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BigData / Data Lake Interview questions

What are effective data partitioning strategies in Data Lakes?

Data partitioning is the practice of dividing large datasets into smaller, more manageable segments based on specific column values. Proper partitioning is critical for query performance, cost optimization, and efficient data management in data lakes.

Partitioning works by organizing files into directory structures that enable query engines to skip irrelevant data—a technique called partition pruning or predicate pushdown. For example, partitioning by date allows querying just one day's data instead of scanning petabytes.

Common Partitioning Strategies:

1. Time-Based Partitioning: The most common strategy, organizing data by year, month, day, or hour. This is ideal for append-only datasets like logs, events, transactions, and IoT sensor readings.

/data/events/year=2024/month=01/day=15/*.parquet
/data/logs/dt=2024-01-15/hour=14/*.parquet

2. Category-Based Partitioning: Partition by discrete categorical values like region, product category, customer segment, or status. Useful when queries frequently filter by these dimensions.

3. Hash Partitioning: Distribute data evenly across partitions using a hash function on a high-cardinality column. This prevents hot partitions and ensures balanced processing.

Best Practices:

  • Choose High-Selectivity Columns: Partition by columns frequently used in WHERE clauses
  • Avoid High Cardinality: Don't partition by columns with millions of unique values
  • Balance Partition Size: Target 128MB-1GB per partition file for optimal performance
  • Consider Query Patterns: Partition to match how data will be accessed
  • Limit Partition Depth: 2-4 levels maximum to avoid metadata overhead
What is the benefit of data partitioning?
What is the most common partitioning strategy?

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