I’m new on Druid and i have a lot of questions about aggregations, i can’t understand how it works.
Aggregation at ingestion time is only create by “metricsSpec” field ? If not, how can we use “Aggregations” Field ?
My typical example is I want to have the number of lines by Country, is it smart to try aggregate this at ingestion time and is it possible ?
When we aggregate before a query or during a query, is the aggregation store somewhere? If not, why aggregate ?