Nested Transactions

Replicated servers are wrapped up in ``meta-servers'', so that the replication is transparent., However, this leads to the requirement to map any transaction to the meta-server, into a transaction or set of them to the servers within. This is called ``nested'' transactions. The idea is generalized in most real distributed system platforms, to provide a way of creating hierarchically structured servers built out of other servers. The idea is to get the same gain for a distributed system that hierarcical modularisation gains for single programs. There is a consequence of this, that the fault/failure models must reflect the nesting of services, and some care is needed in making sure that a system built out of nested servers does not have less fault tolerance than a monolithic one.