I'll pretend I don't know who Hickey is and just say that I expect a lot of stupid decisions can be made when coming up with "a completely new way of looking or storing data". Some databases (cough...cough...starts with M) shipped their database product with unacknowledged writes as the default, oops. Everyone can make a database.
Now let's dig deeper. The reason I asked what I asked it because given the architecture of Datomic and the claims made, that corner case (excision) would not be trivial or and would have to be implemented as a hack on the side. That is why I asked. In some databases it is easier to do, in that architecture it is hard.
> or only when it's talented programmers working on a database?
Who are these talented programmers? Are you a talented programmer?
Couple of scenarios:
1) A runaway data generator. Somehow you end up confusing milliseconds with seconds and now you start logging 1000x more data than you intended, you leave for the weekend and find your storage is full of junk
2) Sensitive data. Felix has just inserted all the passwords and credit card numbers in the database.