Dynamic query re-optimization

Very long-running queries in database systems are not uncommon in non-traditional application domains such as image processing or data warehousing analysis. Query optimization, therefore, is important. However, estimates of the query characteristics before query exe-cution are usually inaccurate. Further, system congu-ration and resource availability may change during long evaluation period. As a result, queries are often eval-uated with sub-optimal plan congurations. To rem-edy this situation, we have designed a novel approach to re-optimize suboptimal query plan congurations on-the- y with Conquest | an extensible and distributed query processing system. A dynamic optimizer con-siders reconguration cost as well as execution cost in determining the best query plan conguration. Experi-mental results are presented.