What is Opcache in php? Introduction to the principles and use of Opcache

The content of this article is about what is Opcache in php? The introduction to the principle and use of Opcache has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Personal practice found that opcache

Recently, in order to cope with the impact of high traffic during Double Eleven, the editor used a stress test to find server performance bottlenecks and found that 100 concurrency At that time, the QPS
was not very high, but the CPU and memory consumption were extremely high, especially the CPU consumption was 100%, and our container and server configurations were almost upgraded to the top level. This is not what such a good server should do. effect, so the editor conducted a comprehensive investigation:

1. View the database query part of the interface. This part is cached, and the consumption of redis is not very high. This eliminates the factors that affect the performance of the database and cache. ;

2. Check whether there are any other external calls that affect performance. It is found that this part of the data acquisition is only through the database and cache, so it is excluded;

3. Check whether there are any complex problems in the interface program code. After logical calculation, it was found that the data processed in this part was cached directly after being processed. The data source for a period of time was redis cache, so it was excluded

4. Since it has been installed, it has been eliminated that may cause interface bottlenecks. Then the most likely thing is that the laravel5.0 framework currently used causes such low interface performance. Then through the framework documents, source code and online materials, it is found that the laravel framework will load a large number of framework files at runtime, and then compile these files to cause server CPU Consumption is extremely high. Through this direction, the editor discovered opcache, a good PHP extension for caching PHP compiled files.

2. The principle of opcache

1. What is Opcache?

Opcache is a method that avoids the overhead of loading and parsing PHP scripts each time by storing the precompiled bytecode (Operate Code) of the parsed PHP script in shared memory. The parser can directly read from the shared memory. Read cached bytecode (Operate Code), thereby greatly improving PHP execution efficiency.

2. What is Operate Code?

When the interpreter completes the analysis of the script code, it generates intermediate codes that can be run directly, also called operation codes (Operate Code, opcode). The purpose of Opcode cache is to avoid repeated compilation and reduce CPU and memory overhead. If the performance bottleneck of dynamic content lies not in the CPU and memory, but in I/O operations, such as the disk I/O overhead caused by database queries, then the performance improvement of the opcode cache is very limited. But since opcode cache can reduce CPU and memory overhead, this is always a good thing. Modern opcode caches (Optimizer, APC2.0, others) use shared memory for storage and can execute files directly from them without having to "deserialize" the code before execution. This results in significant performance acceleration, often lower overall server memory consumption especially at high traffic and high concurrency, and has few drawbacks.

3. Why use Opcode cache?

This starts with the life cycle of the PHP code. When requesting a PHP script, it will go through five steps, as shown in the following figure:

The Zend engine must read a file from the file system, scan its dictionary and expressions, parse the file, create computer code to be executed (called an Opcode), and finally execute the Opcode. Each time a PHP script is requested, the above steps will be executed once. If the PHP source code does not change, then the Opcode will not change. Obviously, there is no need to regenerate the Opcode every time. Combined with the ubiquitous caching mechanism in the Web, we can cache the Opcode. , wouldn’t it be faster to directly access the cached Opcode in the future? The flow chart after enabling the Opcode cache is as follows:

Therefore, using After the Operate Code is cached, the PHP code will directly obtain the opcode and execute it directly. The three steps in the middle will be omitted, which will greatly improve the efficiency of PHP code execution.

3. Installation and use of Opcache

1. Installation

当你的PHP版本低于7.0时，你可以去http://pecl.php.net/package/ZendOpcache 根据自己的PHP版
本下载相应的opcache版本。比如PHP5.5：http://pecl.php.net/get/zendopcache-7.0.5.tgz
tar -zxvf zendopcache-7.0.5.tgz
cd zendopcache-7.0.5
phpize
./configure --with-php-config=/usr/local/php/bin/php-config
make
make install
这是会在php的扩展文件夹内生成opcache.so
PHP7.0之后自带opcache.so无需安装

2. Use

 在php.ini加入zend_extension=opcache.so;
 注意：这里是zend_extension不是extension，关于zend_extension和extension的区别可以去查阅
 相关资料

3. Configuration

关于opcache的详细参数配置比较核心的参数如下：
opcache扩展位置
zend_extension=opcache.so
启用opcache
opcache.enable=1
使用共享内存大小
opcache.memory_consumption=200
字符串缓存大小
opcache.interned_strings_buffer=8
最大缓存文件数量
opcache.max_accelerated_files=8000
出现异常，立即释放全部内存
opcache.fast_shutdown=1
最大允许占用内存百分比，超过此限制会重启进程
opcache.max_wasted_percentage=20
如果置为1，则将当前路径加入到文件key中，以避免可能产生的同文件名的文件key冲突
opcache.use_cwd=1
文件检测周期
revalidate_freq=3600
启用文件缓存时间戳
opcache.validate_timestamps=1

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