OPTIMISTIC LOCKING METHOD AND SYSTEM FOR COMMITTING TRANSACTIONS ON A FILE SYSTEM

• US 20090106248A1
• Filed: 11/26/2008
• Published: 04/23/2009
• Est. Priority Date: 02/06/2004
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: TAN, Yuen-Lin, VAGHANI, Satyam B.
• Granted Patent: US 8,700,585 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 16/1767 Concurrency control, e.g. optimistic or pessimistic approaches

Abstract

In a file system shared by multiple servers, reservation of a data storage unit such as a LUN of a disk array to acquire locks in order to commit a transaction acting on data stored in the data storage unit is deferred until the transaction is completed in RAM and the locks can be acquired in parallel during a single instance of reserving the data storage unit.

Claims

1. In a shared file system, a method for committing a transaction acting upon data stored in a data storage unit, the method comprising:

reading a state of a set of locks relating to the data;

constructing a completed transaction in memory prior to acquiring the locks;

acquiring exclusive possession of the data storage unit;

acquiring the locks if the state of the locks has not changed since said reading; and

committing the completed transaction.

2. The method of claim 1, further comprising:

journaling the completed transaction to the data storage unit prior to said committing.

3. The method of claim 1, wherein each of the locks has a version field that is incremented upon said lock'"'"'s acquisition or release and the checking step comprises examining whether the version field of the locks have changed.

4. The method of claim 1, wherein said acquiring exclusive possession of the data storage unit step uses a SCSI reservation command.

5. The method of claim 4, wherein said acquiring the locks occurs in parallel using SCSI pipelined commands.

6. The method of claim 1, wherein the completed transaction in memory comprises a data structure comprising a record of locks relating to the data and a record of updates to be performed on said data.

7. The method of claim 1, further comprising:

adding pre-commit actions to a pre-commit actions buffer of the completed transaction; and

executing the pre-commit actions after said acquiring the locks and before said committing the completed transaction.

8. The method of claim 1, wherein the data is metadata.

9. The method of claim 1, wherein the data storage unit is a logical unit number (LUN) of a disk array.

10. The method of claim 1, further comprising:

checking a retry counter if the state of the locks has changed; and

re-performing said method if the retry counter is greater than zero.

11. The method of claim 10, wherein the retry counter relates to the transaction.

12. The method of claim 10, wherein the retry counter relates to a context corresponding to the transaction.

13. A computer system with a shared file system accessed by a plurality of servers, the computer system comprising:

a plurality of servers, wherein each of the servers comprises a processor, a random access memory (RAM) and an operating system accessing the shared file system;

a data store coupled to the plurality of servers, wherein the data store comprises a data storage unit storing the shared file system, wherein each server'"'"'s processor is programmed to perform the following steps to commit a transaction for a process running on said server;

reading into said server'"'"'s RAM a first state of a set of locks relating to data to be acted upon by the transaction;

constructing a completed version of the transaction in said server'"'"'s RAM prior to acquiring the locks;

acquiring exclusive possession of the data storage unit;

checking if the locks have changed state since the first state;

acquiring the locks if the state of the locks has not changed since the first state; and

committing the completed transaction to a journal in the data storage unit.

14. The computer system of claim 13, wherein the data store is a disk array and is coupled to the plurality of servers through a storage area network (SAN) and the data storage unit is a logical unit number (LUN) of the disk array.

15. The computer system of claim 13, wherein each of the servers is further configured to instantiate virtual machines.

16. A computer readable storage medium having stored therein a computer program for committing a transaction acting upon data stored in a data storage unit, wherein a computer system executing the computer program carries out:

reading a state of a set of locks relating to the data;

constructing a completed transaction in memory prior to acquiring the locks;

acquiring exclusive possession of the data storage unit;

acquiring the locks if the state of the locks has not changed since said reading; and

committing the completed transaction.

17. The computer readable storage medium of claim 16, wherein a computer system executing the computer program further carries out journaling the completed transaction to the data storage unit prior to said committing.

18. The computer readable storage medium of claim 16, wherein a computer system executing the computer program further carries out:

adding pre-commit actions to a pre-commit actions buffer of the completed transaction; and

executing the pre-commit actions after the step of acquiring the locks and before the step of committing the completed transaction.

19. The computer readable storage medium of claim 16, wherein a computer system executing the computer program further carries out:

checking a retry counter if the state of the locks has changed; and

re-executing the steps if the retry counter is greater than zero.

20. The computer readable storage medium of claim 16, wherein said acquiring the locks occurs in parallel by issuing SCSI pipelined commands.