Briefly: "Seastar is event-driven and supports writing non-blocking, asynchronous server code in a straightforward manner that facilitates debugging and reasoning about performance." -- http://www.scylladb.com/2015/02/20/seastar/
Concurrency model: "Seastar futures/promises/continuations (f-p-c) are a subset of reactive programming.
Seastar performance derives from the sharded, cooperative, non-blocking, micro-task scheduled design, and f-p-c are a friendlier way of feeding tasks to the scheduler.
Seastar’s f-p-c do have some optimizations relative to other f-p-c designs. They trade off thread safety, which is unneeded due to the sharded design, for scheduling efficiency, and have a very low memory footprint." -- http://www.seastar-project.org/faq/
If you'd like to find out more, here are a few links with more information (including examples and tutorials):
- https://github.com/scylladb/seastar/wiki
- https://github.com/scylladb/seastar/blob/master/doc/tutorial...
- http://www.seastar-project.org/futures-promises/
- http://blog.cloudius-systems.com/2015/04/29/seastar-tutorial...
- http://www.slideshare.net/TzachLivyatan/seastar-sayeret-lamb...
In terms of practical applications, ScyllaDB (fully compatible--and significantly faster--drop-in replacement of Apache Cassandra) relies on Seastar: http://www.scylladb.com/
ScyllaDB has been discussed here before: https://news.ycombinator.com/item?id=10262719