Cx: Concurrent Execution for the Cross-Server Operations in a Distributed File System

Distributed metadata service is important for metadata intensive applications. Unfortunately, it leads to cross-server file operation, and maintaining the consistency of cross-server file operation creates a performance challenge because of sequentially executed sub-operations and costly immediate commitment among servers. In this paper, we observe that sub-operations can be executed concurrently and commitments can be delayed and batched for most cases in real applications, because the temporary inconsistency among servers rarely affects subsequent metadata operations. We propose a new protocol, Cx, in which the affected servers Concurrently eXecute the sub-operations of a cross-server file operation, and respond immediately to a client. Unless any sub-operation fails or other clients need to access the updated metadata objects, the commitment is delayed and batched with the other commitments. Evaluations of our Cx implementation in a parallel file system demonstrate Cx can significantly improve the performance of cross-server file operations, while retaining good scalability.