Redis and Memcached are fast caching systems that store data in memory (RAM). Instead of hitting the database (MySQL) every time, frequently needed data is kept in RAM, dramatically speeding up the site. Almost mandatory for high-traffic sites.
The problem: the DB is queried every time
A typical site fetches data from MySQL on every page load. 1000 users at once โ 1000 identical queries. MySQL slows down, the server heats up. Solution: get the answer once and store it in cache.
Memcached โ simple and fast
Stores only "key-value". Very simple, very fast. RAM only โ data is lost when the server shuts down (but it's cache). Ideal for simple page caching, session storage.
Redis โ powerful and versatile
More capabilities: lists, hash, set, sorted set. Disk persistence is possible. Pub/Sub, atomic operations. Modern projects often choose Redis.
Which to choose?
1) Need a simple cache โ Memcached is enough. 2) Complex structures, persistence, queues, real-time โ Redis. 3) Most projects now prefer Redis for its versatility.
In WordPress
The Redis Object Cache plugin + Redis on the server. DB queries drop by 50-80%. On heavy sites like WooCommerce, page loads speed up 2-3x.
In Laravel
Laravel supports Redis natively. Cache, session, queue, broadcasting โ all via Redis. CACHE_DRIVER=redis in .env.
Session storage
When using multiple servers (load balancing), sessions must be centralized in Redis/Memcached.
Cache strategies
1) Cache-aside: check cache first, if missing fetch from DB and write to cache. 2) TTL: an expiry for each entry. 3) Invalidation: clear cache when data changes.
Installation (Ubuntu)
Redis: apt install redis-server. Memcached: apt install memcached. PHP extension: php-redis or php-memcached.
Sayt.uz practice
Redis can be installed on Sayt.uz VPS and dedicated plans. On high-traffic client sites, Redis object cache noticeably reduces DB load.