By default, each histogram has 20 steps, which provides good performance and modeling for columns that have an even distribution of values. A higher number of steps can increase the accuracy of I/O estimates for:
Columns with a large number of highly duplicated values
Columns with unequal or skewed distribution of values
Columns that are queried using leading wildcards in like queries
The histogram tuning factor default of 20 automatically chooses a step value between the current requested step value (default 20) and the increased steps due to the factor (20 * 20 = 400) so that Adaptive Server will automatically choose the optimal steps value to compensate for the above cases. Overriding the step values should take into account the larger number of steps already introduced by the histogram tuning factor.
If your database was updated from a pre-11.9
version of the server, the number of steps defaults to the number
of steps that were used on the distribution page.
