The APC cache in PHP details the APC module installation _php Tutorial

Source: Internet
Author: User
Tags apc apc configuration apc module key string
1. Introduction to APC Cache

APC, the full name is alternative PHP cache, the official translation is called "Optional PHP Caching". It provides us with a framework for caching and optimizing PHP's intermediate code. The APC cache is divided into two parts: the system cache and the user data cache.
System cache
It means that APC caches the compiled results of the PHP file's source code and then compares the time stamp with each call. If it does not expire, it is run with the cached intermediate code. The default cache is 3600s (one hour). However, this can still waste a lot of CPU time. Therefore, you can set the system cache to never expire (apc.ttl=0) in php.ini. However, if you do this, you will need to restart the Web server after changing the PHP code. This type of cache is currently used more often.
User Data caching
Caching is read and written by the user using the Apc_store and Apc_fetch functions when writing PHP code. If you have a small amount of data, you can try it. If the amount of data is large, it is better to use a more specialized memory caching scheme like Memcache
Cache key Generation rules
Each slot in the APC cache will have a key,key that is the apc_cache_key_t struct type, except for key-related properties, the key is the generation of the H field. The H field determines which position of this element falls in the slots array. There are different generation rules for the user cache and the system cache. The user cache generates key through the Apc_cache_make_user_key function. The key string passed in by the user relies on the hash function in the PHP kernel (the hash function used by PHP Hashtable: Zend_inline_hash_ Func) to generate an H value.
The system cache generates key through the Apc_cache_make_file_key function. Different scenarios are differentiated by the switch of the APC configuration item Apc.stat. In the case of open, apc.stat= on, the compiled content is automatically recompiled and cached if it is updated. The H value at this point is the added value of the file's device and Inode. In the case of Apc.stat=off, when the file is modified, you must restart the Web server if you want the updated content to take effect. At this point the H value is generated based on the path address of the file, and the path here is the absolute path. Even if you are using a relative path, you will find the PG (include_path) location file to obtain an absolute path, so using an absolute path skips the check and can improve the efficiency of your code.
Adding a cache procedure
In the case of user caches, the Apc_add function is used to add content to the APC cache. If the key parameter is in a string, APC generates a key based on this string, and if the key parameter is an array, the APC traverses the entire array, generating the key. Depending on these key,apc, the _apc_store will be called to store the values in the cache. Because this is a user cache, the cache currently in use is apc_user_cache. The write operation is performed by the Apc_cache_make_user_entry function, whose final call Apc_cache_user_insert performs a traversal query and write operation. In response, the system cache uses Apc_cache_insert to perform write operations, which eventually call _apc_cache_insert.
Whether the user cache or the system cache, the general process is similar, the steps are as follows:
Position the current key in the slots array by finding the remainder operation: cache->slots[key.h% cache->num_slots];
After locating the position in the slots array, iterate through the slot list of the current key, clearing the current slot if there is a key in the slot and a key match to write or the slot expires.
Insert a new slot after the last slot.

2. APC Module installation


First step: Download Php_apc.dll in/PECL.PHP.NET/PACKAGE/APC to correspond with PHP version Php_apc.dll into your ext directory

Step two: Let PHP.ini support the APC expansion module. Then open php.ini join:
Copy the Code code as follows:
apc.rfc1867 = On
Apc.max_file_size = 100M
Upload_max_filesize = 100M
Post_max_size = 100M
The above parameters can be defined by themselves

Step three: Check if PHP APC apc_store apc_fetch PHP APC configuration parameters are supported to interpret the relevant configuration.
Copy the Code code as follows:
Apc.enabled=1 apc.enabled The default value is 1, you can set it to 0 to disable APC. If you set it to 0, also comment out the (this saves memory resources). Once the APC feature is enabled, opcodes to shared memory is cached.
Apc.shm_segments = 1

In summary 1, the best performance can be achieved using the spinlocks lock mechanism.
The 2,APC provides apc.php for monitoring and managing the APC cache. Don't forget to change your administrator name and password
3,APC By default, the shared memory is created by Mmap Anonymous mappings, and the cache objects are stored in this "large" memory space. The shared memory is managed by APC itself
4, we need to adjust the value of Apc.shm_size, Apc.num_files_hints, apc.user_entries_hint by statistics. Until the best
5, okay, I admit that Apc.stat = 0 can achieve better performance. Anything I can do is acceptable.
6,php pre-defined constants, you can use the apc_define_constants () function. However, according to APC developers said PECL HiDef better performance, define it, it is inefficient.
7, Function Apc_store (), for PHP variables such as system settings, the lifecycle is the entire application (from the httpd daemon until the httpd daemon shuts down), using APC is better than memcached. Must not go through the Network Transport Protocol TCP.
8,APC is not suitable for caching frequently changed user data through the function Apc_store (), there are some strange phenomena.


Copy the Code code as follows:
TAR-ZXVF apc-3.1.8.tgz CD APC-3.1.8
./configure--ENABLE-APC--enable-mmap--enable-apc-spinlocks--disable-apc-pthreadmutex--with-php-config=/usr/ Local/php/bin/php-config
sudo make install
Join in/usr/local/php/etc/php.ini
Extension = "";
; APC setting
apc.enabled = 1
Apc.shm_segments = 1
Apc.shm_size = 64M
Apc.optimization = 1
Apc.num_files_hint = 0
Apc.ttl = 0
Apc.gc_ttl = 3600
Apc.cache_by_default = On

Restart Apache or/usr/local/php/sbin/php-fpm restart true techarticle 1, APC cache introduction APC, the full name is alternative PHP cache, the official translation is called "Optional PHP Caching." It provides us with a framework for caching and optimizing PHP's intermediate code. The APC cache is divided into two parts: ...

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