Efficient logging in non-volatile memory by exploiting coherency protocols

Abstract

Non-volatile memory technologies such as PCM, ReRAM and STT-RAM allow data to be saved to persistent storage significantly faster than hard drives or SSDs. Many of the use cases for non-volatile memory requires persistent logging since it enables a set of operations to execute in an atomic manner. However, a logging protocol must handle reordering, which causes a write to reach the non-volatile memory before a previous write operation. In this paper, we show that reordering results from two parts of the system: the out-of-order execution in the CPU and the cache coherence protocol. By carefully considering the properties of these reorderings, we present a logging protocol that requires only one round trip to non-volatile memory while avoiding expensive computations, thus increasing performance. We also show how the logging protocol can be extended to building a durable set (hash map) that also requires a single round trip to non-volatile memory for inserting, updating, or deleting operations.