Letter from the Special Issue Editor

Editorial work for DEBULL on a special issue on data management on Storage Class Memory (SCM) technologies

Flash Aware Database Management System

Flash Memory is valued in many application as a storage media due to its fast access speed, low power, nonvolatile characteristics.Our survey report will contain characteristics of ash disk, architechture of ash disk, various indexing structure for magnetic disk and ash disk, storage techniques for hard disk and magnetic disk and query processing techniques for ash disk. we have explored detail survey of storage, indexing and query processing techniques developed to make database system ash aware. We have implemented most of the techniques in a database system prototype named Mubase developed at IITH. We present some experimental results on TPC-H dataset demonstrating the benets due to the ash aware storage query processing techniques. We have implemented FD - Tree index structure for ash disk on prototyped named Mubase

ACR: An Adaptive Cost-Aware Buffer Replacement Algorithm for Flash Storage Devices

Abstract—Flash disks are being widely used as an important alternative to conventional magnetic disks, although accessed through the same interface by applications, their distinguished feature, i.e., different read and write cost in the aspects of time, makes it necessary to reconsider the design of existing replacement algorithms to leverage their performance potential. Different from existing flash-aware buffer replacement policies that focus on the asymmetry of read and write operations, we address the “discrepancy ” of the asymmetry for different flash disks, which is the fact that exists for a long time, while has drawn little attention by researchers since most existing flash-aware buffer replacement polices are somewhat based on the assumption that the cost of read operation is neglectable compared with that of write operation. In fact, this is not true for current flash disks on the market. We propose an adaptive cost-aware replacement policy (ACR) that uses three cost-based heuristics to select the victim page, thus can fairly make trade off between clean pages (their content remain unchanged) and dirty pages (their content is modified), and hence, can work well for different type of flash disks of large discrepancy. Further, in ACR, buffer pages are divided into clean list and dirty list, the newly entered pages will not be inserted at the MRU position of either list, but at some position in the middle, thus the once-requested pages can be flushed out from the buffer quickly and the frequently-requested pages can stay in buffer for a longer time. Such mechanism makes ACR adaptive to workloads of different access patterns. The experimental results on different traces and flash disks show that ACR not only adaptively tunes itself to workloads of different access patterns, but also works well for different kind of flash disks compared with existing methods. I

Extending Memory Capacity in Consumer Devices with Emerging Non-Volatile Memory: An Experimental Study

The number and diversity of consumer devices are growing rapidly, alongside their target applications' memory consumption. Unfortunately, DRAM scalability is becoming a limiting factor to the available memory capacity in consumer devices. As a potential solution, manufacturers have introduced emerging non-volatile memories (NVMs) into the market, which can be used to increase the memory capacity of consumer devices by augmenting or replacing DRAM. Since entirely replacing DRAM with NVM in consumer devices imposes large system integration and design challenges, recent works propose extending the total main memory space available to applications by using NVM as swap space for DRAM. However, no prior work analyzes the implications of enabling a real NVM-based swap space in real consumer devices. In this work, we provide the first analysis of the impact of extending the main memory space of consumer devices using off-the-shelf NVMs. We extensively examine system performance and energy consumption when the NVM device is used as swap space for DRAM main memory to effectively extend the main memory capacity. For our analyses, we equip real web-based Chromebook computers with the Intel Optane SSD, which is a state-of-the-art low-latency NVM-based SSD device. We compare the performance and energy consumption of interactive workloads running on our Chromebook with NVM-based swap space, where the Intel Optane SSD capacity is used as swap space to extend main memory capacity, against two state-of-the-art systems: (i) a baseline system with double the amount of DRAM than the system with the NVM-based swap space; and (ii) a system where the Intel Optane SSD is naively replaced with a state-of-the-art (yet slower) off-the-shelf NAND-flash-based SSD, which we use as a swap space of equivalent size as the NVM-based swap space