The Super Database Computer (SOC) project at the University of Tokyo presents an
interesting contrast to other database system projects. This system
takes a combined hardware and software approach to the performance problem. The basic unit,
called a processing module (PM), consists of one or more processors with a shared memory.
These processors are augmented by a special purpose sorting engine that sorts at high speed
(3MB/s at present), and by a disk subsystem. Clusters of processing modules are connected via an
omega network which not only provides non-blocking NxN interconnect, but also
provides some dynamic routing to support data distribution during hash joins. The
SOC is designed to scale to thousands of PMs, and so considerable attention is paid to the problem
of data skew. Data is declustered among the PMs by hashing.
The SOC software includes a unique operating system, and a relational database query
executor. Most publish work so far has been on query execution and on efficient algorithms to
execute the relational operations, rather than on query planning or data declustering. The SOC is a
shared-nothing design with a software dataflow architecture. This is consistent with our assertion
that current parallel database machines systems use conventional hardware. But the special purpose
design of the omega network and of the hardware sorter clearly contradict the thesis that
special-purpose hardware is not a good investment of development resources. Time will tell
whether these special-purpose components offer better price performance or peak performance than
shared-nothing designs built of conventional hardware.