Physical database design is important for query performance in a shared-nothing parallel database system, in which data is horizontally partitioned among multiple independent nodes. We seek to automate the process of data partitioning. Given a workload of SQL statements, we seek to determine automatically how to partition the base data across multiple nodes to achieve o verall optimal or close to optimal performance for that workload. Previous attempts use heuristic rules to make those decisions. These approaches fail to consider all of the interdependent aspects of query performance typically modeled by t o d a y's sophisticated query optimizers.We present a comprehensive solution to the problem that has been tightly integrated with the optimizer of a commercial shared-nothing parallel database system. Our approach uses the query optimizer itself both to recommend candidate partitions for each table that will bene t each query in the workload, and to evaluate various combinations of these candidates. We compare a rank-based enumeration method with a random-based one. Our experimental results show that the former is more e ective.

No abstract

No abstract

HighlightMolecular characterization of dihydroxyacid dehydratase in Arabidopsis reveals its important roles in gametophyte and root development, as well as involvement in salinity stress resistance.

Current gene delivery methods for maize are limited to specific genotypes and depend on time‐consuming and labor‐intensive tissue culture techniques. Here, we report a new method to transfect maize that is culture‐free and genotype independent. To enhance efficiency of DNA entry and maintain high pollen viability of 32%‐55%, transfection was performed at cool temperature using pollen pretreated to open the germination aperture (40%–55%). Magnetic nanoparticles (MNPs) coated with DNA encoding either red fluorescent protein (RFP), β‐glucuronidase gene (GUS), enhanced green fluorescent protein (EGFP) or bialaphos resistance (bar) was delivered into pollen grains, and female florets of maize inbred lines were pollinated. Red fluorescence was detected in 22% transfected pollen grains, and GUS stained 55% embryos at 18 d after pollination. Green fluorescence was detected in both silk filaments and immature kernels. The T1 generation of six inbred lines showed considerable EGFP or GUS transcripts (29%–74%) quantitated by polymerase chain reaction, and 5%–16% of the T1 seedlings showed immunologically active EGFP or GUS protein. Moreover, 1.41% of the bar transfected T1 plants were glufosinate resistant, and heritable bar gene was integrated into the maize genome effectively as verified by DNA hybridization. These results demonstrate that exogenous DNA could be delivered efficiently into elite maize inbred lines recalcitrant to tissue culture‐mediated transformation and expressed normally through our genotype‐independent pollen transfection system.