What are DAU, MAU and the stickiness ratio?
Assesses fundamental understanding of Data Analysis & BI conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
DAU is daily active users, the number of unique users who perform a meaningful action in a day. MAU is the same over a month. The action must be defined consistently: a login may not be meaningful for a content app, while a read or post is.
Stickiness is DAU divided by MAU, the share of monthly users who return on any given day. A high ratio means frequent habitual use. Social and messaging apps often exceed 50 percent, while e-commerce is typically much lower.
SELECT COUNT(DISTINCT CASE WHEN day = current_date THEN user_id END) AS dau,
COUNT(DISTINCT user_id) AS mau
FROM activity
WHERE day >= current_date - INTERVAL '30 days';
Watch for definitional drift and time zones, which can distort daily boundaries. Pair these with retention curves: DAU/MAU shows frequency, retention shows whether users return at all.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.