You have a Fabric tenant that contains a semantic model named model1.

We are optimizing model1 in Fabric with two very large columns:

TransactionKey

Cardinality: 2.5 billion

Size: 160 GB

Description: surrogate key for SalesTransaction fact table.

SaleDateTime

Cardinality: 6.8 million

Size: 120 GB

Description: datetime (to the second) of when a sale occurred.

Goal:

Reduce model size.

Improve refresh performance (Import mode).

Ensure datetime values remain available.

Analysis per column

1. TransactionKey (very high cardinality)

Surrogate keys with extremely high cardinality do not add analytical value in a semantic model because they are not used in measures or grouping.

They take a lot of memory and reduce refresh performance.

Best practice: remove the column from the model.

2. SaleDateTime

Needed to analyze transactions by date and time.

However, storing the full datetime at second-level cardinality causes huge memory usage.

To optimize: split the column into Date and Time columns.

Reduces cardinality significantly.

Preserves full datetime information (can recombine if needed).

Improves compression and refresh speed.

Final Answer:

TransactionKey: Remove the column.

SaleDateTime: Split the column.