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From Jess Holle <je...@ptc.com>
Subject Re: [users@httpd] lbmethods in mod_proxy_balancer
Date Fri, 30 May 2008 13:10:57 GMT
Jim Jagielski wrote:
> On May 29, 2008, at 5:38 PM, andrzej wrote:
>> Hi,
>>
>> module mod_proxy_balancer can make decision basing on volume of 
>> traffic or number of requests. How, for example, this volume is 
>> counted? Is it counted from the time server starts (hope not) or 
>> maybe it is counted in 10 minutes period (after 10 minutes values 
>> read and transfered are reset  and counted from zero)? Where/how can 
>> I change this time?
> It is counted after each request... that each, the counters are
> updated with info after each request.
>
> They are not "reset" or "aged" for a number of reasons:
>
>   1. The overhead associated with it. Esp something like what
>      is done in mod_jk...
>   2. Validity: LBs try to maintain an overall average. If
>      you occasionally "reset" then you lose knowledge of
>      the past and so you are only averaging over smaller
>      time-periods... It's like the difference in tracking
>      stocks short-term rather than long-term. LB is a long
>      term action.
>
> The only reason I can see for some kind of "reset" is to
> avoid overflow, but even then you don't want to "reset" to
> 0 but rather do a uniform normalization.
>
> Why is the current behavior bad and why do you want to change
> it?
I've not experimented with it, but the session-based load balancing in 
the latest mod_jk's looks attractive.  Most AJP traffic is session based 
and a good amount of the time ends up requiring session affinity (rather 
than using Terracotta or some such).  In this scenario, it is possible 
to end up with a lot more sessions stuck on one node than others and any 
way of combatting this without a nasty performance impact is of interest.

--
Jess Holle


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