Automatic reclustering of objects in very large databases for high energy physics
Koen Holtman, Peter van der Stok, Ian Willers · 2002
In the very large object database systems planned for some future particle physics experiments, typical physics analysis jobs will traverse millions of read-only objects, many more objects than fit in the database cache. Thus, a good clustering of objects on disk is highly critical to database performance. We present the implementation and performance measurements of a prototype reclustering mechanism which was developed to optimise I/O performance under the changing access patterns in a high energy physics database. Reclustering is done automatically and on-line. The methods used by our prototype differ greatly from those commonly found in proposed general-purpose reclustering systems. By exploiting some special characteristics of the access patterns of physics analysis jobs, the prototype manages to keep database I/O throughput close to the optimum throughput of raw sequential disk access.