No, we do not impose any limitation on MySQL database size.
However, we do request that you do not store binary data, such as pictures and images, in your MySQL databases. Databases are meant to kept textual, relational data. High-performance databases like MySQL begin to lose their performance quickly with huge records, such as the ones containing binary data.
If you are storing a large amount of binary data in a database, Rhombic Networks’ reserves the right to call into effect our clause of excessive usage in our terms of service.
If you would like more information about why binary data in relational databases is bad, a good article to read is: Serving Images From A Database.