> I like how the time travelling/history is always touted as a feature (which it is), but it really just means the garbage collector/pruning part of the transaction engine is missing. Postgres and other mvcc systems could all be doing this, but they don't.

Postgres actually did tout it as a feature in "THE IMPLEMENTATION OF POSTGRES" by Michael Stonebraker, Lawrence A. Rowe and Michael Hirohama[1] search for "time travel" in the PDF. I added the relevant quotes below for easier access ;)

This was back when PostgreSQL had the postquel language (before SQL was added) there was special syntax to access data at specific points in time:

> The second benefit of a no-overwrite storage manager is the possibility of time travel. As noted earlier, a user can ask a historical query and POSTGRES will automatically return information from the record valid at the correct time.

Quoting the paper again:

> For example to find the salary of Sam at time T one would query:

    retrieve (EMP.salary)
    using EMP [T]
    where EMP.name = "Sam"

> POSTGRES will automatically find the version of Sam’s record valid at the correct time and get the appropriate salary.

[1] - https://dsf.berkeley.edu/papers/ERL-M90-34.pdf