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Code RoomJVM CPU jumps after deploy
HardPrep Room Coding #4559

JVM CPU jumps after deploy

On-callReliability & on-callSenior–Staff~40 min

A JVM (G1GC) microservice's CPU jumps from 35% to 95% after a deploy at 13:00, p99 latency doubles, but request throughput is unchanged. GC dashboards show GC CPU% climbing from 5% to 45%, allocation rate up from 200MB/s to 1.8GB/s, and young-GC frequency 5x higher; old-gen occupancy and full-GC count are normal. Heap size and traffic are unchanged. The 13:00 deploy added a new response-enrichment step that builds large intermediate collections per request. Triage and mitigate.

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

0:00 of about 40 min
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