We built MongoDB from our own experiences building large scale, high availability, robust systems. We didn’t start from scratch, we really tried to figure out what was broken, and tackle that. MongoDB is that if you take MySql, and change the data model from relational to document based, you get a lot of great features: embedded docs for speed, manageability, agile development with schema-less databases, easier horizontal scalability because joins aren't as important. There are lots of things that work great in relational databases: indexes, dynamic queries and updates to name a few, and we haven’t changed much there. For example, the way you design your indexes in MongoDB should be exactly the way you do it in MySql or Oracle, you just have the option of indexing an embedded field.
Why MongoDB?
- Document-oriented
- Documents (objects) map nicely to programming language data types
- Embedded documents and arrays reduce need for joins
- Dynamically-typed (schemaless) for easy schema evolution
- No joins and no multi-document transactions for high performance and easy scalability
- High performance
- No joins and embedding makes reads and writes fast
- Indexes including indexing of keys from embedded documents and arrays
- Optional streaming writes (no acknowledgements)
- High availability
- Replicated servers with automatic master failover
- Easy scalability
- Automatic sharding (auto-partitioning of data across servers)
- Reads and writes are distributed over shards
- No joins or multi-document transactions make distributed queries easy and fast
- Eventually-consistent reads can be distributed over replicated servers
- Rich query language
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