The following exception could be identified within the debug.log file when Neo4j is installed as a service on a Unix machine, under a high-load scenario:
Caused by: java.lang.OutOfMemoryError: unable to create native thread: possibly out of memory or process/resource limits reached
As the error message suggests, the problem is caused by the fact that the JVM is unable to create a new thread at the OS level to operate.
This is typically caused by a limit at the OS level on the number of maximum available threads defined for the service, this option is usually identified as "maxTasks" within the service configuration.
If you're experiencing this problem and Neo4j is installed as a service, you should either increase the amount of available "maxTasks" for the service or remove the limit entirely.