A blockchain is designed to establish consistent and reliable agreements in an untrusted and decentralized environment. In addition, the blockchain enables transaction processing and the creation of smart contracts. It empowers end users to execute contracts without any intermediate entities. However, there are some issues when it comes to retrieving information, such as the state and history of smart contracts and regular transactions in the blockchain. For example, in a smart contract, user-defined data structures can be used to recall the state of the smart contract for a range query, which can decrease the general performance. In addition, an external database can be required to retrieve regular transactions for range queries, which increases management costs. To achieve this, we propose a new scheme that enables SQL query operations to retrieve a smart contract and regular transaction information within the blockchain system. To achieve this, we combine an embedded relational database with an Ethereum-based blockchain system to provide the SQL query. It enables range queries on smart contracts without requiring user-defined data structures and decreases management costs for regular transactions without any external database. We implement the proposed blockchain system on quorum, which is an Ethereum-based blockchain system. Also, we evaluate the proposed system using a synthetic benchmark. The performance of retrieving smart contract data is improved by up to approximately 22×, with low memory usage compared with the existing system. Moreover, the proposed system demonstrates a similar search performance to the existing system, even when considering external databases in regular transactions.

This paper presents a scalable page cache called ScaleCache for improving SSD scalability. Specifically, we first propose a concurrent data structure of page cache based on XArray (ccXArray) to enable access and update the page cache concurrently. Second, we introduce a direct page flush (dflush) which directly flushes pages to storage devices in a parallel and opportunistic manner. We implement ScaleCache with two techniques in the Linux kernel and evaluate it on a 64-core machine with eight NVMe SSDs. Our evaluations show that ScaleCache improves the performance of Linux file systems by up to 6.81× and 4.50× compared with the existing scheme and scalable scheme for multiple SSDs, respectively.

The emergence of non-volatile memories (NVM) brings new opportunities and challenges to data management system design. As an important part of the data management systems, several new file systems are developed to take advantage of the characteristics of NVM. However, these NVM-aware file systems are usually designed and evaluated based on simulations or emulations. In order to explore the performance and characteristics of these file systems on real hardware, in this article, we provide an empirical evaluation of NVM-aware file systems on the first commercially available byte-addressable NVM (i.e., the Intel Optane DC Persistent Memory Module (DCPMM)). First, to compare the performance difference between traditional file systems and NVM-aware file systems, we evaluate the performance of Ext4, XFS, F2FS, Ext4-DAX, XFS-DAX, and NOVA file systems on DCPMMs. To compare DCPMMs with other secondary storage devices, we also conduct the same evaluations on Optane SSDs and NAND-flash SSDs. Second, we observe how remote NUMA node access and device mapper striping affect the performance of DCPMMs. Finally, we evaluate the performance of the database (i.e., MySQL) on DCPMMs with Ext4 and Ext4-DAX file systems. We summarize several observations from the evaluation results and performance analysis. We anticipate that these observations will provide implications for various memory and storage systems.

The Internet of Things (IoT) has been an emerging critical technology platform enabling the development and deployment of smart devices to solve real-world challenges and issues. In addition, IoT applications have gathered various and numerous data from various sources, such as sensor data from IoT devices, system data, status information of IoT devices, and others. However, the quality of sensor data should be thoroughly verified to exploit the benefits of sensor data fully. Due to the importance of sensor data quality, we comprehensively provide a survey on the verification of IoT sensor data in this paper. Thus, we conduct a survey of sensor data verification in IoT regarding six aspects. We focus on 1) anomaly classification, 2) sensor data verification frameworks, 3) sensor data verification methods (including anomaly detection and anomaly correction), 4) evaluation methods to assess sensor data verification methods, 5) technology and tools to build verification tests of sensor data, and 6) challenges and future research directions. In addition, we identify the advantages and disadvantages of the methods in anomaly detection and correction. Hence, this survey provides a comprehensive and better understanding of sensor data verification in IoT, building background knowledge in related topics.

This paper proposes a scalable optimal page replacement policy (OPT) simulator called ScaleOPT to scale the OPT simulation by leveraging multi-core parallelism. Specifically, we first propose AccessMap which collects the future references of pages in parallel before the OPT simulation. It enables calculating the next reference time of the accessed page in a constant time. Second, we introduce Pipelined-Tree consisting of multiple trees which organize caches based on min-max reference times. It enables traverse and update operations of each cache to be performed in a partially parallel manner (i.e., pipelined), thereby scaling out the OPT simulation on multi-cores. Finally, we implement ScaleOPT with two techniques and evaluate it on a 72-core machine. The experimental results demonstrate that ScaleOPT improves the simulation time by up to 6.3×, 7.7×, 20.5×, and 13.9× compared with the long-established standard algorithm-based simulator along with our AccessMap, a variable-size cache scheme, and two widely-used cache simulators (webcachesim and libCacheSim), respectively.