Performing 2-phase commit with presumed prepare

• US 6,684,223 B1
• Filed: 04/18/2002
• Issued: 01/27/2004
• Est. Priority Date: 12/29/1998
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Ngai, Gary C., Ganesh, Amit
• Primary Examiner(s): JUNG, DAVID YIUK
• Application Number:
  US10/125,911
• Time in Patent Office: 649 Days
• Field of Search: 707/1-10, 707/200-206, 707/100-104
• US Class Current: 1/1
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99952 Coherency, e.g. same view to multiple users
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A mechanism for performing a two-phase commit is provided. The mechanisms perform a two-phase commit in a manner that reduces the number of messages transmitted between a coordinating database system and the participating database systems, and the number of log flushes performed to complete a two-phase commit. To determine whether a particular participating database system is prepared to commit, the coordinating database system first examines external log tracking data that resides on the coordinating database system. External log tracking data, which indicates various states of logs on other database systems, is used to determine whether or not a particular participating database system is prepared to commit.

Claims

1. A method of providing atomicity for transactions executing on a database system, the method comprising the steps of:

a coordinating database system receiving a request to begin a transaction;

said coordinating database system transmitting a first request specifying a first set of modifications to data in a first database as part of said transaction;

said coordinating database system transmitting a second request specifying a second set of modifications to data in a second database system as part of said transaction;

said coordinating database system receiving log tracking data that indicates which modifications on said first database system and said second database system are recorded in log records stored to non-volatile storage; and

said coordinating database system determining whether said log tracking data indicates that said first set of modifications are recorded in log records stored in non-volatile storage.

2. The method of claim 1, the method further including the steps of:

if said log tracking data does not indicate that said first set of modifications are recorded in log records stored in non-volatile storage, then said coordinating database system transmitting a prepare request for said transaction to said first database system;

said coordinating database system receiving a message from said first database system indicating that said first database system is prepared to commit said transaction;

said coordinating database system determining whether said log tracking data indicates that said second set of modifications are recorded in log records stored in a non-volatile storage device; and

in response to (1) receiving said message from said first database system, and (2) determining that said log tracking data indicates that said second set of modifications are recorded in log records stored in non-volatile storage device, said first database system committing said transaction on said first database system.

3. A computer-readable medium carrying one or more sequences of one or more instructions for providing atomicity for transactions executing on a database system, the one or more sequences of one or more instructions including instructions which, when executed by one or more processors, cause the one or more processors to perform the steps of:

a coordinating database system receiving a request to begin a transaction;

said coordinating database system transmitting a first request specifying a first set of modifications to data in a first database as part of said transaction;

said coordinating database system transmitting a second request specifying a second set of modifications to data in a second database system as part of said transaction;

said coordinating database system receiving log tracking data that indicates which modifications on said first database system and said second database system are recorded in log records stored to non-volatile storage; and

said coordinating database system determining whether said log tracking data indicates that said first set of modifications are recorded in log records stored in non-volatile storage.

4. The computer-readable medium of claim 3, the computer-readable medium further including sequences of instructions for performing the steps of:

if said log tracking data does not indicate that said first set of modifications are recorded in log records stored in non-volatile storage, then said coordinating database system transmitting a prepare request for said transaction to said first database system;

said coordinating database system receiving a message from said first database system indicating that said first database system is prepared to commit said transaction;

said coordinating database system determining whether said log tracking data indicates that said second set of modifications are recorded in log records stored in a non-volatile storage device; and

in response to (1) receiving said message from said first database system, and (2) determining that said log tracking data indicates that said second set of modifications are recorded in log records stored in non-volatile storage device, said first database system committing said transaction on said first database system.

5. A distributed database system comprising:

a coordinating database system configured to receive a request to begin a transaction;

said coordinating database system configured to transmit a first request specifying a first set of modifications to data in a first database as part of said transaction;

said coordinating database system configured to transmit a second request specifying a second set of modifications to data in a second database system as part of said transaction;

said coordinating database system configured to receive log tracking data that indicates which modifications on said first database system and said second database system are recorded in log records stored to nonvolatile storage; and

said coordinating database system configured to determine whether said log tracking data indicates that said first set of modifications are recorded in log records stored in non-volatile storage.

6. The distributed database system of claim 5, wherein:

said coordinating database system is configured to transmit a prepare request for said transaction to said first database system if said log tracking data does not indicate that said first set of modifications are recorded in log records stored in non-volatile storage;

said coordinating database system is configured to receive a message from said first database system indicating that said first database system is prepared to commit said transaction;

said coordinating database system is configured to determine whether said log tracking data indicates that said second set of modifications are recorded in log records stored in a non-volatile storage device; and

said first database system is configured to commit said transaction on said first database system in response to (1) receiving said message from said first database system, and (2) determining that said log tracking data indicates that said second set of modifications are recorded in log records stored in non-volatile storage device.