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

Patch attached to bug.

On 06/06/2008, at 2:11 PM, Amos Jeffries wrote:

> 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

--
Mark Nottingham       mnot_at_yahoo-inc.com