Performance metrics (response time, throughput) in Testing Fundamentals - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is response time in performance testing?

Response time is the total time taken from sending a request to receiving the complete response. It measures how fast a system reacts to a user action.

beginner

Define throughput in the context of software performance.

Throughput is the number of transactions or requests a system can handle in a given time, usually measured as requests per second or transactions per minute.

intermediate

Why is measuring response time important for user experience?

Because users expect quick feedback, slow response times can frustrate users and cause them to leave. Measuring response time helps ensure the system feels fast and responsive.

intermediate

How does throughput differ from response time?

Response time measures how fast one request is handled, while throughput measures how many requests the system can handle over time. They show different aspects of performance.

beginner

Give a real-life example to explain throughput.

Imagine a cashier at a store: throughput is like how many customers the cashier can serve in an hour. The faster they serve, the higher the throughput.

What does response time measure?

A Time taken to complete one request

B Number of requests per second

C Total users on the system

D Amount of data transferred

Response time measures how long it takes to complete a single request from start to finish.

Throughput is best described as:

A Speed of a single request

B Number of errors in requests

C Number of requests handled in a time period

D Memory used by the system

Throughput counts how many requests or transactions the system processes in a given time.

If a system has low response time but low throughput, what does it mean?

A It handles many requests slowly

B It handles few requests slowly

C It handles many requests quickly

D It handles few requests quickly

Low response time means fast handling per request, but low throughput means few requests handled overall.

Which metric would you check to know how many users can be served simultaneously?

A Throughput

B Response time

C CPU usage

D Disk space

Throughput indicates how many requests or users the system can handle at once or over time.

Why is it important to monitor both response time and throughput?

A They measure the same thing

B To understand speed and capacity of the system

C Only response time matters

D Only throughput matters

Response time shows speed per request; throughput shows how many requests the system can handle. Both are needed for full performance insight.

Explain the difference between response time and throughput using a simple example.

Think about how fast one task is done versus how many tasks are done in total.

Why should testers measure both response time and throughput during performance testing?

Consider what each metric tells about the system.

Practice

1. What does response time measure in performance testing?

easy

A. The total number of requests per second

B. How fast a single request is completed

C. The amount of data transferred in a request

D. The number of users accessing the system

Solution

1. Step 1: Understand response time meaning

   Response time measures the duration taken to complete one request from start to finish.

2. Step 2: Differentiate from throughput

   Throughput measures how many requests happen over time, not the speed of one request.

3. Final Answer:

   How fast a single request is completed -> Option B

4. Quick Check:

   Response time = speed of one request [OK]

Hint: Response time = speed of one request [OK]

Common Mistakes:

• Confusing response time with throughput
• Thinking response time counts total requests
• Mixing data size with response time

2. Which of the following is the correct unit commonly used to measure throughput?

easy

A. Milliseconds (ms)

B. Bytes

C. Requests per second (RPS)

D. Percentage (%)

Solution

1. Step 1: Identify throughput unit

   Throughput measures how many requests are processed per unit time, commonly requests per second (RPS).

2. Step 2: Exclude other units

   Milliseconds measure time, bytes measure data size, and percentage is not a throughput unit.

3. Final Answer:

   Requests per second (RPS) -> Option C

4. Quick Check:

   Throughput = requests per second [OK]

Hint: Throughput counts requests per second [OK]

Common Mistakes:

• Using time units for throughput
• Confusing data size with throughput
• Selecting percentage as throughput unit

3. Given a system that processes 120 requests in 10 seconds, what is the throughput?

medium

A. 10 requests per second

B. 0.12 requests per second

C. 1200 requests per second

D. 12 requests per second

Solution

1. Step 1: Calculate throughput formula

   Throughput = Total requests / Total time = 120 / 10 seconds.

2. Step 2: Perform division

   120 divided by 10 equals 12 requests per second.

3. Final Answer:

   12 requests per second -> Option D

4. Quick Check:

   120 ÷ 10 = 12 [OK]

Hint: Divide total requests by total time [OK]

Common Mistakes:

• Dividing time by requests instead of requests by time
• Multiplying requests and time
• Confusing throughput with response time

4. A tester recorded the following response times (in ms): 100, 200, 150, 250. The average response time was incorrectly calculated as 700 ms. What is the correct average response time?

medium

A. 175 ms

B. 700 ms

C. 150 ms

D. 200 ms

Solution

1. Step 1: Sum all response times

   Add 100 + 200 + 150 + 250 = 700 ms total.

2. Step 2: Calculate average response time

   Divide total 700 ms by 4 requests = 175 ms average.

3. Final Answer:

   175 ms -> Option A

4. Quick Check:

   700 ÷ 4 = 175 [OK]

Hint: Sum times, then divide by count [OK]

Common Mistakes:

• Using total sum as average
• Dividing by wrong number of requests
• Mixing units in calculation

5. A web server has a throughput of 50 requests per second and an average response time of 200 ms. If the server's throughput doubles but response time remains the same, what happens to the server's capacity and user experience?

hard

A. Capacity doubles; user experience stays consistent

B. Capacity stays same; user experience worsens

C. Capacity doubles; user experience worsens

D. Capacity halves; user experience improves

Solution

1. Step 1: Understand throughput doubling

   Doubling throughput means the server can handle twice as many requests per second, so capacity doubles.

2. Step 2: Analyze response time unchanged

   Since response time stays at 200 ms, the speed per request remains consistent, so user experience does not worsen.

3. Final Answer:

   Capacity doubles; user experience stays consistent -> Option A

4. Quick Check:

   Throughput ↑, response time same = better capacity, same experience [OK]

Hint: More throughput + same response time = better capacity, same experience [OK]

Common Mistakes:

• Assuming response time worsens with throughput increase
• Confusing capacity with response time
• Thinking capacity decreases when throughput increases