Techniques for keeping a copy of a pluggable database up to date with its source pluggable database in read-write mode

Patent metadata

Field	Value
Publication number	US-10915549-B2
Application number	US-201615215443-A
Country	US
Kind code	B2
Filing date	Jul 20, 2016
Priority date	Sep 28, 2012
Publication date	Feb 9, 2021
Grant date	Feb 9, 2021

Abstract

Embodiments incrementally refresh a clone of a source PDB while the source PDB accepts write operations. Specifically, refreshing the PDB clone incorporates changes made to the source PDB since a refresh reference time stamp, which marks the time at which the PDB clone was created or, if the PDB clone has been previously refreshed, the time at which the PDB clone was last refreshed. A PDB clone is incrementally refreshed by incorporating, into the PDB clone data, those source data blocks that have changed since the refresh reference time stamp. Recovery is performed on the PDB clone, once the blocks are copied, to apply any changes made to the source PDB while the blocks were being copied, which recovery makes the PDB clone files consistent. This recovery is based on redo entries recorded for the source PDB during the time it took to copy the blocks to the PDB clone.

First claim

What is claimed is:

1. A computer-executed method comprising:
detecting an instruction to refresh a cloned database based on a source database;
wherein a database management system, that manages the source database, maintains a database session for the source database; and
in response to detecting the instruction to refresh the cloned database, performing a refresh operation for the cloned database, wherein the refresh operation causes the cloned database to incorporate changes made to the source database, the refresh operation comprising:
identifying a set of data blocks, of a plurality of data blocks in the source database, that have changed since a time marked by a refresh reference time stamp;
determining a starting time stamp that marks a time occurring before copying any blocks, from the set of data blocks, into the cloned database in connection with the instruction to refresh the cloned database;
at least partly while one or more changes are made to the plurality of data blocks in the source database via the database session, copying the set of data blocks, from the source database, into the cloned database;
wherein the one or more changes includes a particular change made to a particular data block of the plurality of data blocks to produce a changed data block;
wherein copying the set of data blocks into the cloned database comprises copying the changed data block into the cloned database;
recording the particular change in a particular redo entry in one or more redo logs maintained by the database management system;
determining a final time stamp that marks a time occurring after said copying the set of data blocks is complete;
performing recovery on the cloned database based, at least in part, on a set of redo entries, from the one or more redo logs, that comprise information for a set of changes made to the plurality of data blocks in the source database between times marked by the starting time stamp and the final time stamp;
wherein the set of redo entries includes the particular redo entry; and

wherein the method is performed by one or more computing devices.

2. The method of claim 1 , wherein the source database and the cloned database are pluggable databases.

3. The method of claim 1 , further comprising storing, as a new refresh reference time stamp, the final time stamp.

4. The method of claim 1 , further comprising:
maintaining mapping data that maps each file identifier in the source database to a corresponding file number in the cloned database;
wherein performing recovery on the cloned database comprises performing recovery based, at least in part, on the mapping data.

5. The method of claim 1 , further comprising:
receiving an instruction to automatically refresh the cloned database based, at least in part, on a particular regular time interval;
detecting occurrence of a time interval, as indicated by the particular regular time interval, in which the cloned database has not yet been refreshed; and
wherein detecting the instruction to refresh the cloned database is based, at least in part, on detecting occurrence of the time interval in which the cloned database has not yet been refreshed.

6. The method of claim 5 , wherein the particular regular time interval is defined in definition information that is received via the instruction to automatically refresh the cloned database.

7. The method of claim 5 , wherein the particular regular time interval is a default time interval for automatic database refresh.

8. The method of claim 1 , wherein identifying the set of data blocks, of the plurality of data blocks in the source database, that have changed since the time marked by the refresh reference time stamp is based, at least in part, on change tracking information that indicates times at which blocks, of the plurality of data blocks in the source database, have been changed.

9. The method of claim 1 , further comprising, in response to detecting the instruction to refresh the cloned database, reverting a state of data of the cloned database to a state in which the data of the cloned database existed at the time marked by the refresh reference time stamp.

10. The method of claim 1 , wherein said performing recovery on the cloned database results in the cloned database being current as of the final time stamp.

11. The method of claim 1 , further comprising:
receiving a request for the set of data blocks, of the plurality of data blocks in the source database, that have changed since the time marked by the refresh reference time stamp;
wherein said identifying the set of data blocks is performed responsive to said receiving the request; and
wherein determining the starting time stamp is based, at least in part, on a time of receipt of the request.

12. The method of claim 1 , wherein determining the starting time stamp is based, at least in part, on a time at which said identifying the set of data blocks is initiated.

13. One or more non-transitory computer-readable media storing one or more sequences of instructions that, when executed by one or more processors, cause:
detecting an instruction to refresh a cloned database based on a source database;
wherein a database management system, that manages the source database, maintains a database session for the source database; and
in response to detecting the instruction to refresh the cloned database, performing a refresh operation for the cloned database, wherein the refresh operation causes the cloned database to incorporate changes made to the source database, the refresh operation comprising:
identifying a set of data blocks, of a plurality of data blocks in the source database, that have changed since a time marked by a refresh reference time stamp;
determining a starting time stamp that marks a time occurring before copying any blocks, from the set of data blocks, into the cloned database in connection with the instruction to refresh the cloned database;
at least partly while one or more changes are made to the plurality of data blocks in the source database via the database session, copying the set of data blocks, from the source database, into the cloned database;
wherein the one or more changes includes a particular change made to a particular data block of the plurality of data blocks to produce a changed data block;
wherein copying the set of data blocks into the cloned database comprises copying the changed data block into the cloned database;
recording the particular change in a particular redo entry in one or more redo logs maintained by the database management system;
determining a final time stamp that marks a time occurring after said copying the set of data blocks is complete;
performing recovery on the cloned database based, at least in part, on a set of redo entries, from the one or more redo logs, that comprise information for a set of changes made to the plurality of data blocks in the source database between times marked by the starting time stamp and the final time stamp;
wherein the set of redo entries includes the particular redo entry.

14. The one or more non-transitory computer-readable media of claim 13 , wherein the source database and the cloned database are pluggable databases.

15. The one or more non-transitory computer-readable media of claim 13 , wherein the one or more sequences of instructions further comprise instructions that, when executed by one or more processors, cause: storing, as a new refresh reference time stamp, the final time stamp.

16. The one or more non-transitory computer-readable media of claim 13 , wherein the one or more sequences of

Assignees

• Oracle Int Corp

Inventors

• Ravipati Giridhar
• Rajamani Kumar
• Li Yunrui
• Olagappan Muthu
• Lee Jaebock
• Jain Sanket

Classifications

• G06F16/27 Primary

  Replication, distribution or synchronisation of data between databases or within a distributed database system; Distributed database system architectures therefor · CPC title

• G06F16/273 Primary

  Asynchronous replication or reconciliation · CPC title

• G06F2201/82

  Solving problems relating to consistency · CPC title

• G06F11/1471

  involving logging of persistent data for recovery · CPC title

• G06F16/178

  Techniques for file synchronisation in file systems · CPC title