MySQL is a very tested and capable relational database server based on SQL, which supports various database engines including InnoDB. InnoDB is a transactional, locking database engine with strong data integrity features designed for mission critical workloads that demand concurrency, integrity and data protection.
With MySQL 8, MySQL moves closer to standardization and interoperability with competing database engines and newer frameworks and methodologies. I'm testing MySQL 8 in various high-traffic workloads now, and refactoring other projects for compatibility. I have thus far run into only one breaking change in the default configuration, which requires only minor procedural but not structural rewrites of some queries related to grouping.