1) Ab with Apache_1.3.9 results
When I ran ab with apache, I ran with concurrency C = 1 or C = 100. I
initially thought that C had something do with the number of instances of
httpd, but it seems to only indirectly: as load goes up (due to larger
C), more children get spawned. What I noted is that ab+httpd CPU usage
per request goes down slightly as C increases. This appears to be because
accept(2) processing is "amortized" (as Dan Gaudet put it) over C
connections. I ran with N = 100,000 because of variability in results
observed when N was smaller. No errors were observed.
2) ab with tomcat4-4.0-m4
With Tomcat4, there seemed to be some threading problems (thread queue
lockouts, unknown threads waiting to be notified). I don't know enough
about TC to be able to fix or even diagnose what's going on, but
something does seem fishy to me: Once N and C become "large enough": ab
quits producing output; the log files show an unknown thread waiting
notification (possibly an artifact of my shell program); thread queue
locking occurring (which seems like it might be serious); and cpu usage
per request seems to INCREASE with C (in contrast with apache_1.3.9).
I have a dual Celeron 400Mhz machine that I ran under a Redhat6.1 smp and
a up kernel with the JDK1.2 ClassicVM (green threads). The smp kernel
does suck (as noted by Dean Gaudet): thruput tends to DECREASE with
increasing C, thread queue locking is noted in one of the log files, and
ab produces nothing or garbage. I haven't bothered to record data from
the SMP runs. I have 256MB SD100 memory and a WD Caviar disk (there's
very little IO, as expected).
Here are the summarized data, running the following command
/usr/sbin/ab -n N -c C
http://localhost:8080/examples/servlet/HelloWorldExample
N (ab) C (ab) thruput/sec %CPU busy avg proc. time (ab) ms
1000 1 79.11 99.67 11
20 61.53 100 255
40 65.46 100 541
60 63.56 100 784
80 68.63 100 671
100 67.79 100 632
10000 1 83.95 100 11
20 78.21 100 283
40 75.41 100 680
When N = 10,000 and C > 40 catalina.log shows an error mesg re: unknown
thread waiting to be notified. Since the average number of active
connections/threads is a function of the memory available and processor
speed, I expect other people will see similar logfile entries with
different N and C values. I'll send an updated, more flexible, version of
the bash scripts today or tomorrow as I'm feelin' poorly. :-)
Roy
--
Roy Wilson
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