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About usModule 2: VSAM Concepts
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Comparison of features of VSAM types
We have provided the comparison of features of different VSAM organization techniques which can help you to decide which technique is helpful in your business application
| KSDS | ESDS | RRDS (Fixed-length) |
|---|---|---|
| Records are organized in ascending order of key field value | Records are organized in the sequence based on the order in which they are inserted. | Records are organized into the pre-formatted fixed length slots using Relative Record Number (RRN) |
| Sequential and Random access (using Primary key/Alternate Key) is possible | Only sequential access is possible | Sequential and Random access is possible using RRN |
| Records can be fixed or variable length | Records can be fixed or variable length | Records have fixed length |
| Contains both Index and Data Component | Contains only Data component | Contains only Data component |
| Alternate Index can be coded | Alternate Index can be coded | Alternate Index cannot be coded |
| A record’s RBA can change | A record’s RBA cannot be changed | A record’s RRN cannot changed |
| Free space can be used for adding new record or updating(length) of existing records | Free space created out of inactive record cannot be used as deleted records continue to exist physically. Thus new records are only appended(added to end) | Any Empty slots can be used for adding new records |
| Record deletion is possible | Record physical deletion is not possible. REWRITE of same length is possible | Record deletion is possible |
| Spanned records are allowed | Spanned records are allowed | Spanned records are not allowed |
| Highlight of KSDS:- Famous due to easy random access | Highlight of ESDS:- Occupies less space | Highlight of RRDS:- It is consider as fastest access method |