Why Caching Matters in PHP
Understand cache hit/miss, TTL, and when caching helps vs hurts.
Why Caching Matters in PHP is a free PHP Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the PHP Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
The Performance Problem
Every uncached web request may involve: routing, authentication, database queries, template rendering, and possibly external API calls. This stack can easily take 100-500ms+.
What Caching Does
Caching stores the result of an expensive operation. On subsequent requests, the cached result is returned instantly without re-running the operation.
Cache Hit vs Miss
A cache hit occurs when the requested key exists and is valid in the cache — fast, no work needed. A cache miss occurs when the key is absent or expired — triggers the original computation.
TTL (Time To Live)
The TTL determines how long a cached value remains valid before being discarded. Set it based on how frequently the underlying data changes.
Cache Invalidation
One of the hardest problems in computing. When source data changes, the cached version must be deleted or updated to prevent serving stale data.
What to Cache
Good candidates: expensive DB queries, computed reports, external API responses, rendered HTML fragments, authentication tokens, session data.
What NOT to Cache
Do not cache: user-specific real-time data, data that changes more often than the TTL, security tokens (beyond their session), or large binary blobs (use CDN for those).
Cache Storage Types
In-process (APC/OPcache), distributed in-memory (Redis/Memcached), on-disk, database. Each trades off speed, persistence, and cluster-sharing capabilities.
Cache-Aside Pattern
The most common pattern: check cache → miss → fetch from DB → store in cache → return. On data change, invalidate the cache key.
<?php
$key = "user:{$id}";
$user = $cache->get($key);
if ($user === null) {
$user = User::find($id);
$cache->set($key, $user, 300); // 5 min TTL
}
return $user;Laravel Cache Facade
Laravel provides a unified cache API with multiple driver backends.
<?php
$value = Cache::remember("stats", 3600, fn () => DB::table("orders")->count());
// If not cached, runs the closure and caches the result for 1 hourCache Stampede
A cache stampede (dogpile) occurs when many requests hit a cold cache simultaneously, all performing the expensive operation at once. Mitigate with locks or probabilistic early expiry.
Summary
Caching is essential for scalable PHP applications. Identify expensive operations, choose an appropriate TTL, store results in a fast backend (Redis/Memcached), and invalidate on data changes.
Quick Check
What is a cache hit?
Frequently asked questions
Is the “Why Caching Matters in PHP” lesson free?
Yes — the full text of “Why Caching Matters in PHP” is free to read here on the web, and the PHP Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the PHP Academy course, upgrade to CoddyKit PRO.
What will I learn in “Why Caching Matters in PHP”?
Understand cache hit/miss, TTL, and when caching helps vs hurts. You practise PHP Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start PHP Academy?
No prior experience is required. PHP Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Why Caching Matters in PHP” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this PHP Academy lesson?
Yes. Every PHP Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Why Caching Matters in PHP
- Redis as a PHP Cache Backend
- Memcached for Session and Object Caching
- Cache Invalidation Patterns