Performance of distributed information systems

There is an increasing use of distributed computer systems to provide services in both traditional telephony as well as in the Internet. Two main technologies are Distributed Object Computing (DOC) and Web based services. One common DOC architecture investigated in this thesis is the Common Object Request Broker Architecture (CORBA), specified by the Object Management Group. CORBA applications consist of interacting software components called objects. Two other DOC architectures investigated are the Telecommunications Information Net- working Architecture (TINA) and a CORBA based Intelligent Network (IN/CORBA) system. In a DOC environment, the objects of an application are distributed on mul- tiple nodes. A middleware layer makes the distribution transparent to the application. However, the distributed nature creates a number of potential performance problems. Three problems in DOC systems are examined in this thesis: object distribution, load balancing and overload protection. An object distribution describes how objects are distributed in the network. The objective is to distribute the objects on the physical nodes in such a way that intern-node communication overhead is as small as possible. One way to solve the object distribution problem is to use linear programming. The constraints for the problem are then given by both ease of management of the system and performance concerns. Load balancing is used when there are multiple objects that can be used at a particular time. The objective of load balancing is to distribute the load e±ciently on the available nodes. This thesis investigates a number of de- centralized load balancing mechanisms, including one based on the use of intelligent agents. Finally, overload protection mechanisms for DOC systems are investigated. While overload protection is well-researched for telecom networks, only little work has been performed previously concerning DOC and overload protection. Also, this thesis examines the use of overload protection in e-commerce web servers. Two schemes are compared, one which handles admission to the e-commerce site on request basis, and another which handles admission on session basis. The session based mechanism is shown to be better in terms of user-experienced performance

Overload Protection for CORBA Systems with Time Constraints

Scalable and reliable distributed object-oriented computing (DOC) middleware systems is an important technology in, for example, telecommunications service logic and distributed web servers. The Common Object Request Broker Architecture (CORBA), developed by the Object Management Group (OMG) is a speci cation of a common platform for DOC systems. CORBA acts as middleware, by inserting itself between the Operating System (OS) layer and the Application layer on a host. CORBA provides support for transparent interaction of objects situated on different nodes. The original CORBA specications had no support for timing constraints in applications and very little support in the terms of performance optimizations. Present extension to CORBA include support for real-time applications and a number of performance enhancements such as load balancing. However, no work so far address the issue of overload in a CORBA system. This paper presents a discussion of overload issues in distributed CORBA systems with time-constrained tasks. First a performance model of a CORBA system is introduced. Second, overload in distributed CORBA systems is discussed. Third, a number of classic overload protection mechanisms are applied to the performance model and investigated using simulation. The simulations show that even by using very simple protection mechanism, a good throughput can be achieved

Simulation of a distributed CORBA-based SCP

This paper examines load balancing issues relating to a distributed CORBA-based Service Control Point. Two types of load balancing strategies are explored through simulation studies: (i) a novel ant-based load balancing algorithm, which has been devised specically for this type of system. This algorithm is compared to more traditional algorithms, (ii) a method for optimal distribution of the computational objects composing the service programs. This is based on mathematically minimising the expected communication ows between network nodes and message-level processing costs. The simulation model has been based on the recently adopted OMG IN/CORBA Interworking specication and the TINA Service Session computational object model

Migration algorithms for automated load balancing

As distributed systems continue to evolve, automatic resource management is becoming more and more impor tant. The resource management system must be able to dynamically handle large heterogeneous systems in a way that gives good performanceand resource utilization. In the performance context, allocating software modules to nodes in an efficient way is of high interest. This paper considers the problem of allocating software modules to processing nodes in an automatic dynamic manner using module mi gration algorithms. The module allocation problem is NP complete and many heuristics have been proposed. How ever, in systems where the workload changes over time, it may be infeasible to update module allocation often enough to handle changes in workload. This paper presents the Match-maker algorithm that performs load balancing by pairing overloaded nodes with under-loaded ones, initiat ing module migration within the pair. The paper presents a load balancing optimization problem, and uses the bench mark problem to evaluate the algorithm. In addition, the Match-maker algorithm is compared with other previously described algorithms for module migration. The Match maker algorithm is found to be fast and efficient in reducing load imbalance in distributed systems, especially for large systems

To Stina and Hugo

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How does the market structure in a banking sector affect bank profitability during a financial crisis?

This thesis studies how profitability in both emerging and advanced economies is affected by market structure in a financial crisis. The country sample from Mirzaei, Moore, & Liu (2013) is used with a similar methodology, with the distinct difference of using all banks rather than simply active banks, to enable a comparison to the time period 1999-2008. A sample of 1328 banks in 40 countries, 17 advanced countries and 23 emerging countries, from 2005-2014 is used with 934 banks from advanced countries and 394 banks from emerging countries. None of the market power hypotheses, the relative-market-power hypothesis nor the structure-conduct-performance hypothesis, are found to be significant for the crisis period 2008-2010. Instead in advanced economies market concentration is a negative determinant of profits in the financial crisis period 2008-2010, indicating that a high market concentration reduces stability and profitability for the banking sector in advanced economies. In contrast, emerging economies find market concentration as a positive determinant of profitability and market share of the bank as negative. The banks in a concentrated market seem to be able to perform better, but the largest banks are more negatively affected by the financial crisis, resulting in lower profitability. The result of both economies for the entire sample period 2005-2014 is equivalent to the market structure-profit relationship found in emerging economies during the financial crisis period. No signs are found of a market structure and profitability relationship after the crisis, which indicate that something other than market structure mainly affects profitability today. A survivorship bias is present when only including active banks, which speaks for the importance of not excluding data in market structure-profit research

Active Resource Management in Middleware and Service-oriented Architectures

In this thesis, we study load balancing and overload control in two distributed architectures: Distributed Object Computing (DOC) systems and Services-oriented Architecture (SOA) systems. While DOC and SOA have differences in terms of implementation, they are similar from a performance viewpoint. In both DOC and SOA, users access software applications distributed on multiple processing nodes. The applications are composed of intercommunicating objects or services. During execution, one or more of the software resources, distributed on multiple processing nodes, are needed. The complex interaction patterns that arise make overload control and load balancing hard. The first part of this thesis concerns load balancing in DOC systems. The first two papers evaluate request based load balancing in TINA and IN/CORBA respectively, comparing algorithms in terms of efficiency and overhead. The second paper also touches upon using lightweight agents to distribute load information in the network. The following two papers investigate two approaches to allocating objects to nodes. The allocation problem is a hard problem that is solvable in reasonable time only for small systems, however, its solution is crucial for efficient resource utilization. The first paper considers object migration algorithms as a way to dynamically distribute load. Two migration algorithms are are presented and evaluated. In the second paper, the static allocation problem is approached by applying the Cross Entropy Method, a stochastic optimization method, to the problem. The method is shown to be able to find good solutions without knowledge of system structure. The second part of this thesis concerns overload control in DOC and SOA. First comes an investigation of overload control in a real-time CORBA system. Second, request and session based admission control schemes in e-commerce web servers are compared. The session based mechanism is shown to be better in terms of user-experienced performance. The evaluation is continued in an appendix. Third, service protection during transient overload conditions in web services systems is studied. A fine-grained admission control framework is proposed and is shown, using deterministic flow models, to efficiently protect services that are not subject to overload

Load balancing strategies for TINA networks

TINA is an open, object oriented, distributed telecom architecture, with many concepts taken directly from the latest computer research. In TINA, instances of the same object type can be placed on different physical nodes. Therefore, the network performance can be improved by introducing load balancing algorithms. These algorithms should distribute the traffic between the object instances in such way that the overall throughput and setup time are improved. We discuss and examine a number of simple distributed load balancing algorithms, that do not require any extra load information exchange between the nodes. The results show that it is difficult to find an algorithm that behave well for all traffic situations. The main problem is that the algorithms have not enough information about the load situation on the different nodes, since no load information is exchanged between the nodes. This problem can be solved by adding the feasibility of load status information to the TINA protocols

Gateway-based call admission in distributed object oriented systems

Many applications in telecommunications will depend on distributed systems to provide enough capacity. In a distributed system a service is split up into a number of modules (often called objects) that can be placed at different nodes or processors in a network. A service can be seen as a number of invocations of the objects in a certain order. There are a number of performance problems which have to be solved. How shall objects be distributed on the nodes? How shall the load be distributed among the nodes for a given object distribution? How shall the distributed system be protected from temporary overload situations? In our paper we investigate these questions for distributed systems where requests for service arrive to a gateway from which they distributed to the nodes of the system. We assume that the object distribution is given and we concentrate on protecting the system using three different external load control mechanisms: Percent Thinning, Call Gapping and Tokens. Using simulations, we nd that Tokens provide the best system protection

Cross entropy based module alocation for distributed systems

In the module allocation problem a collection of software modules are to be assigned to physical processing nodes, subject to execution and communication cost. The cost of an allocation is a function of the execution costs and the communication costs for any pair of modules allocated to distinct processors. The module allocation problem has been well studied and is known to be NP-complete except for certain communication configurations. To solve the problem, several heuristics have been proposed. This pa per discusses an alternative approach to solving the module allocation problem by applying a stochastic optimization method called the Cross Entropy (CE) Method. The CE Method is a state-of-the-art stochastic method for solving combinatorial and multi-extremal continuous optimization problems. The CE method uses a distribution with parame ter v to generate sample allocation. The generated samples are then used to update v according to sample quality. This process is repeated until the distribution converges to a pos sibly optimal allocation. The results in this paper indicate that the CE method can successfully be applied to the mod ule allocation problem and efficiently generate high qual ity solutions. Also, the CE method allows the use of non standard objective functions that are used to find allocations that have multiple conflicting objectives