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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Slow downloads through mod_jk on Windows XP
Date Wed, 09 May 2012 19:25:26 GMT
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Andy,

On 5/8/12 6:41 PM, Andy Wang wrote:
> Initial benchmarks seem to show that the behavior between tomcats
> is not an issue.

Do you mean that Tomcat performance appears to be the same regardless
of version? That's both good and bad... I thought there were some
performance improvements to the connectors from 5.5-> 6.0. Maybe that
was 4.x->5.5.

> 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.

That is interesting. On the other hand, the server /is/ on a virtual
machine, and you never know what other processes are stealing focus.
Many VMs are notorious for bad IO throughput (I'm looking at you, OpenVZ).

> 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.

Have you tried bare hardware?

> 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?

Some tips for this kind of testing:

1. Don't run ab on localhost: all the numbers will be worthless
2. Run ab with a range of concurrencies, including c=1
3. Make /lots/ of requests. IMO, 5 requests is really a pinhole
analysis. I would make as many requests as you can over 10 minutes and
see what the throughput ends up being.

> 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.

It will be good to see.

If you want some really crappy scripts to get you going, feel free to
start with mine from a while back (look in the "scripts" subdir):
http://people.apache.org/~schultz/ApacheCon%20NA%202010/

Those scripts can run a ... lot of ab tests with lots of different
concurrencies against a series of URLs -- that allows you to set up
everything with, say, a different path or port number to get the
various setups (bare httpd, httpd+mod_jk, httpd+mod_proxy, etc.) and
then let it run all night. It will also produce some tables for you
that can then easily be graphed.

> 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.

It's good to know that the packet size didn't affect performance, but
I agree that localhost communication is always magically-fast no mater
what.

> 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 :(.

Just get a crossover cable and use static IP addresses.

> 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.

Does this happen locally or only remotely? I wonder if you're hitting
some kind of traffic-shaping or QOS rules on your own internal network.

- -chris
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