On 12/08/14 12:18, Kamil Dudka wrote:
> On Tuesday, August 12, 2014 10:05:37 Alastair Scobie wrote:
>> Whilst porting an in-house application, which uses libcurl, from RHEL6
>> to RHEL7 we noticed that the time taken by libcurl to fetch a page had
>> substantially increased. Even an attempt at fetching a non-existent page
>> has increased from 10-20ms to around 150ms. This with just plain HTTP.
>
> What exactly do you mean by a non-existent page?

A page for which you'll receive a 404. Ie. HTTP server address is
correct, but actual page requested doesn't exist.

>> Our first thought was that the API has changed in some subtle way and
>> the fault must be in our code, but then we thought to try measuring the
>> performance of the curl tool itself. To our surprise, we found the same
>> performance disparity.
>>
>> Interestingly...
>>
>> * Adding the DNS address of the HTTP server to /etc/hosts (and
>> specifying files,dns in /etc/nsswitch.conf) does not improve things
>
> Did you try to measure the time consumed by 'getent ahosts'?

Small number of ms for both RHEL6 and RHEl7.

>> * but, performance when using an IP address in the URL is fine (~
>> 10-20ms) for both RHEL6 and RHEL7
>
> I was not able to reproduce this behavior. Is it reproducible locally?

Yip, on several machines. I can ship you an strace if you like?

(Daniel's suggestion of disabling the threaded resolver has fixed the
issue for us).

Cheers, Alastair

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