Issues of organizing computations in multicomputer systems with the software-controlled failure- and fault-tolerance. Part II

This three-part paper analyzes existing approaches and methods of organizing failure- and fault-tolerant computing in distributed multicomputer systems (DMCS), identifies and provides rationale for a list of issues to be solved. We review the application areas of failure- and fault- tolerant control systems for complex network and distributed objects. The second part further investigates the issues of organizing failure- and fault- tolerance in the DMCS. The systemic, functional, and test diagnostics are viewed as the basis for building unattended failure- and fault-tolerant systems. We introduce the concept of self-managed degradation (when the DMCS eventually proceeds to a safe shutdown at a critical level of degradation) as a means to increase the DMCS active life.

Test

Unfortunately, we cannot rely on designed and possibly already manufactured systems to operate as expected. These systems may have become defective during their use, or their function may have been compromised during the fabrication or their design. The purpose of testing is to verify whether or not an existing embedded/cyber-physical system can be operated as expected. In this chapter, we will present fundamental terms and techniques for testing. There will be a brief introduction to the aims of test pattern generation and their application. We will be introducing terms such as fault model, fault coverage, fault simulation, and fault injection. Also, we will be presenting techniques which improve testability, including the generation of pseudo-random patterns, and signature analysis. It would be beneficial to consider testability issues already during design. In case of fault-tolerant systems, resilience must be verified.

An implementation of a fault-tolerant database system using the actor model

Fault-tolerant systems are an important discussion subject in our world of interconnected devices. One of the major failure points of every distributed infrastructure is the database. A data migration or an overload of one of the servers could lead to a cascade of failures and service downtime for the users. NoSQL databases sacrifice some of the consistency provided by traditional SQL databases while privileging availability and partition tolerance. This paper presents the design and implementation of a distributed in-memory database that is based on the actor model. The benefits of the actor model and development using functional languages are detailed, and suitable performance metrics are presented. A case study is also performed, showcasing the system’s capacity to quickly recover from the loss of one of its machines and maintain functionality.