@qwerty Are you freakin' serious or punking us? If basics such as this are beyond you then you have absolutely no business deploying server based anything on the Internet. Much less a juicy target for crackers like a forum. Seriously irresponsible. Your name/reputation will be crap once your site is cracked and your users forever hate you. If this sounds harsh, it is because it is meant to. Moderator was being polite.
Found the solution, importing too much topics in a single category hangs the nodebb, import some data than move it to some temporary category. Thasn import remaining data, meanwhile delete mongodb import Garbaze in using these mongo commands
But keep in mind this will also delete the history of import will result in duplicate categories get imported or the posts, to prevent this keep writing post ids and category ids which you imported and delete them from the old database.