NDC consistency reconnect mechanism

• US 5,946,690 A
• Filed: 12/16/1997
• Issued: 08/31/1999
• Est. Priority Date: 12/17/1996
• Status: Expired due to Fees

• Current Assignee: Inca Technologies
• Original Assignee: Inca Technologies
• Inventors: Pitts, William M.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Shah, Sanjiv
• Application Number:
  US08/991,156
• Time in Patent Office: 623 Days
• Field of Search: 707/10, 707/201, 707/205, 711/113, 711/130, 711/145
• US Class Current: 1/1
• CPC Class Codes: G06F 12/0813 with a network or matrix configuration
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A client (24) in a digital computer network that employs server-driven consistency accesses a file (26) that a caching site (22) supplies from an image of the file (26) projected from a server (28). When the file (26) becomes inactive, the site (22) saves the file onto local permanent storage together with file metadata. A subsequent request to the site (22) to access the file (26) retrieves from local storage the metatadata, including a file-last-write-time attribute. The caching site (22) compares the locally retrieved file-last-write-time attribute with a server supplied file-last-write-time attribute. If the two attributes are identical, then the caching site: 1. reconnects to the projected file image present in storage at the site (22); 2. re-establishes server-driven consistency over the projected file image at the caching site (22); and 3. uses data from the file image retrieved from local storage to respond to a subsequent read request from the client (24).

Claims

1. In a network of digital computers that includes a caching site which supplies data from an image of a file to a client while the client is active on the file, the network of digital computers employing server-driven consistency for maintaining consistency of any portion of the image of the file projected from a server site to the caching site;

a method for reconnecting to, revalidating the consistency of, and using the image of the file cached at the caching site after the file has become inactive at the caching site, the method comprising the steps of;

(a) as the file becomes inactive at the caching site, saving in permanent storage at the caching site the image of the file projected into the caching site together with metadata for the file that includes a file-last-write-time attribute for the file while the file was active; and

(b) after the file has become inactive at the caching site and the image of the file projected into the caching site together with the metadata that includes the file-last-write-time attribute have been saved in permanent storage, upon the caching site receiving a subsequent file-open request from a client for the file;

i. retrieving from permanent storage at the caching site at least the file-last-write-time attribute;

ii. comparing the file-last-write-time attribute retrieved from permanent storage at the caching site with the file-last-write-time attribute now current at the server site; and

iii. if the file-last-write-time attribute retrieved from permanent storage at the caching site equals the file-last-write-time attribute now current at the server site;

A. reconnecting to that portion of the projected image of the file present in permanent storage at the caching site;

B. re-establishing server-driven consistency over that portion of the projected image of the file present in permanent storage at the caching site; and

C. using data from the image of the file that is retrieved from permanent storage at the caching site to respond to a subsequent read request from the client.

2. The method of claim 1 wherein in comparing the file-last-write-time attribute retrieved from permanent storage at the caching site with the file-last-write-time attribute now current at the server site, the method further comprises the steps of:

A. forwarding a file-open request for the file from the caching site to the server site; and

B. receiving from the server site a response to the file-open request that grants the client access to the file, the response including the file-last-write-time attribute now current at the server site.