Comparing Apache Prefork vs Worker MPMs: Which is Better for Your Web Server?

Apache web server is the most widely used web server in the world. It comes with a modular architecture, which allows users to extend its functionality and customize it according to their needs. One of the important modules of Apache is Multi-Processing Module (MPM), which handles incoming requests and manages multiple processes or threads to handle them efficiently.

Apache provides two popular MPMs, Prefork and Worker, each with its own advantages and limitations. Choosing the right MPM for your website is critical to its performance and stability. In this article, we will compare the two MPMs in detail and help you make an informed decision.

Prefork MPM

The Prefork MPM is the traditional and default MPM in Apache web server. It creates multiple child processes to handle incoming requests, each running its own copy of the Apache web server. Each child process can handle only one request at a time, which makes it less efficient than other MPMs. However, it is still popular because of its stability and compatibility with older PHP and other scripts.

Advantages of Prefork MPM:

1. Stable: Prefork MPM is known for its stability and reliability. Each child process runs independently of others, which ensures that if one process crashes, it does not affect other processes.
2. Compatibility: Prefork MPM is compatible with older PHP and other scripts that are not thread-safe. It runs each script in a separate process, which avoids issues related to thread-safety.

Limitations of Prefork MPM:

1. Resource-Intensive: Prefork MPM creates multiple processes, which consume a significant amount of system resources. It can cause high memory usage and slow down the server under heavy load.
2. Limited Concurrency: Each child process can handle only one request at a time, which limits the number of concurrent connections that the server can handle.

Worker MPM

The Worker MPM is a newer MPM in Apache web server, which is designed to improve performance and scalability. It creates multiple threads within a single process, each handling a separate connection. It is more efficient than Prefork MPM in terms of resource usage and concurrency. However, it requires a more modern version of PHP and other scripts that are thread-safe.

Advantages of Worker MPM:

1. Resource-efficient: Worker MPM creates multiple threads within a single process, which reduces the amount of system resources used. It can handle a larger number of connections without slowing down the server.
2. High Concurrency: Each thread can handle a separate connection, which allows the server to handle a higher number of concurrent connections.

Limitations of Worker MPM:

1. Stability: Worker MPM is less stable than Prefork MPM because all threads share the same process. If one thread crashes, it can affect other threads and cause the server to crash.
2. Compatibility: Worker MPM is not compatible with older PHP and other scripts that are not thread-safe. It requires a more modern version of PHP and other scripts to work properly.

Comparing Apache Prefork vs. Worker MPMs

The following table compares the key features of Apache Prefork and Worker MPMs:

As you can see, Apache Worker has several advantages over Apache Prefork. It is more scalable, uses less memory, and performs better for high-traffic websites. Apache Prefork, on the other hand, is simpler and more stable. It is still a good option for small websites or websites that do not receive a lot of traffic.

Configuring Apache Prefork and Worker

Here are some sample configurations for Apache Prefork and Worker:

Apache Prefork:

<IfModule mpm_prefork_module>
  ServerLimit 100
  StartServers 5
  MinSpareServers 5
  MaxSpareServers 10
  MaxClients 100
  MaxRequestsPerChild 0
</IfModule>

Apache Worker:

<IfModule mpm_worker_module>
  ServerLimit 100
  StartServers 2
  MaxClients 150
  MinSpareThreads 25
  MaxSpareThreads 75
  ThreadsPerChild 25
  MaxRequestsPerChild 0
</IfModule>

Wrap Up!

In conclusion, both the Prefork and Worker MPMs have their own advantages and disadvantages. It ultimately depends on the specific needs of your website and the amount of traffic it receives. If you’re unsure which MPM to use, it’s recommended to start with the default Prefork MPM and then switch to the Worker MPM if you experience high traffic and want to improve performance.