In the past, there has also been a lot of work on
implementing database systems over conventional shared-nothing architectures,
as reviewed in DeWitt and Gray (1992). A shared-nothing architecture consists of
a set of independent computer nodes that are connected through some network.
Each node has its own storage devices and there is no expensive local area storage
network with shared storage devices. Additionally, the NPDW does not assume any
specialized fast interconnects between nodes, as it should work over a nondedicated
local area network. In this context, performance is very dependent on strategies to
partition data into nodes??™ storage devices and processing into nodes??™ processing
units, respectively. It is also very dependent on achieving a balance between data
exchange requirements and autonomous processing among nodes. The lack of fast
specialized hardware and interconnects in the target environment means that there
206 Furtado
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would be too large a penalty if relations were not carefully placed among nodes to
explore parallelism power and reduce bottlenecks. This is the reason why one of
the major concerns is to decide how to partition or cluster relations into nodes both
on initial placement and subsequent reorganizations.
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