Abstract: An execution plan for executing one or more iterations of recursive database queries can be generated in accordance with one aspect of the invention. For example, in accordance with one embodiment of the invention, one or more cardinalities (results or size of results, including intermediate results) associated with one or more iterations can be estimated. This estimation can, for example, by performed by using a sampling or sampling-based algorithm. In addition, a plan generated for execution of one or more iteration of a recursive query can be modified or replaced by comparing the actual cardinality with its estimation. As a result, the first one or more iterations may be executed using a first plan but the subsequent one or more iterations may use a modified or different execution plan.

Abstract: Excess capacity of a database system can be used for learning activities in a controlled computing environment. In this context, excess capacity of a database system can be used as needed and/or on a temporary basis. Furthermore, learning activities can be performed without requiring the use of the capacity that is configured or has been allotted for various other database operations, including those deemed, especially by the users of database system, to serve a main function or a more important purpose. As a result, learning can be performed without adversely affecting other operations deemed to be more critical, especially by the users of databases. Learning activities associated with a database environment can, for example, include learning operations directed to optimization of database queries, for example, by using a basic feedback or an expanded or active learning.