Systems and methods for synchronizing databases in a receive-only network

• US 5,649,195 A
• Filed: 05/22/1995
• Issued: 07/15/1997
• Est. Priority Date: 05/22/1995
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Tai, Ling-Ching Wang, Scott, Roderick Keith
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): HO, RUAY L
• Application Number:
  US08/446,996
• Time in Patent Office: 785 Days
• Field of Search: 395/600, 395/617, 395/650, 395/700, 395/800, 395/575, 395/425, 395/601, 395/616, 395/618, 395/619, 395/620, 395/621, 395/622, 395/200.01, 395/200.03 , 395/200.04, 395/200.05, 395/200.08, 395/200.09, 395/200.1, 395/200.19
• US Class Current: 1/1
• CPC Class Codes: G06F 16/275 Synchronous replication
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users

Abstract

Systems and methods for synchronizing a plurality of databases are provided for a plurality of geographically dispersed computers in receive-only communication. Each change made to a master database in a central computer is broadcast to a plurality of remote computers, each containing a replica of the master database, via a packet having an assigned next-broadcast-number and a sequential next-sequence-number. Each remote computer has means for comparing the next-broadcast-number and next-sequence-number of each received packet with the last-broadcast-number-received and last-sequence-number-received from a previous packet, and for selectively updating its replica database.

Claims

1. A method for synchronizing databases among a central computer having a master database therein, and a plurality of remote computers in receive-only communication with said central computer, each of said remote computers having therein a replica of said master database, said database synchronizing method comprising the steps of:

storing a plurality of changes to said master database, which occur during a predetermined time period, in a file which is external to said master database;

assigning a same next-broadcast-number to each of the changes in the file, and assigning a sequential next-sequence-number to a respective one of the changes in the file;

broadcasting each of the changes in the file to each of said plurality of remote computers which are in receive-only communication with said central computer, including the same next-broadcast-number and the sequential next-sequence-numbers;

receiving, at each of said plurality of remote computers which are in receive-only communication with said central computer, the broadcast changes in the file including the same next-broadcast-number and the sequential next-sequence-numbers; and

updating the replica of said master database at each of said plurality of remote computers, which are in receive-only communication with said central computer, based upon the same next-broadcast-number and the sequential next-sequence-number assigned to each change in the received changes.

2. A database synchronizing method according to claim 1 wherein said broadcasting step comprises the step of repeatedly broadcasting each of the changes in the file to each of said plurality of remote computers, including the same next-broadcast-number and the sequential next-sequence-numbers, at predetermined time intervals.

3. A database synchronization method according to claim 2 further comprising the steps of:

storing a plurality of second changes to said master database, which occur during a second predetermined time period, in the file which is external to said master database;

assigning a second same next-broadcast-number to each of the second changes in the file, and assigning a second sequential next-sequence-number to a respective one of the second changes in the file;

broadcasting each of the second changes in the file to each of said plurality of remote computers, including the second same next-broadcast-number and the second sequential next-sequence-numbers;

receiving, at each of said plurality of remote computers, the broadcast second changes in the file including the second same next-broadcast-number and the second sequential next-sequence-numbers; and

updating the replica database at each of said plurality of remote computers based upon the second same next-broadcast-number and the second sequential next-sequence-number assigned to each second change in the received changes.

4. A database synchronization method according to claim 2 wherein said updating step comprises the steps of:

updating the replica database with each record which is associated with a next-broadcast-number which is greater than a last received next-broadcast-broadcast-number; and

updating the replica database with each record which is associated with a next-sequence-number which is greater than a last received next-sequence-number.

5. A database synchronizing method according to claim 1 wherein said broadcasting step operates independently of said storing and assigning steps.

6. A database synchronizing method according to claim 1 wherein said broadcasting step further comprises the step of identifying a last change in a plurality of changes having the same next-broadcast-number.

7. A system for synchronizing databases among a central computer and a plurality of remote computers in receive-only communication with said central computer, said database synchronizing system comprising:

a master database in said central computer;

a replica of said master database in each of said remote computers which are in receive-only communication with said central computer;

packet building means in said central computer, said packet building means comprising;

means for storing a plurality of changes to said master database, which occur during a predetermined time period, in a file which is external to said master database; and

means, responsive to said storing means, for assigning a same next-broadcast-number to each of the changes in the file, and for assigning a sequential next-sequence-number to a respective one of the changes in the file;

broadcasting means in said central computer, and responsive to said packet building means, for broadcasting each of the changes in the file to each of said plurality of remote computers which are in receive-only communication with said central computer, including the same next-broadcast-number and the sequential next-sequence-numbers; and

selective updating means in each of said plurality of remote computers which are in receive-only communication with said central computer, said selective updating means comprising;

means for receiving the broadcast changes in the file including the same next-broadcast-number and the sequential next-sequence-numbers; and

means, responsive to said receiving means, for updating the replica database at each of said plurality of remote computers, which are in receive-only communication with said central computer, based upon the same next-broadcast-number and the sequential next-sequence-number assigned to each change in the received changes.

8. A database synchronizing system according to claim 7 wherein said broadcasting means comprises means for repeatedly broadcasting each of the changes in the file to each of said plurality of remote computers, including the same next-broadcast-number and the sequential next-sequence-numbers, at predetermined time intervals.

9. A database synchronization system according to claim 8:

wherein said storing means further comprises means for storing a plurality of second changes to said master database, which occur during a second predetermined time period, in the file which is external to said master database;

wherein said assigning means further comprises means for assigning a second same next-broadcast-number to each of the second changes in the file, and for assigning a second sequential next-sequence-number to a respective one of the second changes in the file;

wherein said broadcasting means further comprises means for broadcasting each of the second changes in the file to each of said plurality of remote computers, including the second same next-broadcast-number and the second sequential next-sequence-numbers;

wherein said receiving means further comprises means for receiving, at each of said plurality of remote computers, the broadcast second changes in the file including the second same next-broadcast-number and the second sequential next-sequence-numbers; and

where in said updating means further comprises means for updating the replica database at each of said plurality of remote computers based upon the second same next-broadcast-number and the second sequential next-sequence-number assigned to each second change in the received changes.

10. A database synchronization system according to claim 8 wherein said updating means comprises:

means for updating the replica database with each record which is associated with a next-broadcast-number which is greater than a last received next-broadcast-number; and

means for updating the replica database with each record which is associated with a next-sequence-number which is greater than a last received next-sequence-number.

11. A database synchronizing system according to claim 7 wherein said broadcasting means operates independently of said storing and assigning means.

12. A database synchronizing system according to claim 7 wherein said broadcasting means further comprises means for identifying a last change in a plurality of changes having the same next-broadcast-number.

13. A method for selectively updating a replica database in a remote computer, which is in receive-only communication with a central computer having a master database therein, said central computer broadcasting to said remote computer a series of changes to said master database as a series of packets, each of said packets including a next-broadcast-number and a next-sequence number, said remote computer including therein a last-broadcast-number-received and a last-sequence-number-received, said selective updating method comprising the steps of:

receiving, at said remote computer, which is in receive-only communication with said central computer, a packet including a next-broadcast-number and a next-sequence-number;

comparing the received next-broadcast-number with the last-broadcast-number-received;

ignoring the received packet if the received next-broadcast-number is less than or equal to the last-broadcast-number-received;

if the received next-broadcast-number is greater than the last-broadcast-number-received, comparing the received next-sequence-number with the last-sequence-number-received;

updating the replica database with the received packet if the received next-sequence-number is greater than the last-sequence-number-received; and

ignoring the received packet if the received next-sequence-number is not greater than the last-sequence-number-received.

14. A selective updating method according to claim 13 wherein a last packet in said series of packets includes a last change flag, said selective updating method further comprising the steps of:

incrementing said last-broadcast-number-received in response to receipt of said last change flag; and

resetting said last-sequence-number-received in response to receipt of said last change flag.

15. A method for broadcasting changes to a database from a computer comprising the steps of:

storing a copy of a change to said database in a file which is external to said database;

assigning a next-broadcast-number and a next-sequence-number to said copy;

determining if a broadcast time has arrived;

incrementing said next-sequence-number if a broadcast time has not arrived;

performing said storing step, said assigning step, said determining step and said incrementing step on additional changes to said database until the broadcast time has arrived; and

broadcasting each of the changes in the file including the assigned next-broadcast-number and next-sequence-numbers, when the broadcast time has arrived.

16. A broadcasting method according to claim 15 wherein said broadcasting step is followed by the steps of:

incrementing the next-broadcast-number; and

resetting the next-sequence-number.

17. A broadcasting method according to claim 15 wherein said broadcasting step comprises the step of repeatedly broadcasting each of the changes in the file including the assigned next-broadcast-number and next-sequence-numbers, at predetermined time intervals.

18. A broadcasting method according to claim 15 wherein said broadcasting step further comprises the step of identifying a last change in the changes in the file prior to arrival of the broadcast time.

19. A collection of packets for broadcasting a plurality of changes made to a master database to a plurality of replica databases, said packet collection comprising:

a plurality of serially broadcast change records, each of which includes update information for an associated database record;

each of said serially broadcast change records including a same next-broadcast-number associated therewith; and

a respective one of said serially broadcast change records including a sequential next-sequence-number associated therewith.

20. A collection of packets according to claim 19 wherein said plurality of serially broadcast change records includes a last serially broadcast change record, said last serially broadcast change record further comprising a last change flag associated therewith.