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Databricks Certified Data Engineer Professional

Databricks DE Pro Cheat Sheet

Databricks DE Pro Tests Production Pipeline Judgement Under Constraints — Not Syntax Recall

A new nine-section version went live on 9 October 2026, replacing the ten-section exam. Often two options would run; the right one meets the stated latency, cost, privacy or correctness constraint.

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Among the harder certs
Avg: Not published by Databricks
Pass: 750 / 1000
Most candidates understand Databricks Certified Data Engineer Professional concepts — and still fail. This exam tests how you apply knowledge under pressure.

Data Engineer Professional Domain Map (9 Oct 2026 version)

Sixty scored questions in 120 minutes, mostly scenarios with short Python or SQL fragments. Unlike the associate exam, it assumes you know the tools and tests trade-offs: out-of-order CDC, stateful streaming limits, GDPR erasure, cross-organisation sharing, and diagnosing the actual bottleneck before scaling compute.

  1. 01
    Developing Code for Data Processing (23%) — bundles, serverless dependencies, pandas UDFs, AUTO CDC, watermarks, foreachBatch, testing
  2. 02
    Cost & Performance Optimization (15%) — Predictive Optimization, liquid clustering, deletion vectors, Change Data Feed, query profile
  3. 03
    Data Ingestion & Acquisition (12%) — Kafka, Iceberg targets, Lakeflow Connect CDC, OpenSharing, Clean Rooms, federation
  4. 04
    Data Manipulation (12%) — window functions, VARIANT, ai_query and AI functions, expectations and quarantine
  5. 05
    Monitoring and Alerting (10%) — system tables, event_log, Databricks SDK, alerts, duration thresholds
  6. 06
    Debugging and Deploying (10%) — Spark UI, repair runs, bundle targets and modes, Git folders, service principals
  7. 07
    Ensuring Data Security and Compliance (8%) — ABAC with governed tags, pseudonymisation, erasure with REORG PURGE and VACUUM
  8. 08
    Data Governance (5%) — tags vs comments, BROWSE, inheritance, no DENY in Unity Catalog
  9. 09
    Data Modeling (5%) — grain, partitioning vs clustering, compaction, materialized vs metric views

Wrong instinct vs correct approach

Two companies must compute customer overlap, and neither may see the other's raw records
✕ Wrong instinct

Share both customer tables with each other through OpenSharing

✓ Correct approach

Any share exposes rows to the recipient. A Clean Room lets both parties run approved notebooks on combined data and returns only agreed outputs. Without privacy limits, D2D sharing by metastore ID suits Databricks recipients and avoids token management.

A nightly heavy transformation reads a large table from an external PostgreSQL database
✕ Wrong instinct

Query it every night through a Lakehouse Federation foreign catalog

✓ Correct approach

Federation re-reads the source over the network on every run and loads the production database. Repeated heavy work should be ingested, ideally with Lakeflow Connect CDC once logical replication is enabled, keeping federation for occasional queries.

One task in a twelve-task job fails on a bad parameter after upstream tasks already wrote data
✕ Wrong instinct

Fix the parameter and click Run now

✓ Correct approach

A full rerun repeats successful tasks and may duplicate writes. Use a repair run, which reruns only the failed task and its dependants, with a parameter override supplying the corrected value.

Hundreds of tables, including future ones, contain columns tagged as PII that must be masked
✕ Wrong instinct

Build a masked view over each sensitive table

✓ Correct approach

Views do not scale and leave base tables exposed. Define an ABAC policy at catalog or schema level that matches a governed tag and applies a column mask, so newly tagged columns are covered automatically.

Know these cold

  • ▸ Streaming tables process each row once; materialized views reflect upstream updates and deletes
  • ▸ Expectation default keeps bad rows; expect_or_drop removes them; expect_or_fail stops the update
  • ▸ Use row_number, not rank, when exactly one row per key is required
  • ▸ try_variant_get returns NULL on bad casts; variant_get errors and fails the query
  • ▸ Persist ai_query output to a table; inside a view it bills model calls on every read
  • ▸ Liquid clustering takes up to four changeable keys; never combine it with partitioning
  • ▸ Deletion vectors speed DELETE, UPDATE and MERGE, not reads; ZORDER is not incremental
  • ▸ Change Data Feed records changes only after enablement; drop update_preimage rows for current values
  • ▸ Duration threshold notifies and lets the run continue; a timeout cancels it
  • ▸ Unity Catalog has no DENY; grant lower in the tree, and use BROWSE for discovery

Can you answer these without checking your notes?

In this scenario: "Two companies must compute customer overlap, and neither may see the other's raw records" — what should you do first?
Any share exposes rows to the recipient. A Clean Room lets both parties run approved notebooks on combined data and returns only agreed outputs. Without privacy limits, D2D sharing by metastore ID suits Databricks recipients and avoids token management.
In this scenario: "A nightly heavy transformation reads a large table from an external PostgreSQL database" — what should you do first?
Federation re-reads the source over the network on every run and loads the production database. Repeated heavy work should be ingested, ideally with Lakeflow Connect CDC once logical replication is enabled, keeping federation for occasional queries.
In this scenario: "One task in a twelve-task job fails on a bad parameter after upstream tasks already wrote data" — what should you do first?
A full rerun repeats successful tasks and may duplicate writes. Use a repair run, which reruns only the failed task and its dependants, with a parameter override supplying the corrected value.

Common Exam Mistakes — What candidates get wrong

Sequencing AUTO CDC on ingestion time instead of source change time

SEQUENCE BY must use the source's change timestamp or sequence number, so late-arriving events cannot overwrite newer values. stored_as_scd_type = 2 adds __START_AT and __END_AT history columns; a hand-written MERGE in foreachBatch handles neither ordering nor history.

Treating DELETE as a completed GDPR erasure on a Delta table

Old versions and files still hold the rows. With deletion vectors enabled, run REORG TABLE ... APPLY (PURGE) to rewrite files, then VACUUM past the retention threshold, seven days by default, so time travel can no longer reach the data.

Running a stateful streaming aggregation with no watermark

Without withWatermark on the event-time column, state for windows and dropDuplicates is never dropped, so memory grows until the query fails; adding memory only delays it. Each query also needs its own checkpoint location, because sharing one corrupts offsets.

Fixing serverless library conflicts with init scripts or cluster libraries

Serverless notebooks, jobs and pipelines never run init scripts. Dependencies belong in the serverless environment specification or the bundle's environment definition, which is also where version pins resolve conflicts consistently across dev, staging and prod targets.

Reading cost from the Jobs UI or data quality from the audit log

Spend comes from system.billing.usage joined to list_prices; who-did-what comes from system.access.audit; expectation results live in the pipeline event_log flow_progress events. System tables land with delay, so they cannot drive second-level alerting.

Resources to help you pass Databricks Data Engineer Professional on your first attempt

Check whether your pipeline trade-off calls match the new nine-section professional exam.