1. Power BI Performance Tips & Tricks
Callum Green /10/2017
Power BI Performance Tips & Tricks

2. Sponsors

3. About me Senior Business Intelligence Consultant
Power BI / Query Editor for 2+ years
Worked in BI for 8 years & Microsoft MCSE
Blog:

4. Agenda Direct Query / Live Connection Import Data Model
File Size & Memory
Query Folding
Report Design

5. Direct Query / Live Connection
Differences?
Direct Query ONLY
Relationships
Change to Import mode
Database
Analysis Services Cube
Relationships are obvious because an AS cube has pre built relationships built by a developer. Relationships are stored in the Power BI Model for Direct Query.
Import – if you go to query editor and enter data, you are prompted to change to import mode
Will now demo the two connection type and show you how you can access Quick Measures (preview feature) – released April 2017

6. Import Data Model – Table Structure
Short, Wide
Tall, Narrow
Remove all fields not used for analysis
Remove relationship ID’s not in use
Exceptions to the rule?
10’s of millions of rows
Pause and explain import mode
A Power BI model is just an AS cube running on your local machine. Uses the vertipaq engine – now know as xvelocity. Which is designed to get up to 10x compression rates – tall/narrow tables compress better in general because of columnar storage
Exception? - Xvelocity (Vertipaq) engine – partitions rows in 1 million chunks and interfere with compression rates , 8 million for tabular

7. Import Data Model – Data Types
Avoid Strings as an ID
Slower performance
Larger data models
Splitting Date & Time
Avoid GUID’s / large text fields
Split date & time – reduces unique records and splitting this into a time and date dimension massively reduces cardinality and improves compressions rates,

8. Import Data Model – Slicers
Effects Dev/User Experience
Issues 2 queries:
Value in the list
Related rows from table
Cross filtering executed across sets of slicers
High Cardinality Slicers = Slower performance

9. Import Data Model - DAX Calculated Column – Every refresh
Measures – Run time
DAX Examples:
FILTER checks every individual row
MIN/MAX scans entire table
Vertipaq Alberto and Marco’s Excel Macro file that connects to Tabular – show them quickly how to get the connection to import cube.

10. Memory File size a rough estimate Check memory usage
Kasper de Jonge Dashboard
Background Data – Amount of data being processed in the background, not necessary for queries in your model that aren’t being worked on don’t necessarily need to be preview any time soon. Let it preview when needed.

11. Demo
I want to show how we can reduce the size of our workbook file, which will help improve general performance and use less memory.
This will lead to showing these two settings:
Time intelligence – power bi setting – ill show you shortly

12. Query Folding (1 of 3) Reduced workloads Faster performance
Increased productivity
Reduced workloads client side
Productivity from a dev perspective

13. Query Folding (2 of 3) Supported Transformations: Filtering (WHERE)
Merge (JOIN)
Aggregates and GROUP BY
Pivot and Unpivot       
Numeric calculations
Simple string manipulation e.g. UPPER
- more specific to SQL

14. Agenda Query Folding (3 of 3) Limitations:
Only some data sources supported
Certain operations/functions prevent folding
Merge Columns
Replace Errors
Buffer() M Function
Certain filters – ‘This Month’
Currently, only a few sources are supported. Shown in previous slide. Stuff like Flat file sources and Excel doesn’t work.
Also, if you do not structure your transformations correctly, query folding may not be applied
As you’ll see in the demo, the SQL written is basically a sub query per PQ step
Auto generated source code
Reduced performance?

15. Agenda Report Design Performance Considerations: Shapes < 20 Maps
Many data points
Custom Visuals
Third Party
Demo
Performance is mainly data and formula related, but bear these in mind.
D3 for third party tools
Although they are now embedded in Power BI Desktop and reliability of the ones in the store are usually reliable

16. Recap Enterprise: Basic self serve Live Connection / Direct Query
Data mashup:
Import Mode
Remove other columns
Query Fold
Monitor:
DAX
File Size
Memory
Split out LC/DQ and Import mode

17. Agenda
Resources
Vertipaq Analyser -
Memory Usage in Power BI -
Dax Studio-

18. Agenda
Questions

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