Key-sequenced data set: Difference between revisions
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A '''key-sequenced data set''' (KSDS) is a type of [[data set (IBM mainframe)|data set]] used by [[IBM]]'s [[VSAM]] [[computer data storage]] system.<ref name="demystified">{{cite book|url=http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg246105.pdf |series=Redbooks |title=VSAM Demystified |first1=Mary |last1=Lovelace |first2=Jose |last2=Dovidauskas |first3=Alvaro |last3=Salla |first4=Valeria |last4=Sokal |chapter=Chapter 1. VSAM basics |edition=3 |publisher=IBM |date=March 2013}}</ref>{{rp|5}} Each record in a KSDS data file is embedded with a unique key.<ref name="demystified"/>{{rp|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.<ref name="demystified"/>{{rp|13}} Together, the data and index components are called a cluster.<ref name="demystified"/>{{rp|15}} |
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Records can be accessed randomly or in sequence and can be variable-length. |
Records can be accessed randomly or in sequence and can be variable-length. |
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Revision as of 05:21, 7 April 2021
 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (March 2017) |
A key-sequenced data set (KSDS) is a type of data set used by IBM's VSAM computer data storage system.[1]: 5 Each record in a KSDS data file is embedded with a unique key.[1]: 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.[1]: 13 Together, the data and index components are called a cluster.[1]: 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 which are further organized in control areas. 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.
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. An alternate index is itself a KSDS.
See also
External links
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- ^ a b c d Lovelace, Mary; Dovidauskas, Jose; Salla, Alvaro; Sokal, Valeria (March 2013). "Chapter 1. VSAM basics". VSAM Demystified (PDF). Redbooks (3 ed.). IBM.