Optimizing YourCompaq 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 YourCompaq COBOL Program 1523