Method, system, program for determining frequency of updating database histograms

1. For a database management system to be operatively coupled to a data processing system, the data processing system comprising memory for storing a data table, a method of determining frequency of updating a histogram of the data table, the method comprising:

determining sampled histograms for sample portions of the data table over a period of time;

computing a difference between at least two of the determined sampled histograms;

determining a frequency with which to update the histogram of the data table depending on the amount of the computed difference; and

storing the determined frequency in the memory to update the histogram of the data table,

wherein the determined sampled histograms include histogram sections; the step of computing the computed difference comprises:

adjusting the sections of one sampled histogram to line up with sections of another sampled histogram;

subtracting each section of the another sampled histogram from a corresponding section of the one sampled histogram; and

computing the sum of the subtracted sections,

wherein the method further comprises dividing the computed sum by a length of the x-axis of at least one of the one sampled histogram and the another sampled histogram.

2. The method of claim 1 wherein the step of determining the frequency comprises comparing the computed difference against a pre-set threshold level value.

3. The method of claim 1 wherein the computed difference is a geometric aspect representing a difference between the at least two of the sampled histograms.

4. The method of claim 3 wherein the geometric aspect represents an area under a curve.

5. The method of claim 3 , wherein the geometric aspect represents a perimeter length of a curve.

6. A database management system comprising a central processing unit and to be operatively coupled to a data processing system, the data processing system comprising memory for storing a data table, the database management system for determining frequency of updating a histogram of the data table, the database management system further comprising:

means for determining sampled histograms for sample portions of the data table from time to time;

means for computing a difference between at least two of the determined sampled histograms;

means for determining a frequency with which to update the histogram of the data table depending on the amount of the computed difference; and

means for storing the determined frequency in the memory to update the histogram of the data table,

wherein the determined sampled histograms include histogram sections; the means for computing the computed difference comprises:

means for adjusting the sections of one sampled histogram to line up with sections of another sampled histogram

means for subtracting each section of the another sampled histogram from a corresponding section of the one sampled histogram; and

means for computing the sum of the subtracted sections,

wherein the database management system further comprises means for dividing the computed sum by a length of the x-axis of at least one of the one sampled histogram and the another sampled histogram.

7. The database management system of claim 6 wherein the means for determining the frequency comprises comparing the computed difference against a pre-set threshold level value.

8. The database management system of claim 6 wherein the computed difference is a geometric aspect representing a difference between the at least two of the sampled histograms.

9. The database management system of claim 8 wherein the geometric aspect represents an area under a curve.

10. The database management system of claim 8 wherein the geometric aspect represents a perimeter length of a curve.