Redis and Memcached

Object caches make WordPress and other PHP applications noticeably faster. Commands to check, flush, monitor and debug Redis and Memcached.

15 one-liners: 12 harmless, 1 caution, 2 destructive

redis 13 redis-cli 12 cache 4 keys 4 flush 3 memory 2 memcached 2 nc 2 statistics 2 performance 2

Check the Redis Object Cache status in WordPress

$wp redis status --path=/var/www/vhosts/example.com/httpdocs

Check whether Redis is reachable

$redis-cli -h 127.0.0.1 -p 6379 ping

Connect to Redis over a Unix socket

$redis-cli -s /run/redis/redis-server.sock ping

Count Redis keys by pattern without blocking the server

$redis-cli -n 0 --scan --pattern '*transient*' | wc -l

Count the keys in a Redis database

$redis-cli -n 0 DBSIZE

Find the biggest keys in Redis

$redis-cli -n 0 --bigkeys

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Flush a single Redis database (FLUSHDB)

$redis-cli -n 0 FLUSHDB

Flush all Redis databases (FLUSHALL)

$redis-cli FLUSHALL

Flush Memcached completely (flush_all)

$printf 'flush_all\nquit\n' | nc 127.0.0.1 11211

Query Memcached statistics with netcat

$printf 'stats\nquit\n' | nc 127.0.0.1 11211 | grep -E 'STAT (curr_items|bytes|limit_maxbytes|get_hits|get_misses|evictions|curr_connections) '

Show Redis memory usage and limit

$redis-cli INFO memory | grep -E '^(used_memory_human|used_memory_peak_human|maxmemory_human|maxmemory_policy|mem_fragmentation_ratio):'

Show slow Redis commands (SLOWLOG)

$redis-cli SLOWLOG GET 10

Show the Redis cache hit rate

$redis-cli INFO stats | grep -E '^(keyspace_hits|keyspace_misses|evicted_keys|expired_keys):'

Show used Redis databases and key counts

$redis-cli INFO keyspace

Watch Redis commands live for a short time (MONITOR)

$timeout 10 redis-cli MONITOR