Re: What will pdns do when a fast dns server become slow and become fast again?
bert hubert <[email protected]>
| Newsgroups | gmane.network.dns.powerdns.devel |
|---|---|
| Message-ID | <[email protected]> |
Hi Aki, Jacky, This is explained in http://doc.powerdns.com/html/recursor-design-and-engineering.html#idp10119168 : "Whenever a packet is sent to a remote nameserver, the response time is stored in the SyncRes::s_nsSpeeds map, using an exponentially weighted moving average. This EWMA averages out different response times, and also makes them decrease over time. This means that a nameserver that hasn't been queried recently gradually becomes faster in the eyes of PowerDNS, giving it a chance again." Bert On 27 Dec 2013, at 08:50, Aki Tuomi <[email protected]> wrote: > once cache expires the records are removed and are looked for again. if you look > at SyncRes::getAddrs, you'll see the record selection process. > > btw, are you just interested or is there some deeper issue here? > > Aki > > > On Fri, Dec 27, 2013 at 03:29:27PM +0800, jacky wrote: >> hi, Aki tnuomi， >> Thank you for suggestion. I found pdns always get the fastest one from the front of result returned by function "SyncRes::shuffleInSpeedOrder”. If a slow one at the back has no opportunity to be choosed, how pdns know it become fast. I can not find the source code make pdns query the slow one. >> >> on the other hand, I found there is a houseKeeping thread which will erase the stale speed value of a dns server . If a slow dns at the back of t_sstorage->nsSpeeds map, it will be erased because of rarely to be queried, and only fast dns server will have its speed updated by this code " t_sstorage->nsSpeeds[*tns].submit(*remoteIP, lwr.d_usec, &d_now);” at syncres.cc:1003. >> . And then, only dns servers which are mostly queried will stay in t_sstorage->nsSpeeds map. It make me puzzled. >> >> -- >> jacky >> >> >> On Friday, December 27, 2013 at 3:08 PM, Aki Tuomi wrote: >> >>> On Thu, Dec 26, 2013 at 10:34:23PM +0800, jacky wrote: >>>> hi, all, >>>> I think may be it is a question more suitable to dev maillist, so I submit it here. If I made a mistake , please let me know. Thanks. >>>> >>>> I'am reading the source code of pdns-recursor-3.5.3. There is question I can not understand. >>>> When a authoritative dns server become slow because of overload, pdns-recursor will move it backwards in the >>>> t_sstorage->nsSpeeds map, and then a faster dns server will be used preferred. But when the dns server recoverd >>>> from overload and become fast again, what will pdns-recursor do about it ? Will pdns-recursor move it forward >>>> in speed map? I can't find relevant source code. Any suggestion? >>>> >>>> -- >>>> jacky >>>> >>> >>> >>> Hi! >>> >>> It works by moving the fastest one on top. >>> >>>> _______________________________________________ >>>> Pdns-dev mailing list >>>> [email protected] (mailto:[email protected]) >>>> http://mailman.powerdns.com/mailman/listinfo/pdns-dev >>>> >>> >>> >>> >> >> > _______________________________________________ > Pdns-dev mailing list > [email protected] > http://mailman.powerdns.com/mailman/listinfo/pdns-dev _______________________________________________ Pdns-dev mailing list [email protected] http://mailman.powerdns.com/mailman/listinfo/pdns-dev