Using projected timestamps to control the sequencing of file modifications in distributed filesystems

Abstract

It is not possible to maintain extremely tight synchronization of the time keeping clocks of the networked nodes comprising a distributed filesystem. However, when multiple client systems access the same file from different remote locations, a distributed consistency mechanism must ensure that all file read and write requests are only serviced from the latest version of the file. The current industry practice is to disable client-side caching when a concurrent write sharing condition arises (multiple clients active on the file and at least one of them writing). This forces all requests to flow through to the file server and consistency is maintained since all requests are then serviced from the same file image. The current practice sacrifices performance and scalability to maintain consistency. This document discloses methods for projecting and maintaining temporary filesystem timestamps that allow file read and write requests to be serviced from remote cached file images while still providing the same file consistency as the current industry practice. The temporary filesystem timestamps are updated to real filesystem timestamps whenever the client-side cache communicates with the file server.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61 / 666,597 filed on Jun. 29, 2012, which application is incorporated herein by reference in its entirety.[0002]This application is related to co-pending U.S. application Ser. No. ______, filed on Jun. 28, 2013, and entitled, “RECURSIVE ASCENT NETWORK LINK FAILURE NOTIFICATIONS” (Attorney Docket No. 10284.14), which application is incorporated herein by reference in its entirety.[0003]This application is related to co-pending U.S. application Ser. No. ______, filed on Jun. 28, 2013, and entitled, “DISTRIBUTED FILESYSTEM ATOMIC FLUSH TRANSACTIONS” (Attorney Docket No. 10284.15), which application is incorporated herein by reference in its entirety.[0004]This application is related to co-pending U.S. application Ser. No. ______, filed on Jun. 28, 2013, and entitled, “METHOD OF CREATING PATH SIGNATURES TO FACILITATE THE RECOVERY FROM NETWORK LI...

AI Technical Summary

Benefits of technology

The invention relates to a system for accessing files by a client system through a network. The system includes a file service proxy cache node and a downstream site. When a data request is sent, the file service proxy cache node retrieves the file image from the downstream site and compares it with the cached file image to ensure the versions match. If the versions match, the file image is used without discarding the current cached version. If the versions differ, the file image is updated with the version from the downstream site and the original version is replaced. If a flush request is received, the file service proxy cache node compares the versions of the file image with the cached file image and if they match, the cached file image is updated and replaced. This invention ensures efficient access to files and synchronization of data between the client system and the downstream site.

Problems solved by technology

Of course, pre-fetching is only performed for well-behaved clients.

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