arrays, hashmap, concurrency, thread, databases springboot

1. What happens when every column is indexed in an sql table 2. Why a prototype bean cannot be destroyed in spring boot 3. Why memory management in java is important. JMM 4. What is difference between streams pipeline and other method 5. What is spring cloud config how it communicate with others 6. How security is done in spring cloud config 7. When is the microservice is not a good approach 8. Why is spring boot starter important These are the question I remember.