Hello:
I am sorry if this message is a duplicate. I tried to post this same
message a few weeks ago through gmane but I never got a response. I am
trying to post again directly via the c-ares mailing list.
I am a recent libcares user. I hope this is the right forum to post this
question. If not I apologize and please let me know what is the correct
forum or mailing list to use.
The project I am working on recently switched to use libcares for
DNS queries. Prior to that we were using the standard getaddrinfo()
(see "man 3 getaddrinfo") for name to ip resolution. With getaddrinfo()
we could not specify a timeout value to perform the DNS query. Hence we
switched to use libcares.
Our use of libcares is getting some stability issues especially if
we use wireless network. libcares will sometimes fail to resolve the
hostname. Libcares will fail to resolve the hostname within our timeout
of 60 seconds.
Let me elaborate:
- If I do a few DNS queries using libcares then everything is fine.
- I wrote a profiling tool that does many DNS queries in a loop. For
example, we resolve "www.google.com" and we do 100 iterations of that
in a loop.
- If I run that with my laptop that has a wired connection to my router
then everything is fine. Name resolution with libcares is rock solid
and it does not fail to resolve www.google.com to its IP address for
every iteration
- If I run that with my laptop that has a wireless connection to my
router. Then maybe at the 60th iteration libcares will timeout and not
be able to resolve "www.google.com"
There must be something I am doing wrong. I am probably using libcares
in a way that it is not supposed to be used. I am wondering how other
projects such as curl are using libcares.
A few things come to my mind:
[1] By default libcares makes DNS queries using UDP. Should I use the
ARES_FLAG_USEVC to specify libcares to use TCP instead ?
[2] Should I implement caching ? At my application level, should I
cache the name to ip resolution and don't invoke libcares to make a DNS
query. Then this leads to the next question of what timeout should I
use to evict old entries from my cache.
Once again, I am probably using libcares in a wrong way. So your insight
is much appreciated.
Thanks
Richard
Received on 2015-05-27