A relational database system (206; 306; 800), comprising: a query optimizer (212; 312; 612; 812) configured to receive a query (204; 304) from a query-generating entity (202; 302) and to determine a sequence of operations for executing the query, wherein the query optimizer is configured to generate a high-level execution plan (216; 316; 616) that specifies the sequence of operations, and wherein the high-level execution plan does not indicate the physical operators that should be used to perform the sequence of operations; and a query execution engine (214; 314; 414; 514; 614; 814) configured to use real-time statistics (224; 624) to select physical operators (218; 518; 818) for performing the sequence of operations, wherein the query execution engine is configured to: request and receive cost estimates (222; 522) from a plurality of available physical operators; provide real-time statistics to the plurality of available physical operators, wherein the plurality of available physical operators use the real-time statistics to produce the cost estimates; and select the physical operators to perform the sequence of operations using the cost estimates, wherein the real-time statistics reflect current conditions of the relational database system when the query is being executed, and wherein the cost estimate provided by a particular physical operator in relation to a particular operation indicates how efficiently that physical operator can perform the operation under current conditions, taking the real-time statistics into account. a query optimizer (212; 312; 612; 812) configured to receive a query (204; 304) from a query-generating entity (202; 302) and to determine a sequence of operations for executing the query, wherein the query optimizer is configured to generate a high-level execution plan (216; 316; 616) that specifies the sequence of operations, and wherein the high-level execution plan does not indicate the physical operators that should be used to perform the sequence of operations; and a query execution engine (214; 314; 414; 514; 614; 814) configured to use real-time statistics (224; 624) to select physical operators (218; 518; 818) for performing the sequence of operations, wherein the query execution engine is configured to: request and receive cost estimates (222; 522) from a plurality of available physical operators; provide real-time statistics to the plurality of available physical operators, wherein the plurality of available physical operators use the real-time statistics to produce the cost estimates; and select the physical operators to perform the sequence of operations using the cost estimates, wherein the real-time statistics reflect current conditions of the relational database system when the query is being executed, and wherein the cost estimate provided by a particular physical operator in relation to a particular operation indicates how efficiently that physical operator can perform the operation under current conditions, taking the real-time statistics into account. request and receive cost estimates (222; 522) from a plurality of available physical operators; provide real-time statistics to the plurality of available physical operators, wherein the plurality of available physical operators use the real-time statistics to produce the cost estimates; and select the physical operators to perform the sequence of operations using the cost estimates, wherein the real-time statistics reflect current conditions of the relational database system when the query is being executed, and wherein the cost estimate provided by a particular physical operator in relation to a particular operation indicates how efficiently that physical operator can perform the operation under current conditions, taking the real-time statistics into account.