Implementation of the transactor model : fault tolerant distributed computing using asynchronous local checkpointing

Abstract

The Transactor model, an extension to the Actor Model, is a well-formulated way to model distributed concurrent systems while maintaining a global distributed state. This model provides semantics to track dependencies among loosely-coupled distributed components that ensures fault tolerance through a two-phase commit protocol and issues rollbacks in the presence of failures or state inconsistency. We seek to introduce an implementation of this model through a transactor language as an extension of an existing actor language and highlight the capabilities of this programming model.

We developed our transactor language using SALSA, an actor language developed as a dialect of Java. This transactor language will in turn be a dialect of SALSA, which similarly will compile into Java code. We first develop our transactor language as a basic SALSA/Java library in conjunction with the SALSA Java library. This library implements the fundamental semantics of the transactor model following the defined transition rules. We then provide example programs written using this library such as the reference cell, banking transfer, and the house purchase transaction. Furthermore, we seek to expand our language by introducing a state storage property known as the Universal Storage Location as an extension of the Universal Actor Name and Universal Actor Locator in SALSA that levies a Storage Service to maintain checkpointed transactor states. We also introduce the Consistent Transaction Protocol and Ping Director that improves upon the Universal Checkpointing Protocol to aid transactor programs in reaching globally consistent states and perform reliable transactions.