dspace - compute space required for RMSfile
dspace [-h%] [-i%] lfile...
Dspace prints the approximate amount of disk space (in bytes) required
for one record stored in the named RMSfile. It is useful in estimating
the amount of space required for a given number of records. When a single
RMSfile is given, just the space required is printed. If multiple
RMSfile names are given, the space required is prepended with the file name.
The -h flag adjusts the default hashed file loading factor. When estimating
the space required for a hashed RMSfile, dspace assumes the file will be
filled to approximately 70 percent of its total capacity. Most hashed
RMSfiles have a reasonable performance at this level. To estimate the
size with a different loading factor, use the -h flag with a number
between 1 and 100. The higher the percentage, the smaller the space
requirements. The default value is -h70.
The -i flag adjusts the default index tree loading factor. Each index
used with an RMSfile has some wasted space. Worst case is 50 percent
full. Best case is 100 percent full. The average loading and the
loading that gives optimum performance is between 80 to 85 percent full.
To estimate the size with a different index loading factor, use the -i
flag with a number between 50 and 100. The higher the percentage, the
smaller the space requirements. The default value is -i80.
The user has little control over the actual index load factors. The
load factor depends on how the RMSfile is filled, the number of records
stored in the RMSfile, and size of keys stored in the index tree. The
-i flag allows best and worst case estimates to be made.
A hashing load factor of 100 percent is practically impossible.