I have solved this question by myself.
Finally I found a great post with interesting topic.
How to migrate all data from Redis to MongoDB plese help me
Right now you can't do this without writing an exporter and then using https://github.com/akhoury/nodebb-plugin-import to import the data back.
Can give me some links to know more about this exporter as i am newbie here. please give me simple example of exporter?
@suraj There isn't one at the moment. Is there a need for you to migrate to MongoDB?
Just to let you guys know, we are running this forum on Redis on a tiny VPS with no problems. So unless you're thinking that you'll scale to a few million MAU you shouldn't have to worry - my two cents.
That said, would be nice to have a NodeBB DBAL converter, but currently we do not have any plans for that, perhaps in the near future.
I want to transfer my data to redis to mongodb. is there any api available for it to dump data or migrate. please give me one example?
I am also looking to transfer my db from redis to mongoDB.