System and method for decoupling space reservation in transactional logs

The notion of a transaction is an important concept for transactional systems, such as database management systems, recoverable file systems and transaction-based operating systems. Briefly stated, a transaction is an action or set of actions that guarantees the ACID (Atomicity, Consistency, Isolation and Durability) properties. Transactional logging involves maintaining a persistent transactional log that records a time serial history of transactions in a system. A transactional log provides information for restoring a system to a consistent state that existed prior to a system failure.

A traditional transactional logging system uses a dedicated log to support a single log client. The log client communicates with the transactional logging system to ensure that the client\'s log records are properly written to the dedicated log. This type of transactional logging system is typically very robust and achieves a high level of reliability. However, the inventors have determined that the high level of reliability of a single log client using a dedicated logging system may actually result in overall performance degradation for a computing environment where multiple log clients are using multiple dedicated logging systems.

One of the reasons for the performance degradation is that each dedicated logging system independently incurs input/output (I/O) overhead to write and retrieve information from its respective dedicated log. This and other I/O overhead results in adverse performance impact, and the impact is cumulative for each of the independent logging systems. An improved logging system is desirable that could overcome some of these performance problems.

However, the development of an improvement to the existing scheme of transactional logging has met several hurdles. The inventors have determined that one hurdle to an improved transactional logging system is the need to assure that a client\'s log records are reliably written to a transactional log by guaranteeing the availability of space in the log. A solution that offers this guarantee without incurring undue context switching and I/O overhead continues to elude those skilled in the art.

Briefly stated, this invention is directed toward a computer-implemented system and method for decoupling space reservation in a transactional logging system. The transactional logging system handles log records for multiple clients and comprises distributed components, a core component, and a transactional log. The core component allocates a part of the transactional log as common reserved space for use by the clients. Each of the distributed components interacts with one of the clients. The distributed component maintains accounting information for identifying the client\'s portion of the common reserved space. The accounting information is communicated to the core component by the distributed component.

In one aspect, the invention is directed toward a computer-implemented system and method for pre-reserving space in a common transactional log. The computer-implemented method includes receiving log records from clients that use the transactional log. The method determines whether a sufficient amount of free space exists in the transactional log to append the log records. If not, the log records are appended to pre-reserved space associated with the client in the transactional log. The method updates an amount of pre-reserved space available to the client.

In another aspect, the invention is directed toward a method for communicating between a distributed component and a core component in a transactional logging system. The distributed component, which is associated with a client, issues a first message that contains a requested amount of pre-reserved space in a transactional log. The core component receives the first message and determines how much free space in the transactional log to make available to the client as pre-reserved space. The core component returns to the distributed component a second message that identifies the actual amount of pre-reserved space.

In still another aspect, the invention is directed toward a computer-readable medium encoded with a transactional log that has at least two data fields. The first data field contains log records. Each log record is associated with one of the clients that uses the transactional log. The second data field contains accounting information associated with common reserved space shared by the clients.

In yet a further aspect, the invention is directed toward a computer-readable medium encoded with a data structure that has at least two data fields. The first data field identifies an amount of current pre-reserved space and an amount of desired pre-reserved space associated with a distributed component of a transactional logging system. The second data field identifies an amount of actual pre-reserved space available to the distributed component.