Allocating more than 1,000 MB of memory in 32-bit .NET process

Question

I am wondering why I'm not able to allocate more that 1,000 MB of memory in my 32-bit .NET process. The following mini application throws an OutOfMemoryException after having allocated 1,000 MB. Why 1,000 MB, and not say 1.8 GB? Is there a process-wide setting I could change?

static void Main(string[] args)
{
    ArrayList list = new ArrayList();
    int i = 0;
    while (true)
    {
        list.Add(new byte[1024 * 1024 * 10]); // 10 MB
        i += 10;
        Console.WriteLine(i);
    }
}

PS: Garbage collecting does not help.

Edit, to clarify what I want: I have written a server application which deals with very large amounts of data before writing to database/disk. Instead of creating temporary files for everything, I have written an in-memory cache, which makes the whole thing super-fast. But memory is limited, and so I tried to find out what the limits are. And wondered why my small test program threw the OutOfMemoryException after exactly 1,000 MB.

Answer 1

Having enormous blocks of memory is never a good idea, even in 64bit. You get big problems with contiguous memory and fragmentation.

The problem here is finding a contiguous block. You could try enabling 3gb mode (which might help it find a few more bytes) but I really advise against it. The answers here are:

• use less memory
• use a database/file system
• use x64

You might also want to read Eric Lippert's blog (he seems to have a blog entry for every common .NET question...)

Answer 2

The virtual address space limit of a Win32 process is 1.5GB (not entirely true). Additionally in the .NET frameworks there is a limiter to the % of memory a .NET process can consume. The machine.config has a processModel element with an attribute memoryLimit which is the % of available memory a process can consume. The default value is 60%.

If the machine you're running on has 2GB of memory or you haven't enabled the /3GB switch in your BOOT.INI then you're going to get ~1.3GB of memory per process.

I can't find the KB article but if I remember correctly .NET 1.x cannot address beyond the 1.5GB (1.8GB?) limit regardless of your settings.

http://blogs.msdn.com/tmarq/archive/2007/06/25/some-history-on-the-asp-net-cache-memory-limits.aspx http://social.msdn.microsoft.com/Forums/en-US/clr/thread/c50ea343-b41b-467d-a457-c5a735e4dfff http://www.guidanceshare.com/wiki/ASP.NET_1.1_Performance_Guidelines_-_Caching#Configure_the_Memory_Limit