byte[] addPrefix(final byte[] key) {
            final byte[] keyWithPrefix = new byte[prefix.length + key.length];
            System.arraycopy(prefix, 0, keyWithPrefix, 0, prefix.length);
            System.arraycopy(key, 0, keyWithPrefix, prefix.length, key.length);
            return keyWithPrefix;
        }
Manages translation between raw key and the key to be stored into the physical store.
The key for the physical store is the raw key prepended with a fixed-length prefix.
streams/src/main/java/org/apache/kafka/streams/state/internals/LogicalKeyValueSegment.java