From:   Ameer Mawia <>
To:     Tomcat Users List <>
Date:   04/17/2015 06:29 PM
Subject:        Re: GC Issue on Tomcat6
Toronto, ON

On Fri, Apr 17, 2015 at 8:47 AM, David kerber <> 

> On 4/17/2015 8:32 AM, Subhro Paul wrote:
>> Hi Team,
>> For our client website we have two Tomcat servers. Both servers are 
>> same configuration which is 16GB RAM, 8CPUS and Linux 6.5 OS. Tomcat 6 
>> JAVA 6 are installed in both systems.
>> Yesterday, using Jconsole we observed that frequency of GC on one 
>> was very high which was 5 GC hit per Minute and on other server it was 
>> GC hit per 3 Minutes. But today we observed that on both of the servers 
>> frequency is same.
>> Garbage Collection in Oracle Hot spot JVM takes place in generational
manner. GC on young generation is invoked much more frequently, while Full
GC is invoked once in a while. In any case, frequency is much higher than
what you have mentioned.

I'm not sure which GC(Young/Full) you are talking about? What pattern of 
you have earlier observed?

> Is this a know secnario or the server is facing any issue?
> GC issue has nothing to do with Tomcat per say. It is the memory 
of your application which will dictate GC behavior.

In any case, if your application is facing some memory bottle-neck, it is
better to pay attention on the percentage your JVM is spending in GCing
your application. If that percentage is very high, say ~90%, that means
your application is facing sever memory constrain, your application is
almost stalled as JVM has been trying very high to recover some space. 
probably in that case, your JVM will die throwing OOM error in sometime.

> It was probably just receiving more traffic and/or doing more work of 
> other kind.
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Dear Ameer,

I am talking about Young GC which is "PS Scavenge" for both of the 
servers. Full GC was Running 1/Hour. Can you please assist how to check 
the % of memory utilization by GC through JConsole or any other process.

Thanks & Regards,
Subhro Paul
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