Answer: OPTIMIZE

## Explanation In Databricks Delta Lake, the `OPTIMIZE` command is used to compact small files into larger files to improve query performance. Here's why: 1. **OPTIMIZE**: This command performs file compaction (also known as bin-packing) on Delta tables. It merges small files into larger ones, which improves read performance by reducing the number of files that need to be read during queries. 2. **Why other options are incorrect**: - **REDUCE**: Not a valid Delta Lake command for file compaction - **COMPACTION**: While conceptually related, this is not the actual command name in Delta Lake - **REPARTITION**: This is a Spark transformation that redistributes data across partitions, but it doesn't specifically compact existing small files in a Delta table - **VACUUM**: This command removes old files that are no longer referenced by the Delta table (files older than the retention period), but it doesn't compact small files 3. **How to use OPTIMIZE**: ```sql OPTIMIZE table_name ``` Or with Z-ordering: ```sql OPTIMIZE table_name ZORDER BY column_name ``` 4. **Benefits**: - Reduces the number of files to read - Improves query performance - Can be combined with Z-ordering for better data skipping The `OPTIMIZE` command is specifically designed for this purpose in Delta Lake, making it the correct choice for compacting small files to improve performance.

Author: Keng Suppaseth