This is a follow up from #17817 where we only expand one data table at a time.

We've noticed though we're still seeing sometimes memory issues for eg a yearly archive where it exceeds 8GB. This archive has 9 levels down of subtables and overall a lot of rows. One thing that could help with memory be in to not load the data of all data tables at once into memory.:

Each data table is then later expanded one at a time.

The only problem with loading the needed data tables on demand would be performance as we'd need to do a lot more select queries to get each "subchildren" data table. Maybe that means we might not want to do this or maybe we can find a compromise somehow.

refs L3-126