- Why do VSAM take more disk space than other utilities?
- What are the distinctive features of a KSDS, Key sequenced DataSet?
- What is a CI, Control Interval?
- What is Control Interval Split?
- What is a CA, control area?
- What is a cluster?
Thursday, September 18, 2008
Vsam Questions
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Answer
1 - VSAM increases the disk space requirements of systems. This is because VSAM offers certain
capabilities like partial self-reorganization to make things more efficient in data sets that can be
modified.
2 - The index and the distributed free space. CI and CA splits upon updates. Record length may
be changed during update. The records are accessed by a particular Key.
3 - A Control Interval is the unit of information that VSAM transfers between virtual and auxiliary
storage.
4 - A new record stored in same CI, only if there is enough space. If not VSAM locates the free CI
within the same CA, moves approximately half of the records to next CI and stores the new
record at the correct position. This is called Control Interval Split. Whenever CI split occurs the
sequence set is updated.
5 - A group of Control Intervals makes up a control area.
6 - A cluster is the combination of the index, sequence set and data portions of the DataSet. The
operating system gives program access to the cluster, i.e. to all parts of the DataSet
simultaneously.
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