Efficient event stream dissemination is a challenging problem in large-scale Online Social Network (OSN) systems due to the costly inter-server communications caused by the per-user view data storage. To solve the pro...
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Efficient event stream dissemination is a challenging problem in large-scale Online Social Network (OSN) systems due to the costly inter-server communications caused by the per-user view data storage. To solve the problem, previous schemes mainly explore the structure of the social graphs to reduce the inter-server traffics. Based on the observation of high cluster coefficient in OSNs, a state-of-the-art social piggyback scheme proves to be effective in saving redundant messages by exploiting an intrinsic hub structure in an OSN graph. Essentially, finding the best hub structure for piggybacking is equivalent to finding a variation of the densest sub-graph. The existing scheme computes the densest sub-graph by iteratively removing the node with the minimum weighted degree. Such a scheme incurs a worst computation cost of O(n 2 ), making it not scalable to large-scale OSN graphs. Using alternative hub structures instead of the densest sub-graph can speed up the piggybacking assignment. They however greatly sacrifice the communication efficiency of the assignment schedule. Different from the existing designs, in this work, we propose the QuickPoint algorithm, which achieves the removal of a fraction of nodes in each iteration in finding the densest sub-graph. We mathematically prove that QuickPoint converges in O(log a n)(a > 1) iterations in finding the densest sub-graph for efficient piggyback. We implement QuickPoint in parallel using Pregel, a vertex-centric distributed graph processing platform. Comprehensive experiments using large-scale data from Twitter and Flickr show that our scheme achieves a 38.8× improvement in efficiency compared to the existing schemes.
Tightly-coupled parallel applications in cloud systems may suffer from significant performance degradation because of the resource over-commitment issue. In this paper, we propose a dynamic approach based on the adapt...
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ISBN:
(纸本)9781509021413
Tightly-coupled parallel applications in cloud systems may suffer from significant performance degradation because of the resource over-commitment issue. In this paper, we propose a dynamic approach based on the adaptive control over time-slice for virtual clusters, in order to mitigate the performance degradation for parallel applications in cloud and avoid the negative impact effectively on other non-parallel applications meanwhile. The key idea is to reduce the synchronization overhead inside and across virtual machines (VMs) in cloud systems, by dynamically adjusting the time-slices of VMs in terms of the spinlock latency at runtime. Such a design is motivated by our experimental finding that VM's time slice is a key factor determining the synchronization overhead as well as the parallel execution performance. We perform the evaluation on a real cluster environment deployed with XEN, using five well-known benchmarks with 10+ applications. Experiments show that our approach obtains 1.5-10× performance gain for running parallel applications, than other state-of-the-art solutions (including Credit Scheduling of Xen and the well-known methods like Co-Scheduling and Balance Scheduling), with nearly unaffected impact on the performance of non-parallel applications.
Summary The nonuniform memory access (NUMA) architecture has been used extensively in data centers. Most of the previous works used single-threaded multiprogrammed workloads to study the performance of NUMA systems, w...
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Android's permission system offers an all-or-nothing installation choice for users. To make it more flexible, users may choose a popular app tool, called permission manager, to selectively grant or revoke an app&#...
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ISBN:
(纸本)9781450336239
Android's permission system offers an all-or-nothing installation choice for users. To make it more flexible, users may choose a popular app tool, called permission manager, to selectively grant or revoke an app's permissions at runtime. A fundamental requirement for such permission manager is that the granted or revoked permissions should be enforced faithfully. However, we discover that none of existing permission managers meet this requirement due to permission leaks. To address this problem, we propose CICC, a finegrained, semantic-aware, and transparent approach for any permission managers to defend against the permission leaks. Compared to existing solutions, CICC is fine-grained because it detects the permission leaks using call-chain information at the component instance level, instead of at the app level or component level. The fine-grained feature enables it to generate a minimal impact on the usability of running apps. CICC is semantic-aware in a sense that it manages call-chains in the whole lifecycle of each component instance. CICC is transparent to users and app developers, and it requires minor modification to permission managers. Our evaluation shows that CICC incurs relatively low performance overhead and power consumption. Copyright 2015 ACM.
This paper proposes a parallel Newton-Raphson Power Flow (PNPF) method which is suitable for GPU (Graphics Processing Unit). Aiming at the most time-consuming part of power flow-solving the sparse linear equations, an...
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ISBN:
(纸本)9781509053827
This paper proposes a parallel Newton-Raphson Power Flow (PNPF) method which is suitable for GPU (Graphics Processing Unit). Aiming at the most time-consuming part of power flow-solving the sparse linear equations, an efficient hierarchy parallel solver is presented, in which LU decomposition and forward/back substitution were implemented in parallel level by level under the direction of path tree. To improve the efficiency of the method, a short-type path tree was formed, an optimization on data transfer and a self-adapted task-allocation algorithm was designed. In addition, the sparse Jacobian matrix and the right-hand side of the linear equations were also generated in parallel in a fine-grained pattern. At last, the developed GPU-based PNPF program has been tested on large-scale power systems of up to 23215 buses. The method provides a speedup of 3.91 times compared to mainstream commercial software, which proves the effectiveness and practicality of the algorithm proposed in this paper.
Domain name system is among the core part of TCP/IP protocol suite and the standard protocol used by the Internet. The domain name system consists of mapped website names with Internet protocol, which facilitates brow...
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ISBN:
(纸本)9781509025367
Domain name system is among the core part of TCP/IP protocol suite and the standard protocol used by the Internet. The domain name system consists of mapped website names with Internet protocol, which facilitates browsing by not requiring users to remember numeric notation addresses. The nature of the system, which involves transferring information in plain text, makes it vulnerable to security attacks. The domain name system suffers from spoofing and cache poisoning attacks that are intended to steal the private information of users. In this paper, a scheme is proposed to prevent the aforementioned attacks by using an asymmetric cipher to encrypt the important information in messages and to protect these messages from manipulation. The proposed scheme is examined and implemented using Linux platform and C programming language. The proposed scheme protects DNS against spoofing and poisoning attacks while the results show small fraction of delay in time comparing with the applied DNS. There are also additional commercial benefits since it does not result in additional costs.
Within the IoT-cloud, security has a very significant role to play. One of the best means by which the security and privacy of an image may be safeguarded confidentially is through encryption. However, this methodolog...
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ISBN:
(纸本)9781509032068
Within the IoT-cloud, security has a very significant role to play. One of the best means by which the security and privacy of an image may be safeguarded confidentially is through encryption. However, this methodological process engenders a disadvantage in that it is difficult to search through encrypted images. A number of different means by which encrypted image can be searched have been devised, however, certain security solutions may not be used for smart devices within an IoTcloud due to the fact that such solutions are not lightweight. We present a lightweight scheme that is able to provide a content-based search through images that have been encrypted. More specifically, images are represented using local features. A similar methodology further described in [1] is also used for image similarity discrimination. In addition, we use a hashing method concerning a locality sensitive hash (LSH) so that the searchable index can be devised. The use of the LSH index means that the proficiency and effectiveness of the system is increased, which allows the retrieval of only relevant images with a minimum number of distance evaluations. Refining vector techniques are used to refine relevant results efficiently and securely. Our index construction process ensures that stored data and trapdoors are kept private.
In-memory clustercomputingsystems based MapReduce, such as Spark, have made a great impact in addressing all kinds of big data problems. Given the overuse of memory speed, which stems from avoiding the latency cause...
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Recently, security issues are obstructing the development and using of cloud computingservices. Authentication and integrity play an important role in the cloud security, and numerous concerns have been raised to rec...
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It is a huge challenge to deploy a cloud computingsystem in large-scale data centers. In order to help resolve this issue, we propose an automatic cloud system deployment approach with the characteristics of reliabil...
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