Hunting for the holy grail of a blockchain solution with multiply retention policy, we might as well consider the extended version of the multi-hash blockchain structure. There are different transactions or different pieces of data with different retention policies hashed together with a double hashing structure where regularly one of the hashes will be reseted realizing practically a forgetting functionality on the chain. On top data from a longer retention data can be hashed together with data from a smaller retention period realizing a kind of hash-matrix that can be seen on the picture bellow:
The structure is pretty much straightforward at the first stage, as the immutable structure has only one hash chains, however the exact implementation will be questionable at later stages. The problem that in the long retention policy structure there are actually two independent hash-chains, which are of course contain the same set of transaction and data but they differ on the hash value. It is a little bit questionable which of these chain should be hashed together with the next one. Some of the possibilities might be:
- Both hash chain is from the long retention policy chain is hashed together with the short retention policy one. This structure however might cause the exponential explosion of the different hash values, as at the case of short retention policy there might be the possibility that we have to manage 4 chains. There might be some simplification of the reset time of the different policies can divide each other and they are well scheduled.
- Only the data or transaction of the previous retention policy chain is copied into the next phase, without the information of the previous hash values. It can however decrease the reliability of the whole structure.
- Both hash chain is from the long retention policy chain is hashed together with the short retention policy one. This structure however might cause the exponential explosion of the different hash values, as at the case of short retention policy there might be the possibility that we have to manage 4 chains. There might be some simplification of the reset time of the different policies can divide each other and they are well scheduled.
- Only the data or transaction of the previous retention policy chain is copied into the next phase, without the information of the previous hash values. It can however decrease the reliability of the whole structure.
