Why Garbage collector have only 3 generations, not more or less?

Question

As i have gone through Garbage Collection (GC) and its generation(0,1,2). The question strikes to me that, why Microsoft decided to keep it to 3?

Why not to less than 3 or more than 3 ? I need some logical explanation.

Answer 1

Quoting the documentation,

Generations

The heap is organized into generations so it can handle long-lived and short-lived objects. Garbage collection primarily occurs with the reclamation of short-lived objects that typically occupy only a small part of the heap. There are three generations of objects on the heap:

Generation 0.

This is the youngest generation and contains short-lived objects. An example of a short-lived object is a temporary variable. Garbage collection occurs most frequently in this generation.

Newly allocated objects form a new generation of objects and are implicitly generation 0 collections, unless they are large objects, in which case they go on the large object heap in a generation 2 collection.

Most objects are reclaimed for garbage collection in generation 0 and do not survive to the next generation.

Generation 1.

This generation contains short-lived objects and serves as a buffer between short-lived objects and long-lived objects.

Generation 2.

This generation contains long-lived objects. An example of a long-lived object is an object in a server application that contains static data that is live for the duration of the process.

Garbage collections occur on specific generations as conditions warrant. Collecting a generation means collecting objects in that generation and all its younger generations. A generation 2 garbage collection is also known as a full garbage collection, because it reclaims all objects in all generations (that is, all objects in the managed heap).

We can see that Generation 2 is for objects that should last for the duration of the process. It is not sensible to model objects that can live longer than the process, at least on operating systems I know about.

I suspect that there is not a greater granularity of generations because it would prove more cumbersome than the benefits derived. Any extrapolation on that concept is pure conjecture without real world performance testing.

I suspect even a canonical answer from a designer of the GC would be prone to speculation but they may be able to detail how that level of granularity was reckoned.