SeaTunnel CDC synchronizes data across Oracle, MySQL, and SQL Server using a three-stage process. It begins with a Snapshot phase, taking a full database image while recording the current log position as a low watermark. To accelerate this, SeaTunnel splits large tables into smaller chunks based on primary keys, allowing parallel threads to read historical data efficiently without overwhelming the system.

The Backfill stage handles data consistency, which is critical since the snapshot takes time. Simple mode sends data immediately, accepting duplicates. However, the exactly_once mode uses a memory buffer to merge snapshot data with log changes occurring during the read. This prevents duplicates and ensures the final dataset is clean before sending it downstream.

Finally, the Incremental stage takes over, consuming native database logs like MySQL's binlog or PostgreSQL's WAL. To prevent data loss or repetition between splits, SeaTunnel aligns watermarks by starting from the earliest finished split and dynamically filtering out already processed events. This balance of parallel speed and strict consistency makes it a robust tool for real-time synchronization.