Page recovery using volume snapshots and logs

• US 20060224636A1
• Filed: 04/05/2005
• Published: 10/05/2006
• Est. Priority Date: 04/05/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Kodavalla, Hanumantha R., Zwilling, Michael J., Oks, Artem A., Kathuria, Vishal, Sleeman, Martin J., Schmidt, Steven R., Rajan, Rajeev B.
• Granted Patent: US 7,814,057 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 2201/80 Database-specific techniques
• CPC Class Codes: G06F 2201/84 Using snapshots, i.e. a logical point-in-time copy of the data

Abstract

Systems and methods are disclosed that facilitate providing page-level database restore functionality upon detection of a corruption event. Updates to a data page in a database can trigger generation of a snapshot of the data page, and an update log can be maintained that stores information related to page updates. Subsequent snapshots can be generated at predetermined intervals and can trigger truncation of a log segment and initiation of a new log segment. Upon detection of page corruption, a most-recent uncorrupt snapshot of the corrupt page can be identified, copied to the location of the corrupt page in the database, and modified according to the log segment associated with the uncorrupt snapshot to make the page current as of the corrupting event, all of which can be performed to restore the database without having to take the database offline.

Claims

1. A system that facilitates page-level data restore in a database, comprising:

a monitoring component that detects one or more corrupt data values in a data page; and

a backup component that generates backup copies of a data page upon a modification to the data page and generates update logs that store information related to page updates between backup copies, and restores a corrupt data page in the data base with a most-recent backup copy of the data page.

2. The system of claim 1, the monitoring component performs a checksum technique on data in the data page to determine whether the data page is corrupt.

3. The system of claim 1, the backup component generates a first backup copy of the data page upon an indication that an update to the page is imminent.

4. The system of claim 3, the first backup copy is generated before the modification.

5. The system of claim 4, further comprising an update log that records page modification events.

6. The system of claim 5, the backup component generates subsequent backup copies of the data page at predetermined intervals.

7. The system of claim 6, the backup component truncates the update log upon generation of a subsequent backup copy and resumes the log to generate a new log segment that is associated with the subsequent backup copy.

8. The system of claim 7, the backup component traverses the backup copies from a most-recent copy backward upon a determination that the data page is corrupt, and identifies and selects a most-recent uncorrupted backup copy of the data page.

9. The system of claim 8, the backup component reads a log associated with the selected backup copy forward in time, replaces the corrupt page in the database with the selected backup copy, and modifies the selected backup copy according to update information recorded in the log up until a point at which corruption occurred to restore the database.

10. A method of backing up data in a database at a page level, comprising:

detecting a modification to a data page in the database;

generating a pre-modification backup copy of the data page;

generating an update log that records update events to the data page subsequent to generation of the pre-modification copy;

generating subsequent backup copies of the data page at predetermined intervals, each subsequent backup copy triggers a current log segment to be truncated and a new log segment to be generated.

11. The method of claim 10, generating a post-modification image of the data page when a snapshot of the page is taken during, or prior to completion of, modification to the page to facilitate retaining current page modification information.

12. The method of claim 10, further comprising monitoring pages in a database to detect corruption in a data page.

13. The method of claim 12, further comprising assessing backup copies of a corrupt data page in reverse-chronological order starting with a most-recent backup copy and selecting a most-recent uncorrupted backup copy of the data page.

14. The method of claim 13, further comprising reading a log associated with the selected backup copy forward from the time of generation of the backup copy to evaluate update events recorded therein.

15. The method of claim 14, further comprising replacing the corrupt data page with the selected backup copy of the data page.

16. The method of claim 15, further comprising modifying the selected backup copy as indicated by update event information stored in the update log for the selected backup copy to generate a replacement page for the database.

17. The method of claim 16, the selected backup copy is updated to be current to a point immediately prior to the occurrence of a corruption event that caused the corruption of the data page.

18. A computer readable medium having stored thereon computer executable instructions for carrying out the method of claim 10.

19. A system that facilitates page-level restore in a database, comprising:

means for detecting an imminent modification to a page in a database;

means for generating a pre-modification snapshot copy of the page immediately prior to the detected modification;

means for generating a log that records modifications to the page after the pre-modification snapshot;

means for generating at least one subsequent snapshot copy of the page at a predetermined scheduled time; and

means for truncating the log and initiating a subsequent log segment associated with the at least one subsequent snapshot copy.

20. The system of claim 19, further comprising:

means for determining that a page in a database is corrupt;

means for traversing snapshot copies of the corrupt page to identify and select a most recent uncorrupted snapshot copy;

means for replacing the corrupt page with the selected most recent uncorrupted snapshot copy; and

means for updating the selected snapshot copy according to information in the log for the selected snapshot copy to restore the database at a page-level.