Slowly changing dimensions (SCDs) are a common challenge in data management, especially in big data frameworks. SCDs refer to the changes that occur over time in the attributes of data elements. Handling SCDs effectively is crucial for maintaining accurate and up-to-date data in big data environments. In this blog post, we will explore some techniques for handling SCDs in big data frameworks.

1. Type 1 - Overwrite the Old Data

One approach to handling SCDs is to overwrite the old data with the new values. This is known as the “Type 1” technique. With this method, when a change occurs in an attribute, the existing record is updated with the new value, and the old value is lost. This approach is simple and efficient but lacks the ability to track historical changes.

Example code in SQL:

UPDATE table_name 
SET attribute = new_value 
WHERE id = record_id;

2. Type 2 - Add New Records

Another technique for handling SCDs is to add new records for each change that occurs. This is known as the “Type 2” technique. With this method, a new record is inserted into the system with the updated attribute values. The old record is flagged as inactive or historical. This approach allows for tracking the history of changes but can result in a large number of records in the system.

Example code in SQL:

INSERT INTO table_name (id, attribute, start_date, end_date, active_flag) 
VALUES (new_record_id, new_value, current_date, NULL, true);

UPDATE table_name 
SET end_date = current_date, active_flag = false 
WHERE id = old_record_id;

Conclusion

Handling slowly changing dimensions in big data frameworks requires careful consideration. The choice of technique depends on factors such as the need for historical data, performance requirements, and data volume. Type 1 and Type 2 techniques offer different trade-offs in terms of simplicity, efficiency, and tracking historical changes. Understanding these techniques enables data engineers to make informed decisions when designing data systems that can effectively handle SCDs.

#bigdata #SCD #dimensionmanagement