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

In a computing system where a data request has been passed between a file service proxy cache node and a downstream site, the file service proxy cache node being a network node located between a client system and the origin file system node, a non-transitory computer-readable storage medium including instructions that, when executed by the file service proxy cache node, performs the steps:

• dispatching a file access request to the downstream site;
• receiving a response to the file access request, wherein the response includes:
• a version number of a file image cached at the downstream site;
• comparing the version number of the file image cached at the downstream site to a version number of a file image cached at the file service proxy cache node;
• if the version numbers are the same:
• continuing to use the file image cached at the file service proxy cache node;
• if the version numbers are different:
• setting the version number of the file image cached at the file service proxy cache node to the version number of the file image cached at the downstream site;
• setting an arrival time to the file service proxy cache node's current time;
• and
• resetting a delta time to zero;
• and
• if the response to the file access request is not a flush response:
• discarding the current cached file image.

In a computing system where a flush request has been received at a file service proxy cache node from an upstream file service proxy cache node, the file service proxy cache node being a network node located between a client system and the origin file system node, a non-transitory computer-readable storage medium including instructions that, when executed by the file service proxy cache node, performs the steps:

• receiving a flush request from an upstream file service proxy cache node;
• comparing the version number of the file image cached at the upstream site to the version number of the file image cached at the file service proxy cache node;
• and
• if the version numbers do not differ:
• storing the received flush data in shadow extents;
• determining if the file service proxy cache node is a server terminator site;
• if the file service proxy cache node is a server terminator site:
• if all flush batches have been received and at least one of the flush batches has a data complete request flag set:
• determining whether synchronous write mode is being used for the file identified in the request;
• and
• if synchronous write mode is being used:
• writing all file modifications to the underlying origin filesystem;
• determining whether the write to the origin filesystem is successful;
• and
• if the write to the origin filesystem is successful:
• setting an all data received response flag and replacing all extents that have shadow extents with their respective shadow extents;
• fetching the file's last modification timestamp from the origin filesystem;
• and
• responding to the received flush request with a status code that indicates the successful completion of the request;
• and
• if all flush batches have not been received:
• responding to the received flush request with a status code that indicates the successful completion of the request.