Updating distributed data files using active token distributed at different times to different sites

• US 5,884,308 A
• Filed: 11/12/1996
• Issued: 03/16/1999
• Est. Priority Date: 04/21/1994
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Foulston, John H.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): Coby, Frantz
• Application Number:
  US08/727,519
• Time in Patent Office: 854 Days
• Field of Search: 707/1, 707/8, 707/9
• US Class Current: 1/1
• CPC Class Codes: G06F 16/1774 Locking methods, e.g. locking methods for file systems allowing shared and concurrent access to files
• CPC Class Codes: G06F 16/1844 Management specifically adapted to replicated file systems
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99939 Privileged access

Abstract

Each file in a computer system has associated with it a token. No user is permitted to update any file unless that user is the current token holder. Thus, in multi-sited computer installations where nominally identical files are held in several data stores, only one copy of the file is ever updated at any one time. Tokens can only be transferred from one user to another with the permission of the current token holder, and on transfer of a token the latest version of the file accompanies that token. Some nodes of a computer system may have read access to obsolete versions of a file but each node holding an obsolete file is notified of current file versions available.

Claims

1. A computer system comprising:

a plurality of nodes at different locations, each node comprising one or more processor units and data storage containing common data files for which users at different locations have update access,

each such common data file having a single respective data token which permits update access to the data file only at the node currently holding the respective data token,

the data storage including a respective data store at each node, each data store storing a respective copy of at least some common data files to which read access is maintained at all times and for each common data file for which the system holds a plurality of copies one of the data stores is designated a master library, the master library retaining a record of the node currently holding the respective data token.

2. A computer system as in claim 1 wherein, on each transfer of a data token between users, the latest version of the file associated with the respective data token is transferred.

3. A computer system as in claim 2 wherein, on transfer of a token between nodes neither of which includes the master library for the respective token, a copy of the latest version of the respective associated file is also transferred to the node which includes the master library.

4. A computer system as in claim 1 wherein each time a node receives a token from another node in respect of a file for which the receiving node includes the master library, the processor unit forwards an updating indication to all other nodes holding obsolete versions of the received file.

5. A computer system as in claim 1 wherein each time a token is transferred between users on differing nodes the node including the master library for the respective file associated with the transferred token forwards a transfer indication to all other nodes holding copies of that file.

6. A computer system as in claim 1 wherein each file in the system has a designated master library and an associated update token and only the current token holder can authorize the transfer of the token to any other user.

7. A method for updating stored data files in a computer system having a plurality of nodes at different locations, each node comprising one or more processor units and data storage containing common data files for which users at different locations have update access, each such common data file having a single respective data token which permits update access to the data file only at the node currently holding the respective data token, said method comprising:

including a respective data store at each node,

storing at each data store a respective copy of at least some common data files to which read access is maintained at all times, and

designating each common data file for which the system holds a plurality of copies one of the data stores as a master library, the master library retaining a record of the node currently holding the respective data token.

8. A method as in claim 7 wherein, on each transfer of a data token between users, the latest version of the file associated with the respective data token is transferred.

9. A method as in claim 8 wherein, on transfer of a token between nodes neither of which includes the master library for the respective token, a copy of the latest version of the respective associated file is also transferred to the node which includes the master library.

10. A method as in claim 7 wherein each time a node receives a token from another node in respect of a file for which the receiving node includes the master library, the processor unit forwards an updating indication to all other nodes holding obsolete versions of the received file.

11. A method as in claim 7 wherein each time a token is transferred between users on differing nodes the node including the master library for the respective file associated with the transferred token forwards a transfer indication to all other nodes holding copies of that file.

12. A method as in claim 7 wherein each file in the system has a designated master library and an associated update token and only the current token holder can authorize the transfer of the token to any other user.

13. A distributed computer system comprising a plurality of nodes at different locations, each node comprising:

at least one processor unit;

a data store which stores a plurality of data files; and

at least one end user terminal;

said data stores at least two of said nodes including replicated data files, each such replicated file having one of said nodes designated as a respective master library, and having a respective single update token which controls updating of the file such that updating is permitted only at the node holding the token, reading of replicated files being permitted at any node;

said data token being transferred on request between nodes so that sequential updating of files may be carried out at different ones of said nodes, each transfer of the token being accompanied by the replicated file version as held at the transferring node, the replicated file version being simultaneously copied to the master library node, said master library node updating respective file versions at other nodes only when said master library holds said respective associated update token.

14. A distributed computer system as in claim 13 in which on each transfer of an update token between nodes, the node holding the master library notifies the location of the token to all other nodes which hold respective copies of the replicated file.

15. A distributed computer system as in claim 14 in which any node requiring update access to a replicated file forwards an update token request to the node currently holding the token.

16. A distributed computer system as in claim 13 in which said master library node updates file versions at other nodes each time the update token returns to the node.

17. A distributed computer system as in claim 13 in which the master library node transfers an updated file to another of said nodes only if the master library node receives a request for the updated file version.

18. A distributed computer system as in claim 13 in which the master library node notifies all other nodes of the availability of a later version of a replicated file each time the respective update token associated with the file is received at the master library node.

19. A distributed computer system as in claim 13 in which some of the nodes include at least two end user terminals and at least two respective users at the same node have update permission to a respective replicated file, the update token being passed between users at the node without messaging to the master library node.

20. A method for updating a distributed computer system comprising a plurality of nodes at different locations, each node including at least one processor unit;

a data store which stores a plurality of data files; and

at least one end user terminal;

said data stores at least two of said nodes including replicated data files each such replicated file having one of said nodes designated as a respective master library, said method comprising;

using a respective single update token which controls updating of the file such that updating is permitted only at the node holding the token, reading of replicated files being permitted at any node;

transferring said data token on request between nodes so that sequential updating of files may be carried out at different ones of said nodes, each transfer of the token being accompanied by the replicated file version as held at the transferring node, the replicated file version being simultaneously copied to the master library node, said master library node updating respective file versions at other nodes only when said master library holds said respective associated update token.

21. A method as in claim 20 in which on each transfer of an update token between nodes, the node holding the master library notifies the location of the token to all other nodes which hold respective copies of the replicated file.

22. A method as in claim 21 in which any node requiring update access to a replicated file forwards an update token request to the node currently holding the token.

23. A method as in claim 20 in which said master library node updates file versions at other nodes each time the update token returns to the node.

24. A method as in claim 20 in which the master library node transfers an updated file to another of said nodes only if the master library node receives a request for the updated file version.

25. A method as in claim 20 in which the master library node notifies all other nodes of the availability of a later version of a replicated file each time the respective update token associated with the file is received at the master library node.

26. A method as in claim 20 in which some of the nodes include at least two end user terminals and at least two respective users at the same node have update permission to a respective replicated file, the update token being passed between users at the node without messaging to the master library node.