In the stack I am working on we have a variety of databases all serving a different type of data storage:

- memcache: for caching of data that doesn't persist - redis: caching of data that needs a to be persisted short term but not on the longer term (eg. sessions) - MySQL: for user-like data (account details, addresses, projects, ...) - DynamoDB: for millions of data points that only needs to be queried in 1 dimension, so are not related or compared to one another. eg. give me all values from this table containing a given datatype, between 2 dates - MongoDB: for millions of datapoints that need to be queried on deeper levels - etc.