Reducing model size in Power BI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main benefit of reducing the size of a Power BI data model?

Reducing model size improves report performance and decreases load times, making dashboards faster and smoother to use.

beginner

Name one common technique to reduce the size of a Power BI model.

Removing unused columns and tables helps reduce the model size by keeping only necessary data.

intermediate

How does using numeric keys instead of text keys help reduce model size?

Numeric keys use less memory than text keys because numbers are stored more efficiently than strings.

intermediate

What is the effect of disabling 'Auto Date/Time' in Power BI on model size?

Disabling 'Auto Date/Time' prevents Power BI from creating hidden date tables, which reduces model size.

beginner

Why is it better to filter data at the source rather than loading all data into Power BI?

Filtering data at the source reduces the amount of data loaded, which lowers model size and improves performance.

Which of the following reduces Power BI model size the most?

A Removing unused columns

B Adding more visuals

C Increasing report page count

D Using complex DAX measures

Removing unused columns reduces the data stored, directly lowering model size.

What happens if you keep 'Auto Date/Time' enabled in Power BI?

A Model size decreases

B Model size increases due to hidden date tables

C No effect on model size

D Data refresh slows down

Auto Date/Time creates hidden date tables for each date column, increasing model size.

Why should you replace text keys with numeric keys in your data model?

A Text keys reduce model size

B Text keys are faster

C Numeric keys slow down reports

D Numeric keys use less memory

Numeric keys are stored more efficiently, reducing memory usage and model size.

Filtering data at the source before loading into Power BI helps by:

A Reducing model size

B Increasing model size

C Adding more columns

D Slowing down refresh

Filtering data reduces the amount of data loaded, lowering model size.

Which is NOT a good practice to reduce model size?

A Removing unused columns

B Disabling Auto Date/Time

C Loading all historical data without filtering

D Replacing text keys with numeric keys

Loading all data without filtering increases model size unnecessarily.

Explain three ways to reduce the size of a Power BI data model.

Think about what data you really need and how Power BI stores date columns.

Why is reducing model size important for Power BI reports?

Consider how a smaller suitcase is easier to carry.

Practice

1. Which of the following is a simple way to reduce the size of a Power BI data model?

easy

A. Import duplicate tables for safety

B. Add more calculated columns

C. Remove columns that are not used in reports

D. Enable auto date/time for all tables

Solution

1. Step 1: Identify unused data

   Unused columns take up space without adding value to reports.

2. Step 2: Remove unused columns

   Deleting these columns reduces the data model size and improves performance.

3. Final Answer:

   Remove columns that are not used in reports -> Option C

4. Quick Check:

   Removing unused data reduces model size [OK]

Hint: Delete unused columns to shrink model size quickly [OK]

Common Mistakes:

• Keeping all columns regardless of usage
• Adding calculated columns unnecessarily
• Enabling auto date/time increases model size

2. Which syntax correctly disables the auto date/time feature in Power BI using the Options menu?

easy

A. Go to File > Options > Data Load > uncheck 'Auto Date/Time'

B. Use DAX: DISABLE AUTODATE()

C. Right-click table > Disable Auto Date

D. In Power Query, remove date columns

Solution

1. Step 1: Locate auto date/time setting

   It is found under File > Options > Data Load in Power BI Desktop.

2. Step 2: Disable the feature

   Uncheck the 'Auto Date/Time' option to stop Power BI from creating hidden date tables.

3. Final Answer:

   Go to File > Options > Data Load > uncheck 'Auto Date/Time' -> Option A

4. Quick Check:

   Disabling auto date/time reduces hidden data [OK]

Hint: Disable auto date/time in Options to reduce hidden tables [OK]

Common Mistakes:

• Trying to disable auto date/time with DAX
• Removing date columns instead of disabling feature
• Looking for option in Power Query instead of Options menu

3. Given a table with a column 'SalesAmount' stored as Decimal Number, which change reduces model size the most without losing data precision?

medium

A. Keep 'SalesAmount' as Decimal Number

B. Change 'SalesAmount' data type to Whole Number

C. Change 'SalesAmount' data type to Text

D. Change 'SalesAmount' data type to Fixed Decimal Number

Solution

1. Step 1: Understand data types and size

   Decimal Number uses more space; Fixed Decimal Number stores decimals efficiently.

2. Step 2: Choose Fixed Decimal Number

   This type reduces size while keeping decimal precision, unlike Whole Number or Text.

3. Final Answer:

   Change 'SalesAmount' data type to Fixed Decimal Number -> Option D

4. Quick Check:

   Fixed Decimal Number reduces size with decimals [OK]

Hint: Use Fixed Decimal Number for decimals to save space [OK]

Common Mistakes:

• Switching to Whole Number loses decimal data
• Using Text increases model size
• Keeping Decimal Number wastes space

4. You notice your Power BI model size is large. You disabled auto date/time but the size did not reduce. What is the likely cause?

medium

A. You need to refresh the data after disabling auto date/time

B. There are many unused columns still in the model

C. Auto date/time disables only for new reports, not existing ones

D. The model size never changes after disabling features

Solution

1. Step 1: Check for unused columns

   Unused columns consume space even if auto date/time is off.

2. Step 2: Remove unused columns

   Deleting these columns will reduce model size effectively.

3. Final Answer:

   There are many unused columns still in the model -> Option B

4. Quick Check:

   Unused columns keep model large despite disabling features [OK]

Hint: Remove unused columns if disabling features doesn't reduce size [OK]

Common Mistakes:

• Assuming refresh fixes size without removing data
• Thinking auto date/time disables only for new reports
• Believing model size never changes

5. You have a large sales dataset with many columns, including detailed customer info not used in reports. You want to reduce model size and improve report speed. Which combination of actions is best?

hard

A. Remove unused customer columns, disable auto date/time, and change numeric columns to appropriate data types

B. Keep all columns, enable auto date/time, and add calculated columns for analysis

C. Remove only unused columns, keep auto date/time enabled, and leave data types as is

D. Disable auto date/time only, keep all columns and data types unchanged

Solution

1. Step 1: Remove unused columns

   Deleting unused customer info reduces unnecessary data in the model.

2. Step 2: Disable auto date/time

   This stops Power BI from adding hidden date tables that increase size.

3. Step 3: Optimize numeric data types

   Changing numeric columns to smaller or fixed decimal types saves space without losing precision.

4. Final Answer:

   Remove unused customer columns, disable auto date/time, and change numeric columns to appropriate data types -> Option A

5. Quick Check:

   Combining removal, disabling, and data type optimization reduces size best [OK]

Hint: Combine removing unused data, disabling features, and data type tuning [OK]

Common Mistakes:

• Keeping all data and enabling auto date/time
• Only removing columns without disabling features
• Ignoring data type optimization