You can just crunch your data with SQL/service layer code in a background worker and store it in redis. Then you can use the objects from redis to render charts

You can just crunch your data with SQL/service layer code in a background worker and store it in redis. Then you can use the objects from redis to render charts, build dashboards, etc... Structure your code so you crunch your historical data once, store in redis, and then new data gets shoved in the redis cache as your time dimensions on your metrics progress based on business logic. Until your data is at enterprise volume, you really don't need an OLAP system.