Incremental maintenance of an approximate histogram in a database system
US5870752A · kind A · utility
Assignees
Inventors
Key dates
| Filing date | Aug 21, 1997 |
| Grant date | Feb 9, 1999 |
| Priority date | — |
| Expiry date | Aug 21, 2017 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S707/99945
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
Techniques for maintaining an approximate histogram of a relation in a database, in the presence of updates to the relation. The histogram includes a number of subsets, or "buckets," each representing at least one possible value of an attribute of the relation. Each of the subsets has a count associated therewith indicative of the frequency of occurrence of the corresponding value of the attribute. After an update to the relation, the counts associated with the subsets are compared to a threshold. If the count associated with a given subset exceeds the threshold, the given subset is separated at its median into two separate subsets. After the separation operation, the two subsets with the lowest counts are combined such that a constant number of subsets are maintained in the histogram, if the total combined count of the subsets does not exceed the threshold. If no two subsets have a total combined count which does not exceed the threshold, the histogram is recomputed from a random sample of the relation. The invention substantially reduces the number of times the histogram must be recomputed from the random sample, and is particularly well-suited for use with approximate equi-depth…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.