David Hulse

Operating system support for persistent and recoverable computations

The principal tasks of an operating system are to manage the resources of the system, maintain the permanent data of the system and to provide an efficient environment for the execution of user programs. In conventional operating systems these tasks are centred around the file system as the repository of permanent data and virtual memory as the execution environment. Persistent systems offer an alternative view in which the lifetime of data is separated from the access mechanism. In a persistent system all data, regardless of its lifetime, is created and manipulated in a uniform manner. When persistence is included as the basic abstraction of an operating system, many of the inadequacies of existing operating systems are eliminated and the tasks of an application developer are greatly simplified. This results in major improvements both in terms of program development time and execution efficiency. Grasshopper, a persistent operating system being developed by the authors, provides a testbed for the demonstration of these claims.

On page-based optimistic process checkpointing

Persistent object systems must provide some form of checkpointing to ensure that changes to persistent data are secured on non-volatile storage. When processes share or exchange modified data, mechanisms must be provided to ensure that they may be consistently checkpointed. This may be performed eagerly by synchronously checkpointing all dependent data. Alternatively, optimistic techniques may be used where processes are individually checkpointed and globally consistent states are found asynchronously. This paper examines two eager checkpointing techniques and describes a new optimistic technique. The technique is applicable in systems such as SASOS, where the notion of process and address space are decoupled.<<ETX>>

Operating system support for persistent systems: past, present and future

Since the 1980s, various groups have been constructing systems that support a concept known as orthogonal persistence. These systems support objects whose lifetime is independent of the context in which they were created. The benefits of such systems include greater run‐time efficiency, strong semantic guarantees about the existence of data and its type, early error checking, and lower construction costs. However, the implementation of persistent systems has been hindered by the lack of support provided by the operating system. This paper examines the implementation of persistent systems on traditional operating systems and on operating systems that directly support persistence, and looks at current attempts to provide flexible architectures that permit persistence to be provided efficiently above the operating system. Copyright