How does Apache Beam handle out-of-order data?

Apache Beam provides a mechanism called watermark to handle out-of-order data. Watermark is a timestamp that can be used to determine if the data is ready for processing. When processing out-of-order data, Beam uses the watermark to determine if the data has arrived in the correct sequence.

In Apache Beam, data processing order can be controlled by specifying a window. By defining windows and watermarks, Beam ensures that data arrives within the correct time frame, guaranteeing data processing correctness.

Furthermore, Beam also offers some built-in transformation functions (such as WithTimestamps and WithAllowedLateness) to assist users in handling out-of-order data more effectively. Through these transformation functions, users can customize the timestamps of data and the allowed delay time to better manage out-of-order data.