How to Optimize Power Query Performance: Referenced Queries vs Output Tables
Question details
The user needs to improve data refresh speeds by understanding the performance differences between using referenced queries and loading data directly to worksheet output tables.
- Product
- Microsoft Excel Power Query
- Device & OS
- not provided
- Scenario
- Optimizing data transformation pipelines and reducing execution times during Refresh All operations.
- Observed behavior
- Referencing a staging query causes upstream steps to be evaluated multiple times for dependent queries, and loading to a worksheet table does not always reduce the Refresh All duration.
Before restructuring your queries, evaluate your data source type to check if it natively supports query folding, as this heavily impacts referenced query performance.
Preserve Query Folding in Staging Queries
Maintain query folding in a primary staging query to offload processing to the source database, making downstream references more efficient.
When you use referenced queries, Power Query may re-evaluate the upstream steps for each dependent query. If query folding is active, this workload is pushed to the backend data source, greatly improving performance.
In Power Query Editor, connect to your main data source and apply only the transformations supported by the source.
Right-click the last applied step in the 'Applied Steps' pane and check if 'View Native Query' is clickable to ensure the query is folding.
Right-click the staging query in the Queries pane and select 'Reference' to create dependent queries without breaking the fold.
Adjust Cache and Background Refresh Settings
Modify your workbook's refresh settings to prevent unnecessary data reloading during development and operations.
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Frequently Asked Questions
Why does 'Refresh All' take so long with multiple referenced queries?
During 'Refresh All', Power Query often re-evaluates the upstream steps of your staging query for every single dependent query. If query folding isn't active, this multiplies the processing time locally.
Does loading an intermediate query to a worksheet table improve performance?
Loading to a worksheet table only improves performance if you treat that table as a materialized snapshot and avoid refreshing the source connection every time. It offers no performance benefit during a standard 'Refresh All'.
How do I speed up Power Query previews while editing?
You can speed up the Power Query Editor by disabling background refresh. Go to Query Options > Data Load and uncheck the background download option, which forces the editor to use cached preview data.
