Someone told me about the fact that 3 to 4 conversion will fail on join tables that contains invalid records (as in: one or both of the referred object does not exists). In theory this should never happen but we know that sometimes this happens. However I can't find this kind of conversion remarks on the Moving from 3 to 4 guide. So my question is: where can I find this kind of details? Are there more undocumented 'musts knows'?
This problem has been solved since Mendix 4.1.1, see the release notes:
Ticket 13760: Fixed not-null
constraint violation database
exceptions while migrating from Mendix
3 to 4 in case of some database
I am not sure where you could find it, but for one you need to keep in mind that during the conversion you are going to need a lot of space. Because id's are handelled differently in 4 all database id's will be converted and this process takes up quite a bit of disk space.