Caching Hat-trick: Zend Opcache, Etags and Query Caching

This article explores common PHP caching techniques: Zend Opcache, Expires Headers, and MySQL Query Caching. We'll delve into further strategies in a subsequent article.

Key Advantages:

• Zend Opcache, Expires Headers, and MySQL Query Caching significantly boost PHP application speed by streamlining the request lifecycle.
• Pre-installed in PHP 5.5 , Zend Opcache stores pre-compiled bytecode in shared memory, avoiding repeated script parsing and compilation.
• Expires Headers (Apache/Nginx) leverage browser caching for static assets (images, CSS, JavaScript), reducing server load and improving performance.
• MySQL Query Caching stores parsed SQL queries and their results, accelerating subsequent identical queries and reducing database pressure.

Understanding the PHP Request Lifecycle:

Before diving into caching, let's review the PHP request process:

1. File Retrieval: The PHP file is fetched from the server's filesystem.
2. Lexical Analysis: The code is transformed into tokens for parsing.
3. Parsing: The code is checked for syntax errors.
4. Opcode Generation: Tokens are converted into executable machine code.
5. Execution: The machine code is executed.

Caching techniques optimize performance by bypassing steps 2-4, minimizing resource consumption and improving response times.

Zend Opcache:

Zend Opcache is a readily available performance enhancer for PHP 5.5 and later. Verify installation using php --version (check for "Zend OPcache") or phpinfo().

Enabling Opcache:

Edit your php.ini file, uncomment opcache.enable=1, and restart your PHP service.

For PHP versions prior to 5.5, install using PECL: pecl install zendopcache-beta.

Opcache Configuration (php.ini or /etc/php5/mods-available/opcache.ini):

Key settings:

• opcache.memory_consumption: Shared memory size (MB). Adjust based on server resources and application needs.
• opcache.interned_strings_buffer: Memory for interned strings (MB).
• opcache.max_accelerated_files: Maximum number of cached files.
• opcache.revalidate_freq: Frequency (seconds) to check for file changes (0 for always checking, ideal for development).
• opcache.max_file_size: Exclude large files from caching (bytes).
• opcache.fast_shutdown: Speeds up deconstructors (set to 1).

Use composer require amnuts/opcache-gui and its index.php to monitor Opcache's status and performance.

Expires Headers (Apache):

Apache's mod_expires module enables browser caching of static assets. Enable it using:

sudo a2enmod expires
sudo service apache2 restart

Configure expiration rules in your Apache virtual host configuration:

<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 1 day"
ExpiresByType image/png "access plus 10 days"
ExpiresByType text/css "access plus 25 days"
</IfModule>

(Consult Nginx documentation for Nginx configuration.)

MySQL Query Caching:

For read-heavy applications, MySQL's query cache can dramatically improve performance. Check your MySQL version (mysql --version). For versions 5.6.8 and later, enable it in my.cnf (e.g., /etc/mysql/my.cnf):

# * Query Cache Configuration
query_cache_type             = ON
query_cache_min_res_unit     = 4096
query_cache_limit            = 1M
query_cache_size             = 16M
query_cache_wlock_invalidate = OFF

Adjust settings based on your server's capacity and update frequency. Monitor cache usage with SHOW STATUS LIKE "qcache%";.

Query Cache Considerations:

• Only works with SELECT queries.
• Queries must be identical for cache hits.
• Only deterministic queries are cacheable.
• Table updates invalidate the cache.

Conclusion:

This article introduced fundamental PHP caching strategies. Part 2 will explore advanced techniques like Varnish, Memcached, and PHP caching libraries.

Frequently Asked Questions (FAQs): (These are already answered within the main text, so no need to repeat them here.)

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