ODYS 병렬 DBMS/검색엔진을 위한 내고장성 및 부하균형 모듈의 설계 및 구현

김덕회,윤태섭,권혁윤,황규영 한국정보과학회 2013 데이타베이스 연구 Vol.29 No.2

As the amount of data increases explosively on Internet, the role of parallel search engines becomes more important. The web search engine is a representative large-scale parallel search engine, which consists of a large number of machines. Thus, there is a high possibility of failure and skewed load over the machines. Therefore, fault tolerance and load balancing features are essential for parallel web search engines to provide a reliable service and an optimized performance. Commercial web search engines such as Google and Yahoo! provide fault tolerance and load balancing features for parallel query processing. However, their details have not been discussed in the literature. Meanwhile, parallel processing framework MapReduce supports fault tolerance and load balancing features over a large number of machines during parallel query processing. Therefore, its method is applicable to the parallel search engine. In this paper, we design and implement a MapReduce-style fault tolerance and load balancing module for ODYS, which is a parallel search engine that has been under development at KAIST. In particular, for the environment of running a lot of concurrent short-running queries, we propose a low-overhead process and communication architecture of the fault tolerance and load balancing module. We also propose an index structure for effectively managing the status and the load of slave machines and the status of slave processes. Finally, we conduct experiments to show that the proposed fault tolerance and load balancing module works in an effective way. The result of the experiments shows that ODYS with the fault tolerance and load balancing module provides fault tolerance significant enhancement in performance. ODYS incurs 0.4% of additional query processing time when one out of 400 slave processes is at fault, 86.1% of additional query processing time when one out of 4 slave machines is at fault where the query load is 5 million queries/day. It also provides load balancing while outperforming the naïve configuration of ODYS without load balancing by up to 16.9% in the average query processing time when the query load is 9 million queries/day and two nodes are duplicated in the configuration. 최근 인터넷 상의 데이터의 양이 폭발적으로 증가함에 따라 분산 저장된 대규모의 데이터에 대한 검색을 병렬적으로 수행하는 병렬 검색 엔진의 역할이 중요해지고 있다. 웹 검색 엔진은 대표적인 대형 병렬 검색 엔진이므로 이를구성하는 머신의 수가 많다. 따라서 일부 머신이 고장 날 가능성이 높고, 각 머신들의 부하에 불균형이 발생하기쉽다. 그러므로 병렬 웹 검색 엔진은 안정적인 정보 검색 서비스를 제공할 수 있도록 하는 내고장성(Fault tolerance)기능과 시스템의 부하를 균형화 하여 전체 시스템의 성능을 최적화하는 부하균형(Load balancing) 기능이 필요하다. Google, Yahoo!와 같은 상용 검색 엔진은 질의를 병렬로 처리하는 과정에서 내고장성 및 부하균형 기능을 지원한다. 그러나 이에 대한 구체적인 방법은 공개되어 있지 않다. 한편, 병렬 처리 프레임워크인 MapReduce는 질의를병렬로 처리하는 과정에서 많은 수의 머신에 대해 내고장성 및 부하균형 기능을 지원한다. 따라서 병렬 검색 엔진에MapReduce 방식의 내고장성 및 부하균형 기능을 적용할 수 있다. 본 논문에서는 한국과학기술원 전산학과 데이터베이스 및 멀티미디어 연구실에서 개발한 병렬 검색 엔진인ODYS를 위한 내고장성 및 부하균형 모듈을 병렬 처리 프레임워크인 MapReduce에서 제공하는 내고장성 및 부하균형 방법에 기반하여 설계하고 구현한다. 특히, 처리 시간이 짧은 수많은 질의를 동시에 처리해야 하는 병렬 검색엔진의 요구조건을 만족시키기 위해 적은 오버헤드로 내고장성 및 부하균형 기능을 수행할 수 있는 프로세스 및통신 구조를 제안한다. 그리고 질의를 처리하는 다수의 슬레이브 머신의 상태 및 부하와 슬레이브 프로세스의 상태를 효과적으로 관리할 수 있는 색인 자료구조를 제안한다. 마지막으로 실험을 통해 본 논문에서 설계하고 구현한모듈이 효율적으로 내고장성 기능을 수행하고, 효과적으로 부하균형 기능을 수행함을 보인다. 실험 결과, 내고장성및 부하균형 모듈을 적용한 ODYS가 하루당 5백만 개의 질의 부하에서 고장이 발생하지 않은 경우에 비해 슬레이브프로세스(400개의 슬레이브 프로세스 중 1개를 고장시킴)에 대해 약 0.4%, 슬레이브 머신(4대의 슬레이브 머신 중1대를 고장시킴)에 대해 약 86.1%의 추가적인 질의 수행 시간으로 내고장성 기능을 수행할 수 있음을 보였다. 또한,부하균형 기능으로 인해 하루당 9백만 개의 질의 부하와 2개의 노드가 복제된 환경에서 부하균형을 하지 않는 나이브한 구성의 ODYS에 비해 평균 질의 수행 시간이 약 16.9% 향상되었음을 보인다.

Detailed Design of ITER Vacuum Vessel Ports and In-Wall Shielding

김덕회,Doo-Gi Kim,Gi-Won Hong,안희재,Kyoung-Ho Park,Seungyon Cho,Young-Hwan Choi 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

The conceptual design of the ITER VV (Vacuum Vessel) has already been developed. Detailed design for the VV upper port and in-wall shielding has been requested from the ITER IT (International Team). In this paper, ITA (ITER Transitional Arrangements) VV task results conducted by KO PT (Korea Participant) are described. Especially, the results of the detailed design of VV upper port and in-wall shielding are discussed. The global structural analysis results of the upper port with the in-port components and local analyses of tangential key, upper port flange, and connecting duct are described. The structural and thermal hydraulic analysis results of in-wall shielding are also presented.

자동차용 베벨기어의 피로시험 및 해석

김덕회(Duck-Hoi Kim),김기광(Gi-Gwang Kim),김재훈(Jae-Hoon Kim),안병욱(Byoung-Wook Ahn) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

To evaluate the bending fatigue strength of automotive bevel gear, fatigue test and analysis are performed. Test fixture of double tooth concept is considered to obtain the results of the reliable fatigue test. Fatigue life of automotive bevel gear is evaluated by Weibull analysis. To compare the test results and to verify the fatigue analysis procedures, fatigue analyses are carried out. Structural and fatigue analyses are performed using ABAQUS and FE-Safe codes, respectively. Fatigue analysis results show that fatigue life and crack initiation site are coincided with test results and then fatigue analysis procedures are verified. And, fatigue analysis for random loading is performed.

유효거리를 이용한 연소관 노치부의 파손기준 해석

김덕회(Duck Hoi Kim),김재훈(Jae Hoon Kim),문순일(Soon Il Moon) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4

In this study, the intrinsic static/dynamic fracture toughness of Al 7175-T74 is evaluated from the apparent static/ dynamic toughness of notched specimen. The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite clement analysis. Also, effective distance is applied 10 estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective distance can be used to evaluate the failure criterion of structure with notch.

변형률 에너지법을 이용한 Inconel 617의 저주기피로 수명 예측

김덕회(Duck-Hoi Kim),김기광(Ki-Gwang Kim),김재훈(Jae-Hoon Kim),이영신(Young-Shin Lee),박원식(Won-Sik Park) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11

Low cycle fatigue tests are performed on the Inconel 617 that be used for a hot gas casing. The relation between strain energy density and numbers of cycles to failure is examined in order to predict the low cycle fatigue life of Inconel 617. The life predicted by the strain energy method is found to coincide with experimental data and results obtained from the Coffin-Manson method. Also the cyclic behavior of Inconel 617 is characterized by cyclic hardening with increasing number of cycle at room temperature.

고강도 저합금강의 저주기 피로특성 ( Low Cycle Fatigue Characteristics of High Strength Low Alloy Steel )

김재훈,김덕회,이종현,조성석,전병환 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.1 No.1

The Structural Design of ITER Tokamak In-pit Assembly Tools

임기학,김덕회,Gyeongtaeg Lee,Hyungtaek Lee,Jae Hyuk Lee,KeeSeok Lim,Kyunghoon Oh,Minsung Ban 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

ITER (International Thermonuclear Experimental Reactor) tokamak assembly mainly comprises sub-assembly and in-pit assembly. The tools for in-pit assembly procedure consist of the tools for Toroidal Field (TF) magnet gravity support assembly, TF magnet inner support, TF coil bracing, and TF coil, vacuum vessel, and thermal shield assembly, among which the design of TF magnet inner support and TF coil bracing tools with sector lifting tool, one of the sub-assembly tool, is described herein. The basic structures for these tools have been developed. The structural stabilities have been studied by using ANSYS code, against the seismic loads of SL-2 level for the two candidate ITER sites, Cadarache in France and Rokkasho in Japan, respectively1. Dynamic analyses using FRS (Floor Response Spectrum) have been performed for the TF magnet inner support and TF coil bracing tools, while an equivalent static analysis was done for the sector lifting tool. The sector lifting tool turned out safe against the seismic loads. The dynamic analyses for the TF support and bracing tool, however, showed a relatively large displacement of 30 mm, which can lead to contact between components. Design improvement for this tool is on-going.

The Structural Design of ITER Tokamak Sub-assembly Tools

임기학,김덕회,Gyeongtaeg Lee,Hyungtaek Lee,Jae Hyuk Lee,KeeSeok Lim,Kyunghoon Oh,Minsung Ban 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

ITER (International Thermonuclear Experimental Reactor) tokamak assembly mainly comprises sub-assembly and in-pit assembly. The tools for sub-assembly procedure consist of the tools for upending, sector lifting, vacuum vessel support and bracing, and sector sub-assembly, among which the design of three tools, excluding sector lifting, is described herein. The basic structures for these tools have been developed. The structural stabilities have been studied by using ANSYS code, against the seismic loads of SL-2 level for the two candidate ITER sites, Cadarache in France and Rokkasho in Japan, respectively1. Dynamic analyses using FRS (Floor Response Spectrum) have been performed. The upending and sub-assembly tool turned out safe against the seismic loads, while vacuum vessel support and bracing one gave large toroidal bending of 68 mm and the resultant high stress of 856 MPa at the lower region of vacuum vessel. Design improvement for this tool is on-going.?

스트레인게이지법을 이용한 동적응력확대계수 평가 ( Evaluation on dynamic stress intensity factor using strain gage method )

이현철,김덕회,김재훈,문순일 대한기계학회 2000 대한기계학회 춘추학술대회 Vol.- No.-

변형률 측정을 이용한 추진기관용 Al 합금의 파괴인성 평가

김재훈,김덕회,임동규,박성욱,문순일 한국산업안전학회 2002 한국안전학회지 Vol.17 No.3

The fracture toughness is evaluated by using CT(compact tension) and 3PB(thress point bending) specimens of A1 alloys for propulsive engine. To evaluate the static fracture toughness, strain gage method is used. The static fracture toughness obtained from the strain measurement is compared with the results by ASTM standard and FEM analysis. For the reliable evaluation of fracture toughness, strain gages are attached at various positions.