Single table storage (the default storage type) and multiple table storage each have better file size and performance characteristics in different scenarios, so we allow you to choose.

The storage type affects file size because certain types of joins cause data storage redundancy. Previously, Tableau stored the result of the join, so it would store all the redundant data, often resulting in large extract files. If the number of rows after your join is larger than the sum of the rows in your input tables, then your data source is a great candidate for multiple table storage. Joins that are likely to cause data storage redundancy include joins between fact tables and entitlement tables in some row-level security scenarios.

In addition to file size differences, multiple table storage and single table storage can affect extract creation speed and visualization query speed. For single table storage, your source database will perform the join during extract creation. With multiple table storage, however, Tableau Desktop will perform the join inside Tableau's data engine during visualization query time. So, multiple table storage extracts may initially be created faster because they only require copying the individual tables, without requiring a join. On the other hand, multiple table storage extracts might be slower during query time because of the join required at that time.

These performance differences are more noticeable with large amounts of data. If you are working with a large data set, you'll want to experiment with both techniques to determine which gives you the best performance and size benefits.

If you can't decide which to use, stick with the default, single table storage, because multiple table storage has some functional limitations-including no incremental refresh and no extract filters. We plan to address these limitations in future releases.

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Tableau Software Inc. published this content on 03 October 2018 and is solely responsible for the information contained herein. Distributed by Public, unedited and unaltered, on 03 October 2018 19:07:06 UTC