I had been researching on druid and while going through the docs, the below was mentioned as a feature.
Rollup The aggregation of data that occurs at one or more stages, based on settings in a configuration
What exactly does one or more stages mean here? and What are those stages?
Will druid roll up data even after segments are pushed to deep storage [to reduce the amount of data being stored by merging segments]?
How do we specify configurations for rollups? It is not seen anywhere in the spec file. Is there a complete spec file example, with all possible options and values?