Append-only -> Parquet -> bigger Parquet would do the trick. Sadly Parquet is useless for the append-only layer. Feather would work but is quite inefficient with a batch size of 1.
Once you solve enough problems using raw Parquet or Feather or whatever and you end up with something that looks like a DB anyway, so you might as well use a DB.
Once you solve enough problems using raw Parquet or Feather or whatever and you end up with something that looks like a DB anyway, so you might as well use a DB.