midNoSQL
What are Secondary Indexes in NoSQL?
Updated Apr 28, 2026
Short answer
An index that allows querying data based on attributes other than the primary key, though often with performance trade-offs.
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?