@Override
    public void start() {
        this.started = true;
        super.start();
    }
The map to store the start time of each checkpoint.
inlong-sort/sort-flink/sort-flink-v1.15/sort-connectors/pulsar/src/main/java/org/apache/inlong/sort/pulsar/source/reader/PulsarUnorderedSourceReader.java