Non-Volatile Memory (NVM) attracts people's attention because of its large capacity, persistence, bit addressability and low read latency. However, it also has some disadvantages, such as limited writes and asymmetric reading and writing speed. When the traditional linear hash index is implemented directly on NVM, it will lead to a great number of random write operations. To solve this problem, a new NVM-friendly linear hash index called NVM-LH (NVM-oriented Linear Hashing) was proposed. The cache friendliness was achieved by NVM-LH through the cache line alignment during storing data. And a log-free data consistency guaranteeing strategy was presented in NVM-LH. In addition, the split and delete operations were optimized in NVM-LH to minimize the NVM write operations. Experimental results show that NVM-LH outperforms the state-of-the-art NVM-aware hash index CCEH (Cacheline-Conscious Extendible Hashing) in terms of space utilization (30% higher) and NVM write number (about 15% lower), showing better NVM-friendliness.

With the trend of global low-carbon, as well as data-centric computing trends, studying the energy-saving green database systems has become a hot issue of government, business and academia. However, traditional database systems mainly focus on performance, and have little consideration on energy metrics, including energy efficiency and energy proportionality. In this paper, based on the requirement analysis on green database systems, some key issues on this topic were explored, and two critical problems were emphasized, namely the energy efficiency problem for database systems, as well as the energy proportionality problem for database clusters. Furthermore, some future directions on energy-aware green database systems were pointed out to provide some new insights for the research into this new area.