RETROSPECTIVE SNAPSHOTS IN LOG-STRUCTURED STORAGE SYSTEMS

• US 20180089034A1
• Filed: 09/29/2016
• Published: 03/29/2018
• Est. Priority Date: 09/29/2016
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Chiu, Lawrence Y., Gupta, Aayush, Muench, Paul H., Seshadri, Sangeetha
• Granted Patent: US 10,552,404 B2
• Time in Patent Office: Days
• CPC Class Codes: G06F 16/128 Details of file system snapshots on the file-level, e.g. snapshot creation, administration, deletion use of snapshots for error detection or correction G06F11/14, G06F11/16
• CPC Class Codes: G06F 16/2358 Change logging, detection, and notification replication G06F16/27
• 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

Abstract

One embodiment provides a method for retrospective snapshot creation including creating, by a processor, a first snapshot that captures logical state of a data store at a first key. Creation of the first snapshot is based on determining a log offset corresponding to the first key, determining existence of a second snapshot that captures logical state of the data store and recording a retrospective snapshot at a last valid log address offset prior to the first key upon a determination that the second snapshot exists based on determining at least one of: whether log address offsets from a first log entry of a log to a log entry of the log at the first key are contiguous and whether log address offsets from the second snapshot to the first key are contiguous.

Claims

1. A method for retrospective snapshot creation comprising:

creating, by a processor, a first snapshot that captures logical state of a data store at a first key, wherein creation of the first snapshot is based on;

determining a log offset corresponding to the first key;

determining existence of a second snapshot that captures logical state of the data store; and

recording a retrospective snapshot at a last valid log address offset prior to the first key upon a determination that the second snapshot exists prior to the first key based on;

determining at least one of;

whether log address offsets from a first log entry of a log to a log entry of the log at the first key are contiguous; and

whether log address offsets from the second snapshot to the first key are contiguous.

2. The method of claim 1, wherein log addresses are not reused, monotonically increase and are contiguous.

3. The method of claim 2, wherein:

the second snapshot has a largest log address offset than other snapshots prior to the first key.

4. The method of claim 3, wherein the second snapshot is a retrospective snapshot for a log address corresponding to the first key.

5. The method of claim 4, wherein creation of the retrospective snapshot fails upon at least one of:

the log address offsets from the first log entry to the log entry at the first key are non-contiguous; and

the log address offsets from the second snapshot to the first key are non-contiguous.

6. A computer program product for retrospective snapshot creation, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

create, by a processor, a first snapshot that captures logical state of a data store at a first time in a time range, wherein creation of the retrospective snapshot is based on;

determine, by the processor, a log offset corresponding to the first key;

determine, by the processor, existence of a second snapshot that captures logical state of the data store; and

record, by the processor, a retrospective snapshot at a last valid log address offset prior to the first key upon a determination that the second snapshot exists based on;

determining, by the processor, at least one of;

whether log address offsets from a first log entry of a log to a log entry of the log at the first key are contiguous; and

whether log address offsets from the second snapshot to the first key are contiguous.

7. The computer program product of claim 6, wherein log addresses are not reused, monotonically increase and are contiguous.

8. The computer program product of claim 7, wherein:

the second snapshot has a largest log address offset than other snapshots prior to the first key.

9. The computer program product of claim 8, wherein the second snapshot is a retrospective snapshot for a log address corresponding to the first key.

10. The computer program product of claim 9, wherein creation of the retrospective snapshot fails upon at least one of:

the log address offsets from the first log entry to the log entry at the first key are non-contiguous; and

the log address offsets from the second snapshot to the first key are non-contiguous.

11. The computer program product of claim 10, further comprising program instructions executable by the processor to cause the processor to:

record, by the processor, a key for each log entry in the log.

12. The computer program product of claim 11, further comprising program instructions executable by the processor to cause the processor to:

locate, by the processor, a log address for a corresponding key using a secondary.

13. An apparatus comprising:

a memory storing instructions; and

a processor executing the instructions to create a first snapshot that captures logical state of a data store at a first key, wherein creation of the first snapshot is based on the processor;

determining a log offset corresponding to the first key;

determining existence of a second snapshot that captures logical state of the data store; and

recording a retrospective snapshot at a last valid log address offset prior to the first key upon a determination that the second snapshot exists based on the processor further;

determining at least one of;

whether log address offsets from a first log entry of a log to a log entry of the log at the first key are contiguous; and

whether log address offsets from the second snapshot to the first key are contiguous.

14. The apparatus of claim 13, wherein log addresses are not reused, monotonically increase and are contiguous.

15. The apparatus of claim 14, wherein the second snapshot has a largest log address offset than other snapshots prior to the first key.

16. The apparatus of claim 15, wherein the second snapshot is a retrospective snapshot for a log address corresponding to the first key.

17. The apparatus of claim 16, wherein creation of the retrospective snapshot fails upon at least one of:

the log address offsets from the first log entry to the log entry at the first key are non-contiguous; and

the log address offsets from the second snapshot to the first key are non-contiguous.

18. The apparatus of claim 13, wherein the processor further executes instructions comprising recordation of a key for each log entry in the log.

19. The apparatus of claim 13, wherein the processor further executes instructions comprising locating a log address for a corresponding key using a secondary index.