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Minimizing usage of RAM by created objects in runtime in C#

I was wondering what are the best practices when creating objects, performing LINQ in C#. For instance, I realize that when I open up a connection using LINQ I should be putting the model object into a using statement like this:
using(var ctx = new mymodel())
{
}
Now, what about the objects that are EF classes?
They do not implement IDisposable interface thus I can't do something like this when creating an object like this for example:
using(var user = new Users())
{
}
But when an action is called like this:
public ActionResult InsertUser()
{
var user = new Users();
}
I have no clear picture what happens with this object once the insert into the db is finished. Does this object stays allocated in memory or it gets released? If not, what are best practices to release memory once they aren't needed anymore..?
On the other there are static variables as well...
So to sum things up, my questions are:
what are best practices to release memory when creating instances of an object of a class?
Is implementation of IDisposable interface on every class that I have good choice?
When a static variable is created in .NET MVC, what is the best way to release memory taken by this kind of variables?
Same question goes for Session object?
P.S. Guys, I'd really appreciate if all of you that are reading this to post your opinion or post some useful links for some documentations/blog posts so that I can expand my horizons =)

Before you do any performance tweaks I highly recommend to run a memory profiler (for example JetBrains dotMemory, but there are others) and find out the actual source of the problem. Without information from profiler, your optimisations will be like sticking your finger at a sky and shouting "Rainbow!" i.e. useless at best, harmful at worst.
Also after identifying issues with profiler, but before starting changing your code, I recommend reading about how Garbage Collection works in .Net. Here are some references to get you started:
MSDN Garbage Collection
MSDN Garbage Collector Basics and Performance Hints
.Net Garbage Collection in depth
Here are some links to answer your questions:
IDisposable vs Garbage Collector
Static vs Garbage Collector: 1, 2
Session and Garbage Collection

In response to comment.
When you create regular .NET object, .NET runtime knows everything about it, because runtime created it. It knows where in memory it's located, when it is no longer needed and so on. When it is no longer needed - runtime will reclaim its memory. That is managed (by runtime) object. You should not care about memory management for such objects.
Now take for example file handle. When you open file in .NET, it will delegate this operation to OS (for example, Windows). This resource is not managed by runtime, it is managed by OS. So, it is unmanaged resource. So author of .NET library code which works with files (I mean person who created FileStream and similar classes, not uses them) should manually write code to release such resource (close file handle in this case). By convention, author will use IDisposable.Dispose method for code that releases such resources AND ensures that when underlying object (like FileStream) will be collected by GC - unmanaged resources will also be released. So even if you forget to call Dispose - file handle will be closed when GC collects FileStream (not that it will happen not magically but because code author explicitly made it happen like this). But that might happen any time in the future, you don't want to leave file handle open for undetermined time - so you always call Dispose yourself when you are done with IDisposable object.
The same applies to most unmanaged resources. For example, database connection is managed by database, and you don't want to leave database connection open for undetermined time, so you call Dispose and explicitly notify database to close it (and even if you don't call it - author of .NET database code took care to do that when object is collected). EF context wraps database connection, so it also implements IDisposable. If you don't want to leave connection open until context will be collected (and you sure don't want that) - you call Dispose yourself.
Or suppose you write your own code to work with images using ImageMagick. That is C library, so runtime has no idea about its inner workings. You ask library to allocate memory for your image, but .NET cannot reclaim such memory - it does not manage it, it is managed by ImageMagick C library. So you implement IDisposable and tell ImageMagick to release memory in that method.

In the case of var user = new Users(); which does not implement IDisposable, and any object for that matter which is not disposed, will only be guaranteed to exist where there is an active reference to this object; after which it will qualify for disposal the next time the Garbage Collector (GC) tries to free up memory.
In your example above, as soon as this leaves the method InsertUser() it will no longer have any references pointing to it, and therefore will be up for garbage collection.
If however a reference exists, such as in the following code, the object will not be disposed until the reference is cleared, or the containing class is disposed.
private User _insertedUser;
public ActionResult InsertUser()
{
_insertedUser = new Users();
}
The garbage collector fires when the application needs to release some memory. When it fires, it performs several sweeps on objects within memory to tell if any references exist. It first scans every object which has been newly created since the last time the GC was called. Objects which survive this sweep are promoted a generation. If after the sweep more memory is still required, then a 2nd generation sweep is performed. This will scan every object which has survived a single garbage collection to see if it can now be freed. Again if an object survives, it moves up another generation, with 3 generation sweeps in total.
This method helps the GC perform memory management while limiting the high costs involved (newer objects are more likely to be available for release). As GC has a high cost associated to it, it's better if objects are disposed of through user's code to help limit the number of times the GC is called.
tldr;
Dispose objects if they implement IDisposable; an easy way is to
surround it by a 'using'.
If an object cannot be disposed, and it is no longer required, make sure all references to the object is cleared (especially references outside of a method which the object was created).
This enables the GC to release it from memory.

How to dispose heavy set of static variable and collection?

I made a big windows app, and in the program.cs class i am using a lot to static variables
around 20 and some of these are used for big collection of object that i make during the process.
I want to know how should i mange this in the finish of application where and how should i call them dispose. I made GC.Collect but that hangs application and degrade the performance.
And when i dint call GC.Collect it was giving memory lick and hanging for long.
Please let me know how should i manage this static class, static variables. So that performance boost.

I think the way you are using the static variables is completely wrong, you might have misunderstood the concept.
You should mark any field as static only when you know, variables will be accessed through out the life of program i.e. they will be GC'ed only when you terminate the program.
EDIT In C# the memory is automatically managed by the Garbage Collector, the programmer need to know only that when an object which is created is applicable for Garbage Collection. In MSDN ducumentation it is clearly mentioned,
C# employs automatic memory management, which frees developers from manually allocating and freeing the memory occupied by objects. Automatic memory management policies are implemented by a garbage collector. The memory management life cycle of an object is as follows:
When the object is created, memory is allocated for it, the constructor is run, and the object is considered live.
If the object, or any part of it, cannot be accessed by any possible continuation of execution, other than the running of destructors, the object is considered no longer in use, and it becomes eligible for destruction. The C# compiler and the garbage collector may choose to analyze code to determine which references to an object may be used in the future. For instance, if a local variable that is in scope is the only existing reference to an object, but that local variable is never referred to in any possible continuation of execution from the current execution point in the procedure, the garbage collector may (but is not required to) treat the object as no longer in use.
Once the object is eligible for destruction, at some unspecified later time the destructor (Section 10.12) (if any) for the object is run. Unless overridden by explicit calls, the destructor for the object is run once only.
Once the destructor for an object is run, if that object, or any part of it, cannot be accessed by any possible continuation of execution, including the running of destructors, the object is considered inaccessible and the object becomes eligible for collection.
Finally, at some time after the object becomes eligible for collection, the garbage collector frees the memory associated with that object.
In simple words, if an object has no more live references (pointers whose scope has not ended) which are pointing to it, it is eligible for GC.
In your case the static variables are are having the scope which extends across the entire run of the program and once you remove those references either by assigning those to new objects or assigning them to null then old objects will be applicable for GC if no other live references pointing to old objects are alive.

You have IDisposable objects (Forms and Controls, I'm guessing) and need to dispose them at some appropriate time. The best way to solve this is going to be to create an object model appropriate to your domain, and have it manage them. I don't know about your domain, so it's hard to give details about that.
To make it more convenient, you could group these variables together in one class. Instead of holding these variables in the Program class, put them in another class that Program references, and make that class IDisposable. Something like this:
public class Resources : IDisposable
{
public MyForm MyForm {get;set;}
public MyControl MyControl {get;set;}
//etc...
public void Dispose()
{
if(MyForm != null)
MyForm.Dispose()
if(MyControl != null)
MyControl.Dispose()
//etc..
}
}
If the problem with this is that you want to avoid bugs around accessing Disposed objects, don't make them static! If they are not static, you can control what object bind to them more clearly, and make sure those object stop holding a reference to them when they are disposed.

C# - Garbage Collection

Ok so I understand about the stack and the heap (values live on the Stack, references on the Heap).
When I declare a new instance of a Class, this lives on the heap, with a reference to this point in memory on the stack. I also know that C# does it's own Garbage Collection (ie. It determines when an instanciated class is no longer in use and reclaims the memory).
I have 2 questions:
Is my understanding of Garbage Collection correct?
Can I do my own? If so is there any real benefit to doing this myself or should I just leave it.
I ask because I have a method in a For loop. Every time I go through a loop, I create a new instance of my Class. In my head I visualise all of these classes lying around in a heap, not doing anything but taking up memory and I want to get rid of them as quickly as I can to keep things neat and tidy!
Am I understanding this correctly or am I missing something?

Ok so I understand about the stack and the heap (values live on the Stack, references on the Heap
I don't think you understand about the stack and the heap. If values live on the stack then where does an array of integers live? Integers are values. Are you telling me that an array of integers keeps its integers on the stack? When you return an array of integers from a method, say, with ten thousand integers in it, are you telling me that those ten thousand integers are copied onto the stack?
Values live on the stack when they live on the stack, and live on the heap when they live on the heap. The idea that the type of a thing has to do with the lifetime of its storage is nonsense. Storage locations that are short lived go on the stack; storage locations that are long lived go on the heap, and that is independent of their type. A long-lived int has to go on the heap, same as a long-lived instance of a class.
When I declare a new instance of a Class, this lives on the heap, with a reference to this point in memory on the stack.
Why does the reference have to go on the stack? Again, the lifetime of the storage of the reference has nothing to do with its type. If the storage of the reference is long-lived then the reference goes on the heap.
I also know that C# does it's own Garbage Collection (ie. It determines when an instanciated class is no longer in use and reclaims the memory).
The C# language does not do so; the CLR does so.
Is my understanding of Garbage Collection correct?
You seem to believe a lot of lies about the stack and the heap, so odds are good no, it's not.
Can I do my own?
Not in C#, no.
I ask because I have a method in a For loop. Every time I go through a loop, I create a new instance of my Class. In my head I visualise all of these classes lying around in a heap, not doing anything but taking up memory and I want to get rid of them as quickly as I can to keep things neat and tidy!
The whole point of garbage collection is to free you from worrying about tidying up. That's why its called "automatic garbage collection". It tidies for you.
If you are worried that your loops are creating collection pressure, and you wish to avoid collection pressure for performance reasons then I advise that you pursue a pooling strategy. It would be wise to start with an explicit pooling strategy; that is:
while(whatever)
{
Frob f = FrobPool.FetchFromPool();
f.Blah();
FrobPool.ReturnToPool(f);
}
rather than attempting to do automatic pooling using a resurrecting finalizer. I advise against both finalizers and object resurrection in general unless you are an expert on finalization semantics.
The pool of course allocates a new Frob if there is not one in the pool. If there is one in the pool, then it hands it out and removes it from the pool until it is put back in. (If you forget to put a Frob back in the pool, the GC will get to it eventually.) By pursuing a pooling strategy you cause the GC to eventually move all the Frobs to the generation 2 heap, instead of creating lots of collection pressure in the generation 0 heap. The collection pressure then disappears because no new Frobs are allocated. If something else is producing collection pressure, the Frobs are all safely in the gen 2 heap where they are rarely visited.
This of course is the exact opposite of the strategy you described; the whole point of the pooling strategy is to cause objects to hang around forever. Objects hanging around forever is a good thing if you're going to use them.
Of course, do not make these sorts of changes before you know via profiling that you have a performance problem due to collection pressure! It is rare to have such a problem on the desktop CLR; it is rather more common on the compact CLR.
More generally, if you are the kind of person who feels uncomfortable having a memory manager clean up for you on its schedule, then C# is not the right language for you. Consider C instead.

values live on the Stack, references on the Heap
This is an implementation detail. There is nothing to stop a .NET Framework from storing both on the stack.
I also know that C# does it's own Garbage Collection
C# has nothing to do with this. This is a service provided by the CLR. VB.NET, F#, etc all still have garbage collection.
The CLR will remove an object from memory if it has no strong roots. For example, when your class instance goes out of scope in your for loop. There will be a few lying around, but they will get collected eventually, either by garbage collection or the program terminating.
Can I do my own? If so is there any real benefit to doing this myself or should I just leave it?
You can use GC.Collect to force a collection. You should not do it because it is an expensive operation. More expensive than letting a few objects occupy memory a little bit longer than they are absolutely needed. The GC is incredibly good at what it does on its own. You will also force short lived objects to promote to generations they wouldn't get normally.

First off, to Erics seminal post about The truth about value types
Secondly on Garbage collection, the collector knows far more about your running program than you do, don't try to second guess it unless you're in the incredibly unlikely situation that you have a memory leak.
So to your second question, no don't try to "help" the GC.
I'll find a post to this effect on the CG and update this answer.

Can I do my own? If so is there any real benefit to doing this myself or should I just leave it.
Yes you can with GC.Collect but you shouldn't. The GC is optimized for variables that are short lived, ones in a method, and variables that are long lived, ones that generally stick around for the life time of the application.
Variables that are in-between aren't as common and aren't really optimum for the GC.
By forcing a GC.Collect you're more likely to cause variables in scope to be in forced into that in-between state which is the opposite from you are trying to accomplish.
Also from the MSDN article Writing High-Performance Managed Applications : A Primer
The GC is self-tuning and will adjust itself according to applications
memory requirements. In most cases programmatically invoking a GC will
hinder that tuning. "Helping" the GC by calling GC.Collect will more
than likely not improve your applications performance

Your understanding of Garbage Collection is good enough. Essentially, an unreferenced instance is deemed as being out-of-scope and no longer needed. Having determined this, the collector will remove an unreferenced object at some future point.
There's no way to force the Garbage Collector to collect just a specific instance. You can ask it to do its normal "collect everything possible" operation GC.Collect(), but you shouldn't.; the garbage-collector is efficient and effective if you just leave it to its own devices.
In particular it excels at collecting objects which have a short lifespan, just like those that are created as temporary objects. You shouldn't have to worry about creating loads of objects in a loop, unless they have a long lifespan that prevents immediate collection.

Please see this related question with regard to the Stack and Heap.
In your specific scenario, agreed, if you new up objects in a for-loop then you're going to have sub-optimal performance. Are the objects stored (or otherwise used) within the loop, or are they discarded? If the latter, can you optimize this by newing up one object outside the loop and re-using it?
With regard to can you implement your own GC, there is no explicit delete keyword in C#, you have to leave it to the CLR. You can however give it hints such as when to collect, or what to ignore during collection, however I'd leave that unless absolutely necessary.
Best regards,

Read the following article by Microsoft to get a level of knowledge about Garbage Collection in C#. I'm sure it'll help anyone who need information regarding this matter.
Memory Management and Garbage Collection in the .NET Framework

If you are interested in performance of some areas in your code when writing C#, you can write unsafe code. You will have a plus of performance, and also, in your fixed block, the garbage collector most likely will not occur.

Garbage collection is basically reference tracking. I can't think of any good reason why you would want to change it. Are you having some sort of problem where you find that memory isn't being freed? Or maybe you are looking for the dispose pattern
Edit:
Replaced "reference counting" with "reference tracking" to not be confused with the Increment/Decrement Counter on object Reference/Dereference (eg from Python).
I thought it was pretty common to refer to the object graph generation as "Counting" like in this answer:
Why no Reference Counting + Garbage Collection in C#?
But I will not pick up the glove of (the) Eric Lippert :)

Want to understand how a managed language like C# has memory leaks

Since C# is a managed language that performs garbage collection automatically to clean up objects etc, ...
what are the ways one can introduce a memory leak?
Are there some non-obvious ways that one should look out for?
How can you detect or look for memory leaks (once you understand how they are generated etc.)

Usually leaks show up in the form of a developer writing code that "holds on" to objects when they shouldn't be, which subsequently disallows the garbage collector from collecting on those objects.
The garbage collector is pretty good at what it does, but if you don't understand what it's doing, the likelihood of you introducing memory issues into your program is pretty high.
I would suggest reading up on the GC and understanding how it works.
Here's something to get you started:
http://www.simple-talk.com/dotnet/.net-framework/understanding-garbage-collection-in-.net/

Two.
First, building up referenced objects. Like creating objects that subscribe to an event on a form. The form is active, so can not be collected, and the event subscriptions... keep the objects alive.
Second, block the garbage colelctor in native code. Like the oracle ODP.NET driever does under certain conditions. Stops the finalizer, so any object requiring finalization WILL NOT GET IT - and thus never be released.

The obvious "memory leak" one could cause in a GC-ed language would be caused simply be retaining a reference to an object after it's needed - this is especially likely if you roll your own caching or keep other global state.
Another way would be leaking memory in unmanaged resources that weren't disposed of, although most of the standard library classes will probably dispose of those in destructors so the memory will be reclaimed sooner or later.
(I'm marking the post as CW because of the open-ended nature of the question.)

A memory leak means keeping in memory objects you don't need anymore. In C#, considering the GC collects unreferenced objects, it's equivalent to say keeping references to objects you don't need.
Think about uncorrectly scoped declarations, infinite recursion or iteration...

C# memory leak?

I have a C# application that loops through a datatable, and pushes these into some locations such as Sage and a SQL table.
While it used to work fine, I'm inexplicably now getting Out of Memory exceptions after an hour or so of running it. I've noticed in the task manager, the memory usage rises by anbout 1mb every second, and keeps on going!
I was under the impression garbage collection would take of anything, but to be sure I ensure I dispose any objects after using them. I know without code it's hard to diagnose, but there's a lot of it and I'm looking more for general advice.

but to be sure I ensure I dispose any objects after using them
Dispose() is not directly related to memory management or leaks.
You'll have to look for unused objects that are still 'reachable'. Use a memory-profiler to find out.
You can start with the free CLR-Profiler.

There are a couple of potential problems that spring to mind:
There is a large pool of objects that are left inelegible for garbage collection (i.e. they are still "reachable"). For example if you add an object to an list in every loop then the list will grown unboundedly and each element in the list will remain inelegible for garbage collection as long as that list is still reachable. I'm not claiming that this is what is happening, this is just an example of how memory might be allocated and then left without being collected.
For some reason the garbage collector isn't doing a collection.
The high memory use is actually due to an unmanaged component that you are using in your application (e.g. via P/Invoke or COM interop).
Without seeing any code its tricky to give specific advice on how to fix your problem however reading through Investigating Memory Issues should give you some pointers on how to diagnose the memory problem yourself. In particular my first step would probably be to examine performance counters to see if the garbage collector is actually running, and to check the various heap sizes.
Note that Dispose and the IDisposable interface is unrelated to memory use - its important to dispose of objects like database connections once you are done with them as it frees up any associated resources (e.g. handles) however disposing of objects that implement IDisposable is very unlikely to have an impact on memory use.

Garbage collection can only get rid of objects that are no longer referenced from anything else. In addition it can only get rid of managed objects - it has no control about memory created from native code you may be interfacing with. These therefore are the two root causes for memory leaks in C# code.
The first thing to look at is perfmon. Get the counters for the private bytes and the .net heap size for the process. If the heap size remains flat (or rises and drops) but private bytes keeps increasing you've got some native code allocating memory and not releasing it.
If the heap size just keeps growing then the leak is in your managed code and you'll need a profiler like ANTS, DotTrace or even WinDbg (with SOS extension) to inspect the heap and see what objects are lying about.

The most popular "memory leak" on .Net platform is forgotten collection that repeatetly added in some infinite loop.

When you new something for temporary memory use.
Always use following way, it ensures calling dispose.
using (Someclass A = new Someclass())
{
....something about A
}
Someclass is a class implemented interface IDisposable
GC won't save you if there some part of unsafe code is involved(P/Invoke, Com etc..), and if there still a reference some where exists.
If you find memory leaking, use WinDbg will see what is in the heap.
This article may give you some help.
http://www.codeproject.com/KB/dotnet/Memory_Leak_Detection.aspx