Thanks a lot. Got it. Regards
2015-02-23 11:51 GMT+08:00 Dave Warren <[email protected]>: > On 2015-02-22 18:21, Hongyi Zhao wrote: > >> Hi all, >> >> Currently, I use the latest release of unbound 1.5.2 compilled by myself >> on the Debian wheezy. I have some confusion of the using the the >> "prefetch" option in the unbound.conf file. Let me described it as >> follows: >> >> 1- From the manual of unbound.conf, i.e., `man unbound.conf', I can get >> the following >> notes on this option: >> >> prefetch: <yes or no> >> If yes, message cache elements are prefetched before they >> expire >> to keep the cache up to date. Default is no. Turning >> it on >> gives about 10 percent more traffic and load on the >> machine, but >> popular items do not expire from the cache. >> >> 2- From the following webpage: https://calomel.org/unbound_dns.html, >> I can get the explanation on this option as follows: >> >> >> # perform prefetching of close to expired message cache entries. If a >> client >> # requests the dns lookup and the TTL of the cached hostname is going >> to >> # expire in less than 10% of its TTL, unbound will (1st) return the ip >> of the >> # host to the client and (2nd) pre-fetch the dns request from the >> remote dns >> # server. This method has been shown to increase the amount of cached >> hits by >> # local clients by 10% on average. >> prefetch: yes >> As you can see, the above two explanations on the mechanism of >> prefetching in unbound are not so >> well the same. Could someone please give me some hints on the this thing? >> > > To be completely honest, I don't see a conflict between the two > explanations. > > The description in the man unbound.conf is less comprehensive as it only > mentions that this feature keeps the cache up to date, whereas the > description from the webpage quoted explains the mechanism that is used to > determine which records need to be prefetched. > > If you're unclear, just read #2 above, it's more specific and therefore > probably more useful to understand how the feature actually works, but be > aware that it does increase the outbound queries slightly since, from an > external perspective, it drops all TTLs about 10%, while internally it > respects TTLs in a consistent and reliable fashion. I found this feature > made a significant difference when we relocated and were stuck on the end > of a high latency 3Mb line for some months, but it makes little > noticeable-to-end-user difference now that we're back on a high bandwidth, > low latency connection. > > -- > Dave Warren > http://www.hireahit.com/ > http://ca.linkedin.com/in/davejwarren > > > _______________________________________________ > Unbound-users mailing list > [email protected] > http://unbound.nlnetlabs.nl/mailman/listinfo/unbound-users > -- Hongyi Zhao <[email protected]> Xinjiang Technical Institute of Physics and Chemistry Chinese Academy of Sciences GnuPG DSA: 0xD108493
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