cache-observability

name	cache-observability
description	Track cache hit rates, latency, and detect cache-related issues
triggers	["cache metrics","Redis monitoring","cache hit rate","cache performance"]
priority	2

Cache Observability

Cache is performance-critical. Track hit rate, latency, and evictions.

Key Metrics

Metric	Type	Description
cache.hits	Counter	Successful reads
cache.misses	Counter	Reads that missed
cache.gets.duration	Histogram	GET latency
cache.evictions	Counter	Keys evicted
cache.memory.used	Gauge	Memory consumption

Span Attributes

Attribute	Example	Required
cache.system	redis, memcached	Yes
cache.operation	GET, SET	Yes
cache.hit	true/false	Yes
cache.key_prefix	user:*	Recommended (not full key!)

Hit Rate

hit_rate = cache.hits / (cache.hits + cache.misses)

• Good: >90%
• Concerning: <80% → Check TTL, warming strategy

Issues to Detect

Issue	Detection	Fix
Low hit rate	<80%	Tune TTL, warm cache
Cache stampede	Many misses for same key	Distributed locks
High latency	p99 >10ms	Check network, value size
Memory pressure	memory >90% of max	Eviction policy, sizing

Cache Wrapper Pattern

Before GET: Start timer
After GET:  Record duration, increment hits or misses, set cache.hit on span

Anti-Patterns

• Full keys in metrics → High cardinality, use prefix only
• No eviction monitoring → Can't detect memory pressure
• Ignoring serialization time → Track total time including marshal

References

• references/platforms/{platform}/cache.md