Does treasure data have a dedicated storage engine for time series? This kind of data has specific needs which are not met by general purpose storage layers.
To an extent, yes. We wrote our time-partitioned columnar storage from scratch: it has row-based storage for more recent data and column-based storage for historical data, and the data is merged from row-based to column-based periodically for performance. We realized from day one that much of "big data" is log/timestamped data, so our query execution engined are optimized for time-windowed queries.
The free plan allows 10M records per month with a maximum capacity of 150M.
Full disclosure: I work there.