The document discusses improvements made to Apache Flink by Alibaba, called Blink. Blink provides a unified SQL layer for both batch and streaming processes. It supports features like UDF/UDTF/UDAGG, stream-stream joins, windowing, and retraction. Blink also improves Flink's runtime to be more reliable and production-quality when running on large YARN clusters. It has a new architecture using a JobMaster and TaskExecutors. Checkpointing and state management were optimized for incremental backups. Blink has been running in production supporting many of Alibaba's critical systems and processing massive amounts of data.