Simple usage of opcode cache in PHP

This article introduces you to the simple usage of opcode cache in PHP, and shares it with you for reference

1. What is opcode

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

2. The difference between an interpreter and a compiler

The interpreter directly runs the intermediate code after generating the intermediate code, and the runtime control is still in the interpretation In hand.

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 the 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 is generated.

must first undergo lexical analysis. The script code can be regarded as a series of word combinations. The interpreter needs 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

Then find the function implementation code in zend/zend_compile.c , this function implements the conversion of opcode. All opcodes are represented by user integers.

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 through

You can check the cache status,

7.opcode cache expiration

The opcode cache will expire. If it expires, To generate a new one, of course, you can also skip the expiration check mechanism. Set

apc.stat=off

# in php.ini so that the program code must be modified by restarting server to take effect.

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

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

xdebug.trace_output_name = trace.%c

Introduction to opcode cache usage in PHP

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