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Vibe codingHardvc-g506
Subject Ai code reviewLevel Senior–Staff~20 minCommon in Algorithms & data structures interviewsIndustries Technology

Question

An AI wrote this Django aggregation that powers an internal analytics dashboard across a multi-tenant fleet. It's correct but reads the entire events table into memory and N+1s on the project FK; on the largest tenant the worker OOMs. Refactor it to scale.

python
def usage_report(org_id):    events = Event.objects.filter(org_id=org_id)  # can be tens of millions    totals = {}    for e in events:        key = e.project.name        # FK lookup per row        totals.setdefault(key, 0)        totals[key] += e.cost_cents    return totals
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