Deterministic database systems have been shown to significantly improve the availability and scalability of a distributed database system deployed on a shared-nothing architecture across WAN while ensuring strong consistency. However, their scalability and performance advantages highly depend on the quality of data partitioning due to the reduced flexibility in transaction processing. Although a deterministic database system can employ workload driven data (re-)partitioning and live data migration algorithms to partition data, we found that the effectiveness of these algorithms is limited in complex real-world environments due to the unpredictability of machine workloads. In this paper, we present Hermes, a deterministic database system prototype that, for the first time, does not rely on sophisticated data partitioning to achieve high scalability and performance. Hermes employs a novel transaction routing mechanism that jointly optimizes the balance of machine workloads, data (re-)partitioning, and live data migration by looking into the queued transactions to be executed in the near future. We conducted extensive experiments which show that Hermes is able to yield 29% to 137% increase in transaction throughput as compared to the state-of-the-art systems under complex real-world workloads.

Flash translation layers (FTLs) are the core embedded software (also known as firmware) of NAND flash-based solid-state drives (SSDs). The relentless pursuit of high-performance SSDs renders FTLs increasingly complex and intricate. Therefore, testing and validating FTLs are crucial and challenging tasks. Directly testing and validating FTLs on SSD hardware are common practices though, they are time-consuming and cumbersome because 1) the testing speed is limited by the hardware speed of SSDs and 2) just reproducing bugs can be challenging, let alone locating and root causing the bugs. This work presents virtual stress testing (VST), a simulation framework to enable executing SSD FTLs on PCs or servers against virtual SRAM, DRAM, and flash emulated by host-side main memory. FTL function calls, such as moving data from flash to DRAM, are served by the VST framework. Therefore, VST can test FTLs without SSD hardware requirements nor SSD speed limitations, and root causing bugs becomes manageable tasks. We apply VST to representative SSD design, OpenSSD, which is actively utilized and maintained by SSD and FTL communities. Experimental results show that VST can test FTLs at a speed up to 375 GB/s, which is several hundred times faster than directly testing FTLs on SSD hardware. Moreover, we successfully discover seven new FTL bugs in the OpenSSD design using VST, which is a solid evidence of VST's bug-discovering effectiveness.