Resource freshness and replication

• US 7,788,223 B2
• Filed: 02/28/2006
• Issued: 08/31/2010
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Liu, Huisheng, Bjørner, Nikolaj S., Suriyanarayanan, Guhan
• Primary Examiner(s): Ali; Mohammad
• Assistant Examiner(s): Smith; Brannon W
• Application Number:
  US11/364,234
• Publication Number:
  US 20070168516A1
• Time in Patent Office: 1,645 Days
• Field of Search: 707/201, 707/999.201, 707/609, 707/610, 707/611, 707/612, 707/618, 707/638, 707/689, 709/248
• US Class Current: 707/618
• CPC Class Codes: G06F 16/273 Asynchronous replication or reconciliation

Abstract

Aspects of the subject matter described herein relate to resource replication systems. In aspects, a mechanism is described that detects when local resources are stale. Local resources may be stale when the time between a last successful synchronization activity and a current time exceeds a staleness value. If the local resources are determined to be stale, the local member may refrain from certain synchronization activities until the local member is allowed to resume these certain synchronization activities. If the local resources are not stale, additional synchronization activities including synchronizing resources between the member and an upstream or downstream partner may be performed.

Claims

1. A computer-storage medium having computer executable instructions, comprising:

detecting whether local resources stored within a first folder and hosted on a local machine are stale via a first timestamp associated with the first folder, the local machine also storing local resources within a second folder having an associated second timestamp different from the first timestamp, wherein the first timestamp includes a time of a previous synchronization of the local resources within the first folder, wherein the previous synchronization comprised applying updates to the local resources within the first folder received from an upstream partner, wherein the local machine and the upstream partner participate in a replica group, and wherein the first timestamp is updated only upon synchronization of the local resources within the first folder, the synchronization of the local resources occurring at an update frequency;

wherein the detecting further comprises;

determining a difference between the first timestamp and a local system clock; and

comparing the difference to a staleness value to determine whether the difference exceeds the staleness value, wherein the staleness value is greater than the update frequency and less than or equal to a tombstone period that indicates how long a resource is marked as deleted before resource metadata associated with the resource is deleted;

when the local resources are stale, refraining from sending updates of the local resources from the local machine to a downstream partner; and

when the local resources are not stale, sending updates of the local resources from the local resources to the downstream partner.

2. The computer-storage medium of claim 1, wherein detecting whether local resources are stale via a timestamp comprises determining a difference between the timestamp and a time of local system clock of the local machine.

3. The computer-storage medium of claim 1, wherein the staleness value is selectable by a system administrator.

4. The computer-storage medium of claim 1, wherein the synchronization further comprises:

obtaining any resource on the upstream machine that is not identical to a corresponding resource on the local machine;

adding any resource that is contained on the upstream machine that is not contained on the local machine; and

marking the local resources as fresh by updating the timestamp.

5. The computer-storage medium of claim 4, wherein the synchronization further comprises deleting any resource on the local machine that is not on the upstream partner.

6. The computer-storage medium of claim 1, wherein a successful synchronization comprises maintaining a connection with the upstream machine.

7. A method implemented at least in part by a computer, the computer including at least one processor and memory and the method comprising:

storing at a second member a first value in association with a first replicated folder and storing at the second member a second value different from the first value in association with a second replicated folder, the first value including a previous time of a first synchronization of the first replicated folder between the second member and other members that replicate resources with the second member, wherein the-synchronization comprises applying updates made to a resource stored in a first member'"'"'s first replicated folder to a corresponding replicated resource stored in the second member'"'"'s first replicated folder, and wherein the first value is updated only upon synchronization between the second member'"'"'s first replicated folder and the other members that replicate resources with the second member, the synchronization between the second member'"'"'s first replicated folder and the other members occurring at an update frequency;

receiving a request from a third member to engage in a second synchronization, wherein the request is received at the second member and the request comprises both a connection request and a request to transmit updates for the replicated resource stored in the second member'"'"'s first replicated folder to the third member;

determining, by the second member, that the replicated resource stored on the second member'"'"'s first replicated folder is not up-to-date by computing the difference between a current time and the previous time of the first synchronization and determining that the difference exceeds a staleness value, wherein the staleness value is greater than the update frequency and less than or equal to a tombstone period that indicates how long a resource is marked as deleted before resource metadata associated with the resource is deleted; and

in response to the determining step, accepting, by the second member, the connection request from the third member and refusing the request to transmit updates for the replicated resource to the third member.

8. The method of claim 7, wherein the value comprises a timestamp.

9. The method of claim 7, wherein the first synchronization further comprises a successful synchronization of a plurality of resources between the first member and the second member.

10. The method of claim 7, wherein the first member and the third member are the same.

11. In a computing environment, an apparatus, comprising:

a processor for executing computer executable instructions; and

computer storage media storing computer executable instructions that when executed provide;

a resource store arranged to store resource metadata for resources that are replicated by members arranged to participate in a replica group, wherein the resource store is also arranged to store for each folder in the resource store a different value including a time at which a successful synchronization occurred, wherein the successful synchronization comprised applying updates to a resource stored in one of the folders of the resource store, and wherein the value is updated only upon synchronization of the one of the folders with a folder stored on a member of the replica group, the synchronization of the one of the folders occurring at an update frequency; and

an update mechanism arranged to determine whether resources stored in the one of the folders of the resource store are fresh enough to engage in a second synchronization, wherein the second synchronization comprises sending updates for a second resource stored in the one of the folders of the resource store, the update mechanism;

determining a difference between the value and a local system clock; and

comparing the difference to a staleness value to determine whether the difference exceeds the staleness value, wherein the staleness value is greater than the update frequency and less than or equal to a tombstone period that indicates how long a resource is marked as deleted before resource metadata associated with the resource is deleted.

12. The apparatus of claim 11, wherein the update mechanism comprises epoch logic that indicates conditions for which resources of the resource store are fresh enough to engage in the second synchronization.

13. The apparatus of claim 12, wherein the resources are fresh enough when the time at which the successful synchronization occurred is within a staleness value of a time at which the second synchronization is requested.

14. The apparatus of claim 12, wherein the resource and the second resource are the same.