Method for regulating access of computers to data of a central computer

• US 6,061,683 A
• Filed: 02/27/1998
• Issued: 05/09/2000
• Est. Priority Date: 02/27/1997
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Alonso, Luis
• Primary Examiner(s): Fetting, Anton W.
• Assistant Examiner(s): CORRIELUS, JEAN M
• Application Number:
  US09/032,674
• Time in Patent Office: 802 Days
• Field of Search: 707/207, 707/8, 707/10, 707/201, 707/204, 709/221
• US Class Current: 1/1
• CPC Class Codes: G06F 16/27 Replication, distribution or synchronisation of data between databases or within a distributed database system; Distributed database system architectures therefor
• CPC Class Codes: G06F 16/275 Synchronous replication
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A method that regulates the access of a plurality of computers onto data of a central computer. Operations on local copies of a true subset by computers are thereby generally possible in the method. For synchronization, log files that contain the operations on the replicated data are sent to the central computer. When numerous conflicts due to the access of a plurality of computers to the same datasets on the central computer occur in the synchronization, the method can offer regulated access to the shared data and, thus, the resolution of the conflicts. This change in the operating mode for resolving conflicts given access to shared data can also ensue automatically with prescribable thresholds for acceptable and unacceptable numbers of collisions. When conflicts are to be generally avoided, the offers the service of transactions that are either completely executed or can be completely cancelled.

Claims

1. A method for regulating access of remote computers to data of a server computer, comprising the steps of:

a) storing a prescribable portion of the data of the server computer on a first computer as a first copy;

b) performing at least one operation effecting a modification of the first copy on the first computer, by generating a second copy of the first copy and performing the at least one operation on the second copy;

c) storing the at least one operation effecting a modification in a first command sequence;

d) matching the data on the server computer with the data of the second copy on the first computer by transmitting the first command sequence from the first computer to the server computer and executing first command sequence on the server computer;

e) matching the first copy to the second copy by transmitting a second command sequence that takes a modification of the data on the server computer that relate to the first copy into consideration from the server computer to the first computer and executing that command sequence on the first computer on the first copy; and

f) whereby, when a second computer has modified that part of the data of the server computer of significance for the first computer since the creation of the first copy on the first computer, this modification performed on the data by the second computer is taken into consideration in the matching of the first copy on the first computer in that a third command sequence, which represents a modification performed by the second computer, is taken into consideration in the second command sequence in step e) insofar as the prescribable portion of the data of the first copy of the first computer is affected.

2. The method according to claim 1, whereby a transaction that is composed of the first command sequence is cancelled given an interruption of the transaction until a more recent consistent condition has been restored.

3. The method according to claim 1, whereby the data on the server computer and the first copy on the first computer are locked for the exclusive use for the first computer for a prescribable time duration.

4. The method according to any one of the claims 1 to 3, whereby the second copy of the first computer is transmitted to the server computer instead of the first command sequence and data of the server computer corresponding to the first copy on the first computer are transmitted from the server computer to the first computer instead of the second command sequence.

5. The method according to one of the claims 1 through 3, whereby the first and second command sequences only contain operations that lead to modifications on the respective data, and operations that cancel one another out are not transmitted in a command sequence.

6. A method for regulating access of remote computers to data of a server computer, comprising the steps of:

a) storing a prescribable portion of the data of the server computer on a first computer as a first copy;

b) performing at least one operation effecting a modification of the first copy on the first computer, by generating a second copy of the first copy and performing the at least one operation on the second copy;

c) storing the at least one operation effecting a modification in a first command sequence;

d) matching the data on the server computer with the data of the second copy on the first computer by transmitting the first command sequence from the first computer to the server computer and executing first command sequence on the server computer; and

e) matching the first copy to the second copy by transmitting a second command sequence that takes a modification of the data on the server computer that relate to the first copy into consideration from the server computer to the first computer and executing that command sequence on the first computer on the first copy;

whereby,

when a second computer has modified that part of the data of the server computer of significance for the first computer since the creation of the first copy on the first computer this modification performed on the data by the second computer is taken into consideration in the matching of the first copy on the first computer in that a third command sequence, which represents a modification performed by the second computer, is taken into consideration in the second command sequence in step e) insofar as the prescribable portion of the data of the first copy of the first computer is affected;

the data on the server computer and the first copy on the first computer are locked for the exclusive use for the first computer for a prescribable time duration; and

the lock for computers accessing the data of the central computer is triggered as soon as a first prescribable threshold, above which a number of conflicts within a specific number of past accesses onto the data of the server computer that can no longer be accepted is exceeded.

7. The method according to claim 6, whereby the lock for computers accessing the data of the central computer is automatically cancelled as soon as a second prescribable threshold, below which an acceptable number of conflicts within the specific number of past accesses to the data of the central computer is acceptable is not exceeded following an exceeding of the first threshold.

8. The method according to claim 7, whereby a prescribable time period defines an upper threshold for the longest locking of a first or second computer of data of the server computer.

9. A method for replicating database modifications of data shared among a plurality of computers, comprising the steps of:

a) providing a database on a first computer;

b ) generating on a second computer a first copy of at least a portion of said database;

c) generating on said second computer a second copy of said portion of said database;

d) modifying said second copy;

e) storing information relating to said modification in a first command sequence;

f) transmitting said first command sequence from said second computer to said first computer;

g) modifying said database by executing at least said first command sequence on said first computer;

h) transmitting from said first computer to said second computer a second command sequence containing commands for replicating modifications made to said first database within said portion corresponding to said first copy; and

i) executing said second command sequence on said second computer.

10. The method according to claim 9, whereby a transaction that is composed of the first command sequence is cancelled given an interruption of the transaction until a more recent consistent condition has been restored.

11. The method according to claim 9, whereby the portion of the database corresponding to the first copy on the first computer and the first copy on the second computer are locked for the exclusive use for the second computer for a prescribable time duration.

12. The method according to any one of the claims 9 to 11, whereby the second copy on the second computer is transmitted to the first computer instead of the first command sequence and data of the first computer corresponding to the first copy on the second computer are transmitted from the first computer to the second computer instead of the second command sequence.

13. The method according to one of the claims 9 through 11, whereby the first command sequence only contains commands relating to operations that lead to modifications of data, and commands relating to operations that cancel one another out are not transmitted in the first command sequence.

14. A method for replicating database modifications of data shared among a plurality of computers, comprising the steps of:

a) providing a database on a first computer;

b) generating on a second computer a first copy of at least a portion of said database;

c) generating on said second computer a second copy of said portion of said database;

d) modifying said second copy;

e) storing information relating to said modification in a first command sequence;

f) transmitting, said first command sequence from said second computer to said first computer;

g) modifying said database by executing at least said first command sequence on said first computer;

h) transmitting from said first computer to said second computer a second command sequence containing commands for replicating modifications made to said first database within said portion corresponding to said first copy; and

i) executing said second command sequence on said second computer;

wherein

the portion of the database corresponding to the first copy on the first computer and the first copy on the second computer are locked for the exclusive use for the second computer for a prescribable time duration; and

the lock for the data of the first computer is triggered as soon as a first prescribable threshold, above which a number of conflicts within a specific number of past accesses onto the data of the first computer that can no longer be accepted is exceeded.

15. The method according to claim 14, whereby the lock for the data of the first computer is automatically cancelled as soon as a second prescribable threshold, below which an acceptable number of conflicts within the specific number of past accesses to the data of the first computer is acceptable is not exceeded following an exceeding of the first threshold.

16. The method according to claim 15, whereby a prescribable time period defines an upper threshold for the longest locking of the second computer of data of the first computer.