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

[Artyom B. <art...@ya...>]

No there is no such method.

It works this way.

When the request comes to the cppcms service event loop it does all its handling (i.e. preparing get/post data, parsing).
When it is ready, it requests a relevant application from the pool and sends it to the thread pool for handling.

So if there are many connections than many applications would be created and of course if there is a peak many more
would be created and than released after a peak passes

Now about DB connection... What SQL connector are you using?

If you are using cppdb I'd recommend to use its internal connection pooling instead of keeping the connection
withing the application itself.

Now each time you need an sql connection you just create a cppdb::session with connection string and the 
connection would be fetched from a pool. What is more important it would close a connections that are out of
use for a long time.

One of the problems of keeping an open SQL connection withing a application is that an application can be
idle for a long time. One of such cases is for example not using a connection at all because data is fetched
from a cache (some real problem I used to had when I used connection-per-application approach)

Another problem that in case of errors you need to be able to close connection and not use it any more (i.e.
reopen). CppDB does this for you. Connection that received errors on it wouldn't go back to pool.

I hope this helps.

Also having better application pool implementation with more fine grained tuning is something
that would be nice to have + some generic "object" pooling for any type of objects would
be good thing as well.

Artyom Beilis
--------------
CppCMS - C++ Web Framework:   http://cppcms.com/
CppDB - C++ SQL Connectivity: http://cppcms.com/sql/cppdb/

--------------------------------------------
On Thu, 2/13/14, Jean-Frédéric Gaudreault <jfg...@gm...> wrote:

 Subject: [Cppcms-users] How can I limit the total maximum number of synchronous application object in the pool at any given time...
 To: cpp...@li...
 Date: Thursday, February 13, 2014, 6:27 PM
 
 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
 
 
 
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