Question

I am using IIS and JRun to serve coldfusion application.

Something is limiting maximum number of concurrent connections – they never get above 25.

My application is waiting for response from external services for long time and could possibly handle much more concurrent requests.

I’ve found only one value that may have something to do with this:
In jrun.xml activeHandlerThreads is set to 100

Answer 1

Solution finnally found: IIS 6/IIS 7 for ColdFusion 9: Increasing the Number of Worker Threads

There is a magical C:\JRun4\lib\wsconfig\1\jrun_iis6_wildcard.ini file with:

#maxworkerthreads=25 <number of worker threads created for asynchronous request processing>

The default is 25, to increase concurrent requests uncomment this line and change the value.
For example:

maxworkerthreads=50 <number of worker threads created for asynchronous request processing>

Then you need to restart both IIS (whole server, not single website) and JRun service.