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Key-sequenced data set
IBM data record organization type

A key-sequenced data set (KSDS) is a type of data set used by IBM's VSAM computer data storage system.: 5  Each record in a KSDS data file is embedded with a unique key.: 20  A KSDS consists of two parts, the data component and a separate index file known as the index component which allows the system to physically locate the record in the data file by its key value.: 13  Together, the data and index components are called a cluster.: 15 

Records can be accessed randomly or in sequence and can be variable-length.

As a VSAM data set, the KSDS data and index components consist of control intervals: 10  which are further organized in control areas.: 12  As records are added at random to a KSDS, control intervals fill and need to be split into two new control intervals, each new control interval receiving roughly half of the records. Similarly, as the control intervals in a control area are used up, a control area will be split into two new control areas, each new control area receiving roughly half the control intervals.: 17 

While a basic KSDS only has one key (the primary key), alternate indices may be defined to permit the use of additional fields as secondary keys.: 15  An alternate index is itself a KSDS.: 16 

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See also

References

  1. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  2. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  3. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  4. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  5. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  6. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  7. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  8. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩

  9. Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (August 2022). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM. https://www.redbooks.ibm.com/redbooks/pdfs/sg246105.pdf ↩