Search

Data stores and cloud services are typically accessed using a client-server paradigm wherein the client runs as part of an application process which is trying to access the data store or cloud service. This paper presents the design and implementation of enhanced clients for improving both the functionality and performance of applications accessing data stores or cloud services. Our enhanced clients can improve performance via multiple types of caches, encrypt data for providing confidentiality before sending information to a server, and compress data for reducing the size of data transfers. Our clients can perform data analysis to allow applications to more effectively use cloud services. They also provide both synchronous and asynchronous interfaces. An asynchronous interface allows an application program to access a data store or cloud service and continue execution before receiving a response which can significantly improve performance. We present a Universal Data Store Manager (UDSM) which allows an application to access multiple different data stores and provides a common interface to each data store. The UDSM also can monitor the performance of different data stores. A workload generator allows users to easily determine and compare the performance of different data stores. We also present NLU-SA, an application for performing natural language understanding and sentiment analysis on text documents. NLU-SA is implemented on top of our enhanced clients and integrates text analysis with Web searching. We present results from NLU-SA on sentiment on the Web towards major companies and countries. We also present a performance analysis of our enhanced clients. [ABSTRACT FROM AUTHOR]

Ballooning is a popular solution for dynamic memory balancing. However, existing solutions may perform poorly in the presence of heavy guest swapping. Furthermore, when the host has sufficient free memory, guest virtual machines (VMs) under memory pressure is not be able to use it in a timely fashion. Even after the guest VM has been recharged with sufficient memory via ballooning, the applications running on the VM are unable to utilize the free memory in guest VM to quickly recover from the severe performance degradation. To address these problems, we present MemFlex , a shared memory swapper for improving guest swapping performance in virtualized environment with three novel features: (1) MemFlex effectively utilizes host idle memory by redirecting the VM swapping traffic to the host-guest shared memory area. (2) MemFlex provides a hybrid memory swapping model, which treats a fast but small shared memory swap partition as the primary swap area whenever it is possible, and smoothly transits to the conventional disk-based VM swapping on demand. (3) Upon ballooned with sufficient VM memory, MemFlex provides a fast swap-in optimization, which enables the VM to proactively swap in the pages from the shared memory using an efficient batch implementation. Instead of relying on costly page faults, this optimization offers just-in-time performance recovery by enabling the memory intensive applications to quickly regain their runtime momentum. Performance evaluation results are presented to demonstrate the effectiveness of MemFlex when compared with existing swapping approaches. [ABSTRACT FROM PUBLISHER]

Checkpointing and rollback techniques enhance reliability and availability of virtual machines and their hosted IT services. This paper proposes VM-μCheckpoint, a light-weight pure-software mechanism for high-frequency checkpointing and rapid recovery for VMs. Compared with existing techniques of VM checkpointing, VM-μCheckpoint tries to minimize checkpoint overhead and speed up recovery by means of copy-on-write, dirty-page prediction and in-place recovery, as well as saving incremental checkpoints in volatile memory. Moreover, VM-μCheckpoint deals with the issue that latency in error detection potentially results in corrupted checkpoints, particularly when checkpointing frequency is high. We also constructed Markov models to study the availability improvements provided by VM-μCheckpoint (from 99 to 99.98 percent on reasonably reliable hypervisors). We designed and implemented VM-μCheckpoint in the Xen VMM. The evaluation results demonstrate that VM-μCheckpoint incurs an average of 6.3 percent overhead (in terms of program execution time) for 50 ms checkpoint intervals when executing the SPEC CINT 2006 benchmark. Error injection experiments demonstrate that VM-μCheckpoint, combined with error detection techniques in RMK, provides high coverage of recovery. [ABSTRACT FROM AUTHOR]

Disruption tolerant networks (DTNs) are characterized by low node density, unpredictable node mobility, and lack of global network information. Most of current research efforts in DTNs focus on data forwarding, but only limited work has been done on providing efficient data access to mobile users. In this paper, we propose a novel approach to support cooperative caching in DTNs, which enables the sharing and coordination of cached data among multiple nodes and reduces data access delay. Our basic idea is to intentionally cache data at a set of network central locations (NCLs), which can be easily accessed by other nodes in the network. We propose an efficient scheme that ensures appropriate NCL selection based on a probabilistic selection metric and coordinates multiple caching nodes to optimize the tradeoff between data accessibility and caching overhead. Extensive trace-driven simulations show that our approach significantly improves data access performance compared to existing schemes. [ABSTRACT FROM PUBLISHER]

This paper introduces several novel load-balancing algorithms for distributing Session Initiation Protocol (SIP) requests to a cluster of SIP servers. Our load balancer improves both throughput and response time versus a single node while exposing a single interface to external clients. We present the design, implementation, and evaluation of our system using a cluster of Intel x86 machines running Linux. We compare our algorithms to several well-known approaches and present scalability results for up to 10 nodes. Our best algorithm, Transaction Least-Work-Left (TLWL), achieves its performance by integrating several features: knowledge of the SIP protocol, dynamic estimates of back-end server load, distinguishing transactions from calls, recognizing variability in call length, and exploiting differences in processing costs for different SIP transactions. By combining these features, our algorithm provides finer-grained load balancing than standard approaches, resulting in throughput improvements of up to 24% and response-time improvements of up to two orders of magnitude. We present a detailed analysis of occupancy to show how our algorithms significantly reduce response time. [ABSTRACT FROM AUTHOR]

Secure media broadcast over the Internet poses unique security challenges. One important problem for public broadcast location-based services (LBS) is to enforce access control on a large number of subscribers. In such a system, a user typically subscribes to an LBS for a time interval (a, b) and a spatial region (Xbl, Ybl, Xtr, Ytr) according to a 3-dimensional spatial-temporal authorization model. In this paper, we argue that current approaches to access control using key management protocols are not scalable. Our proposal, STauth, minimizes the number of keys that needs to be distributed and is thus scalable to a large number of subscribers and the dimensionality of the authorization model. We also demonstrate applications of our algorithm to quantified-temporal access control (using ∀ and Ǝ quantifications) and partial-order tree-based authorization models. We describe two implementations of our key management protocols on two diverse platforms: a broadcast service operating on top of a publish/subscribe infrastructure and an extension to the Google Maps API to support quality (resolution)-based access control. We analytically and experimentally show the performance and scalability benefits of our approach over traditional key management approaches. [ABSTRACT FROM AUTHOR]