Do you have any custom code active during that import?
Which version of CQ5?
Yes Jorg we are running our custom code for migrating assets. Its a service we are calling it in CQ scheduler. We controlled this scheduler such a way that if any workflow instance are in running state it wont start new job. At present by doing this it should not trigeer more than 1000 DAM update asset and 1000 Metadata write back workflows.
we are using Adobe CQ, Version 188.8.131.5220220 Service Pack 2
Can you check what files are open? On Linux you can use "lsof -p <pid of CQ5 java process>".
The only thing I can imagine is a massive creation of temporary files or a very high rate of new nodes, which are indexed, but no time left to consolidate the index segments. The rest of the repository itself is rather stable in terms of open files.