Query optimizer with join cardinality estimation which mitigates the effects of skew
US7945558B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Jan 9, 2008 |
| Grant date | May 17, 2011 |
| Priority date | — |
| Expiry date | Mar 2, 2029 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06F16/2453
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
One embodiment relates to a computer-implemented method to estimate a cardinality of a database query. Single table cardinalities are determined after application of selection predicates. In addition, pair-wise join selectivities are estimated without assuming independence between selection and join predicates. Said pair-wise join selectivities are multiplied with said single table cardinalities after application of the selection predicates. Another embodiment relates to a computer apparatus including a cardinality estimator. The cardinality estimator includes computer-readable instructions configured to (a) determine single table cardinalities after application of selection predicates from the database query, (b) estimate pair-wise join selectivities without assuming independence between the selection predicates and join predicates of the database query, and (c) multiply said pair-wise join selectivities with said single table cardinalities after application of the selection predicates. Other embodiments, aspects and features are also disclosed.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.