Slim CI with state comparison in dbt - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of dbt slim CI with state comparison command

What is the output of the following dbt command when using slim CI with state comparison?

dbt build --state path/to/previous_run --select state:modified

Assume the previous run had models A, B, and C, and only model B was modified.

dbt

dbt build --state path/to/previous_run --select state:modified

A Builds only model B and its dependencies.

B Builds all models A, B, and C regardless of changes.

C Builds only models A and C, skipping B.

D Builds no models because state comparison disables builds.

💡 Hint

Think about what 'state:modified' selects in dbt.

The --select state:modified flag tells dbt to build only models that have changed since the last run, plus their dependencies. Since only model B was modified, only B and its dependencies are built.

❓ data_output

intermediate

Number of models built with slim CI and state comparison

Given a dbt project with 10 models where 3 models were modified since the last run, how many models will be built using:

dbt build --state path/to/previous_run --select state:modified

Assuming no dependencies outside these 3 models.

dbt

dbt build --state path/to/previous_run --select state:modified

A 10 models

B 3 models

C 0 models

D Depends on the number of dependencies of the modified models

💡 Hint

Consider if dependencies affect the count here.

Since the 3 modified models have no dependencies, only those 3 models are built.

🔧 Debug

advanced

Identify the error in slim CI state comparison usage

What error will occur when running this command?

dbt build --state path/to/previous_run --select state:modified+ --exclude state:modified

dbt

dbt build --state path/to/previous_run --select state:modified+ --exclude state:modified

A Error: Missing required --target flag.

B No error, builds all models.

C Error: Conflicting selection and exclusion of the same state selector.

D Warning: Ignoring --exclude flag.

💡 Hint

Think about what happens when you select and exclude the same models.

The command tries to select models modified and their children, but excludes the modified models themselves, causing a conflict in selection logic.

🚀 Application

advanced

Applying slim CI with state comparison in a CI pipeline

You want to optimize your CI pipeline to only run tests on changed models and their dependencies. Which dbt command should you use?

A dbt test --state path/to/previous_run --exclude state:modified+

B dbt test --select state:modified

C dbt test --exclude state:modified

D dbt test --state path/to/previous_run --select state:modified+

💡 Hint

Consider how to include dependencies of modified models.

The state:modified+ selector includes modified models and their children, ensuring tests run on all affected models.

🧠 Conceptual

expert

Understanding limitations of slim CI with state comparison

Which of the following is a limitation of using slim CI with state comparison in dbt?

A It may miss models affected by indirect dependency changes if state files are outdated.

B It always rebuilds the entire project regardless of changes.

C It cannot be used with incremental models.

D It requires manual specification of changed models.

💡 Hint

Think about how state files affect detection of changes.

If the state files are not up to date, indirect changes in dependencies might not be detected, causing some models to be skipped.

Practice

1. What is the main purpose of using --state and --select state:modified in dbt's Slim CI?

easy

A. To delete all previous run artifacts

B. To run all models regardless of changes

C. To create a backup of the current state

D. To run only the models that have changed since the last run

Solution

1. Step 1: Understand the role of --state

   The --state flag points dbt to the previous run's artifacts, allowing comparison between runs.

2. Step 2: Understand --select state:modified

   This selects only the models that have changed compared to the previous state, skipping unchanged models.

3. Final Answer:

   To run only the models that have changed since the last run -> Option D

4. Quick Check:

   Slim CI runs changed models only [OK]

Hint: Slim CI runs changed models only, saving time [OK]

Common Mistakes:

• Thinking it runs all models every time
• Confusing state with backup or deletion
• Assuming it runs unchanged models too

2. Which of the following is the correct syntax to run dbt with Slim CI to select only modified models?

easy

A. dbt run --state path/to/previous --select all

B. dbt run --select state:modified --state path/to/previous

C. dbt run --select modified:state --state=previous_path

D. dbt run --state-modified --select path/to/previous

Solution

1. Step 1: Identify correct flag usage

   The correct flags are --state to specify previous run artifacts and --select state:modified to select changed models.

2. Step 2: Match syntax to flags

   dbt run --select state:modified --state path/to/previous correctly uses --select state:modified and --state path/to/previous in proper order and format.

3. Final Answer:

   dbt run --select state:modified --state path/to/previous -> Option B

4. Quick Check:

   Correct flags and order [OK]

Hint: Use --state then --select state:modified for Slim CI [OK]

Common Mistakes:

• Mixing up flag names or order
• Using incorrect flag syntax
• Selecting all models instead of modified

3. Given the following dbt command run twice with changes in model 'sales':

dbt run --state ./target/run1 --select state:modified
# After modifying 'sales' model
 dbt run --state ./target/run1 --select state:modified

What will the second command do?

medium

A. Run only the 'sales' model because it was modified

B. Run all models again ignoring state

C. Run no models because nothing changed

D. Throw an error due to incorrect state path

Solution

1. Step 1: Understand the first run

   The first command runs all models and saves state in ./target/run1.

2. Step 2: Analyze the second run with modification

   The second command compares current state to ./target/run1 and runs only models that changed, here 'sales'.

3. Final Answer:

   Run only the 'sales' model because it was modified -> Option A

4. Quick Check:

   Modified model runs only [OK]

Hint: Second run runs only changed models using saved state [OK]

Common Mistakes:

• Assuming all models run again
• Thinking no models run if only one changed
• Confusing state path usage

4. You run dbt run --state ./previous_run --select state:modified but get an error saying the state path is invalid. What is the most likely cause?

medium

A. The path './previous_run' does not contain valid dbt run artifacts

B. You forgot to add '--select all' flag

C. The '--state' flag must come after '--select'

D. The command requires '--full-refresh' to work

Solution

1. Step 1: Check the meaning of the error

   An invalid state path error means dbt cannot find or read previous run artifacts at the given path.

2. Step 2: Evaluate other options

   Flags order or missing '--select all' do not cause this error; '--full-refresh' is unrelated.

3. Final Answer:

   The path './previous_run' does not contain valid dbt run artifacts -> Option A

4. Quick Check:

   Invalid state path means missing artifacts [OK]

Hint: Ensure state path has valid previous run artifacts [OK]

Common Mistakes:

• Assuming flag order causes error
• Thinking '--full-refresh' fixes state errors
• Forgetting to generate previous run artifacts

5. You want to optimize your CI pipeline using Slim CI. Your previous run artifacts are stored in ./target/previous. You have models 'A', 'B', and 'C'. Only 'B' was modified. Which command will run only the modified model and also run its dependent models?

hard

A. dbt run --state ./target/previous --select state:modified

B. dbt run --state ./target/previous --select state:modified --full-refresh

C. dbt run --state ./target/previous --select state:modified+

D. dbt run --select state:modified --state ./target/previous --exclude B

Solution

1. Step 1: Understand the '+' operator in selection

   The '+' after state:modified selects modified models plus their dependents.

2. Step 2: Match command to requirement

   dbt run --state ./target/previous --select state:modified+ uses state:modified+ with correct --state path, running 'B' and its dependents.

3. Step 3: Evaluate other options

   dbt run --state ./target/previous --select state:modified runs only modified models without dependents; C adds unnecessary full-refresh; D excludes 'B' incorrectly.

4. Final Answer:

   dbt run --state ./target/previous --select state:modified+ -> Option C

5. Quick Check:

   Modified plus dependents run [OK]

Hint: Add '+' to include dependents of modified models [OK]

Common Mistakes:

• Not including dependents with '+'
• Using --full-refresh unnecessarily
• Excluding modified models by mistake