INDICATIVE, shared 2-vCPU sandbox, database in a container on the same host.
4000 x 'SELECT ... WHERE id = ?' per round, 100 in flight, pool size 20, 5 rounds after 1 warm-up each.
queries/second, sorted:
  R2DBC DatabaseClient      : [233, 288, 361, 427, 435]  median=361
  JDBC + virtual threads    : [1240, 1281, 1348, 1558, 3084]  median=1348