Re: Round-Robin becomes unbalanced when a peer dies and comes back

Adrian Chadd wrote:
> Hm, that sounds right. You're basically having to recalculate/reconverge
> your peer weightings, and thats the sensible way to do it.
>
> Adrian
>
> On Fri, Jun 06, 2008, Mark Nottingham wrote:
>> Oh, I chopped off the last part; if people agree with that plan, I'll
>> produce a patch.

+1.
Round-robin does not have to worry about weighting artifacts so
Reset/Truncating the counters sounds right.

Amos

>>
>>
>> On 06/06/2008, at 11:46 AM, Mark Nottingham wrote:
>>
>>> <http://www.squid-cache.org/bugs/show_bug.cgi?id=2376>
>>>
>>> When a peer goes down and then comes back, its round-robin counters
>>> aren't
>>> reset, causing it to get a disproportionate amount of traffic until
>>> it "catches
>>> up" with the rest of the peers in the round-robin pool.
>>>
>>> If it was down for load-related issues, this has the effect of
>>> making it more
>>> likely that it will go down again, because it's temporarily handling
>>> the load
>>> of the entire pool.
>>>
>>> Normally, this isn't a concern, because the number of requests that
>>> it can get
>>> out-of-step is relatively small (bounded to how many requests it can
>>> be given
>>> before it is considered down -- is this 10 in all cases, or are
>>> there corner
>>> cases?), but in an accelerator case where the origin has a process-
>>> based
>>> request-handling model, or back-end processes are CPU-intensive, it
>>> is.
>>>
>>> It looks like the way to fix this is to call peerClearRR from
>>> neighborAlive in
>>> neighbors.c. However, that just clears one peer - it's necessary to
>>> clear *all*
>>> peers simultaneously.
>>>
>>> Therefore, I sugest:
>>>
>>> 1) calling peerClearRR from neighborAlive
>>>
>>> 2) changing the semantics of peerClearRR to clear all neighbours at
>>> once, and
>>> change how it's called appropriately.
>>>
>>>
>>> --
>>> Mark Nottingham mnot_at_yahoo-inc.com
>>>
>>>
>> --
>> Mark Nottingham mnot_at_yahoo-inc.com
>>
>

-- 
Please use Squid 2.7.STABLE1 or 3.0.STABLE6