Hyuck Han

MRBench: A Benchmark for MapReduce Framework

MapReduce is Googles programming model for easy development of scalable parallel applications which process huge quantity of data on many clusters. Due to its conveniency and efficiency, MapReduce is used in various applications (e.g., Web search services and online analytical processing). However, there are only few good benchmarks to evaluate MapReduce implementations by realistic testsets. In this paper, we present MRBench that is a benchmark for evaluating MapReduce systems. MRBench focuses on processing business oriented queries and concurrent data modifications. To this end, we build MRBench to deal with large volumes of relational data and execute highly complex queries. By MRBench, users can evaluate the performance of MapReduce systems while varying environmental parameters such as data size and the number of (map/reduce) tasks. Our extensive experimental results show that MRBench is a useful tool to benchmark the capability of answering critical business questions.

A RESTful Approach to the Management of Cloud Infrastructure

Recently, REpresentational State Transfer (REST) has been proposed as an alternative architecture for Web services.In the era of Cloud and Web 2.0, many complex Web service-based systems such as e-Business an de-Government applications have adopted REST. Unfortunately, the REST approach has been applied to few cases in management systems, especially for a management system for cloud computing infrastructures.In this paper, we design and implement a RESTful Cloud Management System (CMS).Managed elements can be modeled as resources in REST and operations in existing systems can be evaluated using four methods of REST or a combination of them.We also show how components of existing management systems can be realized as REST-style Web services.

A scalable lock manager for multicores

Modern implementations of DBMS software are intended to take advantage of high core counts that are becoming common in high-end servers. However, we have observed that several database platforms, including MySQL, Shore-MT, and a commercial system, exhibit throughput collapse as load increases, even for a workload with little or no logical contention for locks. Our analysis of MySQL identifies latch contention within the lock manager as the bottleneck responsible for this collapse. We design a lock manager with reduced latching, implement it in MySQL, and show that it avoids the collapse and generally improves performance. Our efficient implementation of a lock manager is enabled by a staged allocation and de-allocation of locks. Locks are pre-allocated in bulk, so that the lock manager only has to perform simple list-manipulation operations during the acquire and release phases of a transaction. De-allocation of the lock data-structures is also performed in bulk, which enables the use of fast implementations of lock acquisition and release, as well as concurrent deadlock checking.

Cashing in on the Cache in the Cloud

Over the past decades, caching has become the key technology used for bridging the performance gap across memory hierarchies via temporal or spatial localities; in particular, the effect is prominent in disk storage systems. Applications that involve heavy I/O activities, which are common in the cloud, probably benefit the most from caching. The use of local volatile memory as cache might be a natural alternative, but many well-known restrictions, such as capacity and the utilization of host machines, hinder its effective use. In addition to technical challenges, providing cache services in clouds encounters a major practical issue (quality of service or service level agreement issue) of pricing. Currently, (public) cloud users are limited to a small set of uniform and coarse-grained service offerings, such as High-Memory and High-CPU in Amazon EC2. In this paper, we present the cache as a service (CaaS) model as an optional service to typical infrastructure service offerings. Specifically, the cloud provider sets aside a large pool of memory that can be dynamically partitioned and allocated to standard infrastructure services as disk cache. We first investigate the feasibility of providing CaaS with the proof-of-concept elastic cache system (using dedicated remote memory servers) built and validated on the actual system, and practical benefits of CaaS for both users and providers (i.e., performance and profit, respectively) are thoroughly studied with a novel pricing scheme. Our CaaS model helps to leverage the cloud economy greatly in that 1) the extra user cost for I/O performance gain is minimal if ever exists, and 2) the providers profit increases due to improvements in server consolidation resulting from that performance gain. Through extensive experiments with eight resource allocation strategies, we demonstrate that our CaaS model can be a promising cost-efficient solution for both users and providers.

Design and Implementation of Multiple Fault-Tolerant MPI over Myrinet (M^3)

Advances in network technology and computing power have inspired the emergence of high-performance cluster computing systems. While cluster management and hardware highavailability tools are readily available, practical and easily deployable fault-tolerant systems have not been successfully adopted commercially. We present a fault-tolerant system, Multiple fault-tolerant MPI over Myrinet (M3), that differs in notable respects from other proposed fault-tolerant systems in the literature. M3 is built on top of Myrinet since it is regarded as one of the best solutions for highperformance networks and is widely used in cluster computing systems because it can provide a high-speed switching network that is an inevitable ingredient in interconnecting clusters of workstations or PCs. M^3 is a user-transparent checkpointing system for multiple fault-tolerant MPI implementation that is primarily based on the coordinated checkpointing protocol. M3 supports three critical functionalities that are necessary for faulttolerance: a light-weight failure detection mechanism, dynamic process management that includes process migration, and a consistent checkpoint and recovery mechanism. The features of M are that it requires no modifications of application code and that it preserves much of the high performance characteristics of Myrinet. This paper describes the architecture of M3, its detailed design principles and comprehensive implementation issues. We also propose practical solutions for those involved in constructing highly available cluster systems for parallel programming systems. Experimental results substantiate our assertion that M3 can be a good candidate for practically deployable fault-tolerant systems in very-large and high-performance Myrinet clusters and that its protocol can be applied to a wide variety of parallel communication libraries without difficulty.

Improving Hadoop performance in intercloud environments

Intercloud is a federated environment of private clusters and public clouds. The performance of Hadoop could be degraded significantly in intercloud environments. Because previous solutions for intercloud environments rely on speculative execution, they require additional cost in the cloud. In this paper, we propose a new task scheduler that improves performance without the help of speculative execution in intercloud environments.

Scatter-Gather-Merge: An efficient star-join query processing algorithm for data-parallel frameworks

A data-parallel framework is very attractive for large-scale data processing since it enables such an application to easily process a huge amount of data on commodity machines. MapReduce, a popular data-parallel framework, is used in various fields such as web search, data mining and data warehouses; it is proven to be very practical for such a data-parallel application. A star-join query is a popular query in data warehouses that are a current target domain of data-parallel frameworks. This article proposes a new algorithm that efficiently processes star-join queries in data-parallel frameworks such as MapReduce and Dryad. Our star-join algorithm for general data-parallel frameworks is called Scatter-Gather-Merge, and it processes star-join queries in a constant number of computation steps, although the number of participating dimension tables increases. By adopting bloom filters, Scatter-Gather-Merge reduces a non-trivial amount of IO. We also show that Scatter-Gather-Merge can be easily applied to MapReduce. Our experimental results in both cluster and cloud environments show that Scatter-Gather-Merge outperforms existing approaches.

Microglial interleukin-1β in the ipsilateral dorsal horn inhibits the development of mirror-image contralateral mechanical allodynia through astrocyte activation in a rat model of inflammatory pain.

Abstract Damage on one side of the body can also result in pain on the contralateral unaffected side, called mirror-image pain (MIP). Currently, the mechanisms responsible for the development of MIP are unknown. In this study, we investigated the involvement of spinal microglia and interleukin-1&bgr; (IL-1&bgr;) in the development of MIP using a peripheral inflammatory pain model. After unilateral carrageenan injection, mechanical allodynia (MA) in both hind paws and the expression levels of spinal Iba-1, IL-1&bgr;, and GFAP were evaluated. Ipsilateral MA was induced beginning at 3 hours after carrageenan injection, whereas contralateral MA showed a delayed onset occurring 5 days after injection. A single intrathecal (i.t.) injection of minocycline, a tetracycline derivative that displays selective inhibition of microglial activation, or an interleukin-1 receptor antagonist (IL-1ra) on the day of carrageenan injection caused an early temporary induction of contralateral MA, whereas repeated i.t. treatment with these drugs from days 0 to 3 resulted in a long-lasting contralateral MA, which was evident in its advanced development. We further showed that IL-1&bgr; was localized to microglia and that minocycline inhibited the carrageenan-induced increases in spinal Iba-1 and IL-1&bgr; expression. Conversely, minocycline or IL-1ra pretreatment increased GFAP expression as compared with that of control rats. However, i.t. pretreatment with fluorocitrate, an astrocyte inhibitor, restored minocycline- or IL-1ra-induced contralateral MA. These results suggest that spinal IL-1&bgr; derived from activated microglia temporarily suppresses astrocyte activation, which can ultimately prevent the development of contralateral MA under inflammatory conditions. These findings imply that microglial IL-1&bgr; plays an important role in regulating the induction of inflammatory MIP.

Design and evaluation of mobile offloading system for web-centric devices

Increasingly, smartphones are becoming one of the most popular mobile devices in the personal computing environment. As the need for a variety of mobile applications increases, the target mobile platform is a primary concern for mobile application developers. To reduce design complexity for different platforms and enhance the compatibility of applications on various mobile OSes, a JavaScript-based web environment became a main target framework for smartphone applications. Two particular characteristics of a smartphone are restricted power supply and low-end hardware resources, compared to high-end servers. Computing-intensive and rich graphics-based applications in a smartphone may fully utilize the CPU and consume a large amount of the battery power accordingly.In this paper, we propose a platform-independent mobile offloading system, which is a delegated system for a web centric devices environment. Our offloading architecture uses a built-in proxy system that splits the original JavaScript-based application codes into the following two parts: a lightweight code for the mobile client and a computationally heavy code that runs on the server system. We adopt one of the web applications utilizing a combinatory search for our case study. Our evaluation shows that our mobile offloading system reduces the response time of the application running in the web browser and enables a high workload application to run on relatively low-end mobile devices. In addition, this method reduces power consumption of the device. Therefore, this web-based offloading architecture creates a new mobile computing environment and supports various OS platforms of mobile clients.

Role of peripheral sigma‐1 receptors in ischaemic pain: Potential interactions with ASIC and P2X receptors

The role of peripheral sigma‐1 receptors (Sig‐1Rs) in normal nociception and in pathologically induced pain conditions has not been thoroughly investigated. Since there is mounting evidence that Sig‐1Rs modulate ischaemia‐induced pathological conditions, we investigated the role of Sig‐1Rs in ischaemia‐induced mechanical allodynia (MA) and addressed their possible interaction with acid‐sensing ion channels (ASICs) and P2X receptors at the ischaemic site.