The store should save useful length information for Clobs. This allows the length to be found without decoding the whole data stream.
The following thread raised the issue on what information to store, and also contains some background information: http://www.nabble.com/Storing-length-information-for-CLOB-on-disk-tp19197535p19197535.html
The information to store, and the exact format of it, is still to be discussed/determined.
Currently two bytes are set aside for length information, which is inadequate.