On 2017-06-05 19:00 (-0700), "Roger Fischer (CW)" <rfis...@brocade.com> wrote: > Hello, > > is there any intent to support "order by" and "limit" on aggregated values? > > For time series data, top n queries are quite common. Group-by was the first > step towards supporting such queries, but ordering by value and limiting the > results are also required. >
For people interested in reading some related background: https://issues.apache.org/jira/browse/CASSANDRA-10707 (GROUP BY) https://issues.apache.org/jira/browse/CASSANDRA-11871 (Time series aggregation) Distributed sorting/ordering/limits can be hard, but they're not impossible. If someone comes up with a way to do it efficiently, I'm sure the project would love to see it included. In the past, we've had issues where features were like landmines, they perhaps worked for a small subset of use cases, and then became sore points for other users (features like secondary indexes and old style counters). Since then, a lot of committers tend to only want to include features if they know they can scale to massive, busy clusters - because we know what hasn't worked in the past, and what sort of problems have been caused for innocent users. I hope there will eventually be a middle ground where we can be OK with stripping down implementations to support imperfect features on real clusters, as long as it doesn't cause things to blow up for people. I'm not confident this is such a feature that can be reasonably pared down, but perhaps someone will to suggest a way to do it such that it can be included, even if it's not 100% compatible with sql semantics. --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org For additional commands, e-mail: user-h...@cassandra.apache.org
