Limiting Plan Choices For Database Queries Using Plan Constraints

摘要

A database system allows users to specify plan constraint specification that limit choices of execution plans considered by an optimizer of the database system for optimizing database queries. The plan constraint specification specifies attributes of execution plans. The plan constraint specification may identify tables/intermediate results that the plan constraint is applicable to using table names or aliases. The database system applies the plan constraint specification to database queries that match the tables/aliases specified in the plan constraint specification. The database system limits the choice of execution plans evaluated for a database query to execution plans satisfying the attributes specified in an applicable plan constraint specification. The plan constraint specification may specify distribution of a table, a join order for tables, the join mechanism, cardinality of a table or intermediate result, and so on.

主权项

1. A computer-implemented method for limiting the execution plans evaluated by database system for queries, the method comprising:
receiving a plan constraint specification for limiting execution plan choices for optimizing database queries, the plan constraint specification identifying a plurality of tables and specifying attributes of execution plans; matching the plurality of tables of the plan constraint specification with one or more database queries; determining that the plan constraint specification is applicable to a database query if the database query processes each of the plurality of tables; optimizing the database query by limiting the search for execution plans to a set of execution plans that satisfy the attributes of execution plans specified by the plan constraint specification; selecting an execution plan from the set of execution plans for executing the database query; and sending the selected execution plan for executing the database query.