@Override
        public byte[] getOnly(final DBAccessor accessor, final byte[] key) throws RocksDBException {
            final byte[] valueWithTimestamp = accessor.get(newColumnFamily, key);
            if (valueWithTimestamp != null) {
                return valueWithTimestamp;
            }

            final byte[] plainValue = accessor.get(oldColumnFamily, key);
            if (plainValue != null) {
                return convertToTimestampedFormat(plainValue);
            }

            return null;
        }
A persistent key-(value-timestamp) store based on RocksDB.
streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBTimestampedStore.java