Data processing: software development – installation – and managem – Software program development tool – Translation of code
Reexamination Certificate
1998-01-23
2001-06-05
Chaki, Kakali (Department: 2122)
Data processing: software development, installation, and managem
Software program development tool
Translation of code
C717S152000, C717S152000, C702S119000
Reexamination Certificate
active
06243862
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention is directed to distributed transaction processing systems. More particularly, the present invention is directed to methods and apparatus for testing components of a distributed transaction processing system that implements the X/Open Distributed Transaction Processing model.
2. Description of the Prior Art
On-line transaction processing (OLTP) is a technology that has been used successfully for business-critical applications by large enterprises for many years. With OLTP, users at terminals send messages to application programs, and these in turn update databases in real time. This is in contrast to batch or queued processing of transactions where the transactions are processed at a later time.
An example of an OLTP application is an airline reservation system. When a travel agent sends a request to reserve a seat on a plane, a database is updated accordingly, and a confirmation message is sent back to the agent'terminal. All of the tasks are part of a single transaction, and many agents can perform transactions at the same time. OLTP systems are typically used in environments that support large numbers of users, all accessing the same database, with hundreds and sometimes thousands of transactions taking place each second. The systems are typically based on large enterprise servers that can provide the performance, reliability, and data integrity demanded by these environments.
A transaction may be thought of as a set of actions performed by a transaction processing system wherein the actions together exhibit the properties of Atomicity, Consistency, Isolation, and Durability (ACID). The following definitions are given in
Transaction Processing: Concepts and Techniques,
by Jim Gray and Andreas Reuter, Morgan Kaufmann Publishers, Inc., 1993, p. 6:
Atomicity. A transaction'changes to the state are atomic; either all happen or none happen. These changes include database changes, messages, and actions on transducers.
Consistency. A transaction is a correct transformation of the state. The actions taken as a group do not violate any of the integrity constraints associated with the state. This requires that the transaction be a correct program.
Isolation. Even though transactions execute concurrently, it appears to each transaction, T, that other transactions execute either before T or after T, but not both.
Durability. Once a transaction completes successfully, (commits), the state of the data is changed to reflect the successful completion of the transaction, and the state of the data will survive system failures.
To maintain the properties identified above, at the beginning of processing a transaction, a transaction processing application program typically invokes some form of begin-transaction function to indicate processing of a transaction has begun. This operation is typically logged to an audit file to demarcate the operations associated with the particular transaction. Following the begin-transaction function, the other functions associated with the application-defined transaction are performed and are also logged to an audit file. If all operations associated with a transaction complete successfully, a commit function is invoked to make permanent any state changes that have occurred as a result of the transaction. The commit operation is logged to the audit file to indicate that all operations have completed successfully. If an error occurs during processing of the transaction and a commit operation is not performed, a rollback function is invoked to undo the effects of the operations performed to that point in processing the transaction.
Distributed Transaction Processing (DTP) is a form of on-line transaction processing that allows a single transaction to be performed by multiple application programs that access one or more databases on one or more computers across a network. This type of transaction, in which multiple application programs cooperate, is called a distributed transaction. Using DTP, for example, related databases at regional and branch locations can be synchronized. DTP also facilitates transaction processing across multiple enterprises. For example, DTP can be used to coordinate the computers of manufactures and suppliers, or to coordinate the computers of enterprises in related industries, such as the travel agency, airline, car rental, and hotel industries.
Transaction processing in a distributed environment can be either non-global or global. In a non-global transaction, the same work takes place as in a traditional transaction, but the work is distributed in a client/server manner. For example, a travel agent may request an airline reservation via a client application program that has a graphical user interface. The client application program communicates with a server application program that manages the reservation database. The server application program updates the database, commits or aborts its own work, and returns information to the client application program, which notifies the travel agent.
A global transaction consists of multiple, coordinated database updates, possibly occurring on different computers. Global transactions are used when it is important that all databases are synchronized so that either all updates are made or none are made. Continuing with the previous example, the travel agent may also need to reserve a rental car and hotel room. The customer who is traveling wants to make sure that all reservations are coordinated; if a flight is unavailable, the hotel and car reservations are not needed. For the purpose of illustrating a global transaction, the airline, car, and hotel databases are on different transaction processing systems.
The global transaction begins when the travel agent requests the reservation from a workstation client application program with a graphical user interface. The client program contacts three server application programs on different transaction processing systems. One server program books a flight, another reserves a car, and the third makes a hotel reservation. Each of the server application programs updates its respective database. The transactions processed by each of the server application programs may be referred to as subordinate transactions of the global transaction. A global transaction manager coordinates the updates to the three databases, and a subordinate transaction manager on each of the individual transaction processing systems coordinates locally with the server application programs. The server application programs return information to the client application program.
A major advantage of global transaction processing is that tasks that were once processed individually are processed as a group, the group of tasks being the global transaction. The database updates are made on an all-or-nothing basis. For example, if an airline seat is not available, the hotel and car reservations are not made. Thus, with a global transaction, tasks that were once performed independently may be coordinated and automated.
As with non-global transactions, global transactions must possess the ACID properties. In order to preserve the ACID properties for a global transaction, the commit processing is modified to a two-phase commit procedure. Under a two-phase commit, a global transaction manager first requests that each of the subordinate transaction managers prepare to commit their updates to the respective databases. If all the local transaction managers respond that they are prepared to commit, the global transaction manager sends a commit request to the local transaction managers. Thus, the two parts of the two-phase commit process are (i) prepare to commit the database updates, and (ii) commit the database updates. If any one of the transaction managers is unable to commit, the entire global transaction is aborted and each transaction manager performs a rollback function to undo the processing that may have occurred up to that point. In short, the two-phase commit process ensures that multiple databases participating in a single g
Chaki Kakali
Khatri Anil
Rode Lise A.
Starr Mark T.
Unisys Corporation
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