Large Object Heap

  • Thread starter Thread starter eschneider
  • Start date Start date
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eschneider

When determining the size of the object for the LOH, I assume that sub
objects (like Address in the Person class) are excluded?

class Person

string NameLast
string NameFirst
Address AddressHome
Address AddressWork

end class

class Address
string Street
string State
string City
string Zip
end class

Thanks,

Schneider
 
eschneider said:
When determining the size of the object for the LOH, I assume that sub
objects (like Address in the Person class) are excluded?
Click to expand...
They're not, but of course reference types only count as 4 bytes (or 8 bytes
if you're 64-bit). The LOH size determination doesn't recursively walk the
object structure to add up sizes, if that's what you mean. Indeed, since
those sub-objects could be shared, that would yield wrong results.
class Person

string NameLast
string NameFirst
Address AddressHome
Address AddressWork

end class

class Address
string Street
string State
string City
string Zip
end class
Click to expand...
Only the individual strings would be candidates for the LOH; the Person and
Address instances never are because they're far shy of the 85,000 bytes
threshold. And it's also pretty unlikely that you'll have strings bigger
than 85K...
 
Ok, but you point is they do count for something (4 or 8 bytes for each
reference).

So if you have a lot of references it could end-up over the limit.

Thanks,
Schneider
 
eschneider said:
Ok, but you point is they do count for something (4 or 8 bytes for each
reference).

So if you have a lot of references it could end-up over the limit.
Click to expand...
I'm not sure the CLR actually supports a class with over 21,250 fields, but
if it does, yes, an instance of such a class would go in the LOH...

Usually only arrays end up in the LOH. Few instance objects are big enough
to take up >85K on their own.
 
Hello Schneider,

Jeroen has given a very good explanation about this issue.

In addition, a class can also exceed the size threshold if it contains lots
of large structures, since the structure members will also be allocated
inside the memory area of the object instance.

I'd like to provide the following article written by Maoni that is related
to this issue:
Large Object Heap Uncovered -
http://msdn.microsoft.com/en-us/magazine/cc534993.aspx

If you need additional information on this please let me know.

Have a nice day!

Sincerely,
Feng Chen([email protected], remove 'online.')
Microsoft Online Community Support

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--------------------
| Reply-To: "eschneider" <[email protected]>
| From: "eschneider" <[email protected]>
| Subject: Large Object Heap
| Date: Fri, 27 Jun 2008 14:05:29 -0500
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|
| When determining the size of the object for the LOH, I assume that sub
| objects (like Address in the Person class) are excluded?
|
| class Person
|
| string NameLast
| string NameFirst
| Address AddressHome
| Address AddressWork
|
| end class
|
| class Address
| string Street
| string State
| string City
| string Zip
| end class
|
| Thanks,
|
| Schneider
|
|
|
 
Feng said:
In addition, a class can also exceed the size threshold if it contains lots
of large structures, since the structure members will also be allocated
inside the memory area of the object instance.
Click to expand...

....which would only happen if the structures were badly designed in the
first place. A structure should not be larger than 16 bytes, or there
isn't really a point in making it a structure.
 
eschneider said:
When determining the size of the object for the LOH, I assume that sub
objects (like Address in the Person class) are excluded?

class Person

string NameLast
string NameFirst
Address AddressHome
Address AddressWork

end class

class Address
string Street
string State
string City
string Zip
end class

Thanks,

Schneider
Click to expand...

Only the references themselves (plus a little book keeping overhead) are
included when calculating the size, so it is not very likely that a type
by itself will cause instances to be allocated in the LOH. Arrays and
strings are the most likely candidates for LOH.

There's an excellent treatment of how the LOH works in one of the latest
issues of MSDN magazine (I don't have the issue at hand, but I'm sure
you can find it through a search).

Regards,
Brian Rasmussen [MVP C#]
 
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