private void updateTierData(int prevSize) {
        Iterator<Snapshot> iterator = snapshotRegistry.reverseIterator();
        if (iterator.hasNext()) {
            Snapshot snapshot = iterator.next();
            HashTier<T> tier = snapshot.getDelta(SnapshottableHashTable.this);
            if (tier == null) {
                tier = new HashTier<>(prevSize);
                snapshot.setDelta(SnapshottableHashTable.this, tier);
            }
        }
    }
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