Answer: JSON

In Delta Lake tables, the transaction log, known as the DeltaLog, utilizes JSON files to record metadata about changes to the table. This includes transactions like adding, deleting, or updating data, enabling Delta Lake to offer ACID properties. While the actual data is stored in Parquet files, the transaction log's use of JSON is crucial for tracking the history of changes. - **JSON (JavaScript Object Notation)**: The DeltaLog's choice for recording transactions. - **Parquet**: Used for storing the table's data, not the transaction log. - **Delta**: Refers to the table format, not the transaction log's file format. - **Hive-specific format**: Delta Lake operates independently of Hive. - **Both, Parquet and JSON**: Incorrect because Parquet is for data storage, and JSON is for the transaction log. For further reading, consult the [Delta Lake documentation](https://docs.databricks.com/delta/index.html) and [this blog post](https://www.databricks.com/blog/2019/08/21/diving-into-delta-lake-unpacking-the-transaction-log.html).

Author: LeetQuiz Editorial Team