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Browse Prior Art Database

Generic Variable Length Record Support

IP.com Disclosure Number: IPCOM000107257D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 86K

Publishing Venue

IBM

Related People

Anderson, M: AUTHOR [+14]

Abstract

A method for supporting Variable Length Records in both a Relational Data Base Management System (DBMS) and a File (or Direct I/O) DBMS is disclosed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Generic Variable Length Record Support

       A method for supporting Variable Length Records in both a
Relational Data Base Management System (DBMS) and a File (or Direct
I/O) DBMS is disclosed.

      The basic file structure used is one of an "anchor-heap" (see
Fig. 1).  The anchor is essentially the current fixed length file
structure with the following changes:
1.   Heap control and location information (see Fig. 2).
      Heap control and location information is used to navigate to
the Auxiliary SID (Segment IDentifer) area should the variable length
data not fit into the Fixed Allocation Length (FAL) area.  It also
contains the length of the data in either area (Auxiliary SID or
FAL).
2.   FAL Area
      The FAL area will contain variable length data smaller than a
user-defined threshold, i.e., Variable Length (VL) data will "spill"
into the heap should its actual length exceed the FAL.
      A FAL of zero will cause data to always spill, no space is
allocated in the anchor area.
      A FAL equal to the maximum length of a VL field will never
spill, data will always go into the anchor.
      The FAL allows a user to choose a threshold below which the
majority of the length of the VL data falls so as to get performance
equal to fixed length data.  Any variability within the FAL (i.e.,
wasted space) may be compensated by the fact that there will be no
overhead in the heap for the record.
See Fig. 3 for the layout of heap entrie...