Object Management in Stationary Computing Environments

Abstract

In this chapter, we address the issues (object allocation and replication) of OMP in the application domain of DDBSs in SCEs. In general, a DDBS consists of n nodes (as shown in Figure 1.2), denoted as p ₁, p ₂,…, p _n ,interconnected via a communication network. Each node consists of a processor and a local memory (database). Replicas of objects are stored in the local memories. All the local memories are private and accessible only by the processors who own them. Internodes communication is carried out by passing messages through the interconnection network. As mentioned in Chapter 3, transactions on objects arriving at a DDBS can be in the form of either read or write operations, referred to as read requests or write requests, respectively. Requests originating from processors for objects are assumed to arrive at the system concurrently and there exists a concurrency control mechanism to serialize 1 them. Specifically, a read request is serviced with a replica (latest version) of the requested object, while a write request actually modifies (creates a new version) an object. Especially, in order to guarantee the object consistency among multiple replicas of an object, every change to an object must be transferred to all the other available replicas in the remote memories elsewhere. In other words, a write request for an object must be propagated to all the processors that have replicas of the object in their respective local memories. Without loss of generality, these read/write requests can arrive at the system in a random manner and they need not exhibit a regular pattern.