MySQL is a relational database management system (RDBMS) that stores data in tables and uses structured query language (SQL) for database access. In MySQL, you pre-define your database schema based on your requirements and set up rules to govern the relationships between fields in your tables.
If your data structure fits nicely into tables and rows, MySQL will offer you robust and easy interaction with your data. If it's the performance that is your concern, there is a good chance you don't really need MongoDB. Most likely, you just need to index your data properly. If you require SQL or transactions, you'll have to stick with MySQL.
MongoDB stores data in JSON-like documents that can vary in structure. Related information is stored together for fast query access through the MongoDB query language. MongoDB uses dynamic schemas, meaning that you can create records without first defining the structure, such as the fields or the types of their values. You can change the structure of records (which we call documents) simply by adding new fields or deleting existing ones.
If your data seems complex to model in a relational database system, or if you find yourself de-normalizing your database schema you should consider using MongoDB. If you find yourself trying to store serialized arrays or JSON objects, that's a good sign that you are better off MongoDB. If you can't pre-define your schema or you want to store records in the same collection that have different fields, that's another good reason.
Read More.