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To: "JMeter Users List" <jmeter-user@jakarta.apache.org>
Cc: Paul Leclerc <pleclerc@gmail.com>
Subject: Re: Bug? Jmeter only tries one addr in multi-addr DNS round robin
 cluster
References: <864qjxv0ul.fsf@Palimpsest.saic.hq.nasa.gov>
	<e3e948f504111015381344db87@mail.gmail.com>
From: Chris Shenton <Chris.Shenton@hq.nasa.gov>
Date: Fri, 19 Nov 2004 19:53:37 -0500
In-Reply-To: <e3e948f504111015381344db87@mail.gmail.com> (Paul Leclerc's
	message of "Wed, 10 Nov 2004 16:38:53 -0700")
Message-ID: <867johpcha.fsf@Palimpsest.saic.hq.nasa.gov>
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Paul Leclerc <pleclerc@gmail.com> writes:

> Don't forget that by default, Java caches IP addresses for DNS
> lookups.  See this link for more information:
> http://java.sun.com/j2se/1.4.2/docs/guide/net/properties.html and
> look at both networkaddress.cache.ttl and sun.net.inetaddr.ttl

That looked very promising but it doesn't seem to be helping. 
In $JAVA_HOME/jre/lib/security.java.security I set
 
  networkaddress.cache.ttl=1

and see it querying my dnscache often, whereas before it queried it
only once. That's good. However, it's only trying one of the addresses
in DNS for that name. 

The name I configure jmeter to test is "cluster" which evaluates to
two different IPs both with 1s TTL; I have it use 5 threads, and loop
5 times, with a 30-second ramp-up-time.  I do see my DNS being queried
repeatedly for that name, but jmeter only hitting one.

Interestingly, quitting and re-running the "jmeter" startup script has
no effect: it keeps returning to the same target host address.  My
dnscache is documented to return a list of addresses in random order
for each query. The law of probabilities says it should get them both
50% of the time, this is about 10 out of 10 times it gets the same
one. (Is it suspicious it's the lower of the two addrs?).


Also, if I shut down the tomcat on the target it's picked, jmeter
appears to hang. Is it not written to try other addresses in the list
of addresses it got for the target's name?  I don't have the code here
to look.  Perhaps this wasn't a design goal.

Any thoughts? I can't test the robustness of my tomcat-4 session
clustering if my test tools won't try alternate addresses.

Thanks again.

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