Database access

• US 6,934,717 B1
• Filed: 12/02/1996
• Issued: 08/23/2005
• Est. Priority Date: 12/01/1995
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: James, Derek Robert
• Primary Examiner(s): Kindred, Alford
• Assistant Examiner(s): AL HASHEMI, SANA A
• Application Number:
  US09/029,581
• Time in Patent Office: 3,186 Days
• Field of Search: 707 1-206
• US Class Current: 1/1
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: G06F 16/2365 Ensuring data consistency and integrity
• CPC Class Codes: Y10S 707/99945 Object-oriented database structure processing
• CPC Class Codes: Y10S 707/99948 Application of database or data structure, e.g. distributed, multimedia, or image

Abstract

In a client/server computer environment having a fileserver running a mater database and clients supporting cache databases, inconsistent data write accesses are prevented by using a data locking technique, which locks data during the course of an up-date transaction requested by one client. This prevents access to the same data by another client. Data consistency is checked prior to the write access, by comparing a time stamp associated with a respective cache database entry and a time stamp associated with the index to the corresponding data entry in the master database. Time stamp equivalence obviates the need to access the master database or to transfer data across the client/server communications network.

Claims

1. A method for checking the consistency of an item of data in a cache database with a respective item of data in a master database by comparing a first key stored in association with the item of data in the cache database with a second key stored in association with an index entry for the respective item of data in the master database.

3. A method according to claim 1, wherein the first and second keys are time-stamps.

4. Use of a method according to claim 1 in a client/server system.

2. A method for retrieving an item of data from one of a cache or a master database, the master database comprising a plurality of items of master data and an index containing entries corresponding to one or more of the items of master data, the cache database containing a cached copy of at least one item of the master data, the method comprising the steps of:

reading a first key stored in association with a cached copy of a required item of data from the cache database;

reading a second key stored in association with an index entry for a respective item of master data from the master database;

comparing the first key with the second key; and

retrieving in the event the first and second keys are the same the cached copy of the item of data or in the event the first and second keys are different the respective item of master data.

7. A method according to claim 2, wherein the first and second keys are time stamps.

8. Use of method according to claim 2 in a client/server system.

5. A database fileserver apparatus comprising:

input means for receiving a conditional read request for an item of data stored in the database, the request including a first key for a previously-retrieved copy of the item of data;

means for accessing an index of the database and reading an index entry for the requested item of data, the index entry including a second key for the stored item of information;

means for comparing the first and second keys; and

means if the keys are the same for returning an indication that the previously-retrieved copy of the item of data is consistent or if the keys are different for reading from the database and returning a copy of the item of data.

6. A database index, wherein at least one index entry in the index includes at least:

identity information for identifying an item of information in the database;

location information for indicating the location in the database of the item of information; and

version information which changes each time the respective information in the database changes.

9. A method for checking the consistency of an item of data in a cache database with a respective item of data in a master database by comparing a first key stored in association with the item of data in the cache database with a second key stored as a component of an entry for the respective item of data in the master database.