Complex Calculated Fields

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Rationale

The VIZYUL™ Complex Calculated Fields performance tuning rule fires for any calculated field with 400 or more characters.

Insight

Consider this, data blends are a powerful feature of tableau desktop.  This feature allows you to design dashboards with various data sources right inside tableau desktop.  Often, data blends are the most convenient means of adding context and richness to data visualizations.

That said, data blends on large tableau data extracts can degrade performance relatively quickly.  This is because data blends force tableau to evaluate matching values between the data sources for each row included in the worksheet.  So if the main (primary – blue check mark) data source used by the worksheet has 20 million rows of data and the blended (secondary – orange check mark) data source has 100 rows, that means tableau desktop has to make 2 billion value comparisons.  Obviously, if a data blend can be avoided in this scenario, this would have an immediately positive impact on performance.

Here are a few alternatives to data blends, when large extracts are involved.

  1. When possible, use data joins at the origin data sources.  Instead of doing a data blend in tableau desktop, use SQL to join multiple tables prior to bringing the data into tableau desktop.
  2. Use queries in Microsoft Access to join multiple tables prior to bringing data into tableau desktop.

Action

  • Consider using data joins outside of tableau desktop or data joins within tableau when using tableau data extracts with 2,000,000 or more rows of data.
  • Consider the additional resources below

Additional Resources

  • Outstanding Tips and Tricks for Calculations by Alan Eldridge from the Drawing with Numbers Blog – http://drawingwithnumbers.artisart.org/wiki/tableau/tricks-miscellaneous-techniques/