file, space is allocated in major pieces called buddy spaces, and then data is stored in buddy segments within a buddy space.

In order to accurately handle storage allocation, the storage access method must understand the characteristics of the long field file -- for example, the size of a buddy space and the maximum size of a buddy segment. One method of doing this is to hard-code these characteristics into the storage access method. However, if in a future release of the product new file characteristics are supported (such as a larger buddy space to handle larger long fields), the later version of the storage access method will not be able to access old files nor will back-level versions handle files from the new version.

To solve this problem, parameters describing the characteristics of the long field file are stored in the beginning of the long field file when it is created. Before reading or writi...