Hi Hans-Juergen,
I did not investigate further, but I believe that memory problems may
happen with db:create which do not occur using commands.
this is due to the fact that db:create (as an XQuery expression) must adhere to the basic principles of our XQuery Udate module. Insertion sequences have to be cached (for everything that happens within a query), whereas with the commands insertion data is inserted on-the-fly. In this case the command offers the benefit of speed and memory. DB:create increases coding convenience by i.e. allowing to create and fill db's during the same query. So the choice depends on the use case.
However, if you experience severe limitations with db:create regarding memory consumption it'd make sense to take a closer look at it.
Hope this helps, cheers, Lukas