midNoSQL
What is a TTL (Time-To-Live) index?
Updated Apr 28, 2026
Short answer
A feature that automatically removes documents from a collection after a certain amount of time or at a specific clock time.
Deep explanation
Mid-level NoSQL expertise involves understanding how to scale. Sharding is the primary mechanism for horizontal growth. Choosing a 'Shard Key' is the most critical decision: a poor choice leads to 'Hot Shards' where one machine does all the work while others stay idle.
Real-world example
Designing a social media feed where data is denormalized and stored by UserID so that fetching a feed requires only one read operation.
Common mistakes
- Selecting a low-cardinality shard key (like 'Gender' or 'ActiveStatus') which limits scaling potential.
Follow-up questions
- What is the difference between a Partition Key and a Sort Key?
- How does a Gossip Protocol work in NoSQL?