AUTOMATIC DATABASE STATISTICS MAINTENANCE AND PLAN REGENERATION

A system for automatically maintaining database statistics comprises a query optimizer which automatically generates statistics derived from data in a database and selects an executable procedure from a plurality of procedures that operate on data in the database using the automatically generated statistics. The query optimizer maintains counters of changes made to the data and automatically updates statistics derived from the data when the counters exceed a threshold. A statistic schema version is maintained for each statistic and incremented when the underlying data is updated. If the statistic schema version changes from that value with which the execution plan was generated, the execution plan is discarded and a new execution plan developed.