Many concurrency control protocols for B-trees use latch-coupling because its execution is efficient on a single machine. Some studies have indicated that latch-coupling may involve a performance bottleneck when using multicore processors in a shared-everything environment, but no studies have considered the possible performance bottleneck caused by sending messages between processing elements (PEs) in shared-nothing environments. We propose two new concurrency control protocols, “LCFB” and “LCFB-link”, which require no latch-coupling in optimistic processes. The LCFB-link also innovates B-link approach within each PE to reduce the cost of modifications in the PE, as a solution to the difficulty of consistency management for the side pointers in a parallel B-tree. The B-link algorithm is well known as a protocol without latch-coupling, but B-link has the difficulty of guaranteeing the consistency of the side pointers in a parallel B-tree. Experimental results in various environments indicated that the system throughput of the proposed protocols was always superior to those of the conventional protocols, particularly in large-scale configurations, and using LCFB-link was effective for higher update ratios. In addition, to mitigate access skew, data should migrate between PEs. We have demonstrated that our protocols always improve the system throughput and are effective as concurrency controls for data migration.

Many distributed systems use a replication mechanism for reliability and availability. On the other hand, application developers have to consider minimum consistency requirement for each application. Therefore, a replication protocol that supports multiple consistency models is required. Multi-Consistency Data Replication (McRep) is a proxy-based replication protocol and can support multiple consistency models. However, McRep has a potential problem in that a replicator relaying all request and reply messages between clients and replicas can be a performance bottleneck and a Single-Point-of-Failure (SPoF). In this paper, we introduce the multi-consistency support mechanism of McRep to a combined state-machine and deferred-update replication protocol to eliminate the performance bottleneck and SPoF. The state-machine and deferred-update protocols are well-established approaches for fault-tolerant data management systems. But each method can ensure only a specific consistency model. Thus, we adaptively select a replication method from the two replication bases. In our protocol, the functionality of the McRep's replicator is realized by clients and replicas. Each replica has new roles in serialization of all transactions and managing all views of the database, and each client has a new role in managing status of its transactions. We have implemented and evaluated the proposed protocol and compared to McRep. The evaluation results show that the proposed protocol achieved comparable throughput of transactions to McRep. Especially the proposed protocol improved the throughput up to 16% at a read-heavy workload in One-Copy. Finally, we demonstrated the proposed failover mechanism. As a result, a failure of a leader replica did not affect continuity of the entire replication system unlike McRep.

Secret sharing is a method for distributing a secret among a party of participants. Each of them is allocated a share of the secret, and the secret can only be reconstructed when the shares are combined together. We have been proposing a secret sharing distributed database system (SSDDB) that uses a secret sharing scheme to improve confidentiality and robustness of distributed database systems. This paper proposes a vertical partitioning algorithm for the SSDDB, and evaluates the algorithm by computational experiments.

Recently with the advent of the IT and the wide spread use of the Internet, new user oriented production and logistic systems, such as the Supply Chain Management System, have been required in order to cope with the drastic and continuous changes on the markets and users' preferences. Therefore, heterogeneous database systems need to be integrated in a common environment which can cope with the heterogeneous requirements of each company under an ever-evolving changing environment. That is assurance. Autonomous Decentralized Database System (ADDS) is proposed as a system architecture in order to realize assurance in distributed database systems. In this system architecture, a loosely-consistency management technology is proposed in order to maintain the consistency of the system, each database can update autonomously, and confer the real time property. A background coordination technology, performed by an autonomous mobile agent, is devised to adapt the system to evolving situations. The system can achieve real time by allocating the information in advance among the sites that has different time constraints for updating. Moreover, an assurance information allocation technology is proposed when considering that a failure in the background coordination mechanism may lead to loss of data and unavailability of the system. This mechanism, in which the mobile agent autonomously regulate its own capacity for allocating the information, is proposed based on the real-time property and system's availability considerations. The effectiveness of the proposed architecture and technologies are evaluated by simulation.

By using distributed database systems, many advantages can be obtained such as database management cost, efficiency, and high integrity of systems through allocating fragments to many distributed sites with horizontal/vertical fragmentation of global database schema. To minimize costs, distributed algorithms must be applied so that database fragments are allocated to optimal sites. It is useful to replicate fragments, such as allocating many copies in many sites including load balancing. But there are too many possible combinations of each site and fragment, making it impossible to find a solution in real time, i.e., it is an NP-complete problem. This paper proposes near optimal heuristic algorithms for minimizing cost by defining a cost model based on read and update queries that are requested in many sites. Various factors are applied to the proposed algorithms for sizing efficient network resources that compute database transactions as remote query or update requests for consistency in replicated database systems. For network load balancing, incoming network traffic table is defined in each site. A request transaction from unallocated sites to allocated sites can be accessed properly at any other replicated sites by using the network traffic table. Finally, some experimental results verified the proposed algorithms by comparing actual cases of database allocation.

Distributed database systems require a commit process to preserve the ACID property of transactions executed on a number of system sites. With the appearance of main memory database system, the database processing time has been reduced in the order of magnitude, since the database access does not incur any disk access at all. However, when it comes to distributed main memory database systems, the distributed commit process is still very slow since the disk logging at several sites has to precede the transaction commit. In this paper, we re-evaluate various distributed commit protocols and come up with a causal commit protocol suitable for distributed main memory database systems. To evaluate the performance of the proposed commit protocol, extensive simulation study has been performed. The simulation results confirm that the new protocol greatly reduces the time to commit the distributed transactions without any consistency problem.

To meet the highly competitive and dynamic needs in the market, an e-Business company needs to flexibly integrate its heterogeneous database systems together, e.g., the integration of makers and retailers in a Supply Chain Management System (SCM). The customers demand one-click response and also their access requirements change too frequently. Moreover, different retailers and makers in a SCM, being the autonomous entities, have their own specific requirements for stock-cost and opportunity-loss, depending on their local situation that is also changing with time. Under this background, the integrated DBs of the SCM are required to provide real-time response, heterogeneity satisfaction and flexibility to adapt to changing requirements. The conventional approach of strict consistency leads to low response and less flexibility due to the strong interdependence of the systems. In this paper, Autonomous Decentralized Database System has been proposed as an application-oriented database technology based on the concept of autonomy and loose-consistency among the distributed DB systems thus providing real-time, flexibility and high availability. The autonomy in the system has been achieved by defining a data attribute, Allowable Volume, within which each component DB has autonomy to update the data in real-time. Moreover, the system adapts to the dynamically changing heterogeneous access requirements at each DB by managing the distribution of AV among different DBs through an active coordination mechanism. Due to the dynamic and unpredictable environment, the component DBs are provided with complete autonomy for their local and coordination decisions, thus diminishing the interdependency and improving the response time. As the system consists of loosely-connected subsystems, it also has high availability. Therefore, the proposed system provides highly decentralized architecture with flexibility and high availability. The performance of the system has been shown significantly effective by simulating the internet based SCM system, from the communication-cost and response time point of view.

We suggest a new probe message structure and an efficient probe-based deadlock detection and recovery algorithm that can be used in distributed database systems. We determine the characteristics of the probe messages and suggest an algorithm that can reduce the communication cost required for deadlock detection and recovery.

In this paper, we consider optimal mirror allocation problems for the purpose of load balancing in network servers. We focus on constructing high-reliability networks and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trade-off between the reliability and cost. This optimization model is capable of dealing with various kinds of network topologies, although for simplicity, we assume the read-only situation. We formulate this optimization problem into a 0-1 integer programming model, and we use an approximate method for numerical analysis in order to analyze more large-scale systems. Our objective is to find the optimal mirror allocation by solving this model, and to show quantitatively the general characteristics of the load balancing and the improvement of the system reliability by the distributed mirror allocation.

Focusing on a distributed control service-control-node (SCP) that houses a database (DB) distributed across multiple modules, this paper proposes an autonomous distributed SCP architecture using multicasting access to the distributed DB, and highlights its application areas. We assume as a basic condition that neither the network nor the other modules in the system are aware of the DB configuration. Based on this condition, we propose two basic methods: a unicast approach in which the DB management module that is selected at random by the network routes the DB access request to the module where the target data resides (Method A), and a multicast method in which DB access requests are broadcast to all modules (Method B). A quantitative evaluation is made of the number of required modules and required communications performance between modules which is determined by the capacity of the main memory and processing capacity of the processors. Based on the results, we conclude that Method B better exploits the advantages of module autonomous distribution technology within the limits that the economy of inter-module communication overhead is not impaired. Furthermore, in the event a module fails in Method B, a scheme is proposed in which the defective module is cut out of the multicast group, and multicasting continues. This could be implemented most effectively using a separate route under hardware control that is independent of the on-line communications route between modules.

In distributed network systems, it is one of the most important problems how to assign the files to servers in view of cost and delay. It is obvious that there is a trading-off relationship between costs and delays in these systems. In order to evaluate the optimization that the total cost is minimized subject to the total delay, we have presented the Optimal File Allocation Model as 0-1 integer programming, and have investigated the general characteristics in distributed systems. In this model, we have introduced many cost and delay parameters to evaluate the total cost and delay in the system more exactly. In constructing practical systems, it is necessary to investigate the weight and the contribution of each parameter to the total cost. It is very useful to show how to estimate cost and delay parameters on the basis of this analysis. In this paper, we analyze the sensitivity of these parameters and make clear the influence between principal parameters.

The advent of high-speed networks with quality of service guarantees, will enable the deployment of data-server distributed systems over wide-area networks. Most implementations of data-server systems have been over local area networks. Thus it is important, in this context, to study the performance of existing distributed data management protocols in the new networking environment, identify the performance bottlenecks and develop protocols that are capable of taking advantage of the high speed networking technology. In this paper, we examine and compare the scalability of the server-based two-phase locking protocol (s-2PL), and the group two-phase locking protocol (g-2PL). The s-2PL protocol is the most widely used concurrency control protocol, while the g-2PL protocol is an optimized version of the s-2PL protocol, tailored for high-speed wide-area network environments. The g-2PL protocol reduces the effect of the network latency by message grouping, client-end caching and data migration. Detailed simulation results indicate that g-2PL indeed scales better than s-2PL. For example, upto 28% improvement in response time is reported.

In this paper, we study the optimal allocation of multimedia files in distributed network systems. In these systems, the files are shared by users connected with different servers geographically separated, and each file must be stored in at least one of servers. Users can access any files stored in any servers connected with high-speed communication networks. Copies of the files accessed frequently are to be stored in several servers that have databases. So, it is one of the most important problems how to assign the files to servers in view of costs and delays. Considering these problems in heterogeneous network environments, we present a new system model that covers wide range of multimedia network applications like VOD, CALS, and so on. In these systems, it is obvious that there is trading-off relationship between costs and delays. Our objective is to find the optimal file allocation such that the total cost is minimized subject to the total delay. We introduce a 0-1 integer programming formulation for the optimization problem, and find the optimal file allocation by solving these formulae.

This paper proposes the signaling network deployment for mobile networks with a goal of reducing the signaling cost and time to set up calls. In this deployment, we solve the heavy concentration of signaling traffic resulting from the centralized database used in current mobile networks. The solution exploits the features of the distributed databases, data partition, locality of mobile users, and Common Channel Signaling System No.7 (CCSS No.7) network architectures. We assume the area served by the mobile network is partitioned into a few zones. There is a database associated with each zone. A numbering database strategy is proposed in this paper for the mobiles to register at some specific nearby databases according to their mobile identification numbers. Thus, a calling party can directly locate the called party by the mobile identification number he/she dialed. This method can reduce over 95% of the location-updating cost and 70% of the location-tracking cost under a general sumulation model. We also present the implementation considerations of this strategy. This implementation is an enhancement of the routing function of the Signaling Connection Control Part in CCSS No.7 protocol stacks. With few modifications on current mobile networks, the proposed strategy can obtain very excellent results.

In retrieving information from databases widely distributed in a network, the first thing to do is to search and find the database where the required information is stored. We call this the information searches rather than the retrievals. In this paper, we present a search and retrieval method for multimedia information, especially images. First, we formalize the general elements of information search and introduce a new search concept based on entropy reduction. Next, we discuss recent new technologies for image retrieval and introduce a new image retrieval system called VideoReality. Third, we present several methods of searching in the network- for example, the Internet robot TITAN, and a new search method for images distributed in the network that is based on the hierarchical structure of image retrieval. Finally, we discuss the network control and design concepts appropriate for information search and retrival.

In this paper, we analyze the traffic data management requirements of the customers, describe the functions of the traffic database needed to satisfy their requirements, and propose a highly distributed database system which can efficiently implement these functions. Finally, we report the results of system performance evaluations.

The intelligent network services will considerably increase the amount of Control and OAM (Operation, Administration and Maintenance) Information (Ic&o) which will be stored in a huge number of distributed databases. Therefore, the management and the organization of databases have become critical issues for securing network performance. This paper studies one of the IN applications that is likely to be an important user of the Ic&o network, namely the Universal Personal Telecommunication (UPT). UPT enables the personal mobility, based on a UPT number related to the user and not a terminal equipment. The Ic&o information of UPT is carried through an ATM based transport network. Taking two fundamental parameters into consideration, namely delay time and the number of users, and two kinds of data location probabilities, this paper studies two basic procedures for finding target data in UPT databases, i.e., chaining and broadcasting. Results show that, when the data location probability is uniform, the broad-casting mode is the faster mode but, on the other hand, the chaining mode allows a larger number of users because the disk access time is less restrictive than in the broadcasting mode. Moreover, this study shows that increasing the number of databases also increases the allowed number of users up to a specific threshold. With a Broadcast Chaining mode, a better compromise between the delay time and the number of allowed users is obtained. If the probability depends on the location of databases (the probability is conversely proportional to the square of the number of searched databases), the results show that the chaining mode is preferable from both the number of users allowed and the delay time viewpoints. Finally, the implementation aspect is discussed.