TiDB is an open source NewSQL database released under the Apache 2.0 License. Because it speaks the MySQL protocol, your existing applications will be able to connect to it using any MySQL connector, and most SQL functionality remains identical (joins, subqueries, transactions, etc.). Step under the covers, however, and thereare differences.
If your architecture is based on MySQL with Read Replicas, you’ll see things work a little bit differently with TiDB. In this post, I’ll go through the top five key differences I’ve found between TiDB and MySQL. With MySQL, it is common to scale-out via replication.
Typically you will have one MySQL master with many slaves, each with a complete copy of the data. Using either application logic or technology like ProxySQL, queries are routed to the appropriate server (offloading queries from the master to slaves whenever it is safe to do so).
Source: opensource.com