Exerdise 1 Chapter 10
1.10
The INFO service manages a potentially very large set of
resources, each of which can be accessed by users throughout the Internet by
means of a key (a string name). Discuss an approach to the design of the names
of the resources that achieves the minimum loss of performance as the number of
resources in the service increases. Suggest how the INFO service can be
implemented so as to avoid performance bottlenecks when the number of users
becomes very large.
1.10 Ans.
Algorithms that use hierarchic structures scale better than those
that use linear structures. Therefore the solution should suggest a hierarchic
naming scheme. e.g. that each resource has an name of the form ’A.B.C’ etc. where
the time taken is O(log n) where there are n resources in the system. starting
with A at server 1, with B at server 2 and so forth. There could be more than
one level of partitioning as in DNS. To avoid performance bottlenecks the
algorithm for looking up a name must be decentralised. That is, the same server
must not be involved in looking up every name. (A centralised solution would
use a single root server that holds a location database that maps parts of the
information onto particular servers). Some replication is required to avoid
such centralisation. For example: i) the location database might be replicated To
allow for large numbers of users, the resources are partitioned amongst several
servers, e.g. names
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