In this topic, we explain about the below sections -
The VSAM datasets are divided into three types based on the storage of data and accessing of data. They are -
- Entry Sequential Dataset (ESDS) .
- Key Sequential Dataset (KSDS) .
- Relative Record Dataset .
- Fixed-length RRDS (RRDS).
- Variable-length RRDS (VRRDS).
- Linear Dataset (LDS) .
VSAM file types supporting access modes and record length -
|File Organization||Access Type||Record Length|
|Sequential Access||Random Access||Dynamic Access||Fixed-length||Variable-length|
ESDS, KSDS, RRDS, VRRDS, and LDS Comparison -
|ESDS||KSDS||Fixed-length RRDS||Variable-length RRDS||LDS|
|What is the method for sequential access?||Entry/Inserting order||Primary key field ascending order||RRN order||RRN order||No record level processing|
|What are the types of record format?||Allows fixed-length, variable-length and spanned records||Allows fixed-length, variable-length and spanned records||Allows fixed-length||Allows variable-length||No record level processing|
|What is the method for direct access?||RBA||Key or RBA||RRN||RRN||Acess with DIV(Data-In-Virtual)|
|What are the Components the dataset have?||DATA Component only||DATA and INDEX Components||DATA Component only||DATA and INDEX Components||DATA Component only|
|Can RBA or RRN change?||A records's RBA can't change||A records's RBA can change||A records's RRN can't change||A records's RRN can't change||No record level processing|
|Can we delete the record?||Record can't be deleted. We can reuse the record for a record of the same length.||Deleting the record space becomes free space.||Slot freeed by deleting the record can be reused.||Deleting the record space becomes free space.||No record level processing|
|Can we reuse the deleted record space?||No||Yes||Yes||Yes||No record level processing|
|Is record length changeable?||No||Yes||No||Yes||Extended format allowed|
|Where are new records added?||End of the file||Anywhere||RRN Slot||RRN Slot||CI|
|Can you REUSE the file?||Yes (If no AIX)||Yes (If no AIX)||Yes||Yes||Yes|
|Can we access the data set through an alternate index?||Yes||Yes||No||No||No|
|What space used to insert records?||Space at the end of the dataset used||Free space is used for inserting and lengthening records||Empty slots are used||Free space is used for inserting and lengthening records||No record level processing|
|Is embedded free space defined?||No||Yes||No||No||No|
|Was spanned Records allowed?||Allowed||Allowed||No spanned records||No spanned records||No spanned records|
|Was Extended Format/Compression allowed?||Extended format allowed||Extended format or compression allowed||Extended format allowed||Extended format allowed||Extended format allowed|