Breaking the Memory Wall in MonetDB

Abstract

The rate of improvement in microprocessor speed exceeds the rate of improvement in DRAM memory speed — each is improving exponentially, but the exponent for microprocessors is substantially larger than that for DRAMs. The difference between diverging exponentials also grows exponentially. Main-memory access has therefore become a performance bottleneck for many computer applications; a phenomenon that is widely known as the “memory wall.” This report focuses on how research around the MonetDB database system has led to a redesign of database architecture in order to take advantage of modern hardware, and in particular to avoid hitting the memory wall. This encompasses (i) a redesign of the query execution model to better exploit pipelined CPU architectures and CPU instruction caches; (ii) the use of columnar rather than row-wise data storage to better exploit CPU data caches; (iii) the design of new cache-conscious query processing algorithms; and (iv) the design and automatic calibration of memory cost models to choose and tune these cache-conscious algorithms in the query optimizer.