Http Accept filters (accf_http)

[Ivan Voras]

Scott Long wrote:
> Poul-Henning Kamp wrote:
>> In message <480E307B.901 at quis.cx>, Jille writes:
>>> Hello,
>>>
>>> I've read about accf_http(9) some time ago, and I was wondering about 
>>> it's performance.
>>> Does it increase performance on all workloads ?
>>> (I'm intrested in the improvements for a PHP-apache-webserver with 
>>> about 50 request/second average.)
>>
>> I doubt you will see measurable performance difference from using
>> request filters at such low traffic.
>>
> 
> The accept filters do reduce service latency and probably have a small
> benefit in CPU utilization.  50 requests/sec is probably enough to see
> a benefit for something like PHP or PERL.  It definitely won't hurt, and
> even if there's no measurable benefit now, it'll help prepare you for
> scaling in the future.

Does anyone know why accf_accept is disabled by default in the ports' 
stock Apache 2.2 (it's disabled in the default config files)? I thought 
it was because it was dangerous or flawed for some reason, though (at 
least for light loads comparable to those of OP) it seems to work fine.

As to the original question: theoretically it could help requests for 
images and similar small objects - PHP scripts execute too long for the 
benefits to be visible. In my own case, though, I couldn't discern a 
difference with and without accf_httpd. One other thing is that 
keepalives essentially nullify the effects of the filter (as far as I 
understand, the filter only works on the first bytes after the 
connection is established), but keepalives can help performance much 
more than accfs.

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