This is a microbenchmark that compares the official Java MongoDB driver
version 3.2.2 and Scala driver version 1.1 with the Reactivemongo library
(version 0.11.10). The benchmarks run sequential insert and findOne{_id: _}
queries with three types of documents: small docs (four fields, up to 1K chars),
nested docs (binary trees with depth up to 10) and multi-field docs (up to 1K
keys).
Check out the report generated on my laptop. It basically says that Reactivemongo is slightly slower than the Java or Scala driver, but the difference is negligible (Intel i7, 16GB RAM, Arch x86_64).
Launch your local MongoDB instance, run sbt test and go make yourself a
coffee. After 20-30 minutes you should have a nice report on your desk (well, at
least in target/benchmark/reports/index.html). The tests will use
mongo-driver-benchmarks collection in the test database.