D. Kobayashi

VLEI code: an efficient labeling method for handling XML documents in an RDB

A number of XML labeling methods have been proposed to store XML documents in relational databases. However, they have a vulnerable point, in insertion operations. We propose the variable length endless insertable (VLEI) code and apply it to XML labeling to reduce the cost of insertion operations. Results of our experiments indicate that a combination of the VLEI code and Dewey order is effective for handling skewed insertions.

A concurrency control protocol for parallel B-tree structures without latch-coupling for explosively growing digital content

While shared-nothing parallel infrastructures provide fast processing of explosively growing digital content, managing data efficiently across multiple nodes is important. The value-range partitioning method with parallel B-tree structures in a shared-nothing environment is an efficient approach for handling large amounts of data. To handle large amounts of data, it is also important to provide an efficient concurrency control protocol for the parallel B-tree. Many studies have proposed concurrency control protocols for B-trees, which use latch-coupling. None of these studies has considered that latch-coupling contains a performance bottleneck of sending of messages between processing elements (PEs) in distributed environments because latch-coupling is efficient for a B-tree on a single machine. The only protocol without latch-coupling is the B-link algorithm, but it is difficult to use the B-link algorithm directly on an entire parallel B-tree structure because it is necessary to guarantee the consistency of the side pointers. We propose a new concurrency control protocol named LCFB that requires no latch-coupling in optimistic processes. LCFB reduces the amount of communication between PEs during a B-tree traversal. To detect access path errors in the LCFB protocol caused by removal of latch-coupling, we assign boundary values to each index page. Because a page split may cause page deletion in a Fat-Btree, we also propose an effective method for handling page deletions without latch-coupling. We then combine LCFB with the B-link algorithm within each PE to reduce the cost of Structure Modification Operations (SMOs) in a PE, as a solution to the difficulty of consistency management for the side pointers in a parallel B-tree structure. To compare the performance of the proposed protocol with conventional protocols MARK-OPT, INC-OPT, and ARIES/IM, we implemented them on an autonomous disk system with a Fat-Btree structure. Experimental results in various environments indicate that the system throughput of the proposed protocols is always superior to those of the other protocols, especially in large-scale configurations, and LCFB with the B-link algorithm is effective at higher update ratios.

MARK-OPT: A Concurrency Control Protocol for Parallel B-Tree Structures to Reduce the Cost of SMOs

In this paper, we propose a new concurrency control protocol for parallel B-tree structures capable reducing the cost of structure-modification-operation (SMO) compared to the conventional protocols such as ARIES/IM and INC-OPT. We call this protocol the MARK-OPT protocol, since it marks the lowest SMO occurrence point during optimistic latch-coupling operations. The marking reduces middle phases for spreading an X latch and removes needless X latches. In addition, we propose three variations of the MARK-OPT, which focus on tree structure changes from other transactions. Moreover, the proposed protocols are deadlock-free and satisfy the physical consistency requirement for B-trees. These indicate that the proposed protocols are suitable as concurrency control protocols for B-tree structures. To compare the performance of the proposed protocols, the INC-OPT, and the ARIES/IM, we implement these protocols on an autonomous disk system adopting the Fat-Btree structure, a form of parallel B-tree structure. Experimental results in various environments indicate that the proposed protocols always improve system throughput, and 2P-REP-MARK-OPT is the most useful protocol in high update environment. Additionally, to mitigate access skew, data should be migrated between PEs. We also demonstrate that MARK-OPT improves the system throughput under the data migration and reduces the time for data migration to balance load distribution.

A high-availability software update method for distributed storage systems

SUMMARY In this paper, we propose a nonstop system upgrademethod without significant performance degradation fordata management software. To reduce disk accesses andnetwork traffic, we construct logical nodes inside a physicalnode and migrate data between the symbiotic logical nodes.This logical migration is assisted by storage managementfunctions that hide data location and migration from users.We also show the effectiveness of our method using experi-mental results on the system based on the AutonomousDisks we have proposed as a highly available storage sys-tem technology.

Treatment of Rules in Individual Metadata of Flexible Contents Management

The properties of contents stored in a computer system are very wide while the data volume treated in the system becomes very large. It is important to treat each stored object in different manners to reject its properties in the data management for the large amount of stored data. To satisfy the requirement, we propose a method for the autonomous management based on ECA rules stored in metadata of the contents. We study the feasibility of treating a large number of ECA rules corresponding to the number of stored objects. Because the cost for evaluating conditions in the rules becomes dominant to the system perfornzance when the number of objects increases, we divide the conditions into two types, previously evaluable conditions and nuttime evaluable conditions, and construct a discrimination network for the previously evaluable conditions of each event to reduce the cost for processing the rules. We implement the methods in the autonomous disk system, a high functional storage system we proposed, and evaluate the eficiency of them.

An Efficient Access Forwarding Method Based On Caches On Storage Nodes

In this paper, we discuss access forwarding schemes for the replication that achieve balanced access load distribution for data replicas on multiple storage nodes. In parallel storage systems, it is significant to handle skew of accessrequest distribution. Although replication is commonly used to solve such problems, it decreases hit ratios of cache memories on each storage nodes. We first obtain a result that it uses cache memories efficiently to forward accesses that target at data in less demand with a simple experiment. We also propose a method that uses hit ratios of each cache to recognize the popularity of data with low costs. Results of experiments with the method show that it helps the replication use the limited cache space efficiently.

The Versioning System Balancing Data Amount and Access Frequency on Distributed Storage System

In this paper, a method of balancing both access frequency and data amount for a distributed parallel storage system under version management is discussed. We assume the version management method keeps the latest version of file and a number of differential information sets to access previous versions. Since the access frequency for an aged version is tend to be lower than that for the latest version, we control the access frequency distribution by the placement of the latest versions, while the data amount distribution is managed by the placement of the differential information whose size is enough small to adjust the subtle difference of data amount. We propose a distributed directory structure and data placement algorithm, and evaluate its effect on the access frequency and data amount distribution.

Consideration of experimental evaluation about encrypted replica update process

The secure storage systems adopting the encrypt-on-disk scheme, in which files are stored in cipher for efficient data transmission, need to re-encrypt files with new cryptographic keys when a revocation occurs. There are two re-encryption methods, namely active revocation in which the re-encryption is immediately performed and lazy revocation in which the re-encryption is delayed until the file is updated. There is the trade-off between performance and security because active revocation has the expense of immediate re-encryption, while lazy revocation is vulnerable during its re-encryption delay. We consider the environment in which re-encrypted file is pre-computed by using backup data in a parallel storage system effective for this issue. However, the performance of update is decreased on account of the difference of keys used in primary and backup. In this paper, we evaluate a method in which the differential data re-encrypted for backup are not written to the file but be kept on the memory in different key environment, and evaluate the different key environment in parallel storage by experiment.

An Experimental Evaluation of the Adaptive Replica-assisted Migration for Parallel Storage Systems

We have proposed a method replica-assisted migration that use temporally replica data in other storage nodes during executing data migration to keep both qualities of service accesses and data migration duration. However, we have not evaluated the method with real workload including update operations. In this paper, we first improve the method and evaluate an efficiency of the method under file server workloads. Base on the result of it, we also propose adaptive replica-assisted migration for reduce migration duration.

Evaluation of Placement and Access Asignment for Replicated Object Striping

The number of stored objects that should be targets of high throughput retrieval, such as multimedia stream objects, is increasing recently. To implement a high throughput storage system, striping technique using multiple disk drives are commonly used. However, the ordinary disk striping methods implemented in RAID 0, 3-5 have problems of the flexibility, extensibility, and quality of services (QoS). We have proposed the autonomous disk cluster to realize the flexible and extensible storage system by treating each target object as a unit for management. It also adopts the primary-backup technique for the object to satisfy required QoS. We have shown that the autonomous management for the object unit is effective. However, there is room for improving its throughput. In this paper, we consider an approach for importing a flexible striping technique into the autonomous disk system to provide high throughput. It is important to locate fragments of an object into a part of disk cluster appropriately with considering workload skews to derive the required throughput. We use access history to decide their location. We also propose a method to divide access load into fragmented primary and backup adaptively. The experimental results using PC cluster indicate that the proposed methods are effective.