Vector index compaction latency
Your semantic-search service does an ANN lookup in a vector database (HNSW index, ~200M embeddings) before reranking. At 11:30 end-to-end p99 doubled to 900ms; tracing shows the time is entirely in the vector-DB query span, not the embedding model or the reranker. Dashboards: vector-DB CPU is high, the index just finished a large background merge/compaction after a bulk upsert of 20M new vectors this morning, recall@10 dipped slightly, and query node memory is near the cap causing some on-disk index reads. No application deploy. 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 35 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.