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From Mark Montague <m...@catseye.org>
Subject Re: [users@httpd] What is %D in access log meassuring?
Date Thu, 31 Mar 2011 10:51:28 GMT
  On March 31, 2011 4:28 , Janne H <jannehson51@yahoo.com>  wrote:
> In the access log, what is acctually meassured with the %D option?
>
> The docs say:
>
> %D The time taken to serve the request, in microseconds.
>
> but what is included in this time? Is the stopwatch started when the last byte of the
request is received and stoped when the first  byte of the response is ready to be sent?
>
> Or is the stopwatch started when the first byte of the request is received and stoped
when the last byte of the response has been sent? That is, it is including network sending
time?
 From the source code for httpd-2.2.17, modules/loggers/mod_log_config.c, line 650, %D is:

apr_time_now() - r->request_time)

"now" in this context means "the time at which the log line is being written".  This is after
all data has been sent to the client (logging the amount of data sent the the client is one
of the things that can be logged).  Note that the connection may remain open past the last
byte being sent to the client (keepalive, etc.).

r->request_time gets set in server/protocol.c, line 617, after the first non-blank line
of the request (e.g., "GET / HTTP/1.1\r\n")
made by the client is completely received.  This is close to, but a little bit after (16 bytes
after, in the example I just gave) the first byte of the request was received.  So the time
to receive the first line of the request is not counted in %D, but the time to receive any
subsequent lines of the same request are counted.

I hope this helps.


--
   Mark Montague
   mark@catseye.org


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