Re: [Libevent-users] libevent http and lost requests

[Mark Ellzey <mthomas@xxxxxxxxxx>]

On Thu, Aug 11, 2011 at 09:19:41PM +0300, about bus wrote:
> Hello!
> 
> I have a simple my own libevent-based http server written on C, use evhttp.h
> functions.
> I use it like backend with nginx server (about ~2K requests per second).
> Sometimes in nginx error log appears error: "(60: Operation timed out) while
> reading response header from upstream"
> Timeout value is 75 seconds in nginx config file, but my http server does
> not need so long time to handle one request.
> Average request time is about 0.01 second (information from nginx access
> log).
> 
> I've used tcpdump to figure out what's going wrong.
> There is a network activity on timeouted requests:
> 
> nginx -> syn > httpserver
> httpserver -> syn-ack > nginx
> nginx -> ack > httpserver
> nginx -> GET /query/xxx/yyy > httpserver
> httpserver -> ack > nginx
> ...
> 75 seconds left (timeout)
> ...
> nginx -> fin > httpserver
> httpserver -> ack > nginx
> 
> Only after this time (75 seconds) libevent calls my http_handler callback.
> Message about new http request appears in http server log file.
> After less than one second http server ready to send response back to nginx.
> But 75 seconds were lost I don't know where, and connection where closed.
> 
> So, how I can figure out why libevent holds request for 75 seconds?
> Why libevent gives request for handling only when nginx tries to close
> connection to my http server?
> 
> Thanks!


Can you post the source? If not you can try ltrace/strace'ing your
server or enable event debugging by recompiling libevent with
-DUSE_DEBUG
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