How Would You Partition?

Concepts covered: paPartitioning

Partitioning is how you turn a 10 TB table scan into a 50 GB targeted read. The interviewer wants to hear your thought process for choosing a partition key - not just "partition by date." Choosing a Partition Key Start with how the data is queried. If 95% of queries filter on event_date, that's your partition key. If analysts always filter by region first, consider region. The goal is pruning: the query engine should eliminate partitions before reading any data. A table partitioned by date with 3 years of daily partitions has ~1,095 partitions - a query for one day reads 0.09% of the data. Cardinality Analysis The partition key's cardinality determines how many directories you create. Too few partitions (e.g., by continent - 7 values) means each partition is massive and you get minim

About This Interactive Section

This section is part of the The Storage Question: Intermediate lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.