Databricks interview questions

Beginner

Control plane vs data plane, Delta basics, and bronze / silver / gold.

Senior

Unity Catalog grants, MERGE file rewrites, OPTIMIZE, Photon fallbacks.

Scenarios

Workspace vs VPC, job-cluster bills, small-file MERGE, DLT expectations.

Databricks Architecture

Control plane vs data plane: workspace in Databricks SaaS, clusters and files in your cloud.

Compute types

All-purpose clusters, job clusters that terminate, and SQL warehouses for BI.

SQL Warehouses

Serverless vs Pro vs Classic, the caches behind a fast dashboard, and why size and cluster count are different dials.

Unity Catalog

Three-level namespace, governed storage, and how permissions attach to catalogs, schemas, and tables.

Delta Lake

ACID transactions on object storage: the _delta_log, Parquet data files, time travel, and OPTIMIZE.

Time Travel & VACUUM

Read an old version from the commit log, RESTORE as a new forward commit, and the VACUUM that ends time travel.

Medallion Architecture

Bronze keeps the raw files. Silver is typed and joined. Gold is the metric table BI queries.

Delta MERGE

Upserts a change set into Delta by rewriting only the files the join key touches.

OPTIMIZE & Clustering

Compact tiny files, Z-ORDER for skipping, and liquid clustering on write.

Liquid Clustering

CLUSTER BY replaces rigid directories and full Z-ORDER rewrites — and lets you change the keys later.

Auto Loader

Incremental ingest from object storage with notifications, checkpoint, and schema evolution.

Delta Live Tables

Declare medallion tables and expectations. DLT infers the graph and stops downstream on failure.

Workflows

A job is a DAG of tasks with real parallelism, per-task retries, and a repair run that skips what already passed.

Photon

Native vectorized engine for eligible operators — and the UDF fallback that cancels it.