Interview › Databases & Caching
How would you debug rising latency on a service that depends on Redis and RDS together?
Databases & Caching · Advanced level
Answer
To debug latency involving both Redis and RDS, I break the path into cache hit/miss, Redis latency, DB query time, connection wait, and app processing, then correlate hit ratio, Redis metrics, RDS DB load, and top SQL.
Technical explanation
First determine whether Redis is slow, cache misses increased, or RDS is slow independently.
Break request latency into cache time, hit/miss, DB time, connection wait, and app time.
Correlate deploy markers with cache hit ratio, Redis latency, RDS DB load, and top SQL.
Hands-on example
Triage graph:
service p95/p99 latency
Redis hit ratio and evictions
Redis command latency
RDS CPU, connections, DB load
Performance Insights top SQL
If hit ratio drops and RDS load rises, investigate TTL, invalidation, warmup, or eviction.
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