NEHASH: high-concurrency extendible hashing for non-volatile memory

Extendible hashing is an effective way to manage increasingly large file system metadata, but it suffers from low concurrency and lack of optimization for non-volatile memory (NVM). In this paper, a multilevel hash directory based on lazy expansion is designed to improve the concurrency and efficiency of extendible hashing, and a hash bucket management algorithm based on groups is presented to improve the efficiency of hash key management by reducing the size of the hash bucket, thereby improving the performance of extendible hashing. Meanwhile, a hierarchical storage strategy of extendible hashing for NVM is given to take advantage of dynamic random access memory (DRAM) and NVM. Furthermore, on the basis of the device driver for Intel Optane DC Persistent Memory, the prototype of high-concurrency extendible hashing named NEHASH is implemented. Yahoo cloud serving benchmark (YCSB) is used to test and compare with CCEH, level hashing, and cuckoo hashing. The results show that NEHASH can improve read throughput by up to 16.5% and write throughput by 19.3%.