I am coding a web portal which stores a lot user data and later on maybe documents. In the meantime I use MySQL with many relations. I have read much about NoSQL and find that it is an interesting topic.
Is MongoDB or CouchDB ready to fully replace MySQL? Would something change in the usage of Doctrine in my application?
Sure, lots of people are storing their entire data set in MongoDB instead of MySQL and they are doing fine.
But I do not think that is the correct question. The key questions are really the following:
MongoDB is a tool like many others and it does not solve all problems. In my experience, most systems are best implemented with some mix of databases. That would means something like MongoDB for some data and SQL for other data.