Can you describe common issues in Redis caching systems and their typical solutions (such as cache penetration, cache breakdown, and cache avalanche)? What types of indexes are available in MySQL, and what are the differences between a primary key index and secondary indexes? How do you identify and troubleshoot slow SQL queries in MySQL? What is the purpose of consistent hashing? What advantages does Spring Boot have over the traditional SSM (Spring + Spring MVC + MyBatis) architecture? What key issues should be considered when designing a high-concurrency flash sale (seckill) system?