Iterator<T> snapshottableIterator(long epoch) {
        if (epoch == LATEST_EPOCH) {
            return new CurrentIterator(baseElements());
        } else {
            return new HistoricalIterator(baseElements(), snapshotRegistry.getSnapshot(epoch));
        }
    }
Iterate over the values that existed in the hash table during a specific snapshot.

You can use this iterator even if you are making changes to the map.
The snapshot is immutable and will always show up the same.
server-common/src/main/java/org/apache/kafka/timeline/SnapshottableHashTable.java