Accelerating Distributed Updates with Asynchronous Ordered Writes in a Parallel File System

Ordered writes mechanism is an efficient and widely used way to guarantee the consistency of distributed updates in a parallel file system. To keep the write order, remote commit operations should not be sent out until the local updates are forced to be stable. However, this can block the execution of applications and significantly degrade the overall performance. Thus, the I/O and network latency of commit requests serve non-negligible cost for file updates, especially for large amount of small files. In this paper, we argue that the write order keeping can be handed over from the applications to file systems i.e. the order keeping can be removed from the critical I/O path of applications. We propose the Delayed Commit Protocol that the requests of committing sub-operations are submitted to the commit queue and in the meanwhile the execution flow can be returned back to applications immediately. To reduce the total I/O and network overhead, we use space delegation and adaptive RPC (Remote Procedure Call) compound techniques. Experiments show an up to 2.6x speedup while applying such protocol in a CDN (Content Delivery Network) benchmark. No performance degradation occurs for workloads with large files or conflicted operations.