Flash solid-state drives (SSDs) provide much faster access to data compared with traditional hard disk drives (HDDs). The current price and performance of SSD suggest it can be adopted as a data buffer between main memory and HDD, and buffer management policy in such hybrid systems has attracted more and more interest from research community recently. In this paper, we propose a novel approach to manage the buffer in flash-based hybrid storage systems, named Hotness Aware Hit (HAT). HAT exploits a page reference queue to record the access history as well as the status of accessed pages, i.e., hot, warm and cold. Additionally, the page reference queue is further split into hot and warm regions which correspond to the memory and flash in general. The HAT approach updates the page status and deals with the page migration in the memory hierarchy according to the current page status and hit position in the page reference queue. Our empirical evaluation on benchmark traces demonstrates the superiority of the proposed strategy against the state-of-the-art competitors.

The inherent asymmetry of read and write speeds of flash memory poses great challenges for buffer management design. Most of existing flash-based buffer management policies adopt disk-oriented strategies by giving a specific priority to dirty pages, while not fully exploiting the characteristics of the flash memory. In this paper, we propose a novel buffer replacement algorithm named FOR, which stands for Flash-based Operation-aware buffer Replacement. The core idea of FOR is based on novel operation-aware page weight determination for buffer replacement. The weight metric not only measures the locality of read/write operations on a page, but also takes the cost difference of read/write operations into account. We further develop an efficient implementation FOR+ with the time complexity of O(1) for each operation. Experiments on synthetic and benchmark traces demonstrate the efficiency of the proposed strategy, which yields better performance compared with some state-of-the-art flash-based buffer management policies.

Radio Frequency Identification (RFID) has gained a lot of attention as a promising technology that facilitates pervasive computing and the gradual proliferation of RFID-based applications will produce a large amount of urgent and complicated event streams. The RFID middleware system is expected to offer the further complex event processing service to satisfy the high-level query semantics and performance demands, and therefore, how to evaluate the service capability will be a key problem in mission-critical monitoring scenarios. In this paper, we analyze the RFID primitive event arrival and complex event processing model in a novel perspective. Furthermore, based on our proposed models, service capability evaluation method is introduced to estimate whether and how the RFID middleware system can afford the query requirements in a deterministic or statistical manner, which is believed to be very helpful in RFID-based applications. Our experiments demonstrate the utility and feasibility of our models and methods.