What is the memory overhead of an Object in .NET? I'm talking about an arbitrary bare-bones object.... the overhead of the internal .NET workings or references:
var obj = new System.Object();
How much space does obj occupy in the heap?
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1Heap and stack are implementation details. – asawyer May 18 '12 at 15:53
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3@ThePower: Not a duplicate. That other question (and its answers) don't talk about the basic memory overhead of a .NET object at all. – Robert Harvey May 18 '12 at 15:55
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2@ThePower It doesn't answer my question, I want to know the memory overhead, not how to measure it – reach4thelasers May 18 '12 at 15:57
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3@asawyer - could you explain your comment? I thought a heap was an abstract data structure in which all objects are stored... why is it wrong to ask "How much space does it occupy in the heap"? – reach4thelasers May 18 '12 at 16:02
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3How does: "You could use a memory profiler like .NET Memory Profiler...." answer my question???? – reach4thelasers May 18 '12 at 16:03
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@reach4thelasers: Why can't you just measure it to find out? – user541686 May 18 '12 at 16:27
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@reach4thelasers http://blogs.msdn.com/b/ericlippert/archive/2009/04/27/the-stack-is-an-implementation-detail.aspx – asawyer May 18 '12 at 17:07
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I talk about this in a blog post "Of memory and strings". It's implementation-specific, but for the Microsoft .NET CLR v4, the x86 CLR has a per-object overhead of 8 bytes, and the x64 CLR has a per-object overhead of 16 bytes.
However, there are minimum sizes of 12 and 24 bytes respectively - it's just that you get the first 4 or 8 bytes "free" when you start storing useful information :)
(See the blog post for more information.)
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2There may be padding for member variables to fit on address boundaries as well. This padding concept further complicates the calculation of memory overhead of an object. No wonder C# never introduced sizeof operator for instance variables for types. – RBT Aug 16 '16 at 09:13
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1I ran a few tests in a .net console app to check memory usage. Creating 10 million empty objects resulted in ca 340MB usage (includes the list with references). Adding 1 or 2 integers to the class changed nothing. Only when adding the 3rd integer did I see an increase to ca 430MB. This fully supports your statement of 24 bytes minimum with 8 bytes free for information. – JohnF May 04 '20 at 16:13
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Hi @JonSkeet could you add a generic definition for "memory overhead"? I dont really understand what it is. It's like an extra memory allocated for each object? Thank you – BorisD Feb 01 '22 at 15:32
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@BorisD: Yes - it's the memory required in addition to the "obvious" memory required for the data itself. (Housekeeping information etc.) – Jon Skeet Feb 01 '22 at 16:12