Described herein are approaches to implementing dynamic sampling in a way that lessens or eliminates the additional overhead incurred to perform dynamic sampling. Also described are techniques for determining characteristics about predicates not previously determined by conventional techniques for dynamic sampling. Dynamic sampling is used by a query optimizer to dynamically estimate predicate selectivities and statistics. When a database statement is received by a database server, an initial analysis of the database statement is made to determine the efficacy of dynamic sampling, that is, to determine whether optimization of the query would benefit from dynamic sampling and whether performance is not excessively impacted by the dynamic sampling process. If this analysis determines dynamic sampling should be used, then dynamic sampling is undertaken.