In a situation where an application must handle millions of transactions, what aspect of performance testing is essential?

Throughput testing is essential when an application must handle millions of transactions. It measures the number of transactions processed per unit of time, providing insights into the system's capacity. Latency testing assesses delays, transaction rate testing focuses on the number of transactions processed, and response time testing evaluates the time taken for the system to respond to a user request. However, throughput is particularly critical for high transaction volumes.