public boolean isSnapshotReadFinished() {
        return highWatermark != null;
    }
The high watermark is not bull when the split read finished.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/mysql-cdc/src/main/java/org/apache/inlong/sort/cdc/mysql/source/split/MySqlSnapshotSplit.java