8. A system for optimizing query performance in a relational database management system, comprising: a processor; and a memory containing instructions executable by the processor, the instructions being operable to cause the processor to perform the following operations: receiving a query at the relational database management system; determining whether the query is expected to be a long-running query; in response to determining that the query is expected to be a long-running query, starting a full table scan to fetch records needed to satisfy the query from the relational database management system; in parallel with conducting the full table scan, building a performance object capable of satisfying the query in the relational database management system; in response to completing the construction of the performance object prior to completing the full table scan, stopping the full table scan and using the newly built performance object instead to satisfy the query; and storing the performance object in one or more of: storage and memory, for a predetermined time period.
8. A system for optimizing query performance in a relational database management system, comprising: a processor; and a memory containing instructions executable by the processor, the instructions being operable to cause the processor to perform the following operations: receiving a query at the relational database management system; determining whether the query is expected to be a long-running query; in response to determining that the query is expected to be a long-running query, starting a full table scan to fetch records needed to satisfy the query from the relational database management system; in parallel with conducting the full table scan, building a performance object capable of satisfying the query in the relational database management system; in response to completing the construction of the performance object prior to completing the full table scan, stopping the full table scan and using the newly built performance object instead to satisfy the query; and storing the performance object in one or more of: storage and memory, for a predetermined time period. 10. The system of claim 8 , wherein stopping the full table scan includes: stopping the full table scan at a hold position in each table undergoing the full table scan in accordance with a first query plan; migrating to a second query plan; and locating the corresponding hold position in the performance object; continuing the query at the corresponding hold position in the performance object, using a second query plan.