cache-observability

跟踪缓存命中率、延迟并检测缓存相关问题

SKILL.md

--- frontmatter

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

code

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

code

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