Performance Testing metrics to measure | Software Architecture Interview Questions

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Performance testing metrics are essential for evaluating the performance and scalability of an application. They help in identifying bottlenecks, ensuring the application can handle the expected load, and providing a baseline for future optimizations. Here are some key performance testing metrics to measure:

1. Response Time
**Definition**: The time taken to complete a request from the moment it is sent until the response is received.
- **Average Response Time**: The average time taken for all requests.
- **Peak Response Time**: The maximum time taken for any single request.
- **90th Percentile Response Time**: The time within which 90% of the requests are completed.

2. Throughput
**Definition**: The number of requests processed by the application per unit of time (typically measured in requests per second).
- **Transactions Per Second (TPS)**: The number of transactions the system can handle per second.
- **Requests Per Second (RPS)**: The number of HTTP requests the server can handle per second.

3. Latency
**Definition**: The time taken for a data packet to travel from the client to the server and back. It includes network delays and is a critical metric for applications requiring real-time interactions.

4. Error Rate
**Definition**: The percentage of requests that fail compared to the total number of requests.
- **Total Errors**: The total number of failed requests.
- **Error Percentage**: The ratio of failed requests to total requests, often expressed as a percentage.

5. Resource Utilization
**Definition**: Measures how much of the system’s resources (CPU, memory, disk I/O, and network) are being used during the test.
- **CPU Usage**: The percentage of CPU capacity used.
- **Memory Usage**: The amount of RAM consumed.
- **Disk I/O**: The rate of read/write operations on the disk.
- **Network Usage**: The amount of data transmitted and received over the network.

6. Concurrent Users
**Definition**: The number of users simultaneously interacting with the application. This metric helps determine how well the application scales under load.
- **Active Sessions**: The number of active user sessions at any given time.

7. Peak Load
**Definition**: The maximum load the system can handle before performance degrades or it becomes unresponsive. It is essential for understanding the system’s capacity limits.

8. Scalability
**Definition**: The ability of the system to handle increasing load by adding resources. This metric evaluates how well the system performs as the number of users or requests grows.
- **Horizontal Scalability**: The ability to add more instances to handle increased load.
- **Vertical Scalability**: The ability to add more resources (CPU, memory) to existing instances.

9. Availability
**Definition**: The percentage of time the system is operational and accessible. It is crucial for applications requiring high uptime.
- **Uptime Percentage**: The ratio of the time the system is up and running to the total time.

10. Bandwidth
**Definition**: The amount of data that can be transmitted over the network in a given period.
- **Data Transfer Rate**: The rate at which data is transferred, typically measured in Mbps (megabits per second).

11. Load Distribution
**Definition**: How evenly the load is distributed across multiple servers or instances. It helps ensure that no single server is overwhelmed.

12. Session Metrics
**Definition**: Metrics related to user sessions, including session duration, pages per session, and session depth.
- **Average Session Duration**: The average time users spend in a session.
- **Pages Per Session**: The average number of pages viewed per session.
- **Session Depth**: The level of user engagement during a session.

Conclusion
These performance testing metrics provide a comprehensive view of an application's performance under various conditions. By monitoring and analyzing these metrics, developers and testers can identify bottlenecks, optimize performance, and ensure the application meets its performance requirements.