Design a top-k heavy hitters system
PremiumData pipelineMedium
- Top k
- Heavy hitters
- Count min sketch
Quick answer
This data pipeline interview question asks you to design a top-k heavy hitters system. Aim for a design that moves data from sources to consumers reliably and on time, then explain ingestion, processing, storage and trade-offs. Interviewers want to see how you handle volume, late or bad data and failures along the way.
The problem
Design a top-K heavy hitters system for a video platform: it returns the 100 most-watched videos per country and worldwide over the last hour, day and week, from 5 billion plays a day. The hard parts are counting millions of keys cheaply, sliding windows and fresh lists without scanning everything.
The lists power a Most Watched page and are also used to warm caches. They rank by raw play counts; trend detection and personalisation are separate systems.
What must a top-k heavy hitters system do?
- Top lists: Return the top 100 videos by plays for each country and worldwide.
- Windows: Support the last 1 hour, last 24 hours and last 7 days, each sliding rather than reset at midnight.
How well must it do it?
- Freshness: The 1-hour list updates every minute, the 24-hour list every 5 minutes and the 7-day list every hour.
- Accuracy: The 1-hour list may be approximate within a stated error; the 7-day list must match an exact count.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Top k
- Heavy hitters
- Count min sketch
- Sliding windows
- Stream processing
- Hot keys
How you’ll practise
- Requirements
- Data volume
- Ingestion
- Storage and processing
- Serving and freshness
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any data pipeline design round.
- Clarifies sources, consumers and freshness needs
- Chooses batch, streaming or both with reasons
- Handles late, duplicate and malformed records
- Makes each stage safe to retry
- Explains storage formats and partitioning
- Plans monitoring, backfills and data quality checks
Questions people ask about this interview question
- Which design type is this question?
- It is a data pipeline question. You design a top-k heavy hitters system and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
- What should I cover first?
- Start with the data sources, the consumers and how fresh the data must be. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
Related questions
Updated · Written by the SevyDevy team