@Override
        public long startEpoch() {
            return startEpoch;
        }
This is a hash set which can be snapshotted.
<br>
See {@link SnapshottableHashTable} for more details about the implementation.
<br>
This class requires external synchronization.  Null values are not supported.

@param <T>   The value type of the set.
server-common/src/main/java/org/apache/kafka/timeline/TimelineHashSet.java