Increasing Query Speed with Multithreaded Data Prefetching

The Infobright database engine stores data in column wise chunks in a highly compressed form. Access to data is slowed down by the necessity of fetching required chunks from disk and decompressing them. A prefetching mechanism is meant to perform these tasks shortly before a running query needs the data for processing. The prefetching implementation in Infobright is described and evaluated. An average speedup of 1.7 is reported. The speedup reaches 2.4 for some queries and generally is higher for long lasting queries for which the data fetching and decompression cost dominated the execution time. The limitations of the prefetching are presented on both system level and SQL query level.