Multiple header fields written in each log file(Kristofer Gafvert, March 18, 2005)
IIS 6.0 logging are handled by HTTP.sys. Each time a worker process recycles, HTTP.sys will reclaim the memory used for logging, and close the log file. Whenever a new request comes to the webserver, causing a worker process to start, it will open the log file again, and write new headers in the log file.
By default on IIS 6.0, a worker process is configured to stop after being idle for 20 minutes. So, on a low-traffic website, all these headers will look kind of strange, but it is actual nothing to worry about (as long as the worker process is not recycled because it crashed of course). A worker process can also recycle based on number of requests, time-period, CPU usage and more. All this is configurable in IIS Manager.
Example of headers:
#Software: Microsoft Internet Information Services 6.0
#Date: 2005-01-25 04:50:39
#Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) cs(Referer) sc-status sc-substatus sc-win32-status
Applies to [?]