Transaction systems must be able to support a high number of concurrent users and transaction types.

Figure 1 shows the main characteristics of a transaction system. Before the advent of the Internet, a transaction system served hundreds or thousands of terminals with dozens or hundreds of transactions per second. This workload was rather predictable both in transaction rate and mix of transactions.

Figure 1. Characteristics of a transaction system

Transaction systems must be able to support a high number of concurrent users and transaction types.

One of the main characteristics of a transaction or online system is that the interactions between the user and the system are very brief. Most transactions are executed in short time periods--one second, in some cases. The user will perform a complete business transaction through short interactions, with immediate response time required for each interaction. These are mission-critical applications; therefore, continuous availability, high performance, and data protection and integrity are required.

Online transaction processing (OLTP) is transaction processing that occurs interactively; it requires:

• Immediate response time
• Continuous availability of the transaction interface to the end user
• Security
• Data integrity.

Online transactions are familiar to many people. Some examples include:

• ATM transactions such as deposits, withdrawals, inquiries, and transfers
• Supermarket payments with debit or credit cards
• Buying merchandise over the Internet.