All 7 Caching Strategies in PHP questions
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What is the difference between file based caching and in memory caching using tools like Redis or Memcached? What is the difference between page caching, query caching, and object caching, and when should each be used? How does cache invalidation work, and why is deciding when to clear a cache often considered one of the harder problems in caching? What caching strategies are commonly used in Laravel applications, and how does the Cache facade simplify working with different cache backends? How does the cache stampede problem occur, and what strategies help prevent it in a high traffic PHP application? How should a team design a comprehensive multi layer caching strategy for a high traffic PHP application, combining OPcache, application level caching, and a CDN?
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PHP › Caching Strategies in PHP

What is caching in a PHP application, and why is it important for improving performance?

Beginner

Answer

Caching means temporarily storing the result of an expensive operation, such as a slow database query or a complex calculation, so that future requests needing the same data can retrieve it quickly from the cache instead of repeating the expensive operation, which significantly improves application response times and reduces load on backend resources like your database.
if ($cache->has('top_products')) {
    $products = $cache->get('top_products');
} else {
    $products = $database->getTopProducts();
    $cache->set('top_products', $products, 3600);
}
Real-world example An online store caches its list of best selling products for one hour, so the expensive database query calculating those rankings only runs once per hour instead of on every single page load from every visitor.

Common follow-ups: What types of data are good candidates for caching, and what types are not?;How do you decide on an appropriate cache expiration time?

Performance Optimization & OPcache;PDO & Databases
All 7 Caching Strategies in PHP questions