Dremel - Googles Datase tool for analyzing trillion-row tables in seconds

Dremel is a SQL based scalable, interactive ad-hoc query system for analysis of read-only nested data. By combining multi-level 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

Here's an brief introduction:

http://sergey.melnix.com/pub/melnik_VLDB10.pdf