redis-operations

# Skill: Redis Operations > **Expertise:** Redis memory management, eviction, persistence (RDB+AOF), Redis Sentinel, Redis Cluster, K8s Redis (Bitnami/Spotahome operator). ## When to load When investigating Redis memory pressure, configuring persistence, debugging eviction, or setting up Redis HA. ## Health Check Commands ```bash # Connect to Redis redis-cli -h redis-master -p 6379 -a $REDIS_PASSWORD # Server info overview redis-cli INFO server | grep -E "redis_version|uptime|tcp_port" redis-cli INFO memory | grep -E "used_memory_human|used_memory_peak_human|mem_fragmentation_ratio|maxmemory" redis-cli INFO stats | grep -E "total_commands_processed|rejected_connections|evicted_keys" redis-cli INFO keyspace # databases with key counts + expires # Real-time monitoring (ops/sec per command) redis-cli --stat # 1-second interval stats redis-cli MONITOR # log every command (NEVER in production for long — high overhead) # Slow log (commands over threshold) redis-cli CONFIG SET slowlog-log-slower-than 10000 # 10ms threshold redis-cli SLOWLOG GET 20 # last 20 slow commands redis-cli SLOWLOG LEN redis-cli SLOWLOG RESET ``` ## Memory Management ```bash # Check memory usage breakdown redis-cli MEMORY DOCTOR # health analysis + recommendations redis-cli MEMORY STATS # detailed breakdown redis-cli MEMORY USAGE <key> # bytes used by a specific key # Find big keys (scan, not KEYS — non-blocking) redis-cli --bigkeys # sample-based big key finder redis-cli --memkeys # memory usage per key (sample) # Memory fragmentation: ratio > 1.5 = fragmentation, < 1.0 = swap redis-cli INFO memory | grep mem_fragmentation_ratio # Defragment memory online (Redis 4+) redis-cli CONFIG SET activedefrag yes redis-cli CONFIG SET active-defrag-threshold-lower 10 # start at 10% frag ``` ## Eviction Policy ```bash # View current policy redis-cli CONFIG GET maxmemory-policy # Set eviction policy # allkeys-lru — evict any key by LRU (general-purpose cache) # volatile-lru — evict only keys with TTL by LRU (mixed TTL/no-TTL use) # allkeys-lfu — evict by LFU (access frequency, Redis 4+) — best for skewed access # noeviction — return OOM error when full (use for session store / queue — no silent data loss) redis-cli CONFIG SET maxmemory-policy allkeys-lru # Set memory limit redis-cli CONFIG SET maxmemory 4gb # Persist config to redis.conf redis-cli CONFIG REWRITE ``` ## Persistence Configuration ```bash # RDB snapshot (point-in-time) redis-cli CONFIG SET save "3600 1 300 100 60 10000" # save if N changes in M seconds # AOF (append-only file — more durable) redis-cli CONFIG SET appendonly yes redis-cli CONFIG SET appendfsync everysec # fsync every second (balance: perf vs durability) # appendfsync always — safest (every write) — high IOPS # appendfsync everysec — recommended — max 1s data loss # appendfsync no — fastest — OS decides when to flush # AOF rewrite (compaction) redis-cli BGREWRITEAOF # Manual RDB snapshot redis-cli BGSAVE redis-cli LASTSAVE # Unix timestamp of last successful save # Best practice: enable both RDB + AOF # RDB for fast restarts, AOF for minimal data loss ``` ## Redis Sentinel (HA) ```bash # Check Sentinel status redis-cli -p 26379 SENTINEL masters redis-cli -p 26379 SENTINEL slaves mymaster redis-cli -p 26379 SENTINEL sentinels mymaster # Force failover (test) redis-cli -p 26379 SENTINEL failover mymaster # sentinel.conf (minimal) sentinel monitor mymaster redis-master 6379 2 # quorum=2 sentinel down-after-milliseconds mymaster 5000 sentinel failover-timeout mymaster 60000 sentinel parallel-syncs mymaster 1 ``` ## K8s Redis (Bitnami Helm) ```yaml # values.yaml (Redis Sentinel mode) architecture: replication auth: enabled: true existingSecret: redis-password existingSecretPasswordKey: password master: resources: requests: { memory: 256Mi, cpu: 100m } limits: { memory: 1Gi, cpu: 500m } persistence: enabled: true size: 8Gi replica: replicaCount: 2 sentinel: enabled: true resources: requests: { memory: 64Mi, cpu: 50m } limits: { memory: 128Mi, cpu: 100m } ``` ```bash # K8s Redis health check kubectl exec -it redis-master-0 -n cache -- redis-cli ping kubectl exec -it redis-master-0 -n cache -- redis-cli INFO replication # Force failover in K8s kubectl exec -it redis-master-0 -n cache -- \ redis-cli -p 26379 SENTINEL failover mymaster # Check pod resources vs actual memory usage kubectl top pods -n cache -l app.kubernetes.io/name=redis ``` ## Common Issues & Fixes | Symptom | Diagnosis | Fix | |:---|:---|:---| | `OOM command not allowed` | maxmemory reached + `noeviction` | Increase maxmemory or change eviction policy | | High eviction rate | Cache too small or no TTLs on keys | Increase maxmemory; audit keys without TTL | | `WRONGTYPE` errors | Key type mismatch in application | Flush specific key: `DEL <key>` | | Connection refused | maxclients reached | `CONFIG SET maxclients 10000` | | Slow KEYS command | Running `KEYS *` in production | Replace with SCAN; never use KEYS in prod | | AOF growing unbounded | Auto-rewrite threshold too high | Lower `auto-aof-rewrite-percentage` to 50 |