PySpark Lakehouse

6 interview problems on Delta transaction logs, VACUUM, CDC and MERGE, change feeds, time travel and Iceberg partitioning, from easy to hard.

Learn Lakehouse

The Delta transaction log · 8 min read. Commit files, checkpoints and optimistic concurrency: how the _delta_log turns files into a table.
MERGE INTO and upserts · 4 min read. Matched, not-matched and not-matched-by-source clauses, step by step, and the duplicate-source error.
VACUUM and retention · 4 min read. Delete old data files safely without breaking running readers or time travel.
Change Data Feed · 3 min read. Read the row-level inserts, updates and deletes made to a Delta table between two versions.
Time travel and RESTORE · 3 min read. Query or roll back to any earlier version of a table, and what retention does to that promise.
Streaming into Delta tables · 4 min read. Write a stream into a Delta table exactly once, and read a Delta table as a stream.
Constraints and generated columns · 4 min read. NOT NULL and CHECK constraints, generated columns and identity columns in Delta tables.