RE: Response time banding

[Edward Hibbert <Ed...@dataconnection.com>]

Well, it turns out I was wrong about the 2s banding.  This _was_ garbage
collection, and was cured by using -XX:+UseConcMarkSweepGC
-XX:+UseParNewGC.

I still get the 5s banding, though, which is a puzzler.

Edward.

-----Original Message-----
From: Kurt Overberg [mailto:kurt@hotdogrecords.com] 
Sent: 31 July 2006 12:08
To: Tomcat Users List
Subject: Re: Response time banding

Do your 2 second requests happen at a particular time of day?  In the  
early morning, when my database vacuum is running, my response times  
shoot way up (to around 5 seconds).  Check to see what else is going  
on with your system during the times the page response times increase.

/kurt

On Jul 26, 2006, at 4:47 PM, Robert Harper wrote:

> One thing to consider is that the times may not be totally in  
> synch. Some
> threads pending a write to the log might get interrupted while another
> thread runs. You may see log entries out of order. I have seen this  
> myself
> and have added System.out.flush() to my logger. It helps but still  
> does not
> ensure exact order. Make sure you go over the time stamps carefully  
> before
> you pass too much judgment.
>
> Robert S. Harper
> Information Access Technology, Inc.
>
> -----Original Message-----
> From: Leon Rosenberg [mailto:rosenberg.leon@googlemail.com]
> Sent: Wednesday, July 26, 2006 2:35 PM
> To: Tomcat Users List
> Subject: Re: Response time banding
>
> I would measure at all layers during the request processing to
> determine whether irregularities occur somewhere.
>
> Leon
>
> P.S. "the response times as measured by the access log" - don't you
> have the proper tools for that? JMeter?
>
> On 7/26/06, Edward Hibbert <Ed...@dataconnection.com> wrote:
>> Odd one, this.  I'm posting looking for off the wall suggestions.
>> Though not too off the wall, please.
>>
>> We have an application running under Tomcat.  If we analyse the  
>> response
>> times as measured by the access log, then we see that for the same  
>> GET
>> operation there is a distribution of response times.  Well, you'd  
>> expect
>> that.
>>
>> But while the bulk of response times are below about 0.25 seconds (in
>> most cases considerably below), there is a banding effect where we  
>> get a
>> cluster of response times around 2 seconds, and another cluster  
>> around 5
>> seconds, with little or no values in between.
>>
>> We've looked at garbage collection as the most likely source of this,
>> and ruled it out.  Has anyone seen anything similar, or got any  
>> bright
>> ideas?
>>
>> Regards,
>>
>> Edward.
>>
>>
>
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