A fleeting glance between MongoDB and Redis
Storage

MongoDB
Disk, memory-mapped files, index should fit in RAM.

Redis
Typically in-memory.

Data model

MongoDB
Document oriented, JSON-like. Each document has unique key within a collection. Documents are heterogenous.

Redis
Key-value, values are:

• Lists of strings
• Sets of strings (collections of non-repeating unsorted elements)
• Sorted sets of strings (collections of non-repeating elements ordered by a floating-point number called score)
• Hashes where keys are strings and values are either strings or integers

Querying

MongoDB
By key, by any value in document, Map/Reduce.

Redis
By key