requests queued too high?
am 03.01.2007 21:19:00 von MichaelShuttWe've got a web application running on a 2-server IIS6 web farm. The
application is part asp and part asp.net. We were analyzing some performance
data and found something peculiar. We are collecting data from these ASP
counters:
Active Server Pages\Requests Queued
Active Server Pages\Requests Executing
Active Server Pages\Request Wait Time
On each server, during peak usage times, we are seeing 10 - 15 requests per
sec. During those times, the 'Requests Executing' counter runs ~5. The
'Request Wait Time' counter is usually somwhere between 0 and 100 (I think
that means 0 to 0.1 seconds). So those counters look normal to us.
However, the 'Requests Queued' counter will fluctuate and at times can
approach 50. At the same time it is reading 50, the 'Requests Executing'
counter will remain at ~5. IIS is configured for 25 worker threads per CPU,
and the servers have dual CPUs, so I know that IIS6 could be processing 50
concurrent requests.
I am assuming the reason we see the 'Requests Queued' counter climb is a
result of IIS6 trying to minimize the number of actual worker threads that
are spun up at any given time in order to avoid the overhead of uncessary
context switching. The result would be that IIS would only have ~5 threads
working the ASP request queue as long as the 'Request Wait Time' is a
reasonable number. As long as that is the explanation, I am not overly
concerned.
However, there are some types of requests in our application that can take
significantly longer to execute (i.e., a user pulls up a large report). I am
a little concerned that users might run into spots during the day where the
server does not appear to be responsive because it just so happens that at
the same time, 5 users are trying to access reports, which is consuming the 5
worker threads that IIS has spun up.
Can anyone shed some light on how IIS6 manages its threads and if I should
be concerned that the 'Requests Queued' counter can spike at times during the
day?