Optimizing Your Compaq COBOL Program
15.7 Optimizing File Design (OpenVMS)
• Index records:
If a file has more than 65,536 blocks, the 3-byte index record overhead could
increase to 5 bytes.
Use these calculations to determine SIDR record length:
• No duplicates allowed:
• Duplicates allowed:
Note
Bucket packing efficiency determines how well bucket space is used. A
packing efficiency of 1 means the buckets of an index are full. A packing
efficiency of .5 means that, on the average, the buckets are half full.
Consider an indexed file with these attributes:
• 100,000 fixed-length records of 200 characters each
• Primary key = 20 characters
• Alternate key = 8 characters, no duplicates allowed
• Bucket size = 3 (an arbitrary value)
• No fill number
Primary key index level calculations:
In the following calculations, some results are to be rounded up, and some
truncated.
Level 0 (data level buckets):
Level 1 (index buckets):
Optimizing Your Compaq COBOL Program 15–23
