Method of replicating data between computing devices which each use local clocks

• US 20050108289A1
• Filed: 11/26/2002
• Published: 05/19/2005
• Est. Priority Date: 11/26/2001
• Status: Active Grant

• Current Assignee: Synchronoss Software Ireland Limited (Synchronoss Technologies Incorporated)
• Original Assignee: Critical Path Data Centre Limited
• Inventors: Spence, Stephen Timothy, East, Simon Jeremy, Greenwell, Thomas Ralph Edwards
• Granted Patent: US 7,836,264 B2
• Time in Patent Office: Days
• 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: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Where a first computing device is given responsibility for determining whether data that is time stamped by a second computing device is replicated or not, then the first device can compare a time stamp from the second device against a time signal from its own internal clock to determine a delta and use that delta to deduce the correct delta to apply to time stamps associated with later data from the second computing device.

Claims

1. A method of replicating data between computing devices which each use local clocks, in which a first computing device is given responsibility for determining whether data that is time stamped by a second computing device, using a clock running on the second device, is replicated or not;

wherein that first device can compare the time stamp from the second device against a time signal from its own local clock to determine a delta and use that delta to deduce the correct delta to apply to time stamps associated with later data from the second computing device.

2. The method of claim 1 in which the local clock of the first computing device is set to an absolute, externally derived time.

3. The method of claim 1 in which the delta deduced by the first device assumes that the local clock in the second device is drifting in a linear manner.

4. The method of claim 1 in which, if a deliberate time adjustment to accommodate a change of time frame is made to the local clock on the second device, then the second device stores a record of this time adjustment and provides it to the first computing device.

5. The method of claim 4 in which the second device alters one or more time stamps stored on it by the amount of the deliberate time adjustment so that the time stamps remain correct in the new time frame.

6. The method of claim 1 in which the first computing device uses its knowledge of the correct deltas relative to its own clock in order to apply correctly a time dependent arbitration rule to determine which of several inconsistent data replication requests it should action.

7. The method of claim 1 in which the time stamp applied by the second device is not part of a database record containing the data to be replicated.

8. The method of claim 7 in which the time stamp resides in a change log which includes only the minimum data needed to identify a change to data.

10. The device of claim 7 being a server and the second computing devices acting as clients of that server.

9. A computing device capable of replicating data and having responsibility for determining whether data that is time stamped by a second computing device, using a clock running on the second device, is replicated or not;

wherein the device can compare the time stamp from the second device against time signals from its own local clock to determine a delta and use that delta to deduce the correct delta to apply to time stamps associated with later data from the second computing device.