On unreliable computing systems when heavy-tails appear as a result of the recovery procedure

Abstract

For some computing systems, failure is rare enough that it can be ignored. In other systems, failure is so common that how to handle it can have a significant impact on the performance of the system. There are many different recovery schemes for tasks, however, they can be classified into three broad categories: 1) Resume: when a task fails, it knows exactly where it stops and can continue at that point when allowed to resume (i.e., preemptive resume - prs); 2) Replace : when a task fails, then later when the processor continues, it begins with a brand new task (i.e., preemptive repeat different prd); and, 3) Restart: when a task fails it loses all work done to that point and must start anew upon continuing later (i.e., preemptive repeat identical - pri ).In this paper, assuming a computing system is unreliable, we discuss how heavy-tail (hereafter referred to as power-tail - PT) distributions can appear in a job's task stream given the Restart recovery procedure. This is an important consideration since it is known that power-tails can lead to unstable systems [4], We then demonstrate how to obtain performance and dependablity measures for a class of computing systems comprised of P unreliable processors and a finite number of tasks N given the above recovery procedures.