Multi-tier Applications Research Articles

Towards Practical Default-On Multi-Core Record/Replay

We present Castor, a record/replay system for multi-core applications that provides consistently low and predictable overheads. With Castor, developers can leave record and replay on by default, making it practical to record and reproduce production bugs, or employ fault tolerance to recover from hardware failures. Castor is inspired by several observations: First, an efficient mechanism for logging non-deterministic events is critical for recording demanding workloads with low overhead. Through careful use of hardware we were able to increase log throughput by 10x or more, e.g., we could record a server handling 10x more requests per second for the same record overhead. Second, most applications can be recorded without modifying source code by using the compiler to instrument language level sources of non-determinism, in conjunction with more familiar techniques like shared library interposition. Third, while Castor cannot deterministically replay all data races, this limitation is generally unimportant in practice, contrary to what prior work has assumed. Castor currently supports applications written in C, C++, and Go on FreeBSD. We have evaluated Castor on parallel and server workloads, including a commercial implementation of memcached in Go, which runs Castor in production.

Assessment on student performance using Rasch model in multi-tier application development course examination

Assessment and measurement in teaching and learning process is one of the most vital processes in order to assure the quality of education system. This paper describes a measurement model that is used to measure the student performance in the final examination of multi-tier application development (IS333D) course in the Information Systems (IS) Department, College of Computer and Information Sciences (CCIS), Princess Nourah Bint Abdulrahman University (PNU). A sample of final exam results for the third year IS students is compiled and tabulated for evaluation using Rasch measurement model. This study shows that the student performance for the set of IS333D final exam questions comparatively good. This confirms that most of the students able to achieve the three levels of Bloom's taxonomy. The result generated from this study can be used to guide us to determine the appropriate improvement of the teaching method as well as the quality of question prepared.

Assessment on student performance using Rasch Model in Multi-tier Application Development course examination

Assessment and measurement in teaching and learning process is one of the most vital processes in order to assure the quality of education system. This paper describes a measurement model that is used to measure the student performance in the final examination of multi-tier application development (IS333D) course in the Information Systems (IS) Department, College of Computer and Information Sciences (CCIS), Princess Nourah Bint Abdulrahman University (PNU). A sample of final exam results for the third year IS students is compiled and tabulated for evaluation using Rasch measurement model. This study shows that the student performance for the set of IS333D final exam questions comparatively good. This confirms that most of the students able to achieve the three levels of Bloom's taxonomy. The result generated from this study can be used to guide us to determine the appropriate improvement of the teaching method as well as the quality of question prepared.

Workload-Aware Placement of Multi-Tier Applications in Virtualized Datacenters

Virtualization as one of the leading technologies has assisted datacenters to cloudify their products and provide versatile platforms and variety of Internet services. This technology also has facilitated agile deployment of complex Internet services such as Cloud-based multi-tier applications. However implementing multi-tier applications assists providers to set up flexible and scalable services, deploying such applications in virtualized environments faces challenges, which harden collocation of disparate multi-tier applications in a shared environment. In this article, we propose a placement strategy to consolidate multi-tier applications’ tiers in a virtualized datacenter regarding workload demands of individual tiers, utilization of physical hosts’ resources and operational status of virtual machines. The placement strategy identifies over-utilized hosts based on the birth–death stochastic process and ranks tiers based on Data Envelopment Analysis-Analytic Hierarchy Process modeling to be placed on target hosts. A prioritized tier will be placed on an appropriate host though least operational interference with hosted tiers incurred. The efficiency of the proposed model is evaluated using a series of in-depth experiments. We introduce results derived from quantitative and qualitative analyses that are useful for multi-tier applications placement in virtualized datacenters. Simulation results reveal that the proposed solution excels in terms of both load distribution and energy consumption in the datacenter, while the number of unnecessary migrations and consecutive Service Level Agreement violations is considerably reduced.

HAVA: Heterogeneous Multicore ASIP for Multichannel Low-Bit-Rate Vocoder Applications

As are widely used in military and security fields, multiple channels of low-bit-rate vocoders are required to perform on embedded devices efficiently. We propose HAVA, a multicore Application Specific Instruction Set Processor for multichannel low-bit-rate vocoders with real-time performance. To provide both flexibility and efficiency, HAVA integrates two types of processing cores and a shared-memory core on a 2-D-mesh on-chip network. Adopting a single-Instruction Set Architecture heterogeneous multicore architecture, HAVA cuts down the real-time performance requirement of vocoders by over 40% compared with other platforms. By leveraging the on-chip network for intercore communication, HAVA can perform multichannel vocoders with a marginal efficiency loss. The chip implementation of HAVA is finished in a 40-nm CMOS technology and it dissipates 149 mW at 100-MHz operating frequency for four channels of encoders.

Off-chip bus power minimization using serialization with cache-based encoding

The data bus is a major component of high power consumption in small process high-performance systems and in systems-on-chip (SoC) design. This paper presents an analysis of different state-of-the-art techniques for reducing the power of off-chip memory bus interface, with proposing an approach overcoming some limitations existing in the state-of-art methods. More precisely, the paper introduces a serialization (S) method combined with cache-based encoding scheme, aiming at saving the optimal possible power for off-chip memory bus. Bus serialization reduces the number of transmission wires, while a Serialization-Widening (SW) approach reduces the bus capacitance and the number of transmission wires. Experimental results show that, for off-chip data bus, the serialization approach with cache-based encoding achieves 31% and 52% power reduction for single-core and multi-core applications, respectively, when using fixed voltage and frequency with 128 bits data bus.

CTP: A scheduling strategy to smooth response time fluctuations in multi-tier website system

Performance, in terms of quality of service and resource utilization, is one of top attractions in cloud. However, in practice, most multi-tier applications today frequently present large scale fluctuations of response time during periods of high resource utilization. It is hardly to find any reported work that elaborated the reasons causing response time fluctuations, especially when providing quality performance and high effective multi-tier systems in cloud environments. To this end, this paper, through extensive measurements of a multi-tier application benchmark (RUBiS), corroborates the existing of response time fluctuations. In addition, arithmetic mean of response time is not suitable for the measurement of multi-tier services system performance. In light of probing analysis of requests, we show that the large scale response time fluctuations can be caused by concurrent long or mix transactions. The numerical results validate the correctness of our findings. Consequently, an effective scheduling policy called CTP (cross-tier-proportion) is developed to smooth response time fluctuations while maintaining high resource utilization in the system.

Loss-Aware Switch Design and Non-Blocking Detection Algorithm for Intra-Chip Scale Photonic Interconnection Networks

As the number of on-chip processor cores increases, power-efficient solutions are sought for data communication between cores. The Helix-h non-blocking photonic switch is developed to improve physical-layer and network performance parameters for a wide range of silicon nano-photonic multicore interconnection topologies. Traffic benchmarks and practical case studies using a cycle-accurate simulation environment indicate significantly reduced insertion loss providing improved bandwidth density and scalability to manycore plurality. Improvements in system performance parameters are quantified for network bandwidth, transmission efficiency, and latency in popular photonic internconnection topologies, in comparison to previous switch designs. For instance, utilizing the Helix-h switch in a mesh topology, the bandwidth is increased by 112 percent compared to the previously highest performing switch design. Execution time and energy efficiency are improved by up to 92 and 99 percent, respectively, for representative multicore applications. Finally, the technique is generalized to a novel graph-theoretic method for articulating blocking conditions in photonic switches.

Network-aware virtual machine migration in an overcommitted cloud

Virtualization, which acts as the underlying technology for cloud computing, enables large amounts of third-party applications to be packed into virtual machines (VMs). VM migration enables servers to be reconsolidated or reshuffled to reduce the operational costs of data centers. The network traffic costs for VM migration currently attract limited attention.However, traffic and bandwidth demands among VMs in a data center account for considerable total traffic. VM migration also causes additional data transfer overhead, which would also increase the network cost of the data center.This study considers a network-aware VM migration (NetVMM) problem in an overcommitted cloud and formulates it into a non-deterministic polynomial time-complete problem. This study aims to minimize network traffic costs by considering the inherent dependencies among VMs that comprise a multi-tier application and the underlying topology of physical machines and to ensure a good trade-off between network communication and VM migration costs.The mechanism that the swarm intelligence algorithm aims to find is an approximate optimal solution through repeated iterations to make it a good solution for the VM migration problem. In this study, genetic algorithm (GA) and artificial bee colony (ABC) are adopted and changed to suit the VM migration problem to minimize the network cost. Experimental results show that GA has low network costs when VM instances are small. However, when the problem size increases, ABC is advantageous to GA. The running time of ABC is also nearly half than that of GA. To the best of our knowledge, we are the first to use ABC to solve the NetVMM problem.

A Survey of Quality of Service in Multi-tier Web Applications

A Survey of Quality of Service in Multi-tier Web Applications

Characterization of Shared-Memory Multi-Core Applications

The multicore processor architectures have been gaining increasing popularity in the recent years. However, many available applications cannot take full advantage of these architectures. Therefore, many researchers have developed several characterization techniques to help programmers understand the behavior of these applications on multicore platforms and to tune them for better efficiency. This paper proposes an on-the-fly, configuration-independent characterization approach for characterizing the inherent characteristics of multicore applications. This approach is fast because it does not depend on the details of any specific machine configuration and does not require repeating the characterization for every target configuration. It just keeps track of memory accesses and the cores that perform these accesses through piping memory traces, on-the-fly, to the analysis tool. We applied this approach to characterize eight applications drawn from SPLASH-2 and PARSEC benchmark suites. This paper presents the inherent characteristics of these applications including memory access instructions, communication characteristics patterns, sharing degree, invalidation degree, communication slack, and communication locality. The results show that two of the studied applications have high parallelization overhead, which are Cholesky and Fluidanimate. The results also indicate that studied applications of SPLASH-2 have higher communication rates than the studied applications of PARSEC and these rates generally increase as the number of used threads increases. Most of the sharing and invalidation occurs in small degrees. However, two of SPLASH-2 applications have significant fraction of communication with high sharing degrees involving four or more threads. Most of the applications have some uniform communication component and the initial thread is generally involved in more communication compared to the other threads.

A Generic Graph Model for WCET Analysis of Multi-Core Concurrent Applications

Worst-case execution time (WCET) analysis of multi-threaded software is still a challenge. This comes mainly from the fact that synchronization has to be taken into account. In this paper, we focus on this issue and on automatically calculating and incorporating stalling times (e.g. caused by lock contention) in a generic graph model. The idea that thread interleavings can be studied with a matrix calculus is novel in this research area. Our sparse matrix representations of the program are manipulated using an extended Kronecker algebra. The resulting graph represents multi-threaded programs similar as CFGs do for sequential programs. With this graph model, we are able to calculate the WCET of multi-threaded concurrent programs including stalling times which are due to synchronization. We employ a generating function-based approach for setting up data flow equations which are solved by well-known elimination-based dataflow analysis methods or an off-the-shelf equation solver. The WCET of multi-threaded programs can finally be calculated with a non-linear function solver.

Performance Modeling of Multi-tiered Web Applications with Varying Service Demands

Multi-tiered transactional web applications are frequently used in IT enterprise based systems. Due to their inherent distributed nature, pre-deployment testing for high-availability and varying concurrency are important for post-deployment performance. Accurate performance modeling of such applications can help estimate values for future deployment variations as well as validate experimental results. In order to theoretically model performance of multi-tiered applications, we use queuing networks and Mean Value Analysis (MVA) models. While MVA has been shown to work well with closed queuing networks, there are particular limitations in cases where the service demands vary with concurrency. This variation of service demands for various resources (CPU, Disk, Network) is demonstrated through multiple experiments. This is further contrived by the use of multi-server queues in multi-core CPUs, that are not traditionally captured in MVA. We compare performance of a multi-server MVA model alongside actual performance testing measurements and demonstrate this deviation. Using spline interpolation of collected service demands, we show that a modified version of the MVA algorithm (called MVASD ) that accepts an array of service demands, can provide superior estimates of maximum throughput and response time. Results are demonstrated over multi-tier vehicle insurance registration and e-commerce web applications. The mean deviations of predicted throughput and response time are shown to be less the 3% and 9% , respectively. Additionally, we analyze the effect of spline interpolation of service demands as a function of throughput on the prediction results. Using Chebyshev Nodes , the tradeoff between the number of test points and the spline interpolation/prediction accuracy is also studied.Â

Dual Security Testing Model for Web Applications

In recent years, web applications have evolved from small websites into large multi-tiered applications. The quality of web applications depends on the richness of contents, well structured navigation and most importantly its security. Web application testing is a new field of research so as to ensure the consistency and quality of web applications. In the last ten years there have been different approaches. Models have been developed for testing web applications but only a few focused on content testing, a few on navigation testing and a very few on security testing of web applications. There is a need to test content, navigation and security of an application in one go. The objective of this paper is to propose Dual Security Testing Model to test the security of web applications using UML modeling technique which includes web socket interface. In this research paper we have described how our security testing model is implemented using activity diagram, activity graph and based on this how test cases is generated.

Component-based Systems Reconfigurations Using Graph Grammars

Dynamic reconfigurations can modify the architecture of component-based systems without incurring any system downtime. In this context, the main contribution of the present article is the establishment of correctness results proving component-based systems reconfigurations using graph grammars. New guarded reconfigurations allow us to build reconfigurations based on primitive reconfiguration operations using sequences of reconfigurations and the alternative and the repetitive constructs, while preserving configuration consistency. A practical contribution consists of the implementation of a component-based model using the GROOVE graph transformation tool. Then, after enriching the model with interpreted configurations and reconfigurations in a consistency compatible manner, a simulation relation is exploited to validate component systems’ implementations. This sound implementation is illustrated on a cloud-based multitier application hosting environment managed as a component-based system.

Designing Autonomic Management Systems by Using Reactive Control Techniques

The ever growing complexity of software systems has led to the emergence of automated solutions for their management. The software assigned to this work is usually called an Autonomic Management System (AMS). It is ordinarily designed as a composition of several managers, which are pieces of software evaluating the dynamics of the system under management through measurements (e.g., workload, memory usage), taking decisions, and acting upon it so that it stays in a set of acceptable operating states. However, careless combination of managers may lead to inconsistencies in the taken decisions, and classical approaches dealing with these coordination problems often rely on intricate and ad hoc solutions. To tackle this problem, we take a global view and underscore that AMSs are intrinsically reactive, as they react to flows of monitoring data by emitting flows of reconfiguration actions. Therefore we propose a new approach for the design of AMSs, based on synchronous programming and discrete controller synthesis techniques. They provide us with high-level languages for modeling the system to manage, as well as means for statically guaranteeing the absence of logical coordination problems. Hence, they suit our main contribution, which is to obtain guarantees at design time about the absence of logical inconsistencies in the taken decisions. We detail our approach, illustrate it by designing an AMS for a realistic multi-tier application, and evaluate its practicality with an implementation.

Efficient provisioning for multi-core applications with LSF

Tier-1 sites providing computing power for HEP experiments are usually tightly designed for high throughput performances. This is pursued by reducing the variety of supported use cases and tuning for performances those ones, the most important of which have been that of singlecore jobs. Moreover, the usual workload is saturation: each available core in the farm is in use and there are queued jobs waiting for their turn to run. Enabling multi-core jobs thus requires dedicating a number of hosts where to run, and waiting for them to free the needed number of cores. This drain-time introduces a loss of computing power driven by the number of unusable empty cores. As an increasing demand for multi-core capable resources have emerged, a Task Force have been constituted in WLCG, with the goal to define a simple and efficient multi-core resource provisioning model. This paper details the work done at the INFN Tier-1 to enable multi-core support for the LSF batch system, with the intent of reducing to the minimum the average number of unused cores. The adopted strategy has been that of dedicating to multi-core a dynamic set of nodes, whose dimension is mainly driven by the number of pending multi-core requests and fair-share priority of the submitting user. The node status transition, from single to multi core et vice versa, is driven by a finite state machine which is implemented in a custom multi-core director script, running in the cluster. After describing and motivating both the implementation and the details specific to the LSF batch system, results about performance are reported. Factors having positive and negative impact on the overall efficiency are discussed and solutions to reduce at most the negative ones are proposed.

Investigations into elasticity in cloud computing

The pay-as-you-go model supported by existing cloud infrastructure providers is appealing to most application service providers to deliver their applications in the cloud. Within this context, elasticity of applications has become one of the most important features in cloud computing. This elasticity enables real-time acquisition/release of compute resources to meet application performance demands. In this thesis we investigate the problem of delivering cost-effective elasticity services for cloud applications. Traditionally, the application level elasticity addresses the question of how to scale applications up and down to meet their performance requirements, but does not adequately address issues relating to minimising the costs of using the service. With this current limitation in mind, we propose a scaling approach that makes use of cost-aware criteria to detect the bottlenecks within multi-tier cloud applications, and scale these applications only at bottleneck tiers to reduce the costs incurred by consuming cloud infrastructure resources. Our approach is generic for a wide class of multi-tier applications, and we demonstrate its effectiveness by studying the behaviour of an example electronic commerce site application. Furthermore, we consider the characteristics of the algorithm for implementing the business logic of cloud applications, and investigate the elasticity at the algorithm level: when dealing with large-scale data under resource and time constraints, the algorithm's output should be elastic with respect to the resource consumed. We propose a novel framework to guide the development of elastic algorithms that adapt to the available budget while guaranteeing the quality of output result, e.g. prediction accuracy for classification tasks, improves monotonically with the used budget.

FAMA: A Middleware for Fast Deploying and Auto Scaling towards Multitier Applications in Clouds

As the scale of Internet applications increases, the structure and technology used in backend application servers keep on improving. Facing multitier applications with large workload, how to deploy them rapidly and maintain them effectively become challenges. The traditional solution widely adopted is to make up a large physical cluster of homogeneous servers to combine individual computational capability to improve application performance. However, this way has little flexibility for dynamical load, and finally leads to low recourse utilization and delayed reaction. Relatively, though cloud computing provides a more flexibility and scalability model, traditional cloud is still not convenient and intelligent enough to deploy and maintain applications. We present a fast-deploying and auto-scaling middleware named FAMA towards multitier applications in cloud. FAMA solves the fast-deploying problem on one hand, and provides an open and flexible mechanism to scale applications automatically to meet load peak on the other hand. We implement the prototype and combine it within OpenNebula for evaluation. Our work shows that FAMA can deploy and scale applications in a very short time. Comparing to original IaaS platforms, it shortens the VM-creation to only few seconds. Through compatible with users' own monitoring mechanism, FAMA has improved flexibility and scalability.

Fairly Sharing the Network for Multitier Applications in Clouds

A significant trend caused by cloud computing is to aggregate applications for sharing resources. Thus, it is necessary to provide fair resources and performance among applications, especially for the network, which is provided in the best-effort manner in current clouds. Although many studies have made efforts for provisioning fair bandwidth, they are not sufficient for network fairness. In fact, for interactive applications, response time is more sensitive than bandwidth, and users expect a fair response time not just bandwidth. In this study, the authors want to investigate whether the traditional methods of sharing bandwidth can help the fairness of response time. They show that: (1) bandwidth has little relationship to response time, and adjusting bandwidth hardly affects response time in most cases. Thus, the traditional methods cannot help the fairness of response time much; and (2) the fairness between components is different from the one between transactions, and many prior studies only consider the former while ignoring the latter. Thus, the authors cannot help much for multitier applications consisting of multiple transactions either. As a result, they construct a model with two metrics to evaluate the fairness status of the network sharing, while considering the applications' characteristics on both the response time and throughput. Based on the model, they also propose a mechanism to improve the fairness status. The evaluation results show that the authors' mechanism improves the fairness status by 26.5%–52.8%, and avoids performance degradation compared to some practical mechanisms.