private void openCurrent() {
            if (partitionKey == null) {
                // unpartitioned
                this.currentFile = fileFactory.newOutputFile();
            } else {
                // partitioned
                this.currentFile = fileFactory.newOutputFile(partitionKey);
            }
            this.currentWriter = newWriter(currentFile, partitionKey);
            this.currentRows = 0;
        }
Delete those rows with the given key. It will only write the values of equality fields into
the equality-delete file.

@param key is the projected data whose columns are the same as the equality fields.
inlong-sort/sort-flink/sort-flink-v1.13/sort-connectors/iceberg/src/main/java/org/apache/inlong/sort/iceberg/sink/trick/BaseTaskWriter.java