Improved A* Algorithm For Query Optimization

Abstract

Exponential growth in number of possible strategies with the increase in number of relations in a query has been identified as a major problem in the field of query optimization of relational databases. Present database systems use exhaustive search to find the best possible strategy. But as the size of a query grows, exhaustive search method itself becomes quite expensive. Other algorithms like A* algorithm, Simulated Annealing etc. have been suggested as a solution. However, all these algorithms fail to produce the best results; necessarily required for query execution. We did some modifications to the A* algorithm to produce a randomized form of the algorithm and compared it with the original A* algorithm and exhaustive search. The comparison results have shown improved A* algorithm to be almost equivalent in output quality along with a colossal decrease in search space in comparison to exhaustive search method.

In situ observations of carbon nanotube formation using environmental transmission electron microscopy

“…The first set of experiments was performed using 100-1500 mTorr of propylene as precursor gas and Ni-SiO 2 as the catalyst-support system. In the second set of experiments, Ni-SiO 2 catalystsupport samples were heated at low ͑450°C͒ and high ͑750°C͒ temperatures whereas the Co, Mo-MgO catalystsupport samples were heated only at high temperatures in 100-1500 mTorr of acetylene, in order to compare the ETEM results with the bulk synthesis process using CO. 10 Images were recorded using a CCD camera ͑1024ϫ1024 a͒ Electronic mail: renu.sharma@asu.edu APPLIED PHYSICS LETTERS VOLUME 84, NUMBER pixels͒ and a digital video recording system before, after and during the reaction. Ex-situ HREM images were recorded using a JEOL 4000EX operated at 400 KV with 0.17 nm point resolution.…”