  Database management systems (DBMSs) have largely ignored the task of managing
the energy consumed during query processing. Both economical and environmental
factors now require that DBMSs pay close attention to energy consumption. In
this paper we approach this issue by considering energy consumption as a
first-class performance goal for query processing in a DBMS. We present two
concrete techniques that can be used by a DBMS to directly manage the energy
consumption. Both techniques trade energy consumption for performance. The
first technique, called PVC, leverages the ability of modern processors to
execute at lower processor voltage and frequency. The second technique, called
QED, uses query aggregation to leverage common components of queries in a
workload. Using experiments run on a commercial DBMS and MySQL, we show that
PVC can reduce the processor energy consumption by 49% of the original
consumption while increasing the response time by only 3%. On MySQL, PVC can
reduce energy consumption by 20% with a response time penalty of only 6%. For
simple selection queries with no predicate overlap, we show that QED can be
used to gracefully trade response time for energy, reducing energy consumption
by 54% for a 43% increase in average response time. In this paper we also
highlight some research issues in the emerging area of energy-efficient data
processing.
