本番Redis監視:2026年ガイド

Redis is fast enough that teams ship it with default monitoring and forget about it for years. Then one Saturday it’s slow and you have ten minutes to identify why — out of > 200 fields in INFO. This post gives you a working set of probes for Redis production.

The five monitoring surfaces

• INFO: 13 sections, ~200 fields. Scraped at 1Hz it’s your primary feed.
• SLOWLOG: command-level slow log. Tune length + threshold; otherwise the default 128 entries is useless.
• LATENCY: subsystem-level latency events. Detects fork/AOF/expire-cycle pauses INFO can’t.
• CLIENT LIST: who’s connected, their input/output buffer sizes. Catches runaway pipelines.
• --bigkeys / --hotkeys: sampled scans for working-set anomalies. Run weekly, not at incident time.

INFO: what to actually scrape

You don’t need 200 fields. The 14 that predict everything:

SLOWLOG: tune it once and you have a record

Defaults are 10ms threshold and 128-entry ring buffer. On a busy instance the 128 entries cycle in seconds — useless. Set:

# Capture commands slower than 1ms; keep 1024 of them
CONFIG SET slowlog-log-slower-than 1000
CONFIG SET slowlog-max-len 1024

# Read the most recent N
SLOWLOG GET 50

# Reset after analysis
SLOWLOG RESET

LATENCY monitor: catches what SLOWLOG can’t

Different beast. SLOWLOG records commands; LATENCY records events — fast-command, fork, aof-stat, expire-cycle. Enable with CONFIG SET latency-monitor-threshold 100; query with LATENCY HISTORY fork.

A common production incident: AOF rewrite forks, fork takes 1.5s on a 30 GB instance, every command during that 1.5s sees the latency. SLOWLOG shows 1000s of slow commands but no obvious cause; LATENCY shows the single fork event that’s the actual story.

Memory fragmentation: the silent killer

Redis allocates with jemalloc. Long-lived workloads with mixed key sizes fragment over weeks until used_memory_rss is 2× used_memory and you OOM your host. Two early-warning signals:

• mem_fragmentation_ratio drift > 1.4 sustained for 24h.
• active_defrag_running = 1 most of the time means defrag can’t keep up; raise active-defrag-cycle-max.

Replication and cluster monitoring

For Sentinel: alert on +sdown and +odown events. For Cluster:

• Alert on cluster_state != ok immediately.
• Track cluster_slots_assigned; should equal 16384 always.
• Watch cluster_known_nodes; an unexpected drop means a node was forgotten.

Eight alerts every Redis deployment should ship with

• memory_used / maxmemory > 80% for 5m
• mem_fragmentation_ratio > 1.5 for 1h
• evicted_keys delta > 0 for instances that should not be evicting
• master_link_status = down for 10s on a replica
• latest_fork_usec > 500000 (bg-saves are pausing the world)
• blocked_clients > 50 sustained
• connected_clients trending up > 10% / day
• cluster_state != ok (immediate)

FAQ