[Pythonmac-SIG] socket.getaddrinfo problems

[Dudley Carr]

brad.allen at omsdal.com wrote:


> However, from the thread I'm reading up here, you guys are implying 
> there is no DNS cache by default, since you are discussing how to turn 
> it on. Sorry if this is a bit off topic, but I'd be very interesting in 
> learning how to understand this better. Thanks!

Brad,

First off, I'm new to OS X so I can't say for certain whether or not OS X has 
built-in DNS caching. The best way to resolve this is to get a copy of ethereal 
running, and see what's on the network. I'm having some trouble getting ethereal 
to run, so I'll share my performance numbers with you.

def queryTimer(host, numAttempts):
     timings = []
     for i in range(numAttempts):
         start = time.time()
         socket.queryaddrinfo(host, 80)
         end = time.time()
         timings.append(end - start)
      return timings

# With Bind DNS caching turned off
 >>> r = queryTimer('yahoo.com', 50)

# My network is abnormal so I'm going to eliminate the
# occasional query that takes longer than 1 second
 >>> r = [ timing for timing in r if timing <= 1 ]

# The average query time when BIND DNS caching is turned off
 >>> sum(r) / len(r)
0.1006

# With BIND DNS caching turned *on*
 >>> x = queryTimer('yahoo.com', 50)

# The average query time when BIND DNS caching is turned *on*
 >>> sum(x) / len(x)
0.0081

To me this is a pretty good sign that there isn't any DNS caching by default. I 
also took the average query time for the timings submitted by Steven Palm ( 
0.024 seconds if you eliminate the very first query ) and Craig Amundsen ( 0.88 
seconds ).

Steven's timings are the best out of his, and Craig's, and mine. However, my 
BIND DNS caching timing is 3x better than Steven's timings.

Regards,
Dudley