CREATING HYBRID AND TOP-FREQUENCY HISTOGRAMS

摘要

Techniques for processing queries are provided. In one approach, an execution plan for a query includes multiple sub-plans, one or more of which are selected at runtime while one or more other sub-plans are not executed during execution of the execution plan. In another approach, data about misestimate is generated and stored persistently for subsequent queries. In another approach, statistics for a database object are generated automatically and efficiently while the database object is created or data items are added thereto. In another approach, a hybrid histogram is created that includes a feature of frequency histograms and a feature of height-balanced histograms. In another approach, computer jobs are executed in such a way to avoid deadlock. In another approach, changes to a database object trigger a hard parse of a query even though an execution plan already exists for the query.

主权项

1. A method comprising:
analyzing a plurality of values; generating a histogram that includes a plurality of buckets, each of which includes one or more values from the plurality of values; wherein a number of the plurality of buckets is less than a number of distinct values in the plurality of values; wherein each bucket of two or more buckets in the plurality of buckets is associated with two endpoints, each of which indicates (1) either a highest value associated with said each bucket or a lowest value associated with said each bucket and (2) a frequency value that indicates a frequency of the distinct value associated with said each endpoint; wherein the method is performed by one or more computing devices.