How would you debug production issues related to Aggregation Pipeline?

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Quick interview answer

Debug Aggregation Pipeline by confirming blast radius, checking lag/error metrics, grabbing profiles/traces, then mitigating before deep root-cause. Use Aggregation Pipeline as the core idea. Example shape: Monthly revenue by category: $match date range, $unwind items, $group by category sum price..

Detailed answer

Production debug playbook for Aggregation Pipeline: 1) Stabilize: rate-limit, shed load, or roll back if users are hurting. 2) Orient: dashboards for latency, errors, saturation tied to Aggregation Pipeline. 3) Evidence: traces, profiles, logs with correlation IDs. 4) Hypothesize + prove with a safe experiment. 5) Fix + add a regression test/alert so it cannot silently return. Watch for: $lookup before $match blowing working set; missing allowDiskUse on huge sorts. Parent context: Use Aggregation Pipeline as the core idea. Example shape: Monthly revenue by category: $match date range, $unwind items, $group by category sum price..

Full explanation

Interviewers score structured incident thinking: mitigate → measure → root cause → prevent. Stages: $match → $group → $sort → $lookup (join) → $project. Pipeline runs server-side; push filters early in $match for index use.

Follow-up questions

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Parent context — Aggregation Pipeline

Use Aggregation Pipeline as the core idea. Example shape: Monthly revenue by category: $match date range, $unwind items, $group by category sum price..

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