The following table provides estimates of the amount of space each index uses compared to the amount of column data from the source database or flat file.
Type of index |
Estimated space versus raw data |
Comments |
|---|---|---|
Default |
Smaller than or equal to |
If the number of distinct values is less than 255, this index uses significantly less space than the raw data |
High_Group |
Smaller than up to twice as large |
As the number of distinct values decreases (that is, the number of entries per group increases), the space used decreases in proportion to the size of the raw data |
High_Non_Group |
Smaller than or equal to |
Smaller than the raw data in most cases |
Low_Fast |
Smaller than up to twice as large |
Same as High_Group |
Date |
Smaller than or equal to |
Larger than High_Non_Group |
Time |
Smaller than or equal to |
Larger than High_Non_Group |
Datetime |
Smaller than or equal to |
Larger than High_Non_Group |
For LF and HG indexes, the index size depends on the number of unique values. The more unique values, the more space the index requires.
Because CMP indexes are always an additional index, they do not save disk space.