Examining CPU utilization

To investigate CPU consumption of the system as a whole, use the vmstat command with a time interval in seconds, like:

The specific output of this command varies between different operating systems, but it includes the percentage of the time the CPU was spent executing user-space code (user time), the percentage of time spent executing kernel-space code (system time), and the percentage of time not executing any code (idle time).

If the CPUs are spending most of their time executing user-space code, the available processors are being well-utilized. If performance is poor or the server is unresponsive, it can indicate that the server is not optimally tuned. If there is a high system time, it can indicate that the system is performing excessive disk and/or network I/O, or in some cases, there can be some other system-wide problem like an interrupt storm. If the system is mostly idle but the server is performing poorly or is unresponsive, there can be a resource constraint elsewhere (for example, waiting on disk or memory access, or excessive lock contention), or the JVM can be performing other tasks like stop-the-world garbage collection that cannot be run heavily in parallel.

To investigate CPU consumption on a per-CPU basis, use the mpstat command with a time interval in seconds, like:

On Linux systems, it might be necessary to add "-P ALL" to the command, like:

Among other things, this shows the percentage of time each CPU has spent in user time, system time, and idle time. If the overall CPU utilization is relatively low but mpstat reports that one CPU has a much higher utilization than the others, there might be a significant bottleneck within the server or the JVM might be performing certain types of garbage collection which cannot be run in parallel. On the other hand, if CPU utilization is relatively even across all CPUs, there is likely no such bottleneck and the issue might be elsewhere.

To investigate CPU consumption on a per-process basis, use a command such as the top utility on Linux. If a process other than the Java process used to run the PingDirectory server is consuming a significant amount of available CPU, it might be interfering with the ability of the server to run effectively.