KV Key-value stores → Lesson 3: Redis Data Types → Lesson 3: TTL Data model: A key and its associated value; the data is stored in RAM Strengths: • low response latency • The key is automatically deleted after the TTL expires (the duration is explicitly specified) • predefined structures Limitations: • Not a "source of truth": memory is more expensive and there is less of it • No arbitrary queries on the content of values The rankings are recalculated after every match, and the top positions are updated thousands of times per second.