Data consistency in intermittently connected distributed systems
Pitoura, E.; Bhargava, B.
Knowledge and Data Engineering, IEEE Transactions on
Volume 11, Issue 6, Nov/Dec 1999 Page(s):896 - 915
Digital Object Identifier 10.1109/69.824602
Summary:Mobile computing introduces a new form of distributed computation
in which communication is most often intermittent, low-bandwidth, or
expensive, thus providing only weak connectivity. We present a
replication scheme tailored for such environments. Bounded inconsistency
is defined by allowing controlled deviation among copies located at
weakly connected sites. A dual database interface is proposed that in
addition to read and write operations with the usual semantics supports
weak read and write operations. In contrast to the usual read and write
operations that read consistent values and perform permanent updates,
weak operations access only local and potentially inconsistent copies
and perform updates that are only conditionally committed. Exploiting
weak operations supports disconnected operation since mobile clients can
employ them to continue to operate even while disconnected. The extended
database interface coupled with bounded inconsistency offers a flexible
mechanism for adapting replica consistency to the networking conditions
by appropriately balancing the use of weak and normal operations.
Adjusting the degree of divergence among copies provides additional
support for adaptivity. We present transaction-oriented correctness
criteria for the proposed schemes, introduce corresponding
serializability-based methods, and outline protocols for their
implementation. Then, some practical examples of their applicability are
provided. The performance of the scheme is evaluated for a range of
networking conditions and varying percentages of weak transactions by
using an analytical model developed for this purpose
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