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From Jeff Trawick <traw...@gmail.com>
Subject Re: svn commit: r1202255 - /httpd/httpd/trunk/modules/filters/mod_reqtimeout.c
Date Wed, 16 Nov 2011 16:51:12 GMT
On Wed, Nov 16, 2011 at 11:20 AM, Paul Querna <paul@querna.org> wrote:
> On Wed, Nov 16, 2011 at 2:44 AM, Rainer Jung <rainer.jung@kippdata.de> wrote:
>> On 15.11.2011 20:57, Jeff Trawick wrote:
>>>
>>> On Tue, Nov 15, 2011 at 2:32 PM, William A. Rowe Jr.
>>> <wrowe@rowe-clan.net>  wrote:
>>>>
>>>> On 11/15/2011 12:33 PM, Stefan Fritsch wrote:
>>>>>
>>>>> On Tuesday 15 November 2011, Paul Querna wrote:
>>>>>>
>>>>>> On Tue, Nov 15, 2011 at 9:17 AM, Stefan Fritsch<sf@sfritsch.de>
>>>>>
>>>>> wrote:
>>>>>>>
>>>>>>> On Tue, 15 Nov 2011, pquerna@apache.org wrote:
>>>>>>>>
>>>>>>>> Author: pquerna
>>>>>>>> Date: Tue Nov 15 15:49:19 2011
>>>>>>>> New Revision: 1202255
>>>>>>>>
>>>>>>>> URL: http://svn.apache.org/viewvc?rev=1202255&view=rev
>>>>>>>> Log:
>>>>>>>> disable mod_reqtimeout if not configured
>>>>>>>
>>>>>>> Why that? We have just changed the default to be enabled in
>>>>>>> r1199447 and several developers at the hackathon agreed to this
>>>>>>> change.
>>>>>>
>>>>>> Didn't know it was discussed in depth at the hackathon, and there
>>>>>> wasn't any discussion on the list....
>>>>>>
>>>>>> It showed up quite quickly in my profiling of the Event MPM,
>>>>>> because every pull/push on the filters would cause a
>>>>>> apr_time_now() call.
>>>>>>
>>>>>> I don't really like that just by loading the module, it changes the
>>>>>> behavior and performance of the server so drastically.
>>>>>
>>>>> It only acts on reads from the client. Normal non-POST requests arrive
>>>>> in one or two packets, which would mean approx. 3 additional
>>>>> apr_time_now calls per request. I haven't done benchmarks, but I can't
>>>>> imagine that this has a drastic impact on performance. And if it costs
>>>>> 1-2%, then that's a small cost compared to the impact of slowloris
>>>>> type attacks which eat lots of memory.
>>>>>
>>>>> The general intention of the recent changes in default configs and
>>>>> module selection/loading was to make it easier to only load those
>>>>> modules that are really needed, have a reasonable default config, and
>>>>> have the compiled-in default values be the same as those in the
>>>>> example config files.
>>>>
>>>> Which means, build by default, disable by default.  I think that keeps
>>>> everyone happy.  When abuse arrives, it's trivial to load.
>>>
>>> Timeout 60 isn't nearly as bad as the old Timeout 300 that is probably
>>> still in wide use, but mod_reqtimeout can provide a much more
>>> reasonable out of the box configuration.  I think we should keep it in
>>> place by default.
>>
>> +1
>>
>
> What I am really opposed to is that the LoadModule causes such a
> degradation in performance.
>
> I am 100% +1 to adding conf commands to the default configuration in
> the httpd.conf, but what I do not like is that having just a
> LoadModule with nothing else causes reqtimeout to do work.  It is too
> trivial for people to have accidental load modules in many distros.

How many distinct concerns are there?  (Cut through the detail that
the implementation of request phase-specific timeouts is in a module,
and hence conflicts with thoughts for what it means to have code
loaded by LoadModule but not explicitly configured.)  I see at least
two raised.

1) performance degradation out of the box with no explicit configuration*
2) any processing at all out of the box with no explicit configuration
3) relatively complex-to-understand timeout mechanism out of the box
with no explicit configuration (independent of whether it is core or
mod_)
4) disagreement that the mod_reqtimeout defaults are "generally
better" across arbitrary situations than Timeout <somenumber>
5) ???

(I assume that the performance issue related to the apr_time_now()
calls in mod_reqtimeout is addressable, and probably in a way that
helps other modules that don't need to know the time with high
precision.)

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