Dean S. Daniels

Support for Distributed Transactions in the TABS Prototype

The TABS prototype is an experimental facility that provides operating system-level support for distributed transactions that operate on shared abstract types. The facility is designed to simplify the construction of highly available and reliable distributed applications. This paper describes the TABS system model, the TABS prototypes structure, and certain aspects of its operation. The paper concludes with a discussion of the status of the project and a preliminary evaluation.

Distributed logging for transaction processing

Increased interest in using workstations and small processors for distributed transaction processing raises the question of how to implement the logs needed for transaction recovery. Although logs can be implemented with data written to duplexed disks on each processing node, this paper argues there are advantages if log data is written to multiple log server nodes. A simple analysis of expected logging loads leads to the conclusion that a high performance, microprocessor based processing node can support a log server if it uses efficient communication protocols and low latency, non volatile storage to buffer log data. The buffer is needed to reduce the processing time per log record and to increase throughput to the logging disk. An interface to the log servers using simple, robust, and efficient protocols is presented. Also described are the disk data structures that the log servers use. This paper concludes with a brief discussion of remaining design issues, the status of a prototype implementation, and plans for its completion.

An algorithm for replicated directories

This paper describes a replication algorithm for directory objects based upon Giffords weighted voting for files. The algorithm associates a version number with each possible key on every replica and thereby resolves an ambiguity that arises when directory entries are not stored in every replica. The range of keys associated with a version number changes dynamically; but in all instances, a separate version number is associated with each entry stored on every replica. The algorithm exhibits favorable availability and concurrency properties. There is no performance penalty for associating a version number with every possible key except on Delete operations, and simulation results show this overhead is small.

A weighted voting algorithm for replicated directories

Weighted voting is used as the basis for a replication technique for directories. This technique affords arbitrarily high data availability as well as high concurrency. Efficient algorithms are presented for all of the standard directory operations. A structural property of the replicated directory that permits the construction of an efficient algorithm for deletion is proven. Simulation results are presented and the system is modeled and analyzed. The analysis agrees well with the simulation, and the space and time performance are shown to be good for all configurations of the system.

An algorithm, for replicated directories

This paper describes a replication algorithm for directory objects based upon Giffords weighted voting for files. The algorithm associates version number with each possible key on every replica and thereby resolves an ambiguity that arises when directory entries are not stored in every replica. The range of keys associated with a version number changes dynamically; but in all instances, a separate version number is associated with each entry stored on every replica. The algorithm exhibits favorable availability and concurrency properties. There is no performance penalty for associating a version number with every possible key except on Delete operations, and simulation results show this overhead is small.

High Performance Distributed Transaction Processing in a General Purpose Computing Environment

This paper argues that transaction processing adds relatively little overhead to applications that access shared abstract data objects. It also argues that transaction processing can be made easy to use for both users and implementors of shared objects. The implication is that transaction processing can be a very useful technique in a variety of application domains. To provide more evidence as to the utility of transaction systems, the paper briefly describes the Camelot Distributed Transaction Facility, which has been developed at Carnegie Mellon University. Camelot executes on a variety of uni- and multi-processors on top of the Unix-compatible, Mach operating system. The paper also describes Camelots interfaces and contains preliminary performance information gathered on pre-alpha release versions of Camelot.