I don't know much about Liquidbase, but I believe it doesn't support accessing both the old and the new schema versions at the same time? (I could be wrong here)

Backfilling happens in batches, we use the PK of the table to update all rows, a trigger is also installed so any new insert/update executes the backfill mechanism to update any new column.

More details can be found here: https://github.com/xataio/pgroll/blob/main/pkg/migrations/ba...