int vs string in VertiPaq

Hi, pavel118 

The storage space taken by a column in VertiPaq is significantly influenced by its cardinality, which is the number of unique values in the column. If CustomerKey has a higher cardinality than CustomerAlternateKey, it could take up more space despite being numeric. 

Optimizing High Cardinality Columns in VertiPaq - SQLBI

VertiPaq uses dictionary encoding to compress data. For numeric columns, if the range of numbers is large, the dictionary can become quite large. On the other hand, alphanumeric columns with fewer unique values can have smaller dictionaries. While numeric data types generally compress better, this is not always the case if the numeric values are not repetitive or if they span a wide range. Alphanumeric strings that are repetitive can be compressed more efficiently. You can see the folloing link:

Vertipaq optimization and its impact on columnstore compression - Simple Talk

In your case, it seems that CustomerKey might have a higher cardinality or a wider range of values compared to CustomerAlternateKey, leading to more storage space being used. Microsoft's recommendation to convert text to numeric values is generally valid, but specific cases like yours can show different results due to the factors mentioned above.

Based on your information, I create a sample table:

Then create a new calculated column:

CustomerKey = VALUE(MID([CustomerAlternateKey], 3, LEN([CustomerAlternateKey]) - 2))

In DAX Studio, I looked at their data size

In the example, the obvious Int type is smaller than the data size of the string type

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Best Regards

Yongkang Hua

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