Detailed explanation of opcode cache usage in PHP

This time I will bring you a detailed explanation of the use of opcode cache in PHP. What are the precautions when using opcode cache in PHP. The following is a practical case, let's take a look.

1. What is opcode

After the interpreter analyzes the code, it generates an intermediate code that can be run directly, which is called an opcode, opcode

2. Interpreter and compilation The difference between interpreters

The interpreter directly runs the intermediate code after generating the intermediate code. The control of the runtime is still in the hands of the interpreter.

The compiler generates the intermediate code and further optimizes the code to generate a target program that can be run directly, but does not execute it. It waits for the user to trigger execution. Its control is in the target program and has nothing to do with the compiler.

3.php is an interpreted language. Its principle is somewhat similar to compilation, including lexical analysis, syntax analysis, semantic analysis..., the core engine of the php interpreter is zend engine

4.php How to view the opcode of a piece of code

Install the parsekit extension of php, and you can view the opcode of php through the extended api, such as parsekit_compile_string()

php -r "var_dump(parsekit_compile_string('print 1+1;'));"

5.opcode generated

must first undergo lexical analysis. The script code can be regarded as a series of word combinations. The interpreter To classify these words and mark them

For example, print, we look at zend/zend_language_scanner.l in the php source code package. In this file we can find the mark corresponding to print . T_PRINT

After finding the mark, the next step is syntax analysis. In zend/zend_language_parser.y, we can find the function corresponding to T_PRINT

and then Find the implementation code of this function in zend/zend_compile.c. This function implements the conversion of opcode. All opcodes are represented by userinteger.

6. Turn on opcode caching

Generating opcode requires system overhead. Each time an opcode is executed, an opcode must be generated. This overhead is considerable, so the optimization of PHP must enable the opcode cache. , to avoid repeated compilation.

php's opcode cache includes APC, eAccelerator, and XCache, which all put opcode in shared memory.

Take APC as an example: Set

apc.cache_by_default = on

in php.ini to check the cache status,

7.opcode cache expiration

The opcode cache will expire. If it expires, it must be generated again. Of course, you can also skip the expiration check mechanism and set

in php.ini so that the program code can be modified. It takes effect by restarting the server.

8. For script tracking and analysis, you can use xdebug to track. You can use xdebug to implement a performance tracker, find the execution bottleneck of the program, and optimize the program.

apc.stat=off

xdebug function tracking:

xdebug.profiler_output_dir = /tmp/xdebug
xdebug.profiler_output_name = cachegrind.out.%p

You can use wincachegrind to view the xdebug report file under window.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

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