I believe (intuition, haven't checked) it is the latency the TCP adds
to the setup which messes up with the threads scheduler (i'll
ellaborate...)
When you are in Tomcat only, between the http header coming in (IO)
and you sending a response (again IO) you can usually get away with a
single time slice. It is a simple system with IO queueing up and very
little room for "randomness" (used in a loose way but you get my
meaning).
Once the request is divided into two separate workers with IO between
them, there are two things coming into play:
1) You are not taking full advantage of the timeslice so there is more
context switching (twice the threads doing the same work is another
way to look at it).
2) There is more room for randomness in the system. In fact what we
observed in the short time we let it run is that there were times it
worked and then bursts of high CPU usage with very little happening.
Important to note: most of our requests are handled from memory (no IO
in the servlet). I believe this is a big part of it.
What seemed to help (but not enough in our case) was to reduce the
overall number of threads in the system and configure httpd to have
less threads than tomcat (strange, I know). I speculate this reduced
context switching and reduced the connection load between them.
However, throughput was still erratic at times with bursts of very
rapid processing followed by periods of "indigestion" (was not a GC
problem).
Hope this helps...
Yuval Perlov
R-U-ON
PS It is windows.
On Apr 30, 2008, at 4:37 PM, Larry Prikockis wrote:
Yuval Perlov wrote:
Out tomcat servers are handling around 30K SSL hits every 5 minutes
with very little effort (10% cpu average on a dual core machine,
good response time).
We tried to put in httpd in front thinking we can squeeze out better
performance and memory consumption.
The system just couldn't handle the load and we had to roll back
(quickly) to a tomcat only configuration.
hmmm... that sounds suspiciously similar to what we had happening. I
just can't see why Apache Httpd wouldn't be able to handle SSL
connections at least as well as Tomcat, so there's clearly something
else going on here.
Is your system on Windows, Linux, something else? And what versions
of Tomcat/Apache were you using?
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