Reducing rename overhead in full-path-indexed file system

Abstract

Full-path-indexed file systems use a key-value database to store the full path names of files and their metadata. With this pattern, the I/O efficiency can be improved because data is placed on persistent storage in scan order. However, it introduces intolerable overhead on renaming a directory because of the modification on the full path names of files under that directory. In this paper, we introduce prefix replacement mechanism on B+-tree to accelerate renaming directories on full-path-indexed file systems. It consists of three steps: pre-scan prefix deletion, key replacement and floating-split bulk insertion. Unnecessary searches and compares are reduced in these mechanisms. We use Kyoto Cabinet as the key-value database, and implement prefix replacement mechanism on it. We run tests on two benchmarks, the first is generated by Mdtest [18], and the second is the source code of Linux [19]. Compared with LocoFS [4], one kind of full-path-indexed file system, our design is about 5× faster to rename large directories, and the performance is basically same on small directories.