Tomcat consuming high CPU

Question

Tomcat.exe is consuming 75% of CPU. Is anyone having any idea why it happens and how can that be decreased?

I am using Tomcat5.5 & J2SDK v 1.4.2_12

Answer 1

All the answers cover how to do an exact diagnose, in addition I would add that, from my experience, a infinite loop in one of your applications is probably the culprit.

As J-16 SDiZ said, your best bet is to run the profiler to narrow down the problem to one application.

Answer 2

In my case, I had just installed Tomcat8 with default settings. I had to set memory parameters -Xms -Xmx. Once, I increased memory allocation to JVM, CPU utilization came down drastically.

Answer 3

If you're using 75% CPU and dont understand why, I suggest you issue a kill -3 to the tomcat process (ctrl-break if you have a console) to get a thread dump (when the load is high!). In my experience most threads should either be idle or in io-wait. Look for any single branch of code that has repeated occurences in the stack traces and that's your likely culprit (non-io waits!). This is the "poor man's profiler" that is quite often the best and most efficient way to solve these problems.

Answer 4

Lambda Probe is a very handy tool for monitoring Tomcat.

Are you using a quad CPU system? Probably Tomcat is running 100% in 3 of them. I would first test for an infinite loop or something like that in an application.

Answer 5

To understand what's happening, you should try to run it under a profiler. Try the YourKit (http://www.yourkit.com/) or Netbeans (http://profiler.netbeans.org/docs/help/5.5/profile_j2ee_profileproject.html).

The YourKit one have better integration with tomcat.

Answer 6

First of all (this applies to all java applications) you must pin down which thread is using CPU. This is possible in JDK 1.6. It is done by using java.lang.management.ManagementFactory.getThreadMXBean(). Here is example usage (JSP):

<%@ page import="java.lang.management.*, java.util.*" %>
<%!
    Map cpuTimes = new HashMap();
    Map cpuTimeFetch = new HashMap();
%><%
long cpus = Runtime.getRuntime().availableProcessors();
ThreadMXBean threads = ManagementFactory.getThreadMXBean();
long now = System.currentTimeMillis();
ThreadInfo[] t = threads.dumpAllThreads(false, false);
for (int i = 0; i < t.length; i++) {
    long id = t[i].getThreadId();
    Long idid = new Long(id);
    long current = 0;
    if (cpuTimes.get(idid) != null) {
        long prev = ((Long) cpuTimes.get(idid)).longValue();
        current = threads.getThreadCpuTime(t[i].getThreadId());
        long catchTime = ((Long) cpuTimeFetch.get(idid)).longValue();
        double percent = (current - prev) / ((now - catchTime) * cpus * 10000);
        if (percent > 0 && prev > 0) {
            out.println("<li>" + t[i].getThreadName() + " " + percent + " (" + prev + ", " + current + ")");    
        }
    }
    cpuTimes.put(idid, new Long(current));  
    cpuTimeFetch.put(idid, new Long(now));
}
%>

After that you can get a thread dump and analyze the code in this thread to fix excessive CPU usage.