Data Engineering Associate with Databricks Practice Exam

What is the SQL command to vacuum a specified Delta table?

1. DELETE FROM table_name

2. TRUNCATE TABLE table_name

3. VACUUM table_name

4. OPTIMIZE table_name

The correct answer is: VACUUM table_name

The command to vacuum a specified Delta table is accurately identified as VACUUM table_name. This command is essential for managing the data retention and performance of Delta tables. When data is deleted or updated in a Delta Lake table, the old files are not immediately removed but are marked for deletion. The VACUUM command is used to physically delete these files that are no longer needed, which helps reclaim storage space and improve query performance by reducing the amount of data that needs to be scanned during operations. Using VACUUM is particularly important because Delta Lake maintains a transactional log of operations, and if older versions of the data are not vacuumed, they will continue to occupy space. This process can help manage the storage footprint and maintain the efficiency of the data lake over time. The other options, while they are valid SQL commands, do not serve the purpose of cleaning up the files and managing the storage for a Delta table. For instance, deleting data does not remove older versions of it from storage, truncating a table removes all rows but does not manage historical files, and optimizing a table reorganizes its files for better performance but does not delete old data. Thus, the VACUUM command is specifically tailored for the maintenance of Delta tables.