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18 January 2024
10 Min. Read

Bottleneck Testing: What It Is & How It Works

Bottleneck Testing: What It Is & How It Works

Fast Facts

Get a quick overview of this blog

  1. Identify why bottleneck testing is a good practice to perform

  2. Get insights on how it can save your app from failures

  3. Learn step-by-step procedure on performing bottleneck testing

  4. Get to know about different performance and load testing tools

Bottleneck testing, also known as a bottleneck test, is a form of performance evaluation is a form of performance evaluation where you determine the point at which a system's performance starts to degrade due to a single component reaching its capacity limits.

This component is the "bottleneck" because it limits the overall system performance. By identifying and addressing bottlenecks, an application can be saved from failure under high load conditions in real-time, improving the efficiency and capacity of the system.

What is Bottleneck Testing?

Bottleneck testing is a specialized form of performance analysis aimed at identifying the component within a system that severely limits performance, acting as a constraint on the overall throughput or efficiency.

This concept can be likened to a literal bottleneck in a water bottle: no matter how much water the bottle holds, the rate at which the water flows out is limited by the narrow neck of the bottle.

Similarly, in systems ranging from software applications to network infrastructures, the "bottleneck" is the component that becomes the limiting factor in performance under certain load conditions.

Why Bottlenecks happen?

Causing slowdown or complete crash in any application is not something any team would wish for. It’s their worst nightmare, but still it becomes a very frequent sight every now and then. What actually causes bottlenecks? Is it inefficient testing or limitation of resources? Let’s discuss some of the many causes that can lead to bottlenecks and the importance of conducting bottleneck tests to identify these constraints.

These issues can arise at different layers of the application's environment, ranging from hardware limitations to inefficiencies in the code itself.

  1. Resource Limitations: Every application relies on hardware resources like CPU, memory, disk space, and network bandwidth. If an application requires more resources than what's available, it will slow down. For example, a CPU-intensive task can become a bottleneck if the CPU is already overburdened.

  2. Inefficient Code: Poorly written code can cause bottlenecks. This might be due to unoptimized algorithms that require more time or resources than necessary, or due to code that doesn't scale well with increased data volumes or user numbers.

  3. Database Performance: Applications often rely on databases, and bottlenecks can occur when database queries are slow or inefficient. This could be due to poorly designed database schema, lack of proper indexing, or database server resource constraints.

  4. Network Issues: Network latency and bandwidth limitations can become bottlenecks, especially in distributed applications or those that rely heavily on internet connectivity for data transfer.

  5. Concurrency and Synchronization Issues: Multithreaded applications can face bottlenecks if threads are not managed efficiently. Issues like thread contention, deadlock, or too much time spent on synchronization mechanisms can degrade performance.

  6. I/O Bound Processes: If an application spends a lot of time waiting for I/O operations (like reading from disk or writing to disk), these can become significant bottlenecks, especially if the I/O subsystem is slow or overburdened.

  7. Third-party Services and APIs: Dependencies on external services or APIs can introduce bottlenecks, particularly if these services have rate limits, latency issues, or are unreliable.

  8. Memory Management: Poor memory management can lead to bottlenecks. This includes memory leaks (where memory is not properly released) or excessive garbage collection in languages like Java or C#.

Finally, an application's ability to scale effectively is crucial in managing increased loads. If an application isn’t designed to scale well, either horizontally (by adding more machines) or vertically (by adding more power to the existing machine), it might struggle under high traffic conditions, leading to performance bottlenecks.

Core Principles of Bottleneck Testing

Say it principles or the primary focus of performing bottleneck testing, it should always start with pinpointing the root cause of failure. To get to specific component or resource that is limiting the performance should be a goal while starting bottleneck testing. It could be CPU, memory, I/O operations, network bandwidth, or even a segment of inefficient code in an application.

It will not only help in gaining insight on how a system scales under increased load but also helps in validating the resource allocation that you did for your SUT.

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Steps in Bottleneck Testing

Bottleneck testing is a specialized process in performance testing where the goal is to identify performance limitations in your system. This is a general overview that companies can alter or modify to suit there infra better:

  1. Define Performance Criteria: Before starting, you should have clear performance goals. These could include metrics like response time, throughput, and resource utilization levels.

  2. Understand the System Architecture: It's crucial to have a detailed understanding of the system's architecture. Know the hardware, software, networks, and databases involved. This knowledge will help you identify potential areas where bottlenecks might occur.

  3. Select the Right Tools: Choose performance testing tools that are appropriate for your system. These tools should be capable of simulating a realistic load and monitoring system performance under that load.

  4. Create a Test Plan: Develop a detailed test plan that includes the type of tests to be performed, the load under which the tests will be executed, and the metrics to be collected.

  5. Configure the Test Environment: Set up a test environment that closely replicates the production environment. This includes similar hardware, software, network configurations, and data volumes.

  6. Implement Performance Monitoring: Set up monitoring tools to collect data on various aspects of the system, such as CPU usage, memory usage, disk I/O, network I/O, and database performance.

  7. Execute Tests: Run the tests according to your test plan. Start with a low load and gradually increase it until you reach the load under which you expect the system to operate in production.

  8. Analyze Results: After the tests are complete, analyze the data collected. Look for trends and points where performance metrics start to degrade. This will help you identify the bottlenecks.

  9. Identify Bottlenecks: Based on the analysis, identify the components of the system that are causing performance issues. Bottlenecks can occur in various places like the application code, database, network, or server hardware.

  10. Address Bottlenecks: Once bottlenecks are identified, work on resolving them. This might involve optimizing code, upgrading hardware, tweaking configurations, or making changes to the database.

  11. Retest: After making changes, retest to ensure that the performance issues have been resolved. This may need to be an iterative process of testing and tweaking until the desired performance level is achieved.

  12. Document and Report: Finally, document the testing process, the findings, the actions taken, and the results of the retests. This documentation is valuable for future reference and for stakeholders who need to understand the testing outcomes.

Remember, bottleneck testing is an iterative process. It often requires multiple rounds of testing and adjustments to identify and address all the performance issues. Also, the process can differ based on the specific technologies and architecture of the system you are testing.

Examples of Bottleneck Testing

We are covering two examples to better showcase bottleneck testing under real scenarios. One example shows the bottleneck in database server and the other one shows the bottleneck in resources context, i.e., CPU.

Both these examples are simplified version of bottleneck testing. Real-world scenarios might involve more complex interactions, different types of bottlenecks, and multiple rounds of testing and optimization.

1) An E-Commerce App Bottleneck Testing


E-Commerce Application: An online store with a web interface that allows users to browse products, add them to their cart, and complete purchases. The application uses a web server, an application server, and a database server.


To ensure that the website can handle a high number of simultaneous users, especially during peak shopping seasons like Black Friday or holiday sales.

Steps for Bottleneck Testing:

  1. Define Performance Goals:

    • Maximum response time of 2 seconds for page loads.

    • Handle up to 10,000 concurrent users.

  2. Set Up the Testing Environment:

    • Replicate the production environment (same hardware specifications, software versions, network setup, and database configuration).

    • Use a testing tool like Apache JMeter or LoadRunner to simulate user requests.

  3. Baseline Test:

    • Run a baseline test with a normal load (e.g., 1,000 concurrent users) to establish performance metrics under normal conditions.

  4. Load Testing:

    • Incrementally increase the number of virtual users to simulate different load levels (2,000, 5,000, 10,000 users).

    • Monitor and record the performance metrics at each load level.

  5. Identify Potential Bottlenecks:

    • Analyze the test results to identify at which point performance degrades.

    • For instance, at 5,000 users, the response time may start exceeding 2 seconds, indicating a potential bottleneck.

  6. In-Depth Analysis:

    • Utilize monitoring tools to examine CPU, memory, database queries, network I/O, etc.

    • Discover that the database server CPU usage spikes dramatically at higher loads.

  7. Pinpoint the Bottleneck:

    • Investigate further to find that specific database queries are taking longer to execute under high load, causing the CPU spike.

  8. Optimization:

    • Optimize the database queries, add necessary indexes, or adjust query logic.

    • Consider scaling the database server resources (upgrading CPU, RAM) or implementing load balancing.

  9. Retesting:

    • Repeat the load testing with the optimized database.

    • Observe if the response time has improved and if the system can now handle 10,000 concurrent users within the defined response time.

  10. Documentation and Reporting:

  • Document the entire process, findings, and the impact of optimizations.

  • Share the report with the development team and stakeholders.

In this scenario, the bottleneck was identified in the database server, specifically in how certain queries were executed under high load. The bottleneck testing process not only helped in pinpointing the exact issue but also guided the team in optimizing the application for better performance.

2) Identifying a CPU Bottleneck in Python

Let's use a Python script to demonstrate a CPU bottleneck. We will create a function that performs a CPU-intensive task, and then we will monitor its performance.

import time
import multiprocessing

def cpu_intensive_task():
    result = 0
    for i in range(100000000):
        result += i

if __name__ == "__main__":
    start_time = time.time()
    processes = []

    for _ in range(multiprocessing.cpu_count()):
        p = multiprocessing.Process(target=cpu_intensive_task)

    for process in processes:

    print(f"Total time taken: {time.time() - start_time} seconds")

In this script, we create a process for each CPU core. If the CPU is the bottleneck, we will see that adding more processes (beyond the number of CPU cores) does not improve performance, and might even degrade it.

Advantages of Bottleneck Testing

Bottleneck testing is not just about improving performance; it's about making the system more efficient, reliable, and prepared for future growth while managing risks and optimizing resources.

Bottleneck testing zeroes in on performance degradation under stress, crucial for optimizing systems handling complex tasks and high loads. It identifies precise points of failure or slowdown, enabling targeted improvements.

This process is essential for systems where performance under peak load is critical. By understanding where and how a system falters, you can make informed decisions about resource allocation, whether it's server capacity, network bandwidth, or code efficiency.

This testing is vital for scalability. It reveals how much load the system can handle before performance drops, guiding infrastructure scaling and code optimization. Addressing bottlenecks enhances system reliability and stability, especially under unexpected or high traffic, reducing the risk of crashes or significant slowdowns.

Furthermore, bottleneck testing informs capacity planning. It provides concrete data on system limits, facilitating accurate predictions for infrastructure expansion or upgrades. This preemptive approach is essential for maintaining performance standards during growth periods or demand spikes.

Tools for Bottleneck Testing

Since Bottleneck testing is a subpart of performance testing only, any tool that can do perform testing well, can also be used to perform bottleneck testing. We are providing a list of most commonly identified tools when it comes to performance and load testing:

1. Apache JMeter - Tool for Bottleneck Testing:

Type of Apache JMeter: Load Testing Tool.

Key Features of Apache JMeter:

  • Simulates heavy loads on servers, networks, or objects to test strength and analyze overall performance.

  • Offers a variety of graphical analyses of performance reports.

  • Supports various protocols including HTTP, HTTPS, FTP, and more.

  • JMeter is Java-based and allows for extensive scripting and customization. It can be integrated with other tools for comprehensive testing scenarios.

2. LoadRunner (Micro Focus) - Tool for Bottleneck Testing:

Type of LoadRunner (Micro Focus): Performance Testing Tool.

Key Features of LoadRunner (Micro Focus):

  • Provides detailed information about system performance under load.

  • Supports a wide range of applications.

  • Allows testing for thousands of users concurrently.

  • LoadRunner scripts can be written in C-language, which makes it powerful for complex scenarios. It includes monitoring and analysis tools that help in identifying bottlenecks.

3. Gatling - Tool for Bottleneck Testing:

Type of Gatling: Load Testing Tool.

Key Features of Gatling:

  • Open-source tool, known for its high performance.

  • Simulates hundreds of thousands of users for web applications.

  • Provides clear and detailed reports.

  • Uses a DSL (Domain-Specific Language) for test scripting, which is based on Scala. It's more programmer-friendly and integrates well with Continuous Integration (CI) tools.

4. Wireshark - Tool for Bottleneck Testing:

Type of Wireshark: Network Protocol Analyzer.

Key Features of Wireshark:

  • Analyzes network traffic and measures bandwidth.

  • Helps in identifying network-related bottlenecks.

  • Provides detailed information about individual packets.

  • Wireshark captures network packets in real-time and allows for deep inspection of hundreds of protocols, with more being added continuously.

5. New Relic APM - Tool for Bottleneck Testing:

Type of New Relic APM: Application Performance Management Tool.

Key Features of New Relic APM:

  • Monitors web and mobile applications in real-time.

  • Provides insights into application performance and issues.

  • Tracks transactions, external services, and database operations.

  • New Relic uses agents installed within the application to collect performance metrics, making it suitable for in-depth monitoring of complex applications.

6. HyperTest - Tool for Bottleneck Testing:

Type of HyperTest: Load Testing Tool.

Key Features of HyperTest:

  • Monitors real-world user-scenarios across all endpoints.

  • It can simulate both expected and unexpected user loads on the system

  • Simulates different environments and conditions, which can be critical in identifying bottlenecks that only appear under certain configurations

  • HyperTest can automate the process of performance testing, which is crucial in identifying bottlenecks.

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7. Profiler Tools (e.g., VisualVM, YourKit) - Tool for Bottleneck Testing:

Type of Profiler Tools (e.g., VisualVM, YourKit): Profiling Tools.

Key Features of Profiler Tools (e.g., VisualVM, YourKit):

  • Offer insights into CPU, memory usage, thread analysis, and garbage collection in applications.

  • Useful for identifying memory leaks and threading issues.

  • These tools often attach to a running Java process (or other languages) and provide visual data and metrics about the performance characteristics of the application.

Each of these tools has its own strengths and is suitable for different aspects of bottleneck testing. The choice of tools depends on the specific requirements of the system being tested, such as the technology stack, the nature of the application, and the type of performance issues anticipated.


In conclusion, bottleneck testing is a critical process in software development, aimed at identifying and resolving performance issues that can significantly impede application efficiency.

Get free access to our exclusive cheat sheet on best practices for performing software testing .

Through various methodologies and tools like HyperTest, it allows developers to pinpoint specific areas causing slowdowns, ensuring that the software performs optimally under different conditions. Understanding and implementing bottleneck testing through systematic bottleneck tests is, therefore, essential for delivering a robust, efficient, and scalable software product to users.

Related to Integration Testing

Frequently Asked Questions

1. What is bottleneck testing?

Bottleneck testing is a type of performance evaluation where specific parts of a system or application are intentionally stressed to identify performance limitations. This process helps to pinpoint the weakest links or "bottlenecks" that could hinder the system's overall efficiency and capacity.

2. What is an example of a black box?

A common example of a bottleneck in performance testing is slow database queries that hinder overall system response time. If the database queries take a disproportionately long time to execute, it can impact the system's ability to handle concurrent user requests efficiently, leading to a performance bottleneck.

3. What is bottleneck analysis with example?

Bottleneck analysis involves identifying and resolving performance constraints in a system. For example, if a website experiences slow loading times, bottleneck analysis may reveal that the server's limited processing power is the constraint, and upgrading the server can address the issue.

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