How to design a tagging system like tags in Stack Overflow or labels in Jira
Functional requirement :

1. You should be able to get results based on tags.
2. Tags should be auto suggested.
3. What all API's you will expose?
4. Database design / schema design
5. Type of database sql vs no sql
6. What happens when multiple tags are assigned to one ticket?

Performance :

1. How will you scale database?
2. Scale of service?
3. how to solve concurrency issue?

Anyone has good understanding on how these tags works internally? What api's are required and whatdata model etc system like stack overflow is using? Or anyone has any link or pointers to read more about this?