[Cppcms-users] How can I limit the total maximum number of synchronous application object in the pool at any given time...

[Jean-Frédéric G. <jfg...@gm...>]

Thanks a lot for creating CppCms, it is a wonderful framework.

I made a simple project, with a synchronous application pool (like
hello_world), and I was hoping I could create a DB connection inside each
application object and keep it cached for reusing.
Now, I am using the configuration service.applications_pool_size to set my
pool size, but it seems this configuration is only for the number the
maximum number of app object to cache, it does not limit the maximum number
of objects created at any time.

For instance, I have set the service.applications_pool_size to 24, and if I
run a load test and increase the number of concurrent requests, I am able
to go over 24 app objects. In fact I don't really see a limit easily, it
would go over 200 app objects living at any time (in my case this
translates to 200 DB connections), as long as I am hitting the service with
over 200 concurrent requests.

Even if I play with the worker_thread config it does not seem to limit in
any way the max number of app objects.

Once I stop my load test, I will see the number of app objects/db
connections go back to the service.applications_pool_size I have configured.

Is there any way to really limit the app pool size so that it will only go
up to a maximum setting configured?
Under heavy load, once this limit is reached, it should queue the requests
and dispatch them at the next available application object.

Also, I am using nginx with my cppcms app configured as fastcgi. I tried to
see if I could limit the concurrent requests in nginx to queue them but
could not find how or if this is possible.

Overall, I find that being able to control the maximum number of app
objects is important, in order to properly manage the memory and CPU
resources used under heavy load.

Also, please let me know if I'm missing something, I am just starting with
cppcms but I find great potential.

Thanks,
Jeff