• The KIPS Transactions:PartD
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• v.14D no.1 s.111
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• pp.21-34
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• 2007

According to recent rapid price drop and capacity growth of main memory, the number of applications on main memory databases is dramatically increasing. Cache miss, which means a phenomenon that the data required by CPU is not resident in cache and is accessed from main memory, is one of the major causes of performance degradation of main memory databases. Several cache-conscious trees have been proposed for reducing cache miss and making the most use of cache in main memory databases. Since each cache-conscious tree has its own unique features, more than one cache-conscious tree can be used in a single application depending on the application's requirement. Moreover, if there is no existing cache-conscious tree that satisfies the application's requirement, we should implement a new cache-conscious tree only for the application's sake. In this paper, we propose the cache-conscious generalized search tree (CC-GiST). The CC-GiST is an extension of the disk-based generalized search tree (GiST) [HNP95] to be tache-conscious, and provides the entire common features and algorithms in the existing cache-conscious trees including pointer compression and key compression techniques. For implementing a cache-conscious tree based on the CC-GiST proposed in this paper, one should implement only a few functions specific to the cache-conscious tree. We show how to implement the most representative cache-conscious trees such as the CSB+-tree, the pkB-tree, and the CR-tree based on the CC-GiST. The CC-GiST eliminates the troublesomeness caused by managing mire than one cache-conscious tree in an application, and provides a framework for efficiently implementing arbitrary cache-conscious trees with new features.

• Journal of Korea Multimedia Society
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• v.13 no.7
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• pp.1023-1043
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• 2010

As main memory get cheaper, it becomes increasingly affordable to load entire index of DBMS and to access the index. Since speed gap between CPU and main memory is growing bigger, many researches to reduce a cost of main memory access are under the progress. As one of those, cache conscious trees can reduce the cost of main memory access. Since cache conscious trees reduce the number of cache miss by compressing data in node, cache conscious trees can reduce the cost of main memory. Existing cache conscious trees use only fixed one compression technique without consideration of properties of data in node. First, this paper proposes the DC-tree that uses various compression techniques and change data layout in a node according to properties of data in order to reduce cache miss. Second, this paper proposes the level of compression locality that describes properties of data in node by formula. Third, this paper proposes Forced Partial Decomposition (FPD) that reduces the nutter of cache miss. DC-trees outperform 1.7X than B+-tree, 1.5X than simple prefix B+-tree, and 1.3X than pkB-tree, in terms of the number of cache misses. Since proposed DC-trees can be adopted in commercial main memory database system, we believe that DC-trees are practical result.

• Journal of KIISE:Databases
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• v.32 no.1
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• pp.12-23
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• 2005

In the past decade, advances in speed of commodity CPUs have iu out-paced advances in memory latency Main-memory access is therefore increasingly a performance bottleneck for many computer applications, including database systems. To reduce memory access latency, cache memory incorporated in the memory subsystem. but cache memories can reduce the memory latency only when the requested data is found in the cache. This mainly depends on the memory access pattern of the application. At this point, previous research has shown that B+ trees perform much faster than T-trees because B+ trees are more cache conscious than T-trees, and also proposed 'Cache Sensitive B+trees' (CSB. trees) that are more cache conscious than B+trees. The goal of this paper is to make T-trees be cache conscious as CSB-trees. We propose a new index structure called a 'Cache Sensitive T-trees (CST-trees)'. We implemented CST-trees and compared performance of CST-trees with performance of other index structures.

• Journal of KIISE:Databases
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• v.34 no.4
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• pp.328-342
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• 2007

We propose a new cache conscious indexing structure for processing frequently updated data efficiently. Our proposed index structure is based on a KDB-Tree, one of the representative index structures based on space partitioning techniques. In this paper, we propose a data compression technique and a pointer elimination technique to increase the utilization of a cache line. To show our proposed index structure's superiority, we compare our index structure with variants of the CR-tree(e.g. the FF CR-tree and the SE CR-tree) in a variety of environments. As a result, our experimental results show that the proposed index structure achieves about 85%, 97%, and 86% performance improvements over the existing index structures in terms of insertion, update and cache-utilization, respectively.

• Journal of KIISE:Databases
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• v.30 no.6
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• pp.651-665
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• 2003

To reduce cache misses emerges as the most important issue in today's situation of main memory databases, in which CPU speeds have been increasing at 60% per year, and memory speeds at 10% per year. Recent researches have demonstrated that cache-conscious index structure such as the CR-tree outperforms the R-tree variants. Its search performance can be poor than the original R-tree, however, since it uses a lossy compression scheme. In this paper, we propose alternatively a cache-conscious version of the R-tree, which we call MR-tree. The MR-tree propagates node splits upward only if one of the internal nodes on the insertion path has empty room. Thus, the internal nodes of the MR-tree are almost 100% full. In case there is no empty room on the insertion path, a newly-created leaf simply becomes a child of the split leaf. The height of the MR-tree increases according to the sequence of inserting objects. Thus, the HeightBalance algorithm is executed when unbalanced heights of child nodes are detected. Additionally, we also propose the CCMR-tree in order to build a more cache-conscious MR-tree. Our experimental and analytical study shows that the two-dimensional MR-tree performs search up to 2.4times faster than the ordinary R-tree while maintaining slightly better update performance and using similar memory space.

• International Journal of Contents
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• v.3 no.1
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• pp.19-23
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• 2007

Recently, several main-memory index structures have been proposed to reduce the impact of secondary cache misses. In mainmemory storage systems, secondary cache misses have a substantial effect on the performance of index structures. However, recent studies still stiffer from secondary cache misses when visiting each level of index tree. In this paper, we propose a new index structure that minimizes the total amount of cache miss latency. The proposed index structure prefetched grandchildren of a current node. The basic structure of the proposed index structure is based on that of the CSB+-Tree, which uses the concept of a node group to increase fan-out. However, the insert algorithm of the proposed index structure significantly reduces the cost of a split. The superiority of our algorithm is shown through performance evaluation.

• 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.

• The KIPS Transactions:PartD
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• v.13D no.4 s.107
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• pp.463-476
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• 2006

R-trees have been traditionally optimized for the I/O performance with the disk page as the tree node. Recently, researchers have proposed cache-conscious variations of R-trees optimized for the CPU cache performance in main memory environments, where the node size is several cache lines wide and more entries are packed in a node by compressing MBR keys. However, because there is a big difference between the node sizes of two types of R-trees, disk-optimized R-trees show poor cache performance while cache-optimized R-trees exhibit poor disk performance. In this paper, we propose a cache and disk optimized R-tree, called the PR-tree (Prefetching R-tree). For the cache performance, the node size of the PR-tree is wider than a cache line, and the prefetch instruction is used to reduce the number of cache misses. For the I/O performance, the nodes of the PR-tree are fitted into one disk page. We represent the detailed analysis of cache misses for range queries, and enumerate all the reasonable in-page leaf and nonleaf node sizes, and heights of in-page trees to figure out tree parameters for best cache and I/O performance. The PR-tree that we propose achieves better cache performance than the disk-optimized R-tree: a factor of 3.5-15.1 improvement for one-by-one insertions, 6.5-15.1 improvement for deletions, 1.3-1.9 improvement for range queries, and 2.7-9.7 improvement for k-nearest neighbor queries. All experimental results do not show notable declines of the I/O performance.

• Journal of KIISE:Databases
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• v.31 no.4
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• pp.384-394
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• 2004

Recently, to relieve the performance degradation caused by the bottleneck between CPU and main memory, cache conscious multi-dimensional index structures have been proposed. The ultimate goal of them is to reduce the space for entries so as to widen index trees and minimize the number of cache misses. The existing index structures can be classified into two approaches according to their entry reduction methods. One approach is to compress MBR keys by quantizing coordinate values to the fixed number of bits. The other approach is to store only the sides of minimum bounding regions (MBRs) that are different from their parents partially. In this paper, we propose a new index structure that exploits the properties of the both techniques. Then, we investigate the existing multi-dimensional index structures for main memory database system through experiments under the various work loads. We perform various experiments to show that our approach outperforms others.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.7B
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• pp.605-619
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• 2003

The main memory DBMS(MMDBMS) efficiently supports various database applications that require high performance since it employs main memory rather than disk as a primary storage. In this paper, we discuss the index manager of the Tachyon, a next-generation MMDBMS. Recently, the gap between the CPU processing and main memory access times is becoming much wider due to rapid advance of CPU technology. By devising data structures and algorithms that utilize the behavior of the cache in CPU, we are able to enhance the overall performance of MMDBMSs considerably. In this paper, we address the practical implementation issues and our solutions for them obtained in developing the cache-conscious index manager of the Tachyon. The main issues touched are (1) consideration of the cache behavior, (2) compact representation of the index entry and the index node, (3) support of variable-length keys, (4) support of multiple-attribute keys, (5) support of duplicated keys, (6) definition of the system catalog for indexes, (7) definition of external APIs, (8) concurrency control, and (9) backup and recovery. We also show the effectiveness of our approach through extensive experiments.