[avahi] Resolving many ( > 200 ) items seems to lead to apparent congestion in the dbus

Sun Oct 18 06:31:50 PDT 2009

lennart is really the only person that can respond to this since he  
moved to git I no longer have direct commit access so he is the gate  
keeper!

Trent

On 16/10/2009, at 3:03 PM, Daniel Wynne wrote:

> Hey Guys!
>
> Really dont want to be annoying, but it would be really nice if we  
> could
> get at least one reliable statement from somebody responsible  
> regarding
> the issue below.
>
> Thanx
>
> Daniel
>
>> Hi again!
>>
>> Is there anyone responsible available who is capable of answering my
>> previous question? Everybody on vacation? ;-)
>>
>> Kind Regards
>>
>> Daniel
>>
>>
>>
>> Daniel wrote:
>>
>>> Hi Folks,
>>>
>>> just returning from my summer vacation I reflected about past  
>>> projects.
>>>
>>> Thereby I also wondered about our little conversation concerning  
>>> Avahi
>>> cache sizes.
>>>
>>> Trent, you made those promising hints that you will loosen the  
>>> strict
>>> limitations to meet requirements of larger network implementations.
>>>
>>> Could you, or any other responsible person please make a definite
>>> authorative statement about this issue so we can proceed with  
>>> development?
>>> Me and my boss would be very appreciated about this ;-)
>>>
>>> Kind Regards
>>>
>>> Daniel
>>>
>>>
>>> Daniel wrote:
>>>
>>>
>>>> Hi Trent!
>>>>
>>>> These are great news for us! :-)
>>>> We were seriously concerned about the issue, that the Avahi mDNS
>>>> implementation prevented us from developing Linux camera management
>>>> applications for huge setups.
>>>>
>>>> In the following I provide a short calculation to give you a hint  
>>>> of
>>>> what we need:
>>>>
>>>>    - Right now we have setups with deployments of up to 800  
>>>> devices We
>>>> do not think that deployments with even more devices in one  
>>>> network make
>>>> sense, as this already can be considered as a individual  
>>>> feasibility
>>>> study. But lets calculate with this worst case scenario and for  
>>>> the sake
>>>> of convenience we even round it up to N = 1000 devices per network.
>>>>
>>>>    - Since every device typically comes up with 2-3 ip addresses,  
>>>> we
>>>> have to reserve cache entries for N*( 3 A's, 1 PTR, 1 SRV, 1  
>>>> TXT. ) =>
>>>> AVAHI_CACHE_ENTRIES_MAX >= 6*N = 6000 entries.
>>>>
>>>>    - As the dbus limitations are concerned the maximum number of  
>>>> dbus
>>>> objects per client will have to be increased, too. Since we have to
>>>> create N*3 AddressRecordBrowsers, N*1 ServiceResolver, 1 Client, 2
>>>> ServiceBrowsers => OBJECTS_PER_CLIENT_MAX >= 4*N + 3 = 4003 ~  
>>>> 4000 entries
>>>>
>>>> As I do not have that much insight into the Avahi-code there  
>>>> might be
>>>> even more limits that might have to be adapted to achieve a  
>>>> coherent
>>>> configuration.
>>>>
>>>> If you need any additional information, let me know.
>>>>
>>>> Thank you Guys for the great support so far!
>>>>
>>>> Kind Regards
>>>>
>>>> Daniel
>>>>
>>>>
>>>> Trent Lloyd wrote:
>>>>
>>>>
>>>>
>>>>> FWIW, I've always felt this was a little restrictive as well but  
>>>>> never
>>>>> really ran into it in production.
>>>>>
>>>>> I am personally keen on upping them a little - Daniel, can you  
>>>>> tell us
>>>>> what values seem to work well for you?
>>>>>
>>>>> Thanks,
>>>>> Trent
>>>>>
>>>>> On 27/06/2009, at 12:04 AM, Daniel Wynne wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>> Hi Lennart!
>>>>>>
>>>>>> After a short interrupt I am back in avahi-business ;-)
>>>>>>
>>>>>> PLaying around a little bit with parameters I boiled it down to
>>>>>> AVAHI_CACHE_ENTRIES_MAX
>>>>>> OBJECTS_PER_CLIENT_MAX
>>>>>>
>>>>>> These Parameters are slightly tight I think when it comes to  
>>>>>> bigger
>>>>>> networks i.e. more than 100 Services.
>>>>>>
>>>>>> You said these limitations are implemented to avoid misuse, i.e.
>>>>>> DOS-Attacks.
>>>>>>
>>>>>> Do you think it is possible in future releases of Avahi to loosen
>>>>>> these
>>>>>> limitations a little bit, to enable more comprehensive usage of  
>>>>>> Avahi,
>>>>>> even for professional applications like ours ;-)
>>>>>> DOS Attacks are way above the limitations of 500, even way above
>>>>>> 5000. I
>>>>>> think when talking about DOS we are in millions and above.
>>>>>>
>>>>>> What do you say?
>>>>>>
>>>>>> Kind Regards
>>>>>>
>>>>>> Daniel
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Sun, 2009-06-07 at 01:47 +0200, Lennart Poettering wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>> On Thu, 28.05.09 13:43, Daniel Wynne (daniel.wynne at mobotix.com)
>>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> But I think thats exactly the problem in our case. In our
>>>>>>>> Testnetwork
>>>>>>>> reside about 250 cameras we want to find and resolve via  
>>>>>>>> Avahi. So
>>>>>>>> the
>>>>>>>> cache is way big enough.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>> No. The limit of 500 entries in the cache that Avahi enforces  
>>>>>>> is for
>>>>>>> RRs, not services or hosts.
>>>>>>>
>>>>>>> For each service you need (at least) one A, one PTR one SRV  
>>>>>>> and one
>>>>>>> TXT RR. Usually even more. I.e. if you register 250 services  
>>>>>>> and want
>>>>>>> to browser for them all at the same time you need as absolute  
>>>>>>> minimum
>>>>>>> space for 1000 entries, and practically even more.
>>>>>>>
>>>>>>> Lennart
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> _______________________________________________
>>>>>> avahi mailing list
>>>>>> avahi at lists.freedesktop.org
>>>>>> http://lists.freedesktop.org/mailman/listinfo/avahi
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
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>>
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>
>
> -- 
> ---------------------------------------------------------------------
> Daniel Wynne, Softwareentwicklung
> MOBOTIX AG - Security Vision Systems
> Kaiserstrasse, 67722 Langmeil
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