KNOWLEDGE BASE

Out of Memory Error When Blending Few Million Rows


Published: 13 May 2013
Last Modified Date: 22 Jul 2016

Issue

Data blending on a field with over 300,000 unique values causes an out of memory error. 

Environment

  • Tableau Desktop
  • Data blending when linking field contains more than 300,000 unique values

Resolution

Create a single connection that includes all the columns from multiple tables by defining all joins between tables as part of the data connection.

Cause

Data blending is not a database join engine, but an in-memory method for visualizing data from different data sources. Using data blending as a substitute for database level joins will result in out of memory errors because Tableau Desktop is forced to do the computations rather than the underlying database.

Additional Information

Data blending is best suited for post-aggregate queries instead of individual detail row joins. For example, data blending can be used to examine the sum of sales across time from one data source and blend it with sum of sales quotes across time from another data source. Data blending matches the resulting rows of the two queries together based on the values of time instead of joining the individual atomic data then doing aggregations on it.
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