Redis & Memcached for WordPress¶

Install Redis¶

apt install -y redis-server
systemctl enable --now redis

Redis Config¶

/etc/redis/redis.conf

bind 127.0.0.1
port 6379
maxmemory 256mb
maxmemory-policy allkeys-lru
save 900 1
save 300 10
save 60 10000

Redis as WordPress Object Cache¶

Install Redis PHP Extension¶

apt install -y php8.2-redis
systemctl reload php8.2-fpm

Install Redis Object Cache Plugin¶

# Via WP-CLI
wp plugin install redis-cache --activate

# Enable Redis cache
wp redis enable

# Verify
wp redis status

Or manually: Download and copy redis-cache plugin to wp-content/plugins/, then activate.

Add to wp-config.php¶

define('WP_REDIS_HOST', '127.0.0.1');
define('WP_REDIS_PORT', 6379);
define('WP_REDIS_DATABASE', 0);
define('WP_REDIS_TIMEOUT', 1);
define('WP_REDIS_READ_TIMEOUT', 1);

Verify Caching¶

# Check Redis hits/misses
redis-cli info stats | grep keyspace

# Monitor live
redis-cli monitor

# Check WordPress cache stats
wp redis info

Install Memcached¶

apt install -y memcached php8.2-memcache
systemctl enable --now memcached

Memcached Config¶

/etc/memcached.conf

-d
logfile /var/log/memcached.log
-p 11211
-l 127.0.0.1
-m 256
-c 1024

When to Use What¶

Cache	Best For	Pros	Cons
Redis	Object cache, sessions, full-page cache	Persistence, data types, replication	Slightly more RAM
Memcached	Simple key-value cache	Simpler, lower memory overhead	No persistence, no replication

Flush Cache¶

# Redis
redis-cli FLUSHALL

# Memcached
echo "flush_all" | nc -q1 localhost 11211

# WordPress (redis-cache plugin)
wp cache flush

# Redis CLI specific DB
redis-cli -n 0 FLUSHDB

Performance Test¶

# Redis benchmark
redis-benchmark -q -n 1000

# Memcached benchmark
memcached-tool localhost:11211 stats

Monitoring¶

# Redis
redis-cli info stats
redis-cli info memory
redis-cli info keyspace

# Memcached
echo "stats" | nc -q1 localhost 11211

Troubleshooting¶

Symptom	Cause	Fix
Cache not working	PHP extension missing	`apt install php-redis`
Connection refused	Redis not running	`systemctl status redis`
Out of memory	`maxmemory` too low	Increase in redis.conf
Stale cache	TTL too long	Clear cache, reduce TTL