The recent launch of PHP 8.0 has introduced a range of innovative features, with the JIT (Just in Time) compiler being one of the most prominent. This compiler has brought about a significant change in the way PHP code is executed. Through this tutorial, you will understand what the JIT compiler is and why it is so important.

Diving Deep into PHP 8.0's JIT Compiler

The Evolution of PHP Compilation

PHP was designed to be an interpreted language that converts your written script into an intermediate bytecode. This bytecode gets interpreted by the Zend Engine whenever the script runs. In simpler terms, whenever you request a PHP page, it gets translated into a language the machine understands. This process, although efficient, does have overhead.

PHP Script → Opcodes → CPU Execution

Understanding the Idea of Just-in-Time (JIT)

As its name suggests, Just-in-time (JIT) compilation is a method where parts of the code are compiled "just in time" during execution, not before. It is a change from the traditional compilation process. Instead of initially translating the entire script, the JIT dynamically compiles parts of the code as needed.

PHP Script → Opcodes → Machine Code → CPU Execution

PHP achieves a streamlined and efficient execution process by translating code into native machine instructions only when necessary. It eliminates redundancy. If a code segment is frequently used during a script's execution, it does not need to be translated repeatedly.

The Impact of JIT in PHP 8.0

The JIT compiler in PHP 8.0 brings forth a two-fold advantage:

  • On-the-Fly Compilation: During the script's execution, PHP bytecode is dynamically converted into machine code. This direct translation means the machine no longer relies solely on the Zend Engine for interpretation. The result? Faster script execution for certain types of operations.
  • Caching Mechanism: After the creation of machine code, PHP does not discard it. Instead, it stores the code in the cache for future use. When the same bytecode requires translation again, PHP retrieves the previously translated machine code from the cache. This process avoids recompilation, leading to time and resource savings.

Visualizing the JIT Process

Imagine yourself in a foreign land where you encounter people who speak a language you don't understand. In this scenario, you would require the services of a translator whenever you have a conversation with someone. Similarly, traditional PHP execution requires constant translation, which can be compared to the continuous need for a translator. However, with JIT, you only need to translate sentences once, after which you can memorize or cache commonly spoken sentences. This results in faster and smoother conversations, reducing your dependence on a translator.

Here is a comparison between the normal compilation process and the JIT compilation process in PHP:

Traditional Compilation JIT Compilation
Compile the entire code ahead of time. Compile parts of code just when needed.
Sometimes slower startup time. Faster execution during run time.
Fixed compiled code. Ability to optimize code during run time.

Benchmarks and Real-World Performance

While benchmarks show incredible speed improvements in synthetic tests, real-world web applications might not see as dramatic a performance boost. It is because many web apps are I/O bound rather than CPU bound.

Task Type Performance Improvement with JIT
Mathematical operations High
String operations Moderate
Database queries Low
File I/O Low

Benefits of JIT in PHP 8.0

  • Performance Improvement: One of the most significant advantages of the JIT compiler is its ability to improve performance, particularly in tasks heavy on CPU usage.
  • Adaptive Optimization: JIT can analyze the code as it runs and make optimization decisions based on actual run-time behavior, leading to more targeted improvements.
  • Flexibility: With JIT, PHP is now adaptable well beyond web development. It allows for use in various fields, such as game development or scientific computing.

Setting Up JIT in PHP 8.0

Enabling the JIT compiler in PHP 8.0 is relatively straightforward. You need to configure the php.ini file with specific settings. Here's how:

  1. Open your php.ini file.
  2. Locate or add the section for opcache.
  3. Add or modify the following lines:
  4. Save the file and restart your web server.

The above configuration will enable JIT with a 50MB buffer size and the 'tracing' compilation strategy.


PHP has been a reliable and robust server-side scripting language for a long time. And now, with the introduction of the JIT compiler in PHP 8.0, it has improved even more. JIT compilers not only have the potential to improve PHP performance but also emphasize language development keeping in mind modern requirements and technological advancements.

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