What is the output mode of Spark?

The output mode of Spark refers to how streaming data is written to an external storage system in a Spark Streaming program. Common output modes include:

1. Append mode: Only add new data to the end of existing data.
2. Update mode: Refresh existing data, only keeping the latest status.
3. Complete mode: Rewrite the entire results table into an external storage system, including all data.

Different output modes are suitable for different scenarios, and appropriate output modes can be selected based on the requirements to achieve data writing and updating operations.