...by Daniel Szego
"Simplicity is the ultimate sophistication."
Leonardo da Vinci

Saturday, July 28, 2018

Data retention policy and multi-hash Blockchain

As we have seen in our previous blog, there is a possibility to build up a multihash blockchain system, where some of the hashes are reseted regularly. Such a structure provides the possibility to define different variables on the blockchain with different retention policies, or with different memories. There might be a system that contains several different variables with several different retention policies, like:
- classical hash pointers without reset going back to the genesis block are the real variables of the system providing real immutability. 
- variables controlled by hash pointers with regularly reset have a retention time between [N/2 - N] to the system, as older values can be practically forgotten without effecting the consistency of the blockchain. 
- there can not only one, but several different level of variables, with several different sets of retention policies, like storing the value for a year, for 3 years, or for forever. 

One question must be still answered: what should happen if the two variables are combined but they have different retention policies. As a general rule, we can say that variables with big retention time can always influence variables with small retention time. Unfortunately, it is not true in the other direction, if a small retention time value influences a big retention time value, the retention policy might be compromised. 

Another idea might be to implement the actual retention time configuration on chain, meaning that a common on.chain consensus might do some reconfiguration on-the-fly, without re-initializing the whole chain.