Redis memory high

What does this alert mean?

Redis memory usage exceeds 90% of maxmemory.

Contributing factors

• No TTL set on keys — keys accumulate indefinitely
• Sudden data ingestion spike
• Eviction policy not configured or misconfigured

Affected components

• Redis key eviction behavior
• Application services relying on data persistence in Redis

Expected action

Review eviction policy and key TTLs. If memory is genuinely exhausted, increase maxmemory or add a node.

Metric

Description & unit

Ratio of used memory to configured maxmemory.

Unit: ratio (0–1), alert threshold at 0.9

Threshold rationale

At 90% of maxmemory, Redis is close to either evicting keys aggressively or refusing writes (noeviction).

Normal behavior

For a cache workload, 70–85% is expected. For a persistent store, it should stay well below maxmemory.

Screenshots

Silencing

Silence during bulk data loads when temporary high memory is expected.

Expected frequency

Occasional — typically precedes a Redis down event if not addressed.

Severity guidance

Warning. Escalate if memory reaches 100% and eviction policy is noeviction.

Impacted users

Users of services that store data in Redis.

Things to check to determine severity

• What is the eviction policy? (`redis-cli CONFIG GET maxmemory-policy`)
• Are there keys with no TTL? (`redis-cli INFO keyspace`)

Prometheus query

Dashboards

• Redis Memory — Fill in: dashboard URL

Steps

1. 1Check memory stats: redis-cli INFO memory | grep -E 'used_memory_human|maxmemory_human|mem_fragmentation_ratio'
2. 2Check eviction policy: redis-cli CONFIG GET maxmemory-policy
3. 3Check key distribution and TTLs: redis-cli INFO keyspace
4. 4Find large keys (use carefully on production): redis-cli --bigkeys
5. 5If no eviction policy, set one for cache workloads: redis-cli CONFIG SET maxmemory-policy allkeys-lru

Useful commands

Guidance

Escalate if memory hits 100% with noeviction policy — writes will start failing.

Slack channels

• #infrastructure-oncall — Fill in: channel URL

Alert rule

Tuning notes

The 90% threshold is a ratio of maxmemory — self-normalizing. Only adjust if your eviction policy safely handles higher saturation.