Application Module Pooling in ADF

Here I got a time to share a few things. Now days, one of the basic interview question in application module is what is application module pooling.

Oracle documentation says that,  "An application module pool is a collection application module instances of the same type."

While speaking application module pooling, activation and passivation comes into the picture.
 
Say as an e.g: If an application module pool has 5 application module instance. All of the application module instance are occupied. 4 instance are occupied and servicing their request. one instance is occupied. but user is in idle state.

Now this time a new user performing a request means application module pool check for application module instance Is there any idle.? 

If so, suddenly scan the user session data into insert into PS_TXN table. This store mechanism is called passivation. Now new user can utilizes the application module instance.

When idle user resume his work, framework will automatically retrieve his own data.
id will be handled at PS_TXN table level and Session Management too.

In below figure you can see the PS_TXN table.