System and method to refresh proxy cache server objects

• US 20040068579A1
• Filed: 08/12/2003
• Published: 04/08/2004
• Est. Priority Date: 08/13/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Marmigere, Gerard, Picon, Joaquin, Secondo, Pierre
• Granted Patent: US 7,552,220 B2
• Time in Patent Office: Days
• US Class Current: 709/242
• CPC Class Codes: H04L 67/02 based on web technology, e.g. hypertext transfer protocol [HTTP]
• CPC Class Codes: H04L 67/564 Enhancement of application control based on intercepted application data
• CPC Class Codes: H04L 67/5682 Policies or rules for updating, deleting or replacing the stored data
• CPC Class Codes: H04L 69/329 in the application layer [OSI layer 7]
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A method and computing systems for refreshing objects stored by a Proxy cache server from Web content servers. The refresh is requested by the Proxy cache server only if the expiration date attached to a stored object has expired. The refresh of one object is requested by the Proxy cache server to the Web content server upon a request from the browser of a client device. Additionally, the Proxy cache server can send a Refresh_request command to the Web content servers applying to a list of objects for which the expiration date has expired. The refreshed objects are not sent by the Web content server if the last modified date has changed but rather if, and only if, the object content, identified by a signature, has been changed. This method and system have the advantage of offloading the computing resources involved for data transfer through the network connecting the servers.

Claims

1. A method for refreshing objects stored in a Proxy cache server, with new versions of objects stored by Web content servers communicating with messages through a network with the Proxy cache server, the Proxy cache server and the Web content servers supporting a standard request for one object and a standard refresh request for one object based on a last modified date, said method comprising the steps of:

storing, in the Proxy cache server, a cache index table containing, for each object stored, an identification of the object, a file name of the object in the Proxy cache server, a network address of the Web content server owning the object, an object validity expiration date and a signature identifying the object content;

reading the cache index table and, selecting one object for which the expiration date is exhausted;

sending from the Proxy cache server to the Web content server address owning the selected object, a Refresh_request command in a payload of a message, an argument of the message being the object identifier and the object signature;

receiving from the Web content server a Refresh_response command in the payload of a message, arguments of the message being the object identifier and, if the signature of the object stored in the Web content server is different from the signature in the Refresh_request, the object stored in the Web content server, its signature and the new expiration date;

updating, in the Proxy cache server, the cache index table with the new signature and expiration date of the object and updating the object file name with the object received from the Web content server.

2. The method of claim 1 wherein

the step of reading the cache index table is repeated for all the objects of the table for which the expiration date is exhausted;

the sending step is performed once for all the selected objects owned by a same Web content server, to said same Web content server address, the Refresh_request command arguments being a list of couples comprising the object identifier and its signature for all the selected objects;

the receiving step is performed once for all the selected objects, the Refresh_response arguments being a list of quadruplets, for each selected object for which the signature of the version stored in the Web content server is different from the signature in the Refresh_request, the object identifier, the object stored in the Web content server, its signature and the new expiration date;

the updating step is performed on the Proxy cache server for all the objects received in the list with the Refresh_response command.

3. The method of claim 1 further comprising the steps of:

sending from the Proxy cache server a standard request for one object;

receiving a message back from the Web content server containing the object requested and the last modified date of the object;

if the message further contains the object signature and an indication that the Web content server supports the Refresh_request command, updating, in the Proxy cache server, a Web content server table containing, for each Web content server having already sent to the Proxy cache server one object, the network address of the Web content server and an indication that the Web content server supports the Refresh_request command;

if the message does not further contain the object signature and an indication that the Web content server supports the Refresh_request command, updating in the Proxy cache server, the Web content server table with an indication that the Web content server does not support the Refresh_request command and updating the Proxy cache index table with the last modified date of the object;

updating, in the Proxy cache index table, the file name containing the object received and an object expiration date.

4. The method of claim 3 further comprising the steps of:

before sending any Refresh_request command for at least one object to a Web content server, checking in the Web content server table the indication if the Web content server supports the Refresh_request command;

if the indication that the Web content server supports the Refresh_request command is stored in the Web content server table, sending a Refresh_request command for the at least one object;

if the indication that the Web content server does not support the Refresh_request command is stored in the Web content server table, sending a standard request refresh for each of the at least one object based on its last modified date.

5. The method for sending refreshed objects from a Web content server to a Proxy cache server, said method comprising the steps of:

upon reception of a Refresh_request command according to claim 1, from a Proxy cache server, sending a Refresh_response command in a payload of a message to the Proxy cache server, arguments for the message including, for each of the object identified in the Refresh_request command, the object identifier and, if the signature of the object stored in the Web content server is different from the signature in the Refresh_request, the object stored in the Web content server and its signature.

6. The method of claim 5 further comprising the steps of:

receiving a standard request for one object from a Proxy cache server;

sending back a message to the Proxy cache server with the object, said message further containing the object signature and an indication that the Web content server supports the Refresh_request command.

7. The method of claim 1 wherein the Refresh_response sent by the Web content server has an additional argument which is a status code associated to each object, one possible code value being that the object is modified, one other possible code value being that the object is not modified and one other possible value being that the object is not found, said Proxy cache server not updating the object nor modifying the entry corresponding to this object in the Cache index table if the code value received in the Refresh_response is that the object is not modified, said Proxy cache server deleting the entry corresponding to this object in the Cache index table if the code value received in the Refresh_response is that the object is not found.

8. The method of claim 7 wherein all the possible code values are HTTP protocol code values, the Proxy cache server updating the Cache index table and the Web content server table according to the code values.

9. The method of claim 1 wherein the messages are sent under an HTTP protocol.

10. The method of claim 1 wherein the object signature and an indication that the Web content server supports the Refresh_response command are sent by the Web content server in an HTTP message header, the object itself being sent in the payload according to an HTTP protocol.

11. A computer program product comprising programming code instructions for executing the steps of the method according to claim 1 when said program is executed on a server.

12. A computer program product comprising programming code instructions for executing the steps of the method according to claim 5 when said program is executed on a server.

13. A computing system comprising means adapted for executing the computer program of claim 11.

14. A computing system comprising means adapted for executing the computer program of claim 12.