I've been attempting to discover the "best" blocking factors to use
on by datasets. My goal is to reduce the wasted space in each block.
I've setup an Excel spreadsheet which processes each block size, and
calculates the percent waste. I'm using the "Solver" feature to
determine the valid block sizes, and to show me the one with the minimum
percent waste.
Could someone please let me know if these are the correct
calculations? They don't match what DBGeneral indicates as the block
size to use for minimum disk. In the spreadsheet, the "Rounded Block
Size" is the "true" block size.
Bit Map Words Required
=CEILING(Blocking_Factor/16,1)
Block Size (Buffer Length)
=Bit Map Words Required+(Blocking_Factor*Media Length)
Number of 128 Word Blocks
=CEILING(Block Size/128,1)
Rounded Block Size
=Number of 128 Word Blocks*128
Wasted Space (Words) per Block
=Rounded Block Size-Block Size
Percent Waste
=Wasted Space/Rounded Block Size*100
I'm imposing the following restrictions:
Blocking Factor must be an integer.
Blocking Factor must be greater than or equal to 1.
Rounded Block Size must be less than or equal to 2560.
Rounded Block Size must be greater than or equal to 128.
For instance, on a dataset with a media length of 262, DBGeneral is
indicating that the block size for minimum disk is 896, with a 12.2
percent waste. My spreadsheet shows that if I use a "Rounded" block
size of 896, there is 12.17 percent waste. My spreadsheet is showing
that the block size for minimum disk is 2432, with a 3 percent waste.
Does anyone know if the above calculations are correct, or why
DBGeneral is reporting different numbers?
Thanks in advance,
David N. Lukenbill
--------------------------------------------
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Raytheon Missile Systems Company, Louisville
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