The alternate index in VSAM to access records other than the base key defined on the dataset is called a base cluster.
Advantages
- Can be defined for both KSDS and ESDS
- reduce data redundancy
- Can have duplicates
- Easy to define using IDCAMS
- allow datasets to be accessed by both sequentially and randomly
Disadvantages
- Performance degradation
- Complex update logic
Click here for VSAM alternate index example.
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