How does Athena work? The charge is $5 per terrabyte scanned, which indicates (maybe) that no indices are used and queries are processed by a scan through the data. Is this correct?
There are no indexes in the traditional MySQL / Postgres sense of the word. You can, however, layout the data to make your querying more efficient. See: https://docs.aws.amazon.com/athena/latest/ug/partitions.html