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From Andy Wang <aw...@ptc.com>
Subject Re: Slow downloads through mod_jk on Windows XP
Date Tue, 08 May 2012 22:41:25 GMT

> He did that previously, and the result seemed to be that Tomcat alone 
> was comparable to httpd alone, and both were better than httpd/mod_jk 
> + Tomcat; which is indeed physically to be expected : more tubing, 
> less throughput (excepting quantum tunelling effects of course).
> The question is more : how much of a degradation ?
> 15.0/19.3 = 0.77 = 23% less throughput.  I don't know if this is "a 
> good chunk" or the "to be expected" kind of degradation.
>
> According to the (looking seriously outdated) AJP protocol 
> documentation at 
> http://tomcat.apache.org/connectors-doc/ajp/ajpv13a.html, it would 
> seem that the maximum data size "chunk" which AJP can send back from 
> Tomcat to the front-end httpd is 8K at a time.  So AJP might not be 
> very well suited, when it comes to send back big blobs of data.
>
> Rainer would need to confirm if that is still the case now.
>
> One earlier message seemed to indicate that this "httpd/mod_jk+tomcat 
> deficit" only happened under Windows though, and not under Linux.  If 
> that is confirmed, maybe there is some subtle difference in how the 
> TCP/IP stack is being used under the one vs the other ?
Thanks for that summary,
That's about what I'm seeing.  I just created a directory containing 
Apache configured to serve up the iso file directly as well as through 
three tomcats (tomcat5.5, tomcat6, and tomcat7) to see if the behavior 
is related to tomcat that I can easily copy between different Windows 
systems.  Initial benchmarks seem to show that the behavior between 
tomcats is not an issue.    Tomcat7 is using JDK 1.7 and this is 
interesting.  The benchmarks with tomcat7+jdk1.7 vary widely across the 
board (both through ajp and direct http to tomcat) from 30s-40sMB/s.  
Java 1.6 seems alot more consistent.  Not sure why yet.

I've also moved off the crappy Windows XP VM I was provided to a more 
recent Windows 2008 VM as well as a fresh Windows XP SP3 VM.  In past 
experience it seems windows XP and windows 2003 were the worst of the 
bunch with the ajp downloads dropping as low as 4-5MB/s over time.

I'm going to run a barrage of tests and provide the numbers.  Do you 
think ab -n 5 and allowing ab to average the values of 5 hits for the 
~440MB iso is a sound average?

I'll compare Windows XP performance and Windows 2008 performance and 
after that I'll do the same on a Linux VM to get a better comparison.

I also did bump up the ajpPacket size to 64K with no noticeable change 
to the benchmark numbers.  So while 8k seems crappy it doesn't seem to 
be an issue.  Given that apache and tomcat are both local I wouldn't 
expect that to be a big problem with 8k chunks given the near 
non-existent latency of local connections.

I plan on doing both local ab requests as well as remote.  The problem 
with remote is that our network is busy, so it may account for some 
variations but I don't think I can get our IT to segment me anything for 
this purpose :(.

I'm not so concerned about a 25% hit.  I'm really more concerned with 
the drop to 4-5MB/s over time that seems to happen.

Thanks,
Andy

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