Dremel is a scalable, interactive ad hoc query system for analysis of read-only
nested data. By combining multilevel execution trees and columnar data layout, it
is capable of running aggregation queries over trillion-row tables in seconds. The
system scales to thousands of CPUs and petabytes of data, and has thousands of
users at Google. In this paper, we describe the architecture and implementation of
Dremel, and explain how it complements MapReduce-based computing. We present a
novel columnar storage representation for nested records and discuss experiments on
few-thousand node instances of the system.