What is a Rapidly changing dimension (RCD) or Fast growing dimension?
The Rapidly changing dimension (RCD) is a dimension which has attributes where values will be getting changed often.
How to handle the RCD type table?
We have three major types of solutions to handle the slowly changing dimensions (SCD). By creating mini dimension the rapidly changing dimension can be handled.
Structure of Junk dimension:
Typically it has a surrogate key and rapidly changing columns.
Steps to form a Mini dimension:
- Identify the rapidly changing attributes
- Create new dimension table for above-identified attribute column along with surrogate key
- Remove the columns from parent dimension
- Create a reference key in the fact table for this mini dimension
- Develop ETL jobs to load
Advantage of having this mini dimension:
The main advantage of this dimension is the data changes can be loaded as part fact table itself. No need of worrying about capturing changes in dimension level.
For example, employee table has a field for appraisal rating attribute where the value changes very often.
Now the employee dimension is a fast growing dimension, as said it will be handled by creating mini-dimension.
A new dimension will be created with rating column along with the surrogate key. The possible default values will be inserted/loaded into this dimension.
The rating column will be removed from Employee dimension. The surrogate key will be linked with Salary fact table.