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From Peter Warren <tomcat.subscript...@gmail.com>
Subject Re: nio connector configuration
Date Fri, 13 Feb 2009 09:16:46 GMT
I'm trying to figure out how best to configure nio so that my comet
timeout events get generated in a timely manner.  I have the comet
events set to generate a timeout every 50 seconds.  Works fine with
few users.  Under a moderate but reasonable load the timeout gets
generated on average every 113 seconds.  My configuration tweaks
haven't yielded any noticeable changes (see below).

Test results...

Background:
- using JMeter
- 300 threads executing normal http requests, averaging ~9.8 requests/second.
- 300 threads executing comet requests that simply wait for the server
to close the connection every 50 seconds, averaging ~2.6
requests/second.
- server is ubuntu 8.10 running tomcat 6.0.18.
- server is not cpu constrained, averaging about 8-12% cpu
- server doesn't seem to be memory constrained.  top shows 80% of
memory after hours of test (machine has 512MB physical memory and
tomcat has a max heap set to 384MB)
- network latency isn't a problem

I ran 2 tests with different configurations for the nio connector: 1
test with bare-bones settings, and 1 test with everything that seemed
like it might make a difference.

    <Connector port="80" protocol="org.apache.coyote.http11.Http11NioProtocol"
	redirectPort="8443"
	enableLookups="false" />

Ran for 3+ hours.
8-12% cpu.
12.4 requests/second.
comet requests: average response time 112 secs, min 21 secs, max 179 secs

    <Connector port="80" protocol="org.apache.coyote.http11.Http11NioProtocol"
	maxThreads="1000"
	minSpareThreads="200"
	acceptorThreadCount="20"
	acceptorThreadPriority="10"
	pollerThreadCount="20"
	pollerThreadPriority="10"
	redirectPort="8443"
	enableLookups="false" />

Ran for 1 1/2 hours.
8-12% cpu.
12.2 requests/second.
comet requests: average response time 113 secs, min 50 secs, max 133 secs

So how can I get my comet timeouts generated at close to 50 secs under load?

I thought maybe the poller thread priority was too low (does the
poller thread generate the timeouts?), but setting its priority to max
didn't change anything.

Just to make sure I wasn't doing anything dumb in my client code, I
replaced my event() method with the one below and still got the same
disparity in comet timeouts, ranging from 50 to 120 secs:

    public void event(CometEvent event) throws IOException, ServletException {
        HttpServletRequest request = event.getHttpServletRequest();
        if (event.getEventType() == CometEvent.EventType.BEGIN) {
            event.setTimeout(50000);
        } else if (event.getEventType() == CometEvent.EventType.ERROR) {
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.END) {
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.READ) {
            InputStream is = request.getInputStream();
            byte[] buf = new byte[512];
            do {
                is.read(buf); // can throw an IOException
            } while (is.available() > 0);
        }
    }

I just checked the priority of the thread issuing the comet timeout
event and its priority is 5.  I have both the acceptor and poller
thread priorities set to 10.  How can I bump up the priority of the
thread that issues the timeout events (in this case named
"http-80-exec-1")?

Thanks for any ideas,
Peter

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