1. One or more storage media storing instructions which, when executed by one or more processors, cause: in response to receiving a query, determining an execution plan that comprises a plurality of sub-plans; after determining the execution plan, executing a portion of the execution plan, wherein executing a portion of the execution plan comprises determining whether one or more criteria are satisfied; if the one or more criteria are satisfied, then executing a first sub-plan of the plurality of sub-plans; if the one or more criteria are not satisfied, then executing another portion of the execution plan without executing the first sub-plan.