The "java.lang.OutOfMemoryError: unable to create new native thread" occurs when an application cannot create new threads due to memory constraints or exceeding operating system limits. Solutions include adjusting thread creation rates, increasing thread limits, allocating more memory, reducing heap space, minimizing processes, and managing thread stack size.
The article outlines strategies for troubleshooting CPU spikes in Java applications, highlighting issues like repeated Full GC, non-terminating loops, and non-synchronized access to HashMap. It presents tactical and strategic solutions, including monitoring garbage collection, analyzing thread dumps, and replacing HashMap with ConcurrentHashMap to mitigate CPU performance issues.