Can you explain the difference between optimistic and pessimistic locking? In what scenarios would you employ each?

LeetCode #146 - LRU Cache\nDesign and implement a data structure that allows you to add key-value pairs and retrieve the value of a given key. If the key does not exist, return -1. If the cache reaches its capacity, it should invalidate the least recently used item before inserting a new item.\nInput: An integer capacity and a list of operations in the format ['put(key, value)', 'get(key)', ...]\nOutput: Return the result of get operations in order.\nConstraints: 1 <= capacity <= 3000 and all keys are unique.

Describe a time when you contributed to improving a system's performance. What tools and methods did you use to identify and solve the performance bottlenecks?