Constant time database recovery

1. A database recovery system, comprising:

a processor coupled to a memory, the processor configured to execute computer-executable instructions stored in the memory that when executed cause the processor to perform the following actions:

determining a state of one or more transactions identified in a transaction log associated with a database, wherein the database supports versioning of user data;

redoing the one or more transactions sequentially as specified by the transaction log starting from the beginning of a last successful checkpoint to the end of the transaction log;

marking one or more uncommitted transactions of the one or more transactions as aborted;

identifying a data element associated with a transaction identifier of one of the one or more uncommitted transactions marked as aborted; and

reverting the data element to a prior committed version in an asynchronous background process or when the data element is updated.

2. The system of claim 1 , wherein the actions further comprise performing a logical revert by applying compensating operations to the data element to produce the prior committed version.

3. The system of claim 1 , wherein the actions further comprise:

acquiring a secondary log that stores logical operations that are non-versioned; and

using the acquired secondary log in a database recovery procedure.

4. The system of claim 3 , wherein using the acquired secondary log in the database recovery procedure comprises:

redoing the logical operations captured by the secondary log chronologically starting from the oldest active transaction to the end of the secondary log; and

undoing uncommitted logical operations in reverse chronological order from the end of the secondary log to the oldest active transaction.

5. The system of claim 4 , wherein the actions further comprise applying a transaction lock on a transaction identifier during recovery and releasing the transaction lock after completion of the undoing uncommitted logical operations.

6. The system of claim 3 , wherein the actions further comprise truncating the secondary log based on the longest active transaction.

7. The system of claim 1 , wherein the actions further comprise truncating the transaction log based on a most recent successful checkpoint.

8. The system of claim 1 , wherein the actions further comprise redoing the transactions sequentially as specified by the transaction log starting at the earlier of an oldest dirty page or the beginning of a last successful checkpoint.

9. A method of database recovery, comprising:

employing at least one processor configured to execute computer-executable instructions stored in a memory that when executed cause the at least one processor to perform the following acts:

determining a state of transactions specified in a transaction log of a database, wherein the database stores versions of user data;

redoing one or more transactions sequentially as specified by the transaction log starting from the beginning of a last successful checkpoint to the end of the transaction log;

marking one or more uncommitted transactions of the one or more transactions as aborted;

identifying a data element associated with a transaction identifier of one of the one or more uncommitted transactions marked as aborted; and

reverting the data element to a prior committed version in an asynchronous background process or when the data element is updated.

10. The method of claim 9 , wherein the acts further comprise identifying the data element in response to receiving a request to update the data element.

11. The method of claim 9 , wherein the acts further comprise:

generating a secondary log that stores logical operations that are non-versioned; and

using the generated secondary log in a database recovery procedure.

12. The method of claim 11 , wherein using the generated secondary log in the database recovery procedure comprises:

redoing one or more transactions captured by the secondary log starting from the oldest active logical transaction; and

undoing one or more uncommitted transactions backward from the end of the secondary log to the oldest active transaction.

13. The method of claim 9 , wherein the acts further comprise truncating the transaction log based on a most recent checkpoint.

14. The method of claim 9 , wherein the acts further comprise:

identifying one or more system transactions captured in the transaction log;

redoing one or more system transactions chronologically starting from the oldest active transaction to the end of the transaction log; and

undoing one or more uncommitted system transactions in reverse chronological order from the end of the transaction log to the oldest active transaction.

15. A system of database recovery, comprising:

a processor coupled to a memory, the processor configured to execute computer-executable instructions stored in the memory that when executed cause the processor to perform the following actions:

determining state of transactions from a transaction log after a crash of a database, wherein the database supports versioning of user data;

redoing one or more transactions from a last successful checkpoint forward to the end of the transaction log;

marking one or more uncommitted transactions as aborted and deferring undo;

acquiring a secondary log that that stores logical operations that are non-versioned; and

using the acquired secondary log in a database recovery procedure.

16. The system of claim 15 , wherein the actions further comprise:

identifying data elements associated with a transaction identifier marked as aborted; and

reverting at least one of the data elements to a previous saved version.

17. The system of claim 16 , wherein using the acquired secondary log in the database recovery procedure comprises:

redoing the logical operations captured by the secondary log forward starting from the oldest active transaction to the end of the secondary log; and

undoing uncommitted logical operations backward from the end of the secondary log to the oldest active transaction.

18. The system of claim 16 , wherein the actions further comprise identifying the data elements in response to receiving a request to update the data elements.

19. The system of claim 16 , wherein the actions further comprise:

performing a logical revert by applying compensating operations to the data elements to produce the prior committed version.

20. The system of claim 15 , wherein the actions further comprise truncating the transaction log based on a most recent checkpoint.