Wenbin Zhu

Hybrid SSDs, which allow flash cells to convert among different types of flash cells (e.g., SLC/MLC/QLC), are designed for achieving both high performance and high density. However, previous designs with two types of flash cells encounter a performance cliff degradation once the flash cells of single bit mode (SLC) are consumed. In this work, we propose a novel level-based hybrid SSD (e.g., including SLC-MLC-QLC), named RL-hybridSSD, that adopts an intermediate layer (e.g., MLC) as a performance cushion. We design a workload-aware dynamic placement mechanism that adaptively routes hot and cold writes among SLC, MLC, and QLC regions based on workload dynamics and device space pressure. Further, a multi-agent reinforcement learning-assisted space management scheme is designed to coordinate the garbage collection and mode conversion processes considering both the SSD internal status and workload patterns. We evaluated RL-hybridSSD with various real-world workloads based on simulation. The experimental results show that the proposed RL-hybridSSD provides 2.03× higher performance on average compared with state-of-the-art schemes.

Winternitz one-time signature (WOTS) is a quantum-resistant signature mechanism that has been widely used in direct acyclic graph (DAG)-based blockchain systems. However, it needs to generate a unique private/public key pair for each transaction, which severely limits blockchain performance by performing a time-consuming unique address checking process when generating transactions. This article proposes a bloom-filter-based approach, called ABACUS, to optimize the unique address checking process in WOTS. In ABACUS, we separate the large address space into multiple small subspaces and apply bloom filters to perform uniqueness checking for all addresses in one subspace. Specifically, we propose a two-level address space mechanism to strike a balance between the checking efficiency and the memory/storage space overhead of the bloom filter design. A bucket-based scalable bloom filter (SBF) design is proposed to match the growth of used addresses with efficient I/O access by storing all sub-bloom-filters together in one bucket. To further reduce disk I/Os, ABACUS incorporates an in-memory write buffer and a read-only cache. To reclaim wasted addresses, we also propose a layered address recycling mechanism by efficiently checking and reusing unused addresses that were identified as used due to false positives of bloom filters. We have implemented a fully functional prototype of ABACUS and integrated it into IOTA, a widely used DAG-based blockchain system. A series of experiments have been conducted on a private IOTA system. Experimental results show that ABACUS can significantly reduce the transaction generation time by up to four orders of magnitude, and achieve up to $3\times $ boost on the system throughput with more than 80% space-saving. We have released the open-source code of ABACUS for public access.

Biobutanol offers several advantages and a larger market, that make it a biofuel to be studied with great interest. In fact, butanol has an energy content similar to that of gasoline, and it can be used as an alternative fuel to gasoline. It is a biofuel that is safe for the environment. The optimization of the production of butanol thus appears as an attractive option. Butanol production from food waste (FW) is a process for carbon recovery and a method for solid waste recycling. Recently, the use of FW and food processing waste (FPW) as raw material for the production of butanol has attracted much interest. However, an efficient fermentation process is vital to improve the production of biobutanol. To the best of our knowledge, no review on butanol production from FW has been presented so far. Thus, this review focuses on the characteristics of FW and its potential to produce butanol. In addition, the main factors that affect their use for the production of butanol are also discussed.