Quote from: PremiumCodeX on November 27, 2016, 10:50:31 AM

It depends on the use-case then because in some DBs there are frequent delete operations. But I agree that most DBs are not like that so the possibility is worth to take into consideration.

For blockchains (whose very purpose is to be a non-mutating structure) the "deletes" are only re-orgs (which although not that uncommon are generally not very large delete operations as most re-orgs are only one or two blocks deep) and depending upon how things are structured (such as if the structure of the chain itself is separated from the content of the blocks) would not need to involve much data.

Quote from: PremiumCodeX on November 27, 2016, 10:50:31 AM

The question is how much it would increase the necessary space and the issue of SRP because even though rollbacks are infrequent operations, when they need them they usually need them ASAP.

A "true rollback" (which as I said isn't being used by an major RBDMS that I am aware of) would actually be much faster than any other method (i.e. you either are going to have to issue update queries to act as though things are being unwound or restore an earlier backup which you'd then have to perform a partial log restore from).

Understand also that even if deletes involve appending the data to the log you would still be able to truncate the log for "checkpoints" (at which point any of that extra wasted space is recovered).