The objective of our research has been to achieve energy-saving key-value store system. We introduce architecture of our distributed key value store and control framework for energy saving. To reduce power consumption, the control framework should reduce the time required before node power-down. Since this time depends heavily on the amount of data migration, we employ an approach which reduce that amount. We describe and evaluate three control strategies that can be executed on this control framework, each consisting of a data allocation algorithm and data control layout algorithm for use when nodes are to be powered down. With a prototype system developed for evaluation purposes, the time required before node power down is reduced by use of our proposed data allocation algorithm, by means of its taking into account the possible presence of Write off-loading nodes.

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.

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.

We have previously reported the development and operation of a lateral tunneling unit (LTU), a micromachined device which can control the magnitude of a tunneling current passing through a vacuum gap by adjusting the distance of the gap. The amplitude of the actuator driving voltage necessary to vary the current certain range was much larger than the theoretically expected value. Its cause has been left unclear. We carried out experiments in the air and in ultrahigh vacuum (UHV), in order to determine the mechanism of the disagreement. The results of them indicated that an atomic force affects the behavior of the LTU. The estimated magnitude of the force was so large as not to be neglected compared with the actuation force of the LTU. We increased the rigidity and actuation force over 50 times and achieved stabilization. A guide to design a stable LTU and its controller will be given based on the experimental results.