USING COPAR TO FACILITATE QUICK DISTRIBUTION OF DISASTER RELIEF Joel M. Crichlow, Rowan University, Glassboro NJ 08028, USA, crichlow@rowan.edu Steve Hartley, Rowan University, Glassboro NJ 08028, USA, hartley@elvis.rowan.edu Michael Hosein, University of the West Indies, St Augustine, Trinidad, mhosein2006@gmail.com ABSTRACT Getting relief quickly to people and areas of need in large- scale disaster situations is a concern that arises ever so frequently. Computer technologies can be very helpful in these situations and in particular a computerized distributed system to manage resources could be quite appropriate. In order to increase availability of resources in a distributed system some or all of the data items are replicated and stored at separate sites. We have built a distributed service, COPAR that manages updates to widely deployed counter-like replicas. We demonstrate in this paper how COPAR can be used in the distribution of disaster relief. KEY WORDS Distributed System, Transaction Processing, Replica Control and Management 1. Introduction The need to distribute resources very quickly in disaster areas cannot be overstated. This distribution system comprises a receiving side (collecting and storing resources) and a giving side (identifying the needy and supplying them quickly with relief). The physical structure for such a distribution system can be supported by one or more receiving/distribution centers as in Figure 1. In addition to receiving from and giving to agencies/people the distribution centers exchange resources among themselves. The activities of receiving/giving are supported by a distributed computer system which allows each center to maintain both a global and a local database connected by a network of wired and wireless nodes which capture and monitor all the transaction activity in the system. In this system every resource is available irrespective of where it is stored. However, the objective is to meet the demand quickly by moving resources expeditiously to the centers closest to where the demand is. In this paper we present the computer system only. We do not handle the distribution infrastructure – transportation, warehouses, people, etc. However, we feel that our system presents no special challenges for the physical infrastructure. Our system is called COPAR: it Combines Optimism and Pessimism in Accessing Replicas in a distributed transaction processing system. The COPAR service runs on a collection of computing nodes connected by a communications network. We have had test runs on private LANs as well as over the Internet. Replicas (copies) of the data that transactions access can be stored at some or all of the nodes. Transactions can originate at any node and the transaction processing system attempts to treat all transactions in a uniform manner through cooperation among the nodes. One of the main reasons for replicating data in distributed systems is to increase availability. Replication has become increasingly more useful in the face of wireless technology and roaming users. However, this replication increases the need for effective control measures to preserve some level of mutual consistency. Several replica control techniques have been proposed to deal with this issue and these techniques are described to different levels of detail in many articles and presentations e.g. Birman [1], Crichlow [3], Jajodia & Mutchler [5], Wolfson et al [6], Yu and Vahdat [7]. Every transaction submitted to COPAR enters concurrently a global pessimistic two-phase commit sequence and an optimistic individual replica sequence. The optimistic sequence is moderated by a cost bound, which captures the extent of inconsistency the system will tolerate. The pessimistic sequence serves to validate the processing and commit the changes to the replicas or undo an optimistic run if it generated an inconsistency. Using this scheme we built a service that can provide highly available access to counter-like replicas widely deployed over a network. Figure 1. Distribution centers interact with external agencies/people as well as with other centers. 632-811 100 Proceedings of the 9th IASTED International Conference November 16 - 18, 2008 Orlando, Florida, USA Software Engineering and Applications (SEA 2008)