Design an ads event reporting system
Quick Overview
This question evaluates a candidate's ability to design scalable, reliable event ingestion and analytics systems, testing competencies in distributed data pipelines, stream and batch aggregation, storage partitioning, API/query design, and correctness concerns such as deduplication and handling late or out-of-order events.
Pinterest
Jan 22, 2026, 12:00 AM
Software Engineer
Onsite
System Design
13
0
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Design an ads event reporting system that collects user-ad interaction events and serves aggregated metrics.
Requirements
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Ingest events
from multiple platforms (web/mobile/server):
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impression,click,conversion(extendable to more event types)
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Event schema
includes at minimum:
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event_id(unique),timestamp(event time),ingest_time,user_id(or anonymized id),ad_id,campaign_id,event_type, plus optional attributes (geo, device, app version).
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Reporting queries
:
- Time-series aggregates (e.g., per minute/hour/day)
- Group-by dimensions: campaign/ad, geo, device
- User cohort / segment partitioning (e.g., users grouped by country, or an offline-defined cohort id)
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Correctness and reliability
:
- Handle duplicates (retries), out-of-order and late events
- Support backfills and reprocessing
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Latency goals
(assume):
- Near-real-time dashboards (e.g., p95 < 1–5 minutes)
- Accurate daily finalized reports
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Scale goals
(assume):
- 50k–500k events/sec peak
- Store raw events for 30–90 days; aggregates longer
Deliverables
Propose an end-to-end architecture, storage layout/partitioning, aggregation strategy, APIs for querying, and how you ensure deduplication + correctness with late events. Include key tradeoffs.
Solution
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