Failed to create child event loop in springboot

we are connecting neo4j through spring boot using neo4j java driver....we just execute a simple get query to retrive data from neo4j db now for less concurrent users the result was good when i try to increase my concurrent user( above 500) it gives me failed to create child event loop below 500 concurrent users there was no problem....eventhough I have added neo4j configuration but still the problem occurs... Please help on this