Abstract
A multidatabase system (MDBS) is a system implemented on top of a collection of autonomous preexisting local database systems (LDBSs). In this paper, we show a reliable approach to nested transaction management in MDBSs. Our approach is reliable in the sense that it ensures global serializability in the face of failures. We support global nested transactions under the constraint that LDBSs only support flat transactions. We assume autonomous LDBSs which provide either a single or multiversion data manager. We adopt a deferred-update approach to replace the need for atomic commitment protocols. As a result, our approach limits the problem of indefinite blocking of local resources. This is achieved at the expense of access restrictions on some global transactions. We show how to enforce these access restrictions at a local site without modifying local application programs.
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