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ESDS

Entry-Sequenced Dataset

Enhanced Definition

A VSAM dataset where records are stored in the order they are written, similar to sequential files but with VSAM's advanced features. ESDS provides sequential access with VSAM's recovery and performance benefits.

Key Characteristics

- Records added at end of dataset
- No key fields required
- Sequential access primary method
- Supports addressed access via RBA
- Cannot delete records (only mark inactive)
Access Methods:
- Sequential processing (forward)
- Direct access via RBA (Relative Byte Address)
- Skip-sequential processing
- Backward processing (with alternate index)
ESDS Structure:
- Data component (records)
- No index component
- Optional alternate indexes
- Control intervals for records
- Control areas for management
When to Use ESDS:
- Log files and audit trails
- Time-stamped transaction records
- Message queues
- Sequential batch processing
- Data requiring insertion order preservation
Operations:
- Add: Append records at end
- Read: Sequential or by RBA
- Update: Modify existing records in place
- No Delete: Records can only be marked inactive