I have checked several Mendix applications and a 1GB m2ee.log is not common. Normally this logfiles is not bigger then several MB’s. I’m not aware of a possibility to change the maximum size or set a rollOver-mechanisme. I don’t see any settings available for that in the m2ee yaml configuration.
The log file is available on runtime and also in the modeler environment and will give information about for example the build-in database in modeler or from Mendix 7 and higher if you have multiple versions of the same library in your
userlib, only the latest one will be loaded. The other libraries will be evicted automatically. Eviction information is available in the M2ee log file.
To answer the question why the logfile is that big you can open the logging in example ultra edit and look at the errors.