• The KIPS Transactions:PartC
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• v.12C no.4 s.100
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• pp.603-608
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• 2005

Disk I/O is a major performance bottleneck of web proxy server. Today's most web proxy sowers are design to run on top of a general purpose file system. But general purpose file system can not efficiently handle web cache workload, small files, leading to the performance degradation of entire web proxy servers. In this paper we evaluate the performance potential of raw disk to reduce disk I/O overhead of web proxy servers. To show the performance potential of raw disk, we design a storage management system called Block-structured Storage Management System (BSMS). And we also actually implement web proxy server that incorporate BSMS in Squid. Comprehensive experimental evaluations show that raw disk can be a good solution to improve disk I/O performance significantly for web proxy servers.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.5
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• pp.293-299
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• 2007

Intelligent pipeline inspection gauges (PIGs) are inspection vehicles that move along within a (gas or oil) pipeline and acquire signals (also called sensor data) from their surrounding rings of sensors. By analyzing the signals captured in intelligent PIGs, we can detect pipeline defects, such as holes and curvatures and other potential causes of gas explosions. There are two major data access patterns apparent when an analyzer accesses the pipeline signal data. The first is a sequential pattern where an analyst reads the sensor data one time only in a sequential fashion. The second is the repetitive pattern where an analyzer repeatedly reads the signal data within a fixed range; this is the dominant pattern in analyzing the signal data. The existing PIG software reads signal data directly from the server at every user#s request, requiring network transfer and disk access cost. It works well only for the sequential pattern, but not for the more dominant repetitive pattern. This problem becomes very serious in a client/server environment where several analysts analyze the signal data concurrently. To tackle this problem, we devise a fast in-memory cache manager, called T-Cache, by considering pipeline sensor data as multiple time-series data and by efficiently caching the time-series data at T-Cache. To the best of the authors# knowledge, this is the first research on caching pipeline signals on the client-side. We propose a new concept of the signal cache line as a caching unit, which is a set of time-series signal data for a fixed distance. We also provide the various data structures including smart cursors and algorithms used in T-Cache. Experimental results show that T-Cache performs much better for the repetitive pattern in terms of disk I/Os and the elapsed time. Even with the sequential pattern, T-Cache shows almost the same performance as a system that does not use any caching, indicating the caching overhead in T-Cache is negligible.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.157-159
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• 2007

The conventional hard disk has been the dominant database storage system for over 25 years. Recently, hybrid systems which incorporate the advantages of flash memory into the conventional hard disks are considered to be the next dominant storage systems to support databases for desktops and server computers. Their features are satisfying the requirements like enhanced data I/O, energy consumption and reduced boot time, and they are sufficient to hybrid storage systems as major database storages. However, we need to improve traditional index node management schemes based on B-Tree due to the relatively slow characteristics of hard disk operations, as compared to flash memory. In order to achieve this goal, we propose a new index node management scheme called FNC-Tree. FNC-Tree-based index node management enhanced search and update performance by caching data objects in unused free area of flash leaf nodes to reduce slow hard disk I/Os in index access processes.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.3
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• pp.324-336
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• 2000

The paper proposes an efficient buffer management scheme to enhance performance of the disk I/O system. Without any user level information, the proposed scheme automatically detects the block reference patterns of applications by associating block attributes with forward distance of a block. Based on the detected patterns, the scheme applies an appropriate replacement policy to each application. We also present a new block allocation scheme to improve the performance of buffer cache when kernel needs to allocate a cache block due to a cache miss. The allocation scheme analyzes the cache hit ratio of each application based on block reference patterns and allocates a cache block to maximize cache hit ratios of system. These all procedures are performed on-line, as well as automatically at system level. We evaluate the scheme by trace-driven simulation. Experimental results show that our scheme leads to significant improvements in hit ratios of cache blocks compared to the traditional schemes and requires low overhead.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.2
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• pp.134-145
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• 2004

With rapid growth in the amount of data transferred on the Internet, traditional storage systems have reached the limits of their capacity and performance. SAN (Storage Area Network), which connects hosts to disk with the Fibre Channel switches, provides one of the powerful solutions to scale the data storage and servers. In this environment, the maintenance of data consistency among hosts is an important issue because multiple hosts share the files on disks attached to the SAN. To preserve data consistency, each host can execute the disk I/O whenever disk read and write operations are requested. However, frequent disk I/O requests cause the deterioration of the overall performance of a SAN cluster. In this paper, we introduce a SANtopia global buffer manager to improve the performance of a SAN cluster reducing the number of disk I/Os. We describe the design and algorithms of the SANtopia global buffer manager, which provides a buffer cache sharing mechanism among the hosts in the SAN cluster. Micro-benchmark results to measure the performance of block I/O operations show that the global buffer manager achieves speed-up by the factor of 1.8-12.8 compared with the existing method using disk I/O operations. Also, File system micro-benchmark results show that SANtopia file system with the global buffer manager improves performance by the factor of 1.06 in case of directories and 1.14 in case of files compared with the file system without a global buffer manager.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1B
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• pp.99-107
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• 2002

Broadcast disks are suited for disseminating information to a large number of clients in mobile computing environments. In broadcast disks, the server continuously and repeatedly broadcasts all data items in the database to clients without specific requests. The clients monitor the broadcast channel and retrieve data items as they arrive on the broadcast channel. The broadcast channel then becomes a disk from which clients can retrieve data items. In this paper, we propose a cache conscious concurrency control ($C^4$) scheme to preserve the consistency of client transactions, when the values of broadcast data items are updated at the server. $C^4$ scheme is novel in the sense that it can reduce the response time of client transactions with minimal control information to be broadcast from the server. This is achieved by the judicious caching strategy of the clients.

• Journal of Computing Science and Engineering
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• v.11 no.3
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• pp.92-99
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• 2017

Memcached, commonly used to speed up the data access in big-data and Internet-web applications, is a system software of the distributed-cache mechanism. But it is subject to the severe challenge of the loss of recently uncommitted updates in the case where the Memcached servers crash due to some reason. Although the replica scheme and the disk-log-based replay mechanism have been proposed to overcome this problem, they generate either the overhead of the replica synchronization or the persistent-storage overhead that is caused by flushing related logs. This paper proposes a scheme of backing up the write requests (i.e., set and add) on the Memcached client side, to reduce the overhead resulting from the making of disk-log records or performing the replica consistency. If the Memcached server fails, a timestamp-based recovery mechanism is then introduced to replay the write requests (buffered by relevant clients), for regaining the lost-data updates on the rebooted Memcached server, thereby meeting the data-consistency requirement. More importantly, compared with the mechanism of logging the write requests to the persistent storage of the master server and the server-replication scheme, the newly proposed approach of backing up the logs on the client side can greatly decrease the time overhead by up to 116.8% when processing the write workloads.

• ETRI Journal
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• v.39 no.6
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• pp.820-831
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• 2017

File systems and applications try to implement their own update protocols to guarantee data consistency, which is one of the most crucial aspects of computing systems. However, we found that the storage devices are substantially under-utilized when preserving data consistency because they generate massive storage write traffic with many disk cache flush operations and force-unit-access (FUA) commands. In this paper, we present DJFS (Delta-Journaling File System) that provides both a high level of performance and data consistency for different applications. We made three technical contributions to achieve our goal. First, to remove all storage accesses with disk cache flush operations and FUA commands, DJFS uses small-sized NVRAM for a file system journal. Second, to reduce the access latency and space requirements of NVRAM, DJFS attempts to journal compress the differences in the modified blocks. Finally, to relieve explicit checkpointing overhead, DJFS aggressively reflects the checkpoint transactions to file system area in the unit of the specified region. Our evaluation on TPC-C SQLite benchmark shows that, using our novel optimization schemes, DJFS outperforms Ext4 by up to 64.2 times with only 128 MB of NVRAM.

• Journal of the Korea Society of Computer and Information
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• v.14 no.4
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• pp.9-17
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• 2009

In this paper, we propose a dynamic load distribution technique at the operating system level in mobile storage systems with a heterogeneous storage pair of a small form-factor and disk and a flash memory, which aims at saving energy consumption as well as enhancing I/O performance. Our proposed technique takes a combinatory approach of file placement and buffer cache management techniques to find how the load can be distributed in an energy and performance-aware way for a heterogeneous mobile storage air of a hard disk and a flash memory. We demonstrate that the proposed technique provides better experimental results with heterogeneous mobile storage devices compared with the existing techniques through extensive simulations.

• Journal of KIISE:Databases
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• v.27 no.2
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• pp.209-215
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• 2000

In the on-demand services like AOD(Audio On Demand) over the internet, existing operating systems cannot serve repeatedly requested data efficiently. This paper proposes a web cache architecture. It predicts the songs to be requested in near future, based on the intervals between the requests in the past on the same song and keeps the songs in the web cache. For the replacement strategy of the web cache, LFRR(Least Frequently Requested Recently) is proposed. LFRR replaces the song that has less probability to be requested in near future. The average of the intervals between the requests in the past and the new request is used as the probability of the requests. It is more likely to be requested in near future as the average is less. The web cache decreases the number of disk access extremely, and support to serve more users with restricted resources. From the simulation result based on the data at the AOD site currently operating, it is shown that the high performance enhancement is achieved.