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Abstract

Atomicity and isolation of transactions are key requirements of advanced
applications in federated systems consisting of distributed and heterogeneous
components. While all existing federated systems support atomicity using the
two-phase commit protocol, they lack support for federated concurrency control.
Many possible solutions have been proposed in the literature, but they failed
to make impact on real systems because they
completely ignored the widely used concept of isolation levels, which offer
optimization options to applications at the cost of less rigorous control over
data consistency.

This thesis compares existing definitions for isolation levels and develops a
new characterization for Snaphot Isolation, an isolation level provided by
Oracle, the market leader in the database field. We present algorithms for
federated concurrency control that provably guarantee the correct execution of
federated transactions even under local Snapshot Isolation, and discuss
isolation levels for federated transactions. The algorithms are integrated into
a federated system prototype. Performance measurements with this prototype show
the practical viability of the developed methods.