CODEWITHSUNDEEP
c#wpfvb.netwindowsmemory-leaks
Faris Zacina
Faris Zacina

Reputation: 14274

Windows - WPF Process out of memory crash with plenty of available physical memory

i have a WPF desktop app that crashed with the following exception:

System.Data.SqlServerCe.SqlCeException (0x80004005): There is not enough memory on the device running SQL Server

However, the memory values at crash time are somewhat not clear to me:

btw. The Current Process values are taken from the C# Process class. The ComputerInfo values are taken from the VB.NET ComputerInfo class.

My app is compiled with (x86) configuration. The process is running on a Windows 7 64 Bit machine.

I see that the Available Virtual Memory is 166MB which looks pretty low.

How is it possible that the process crashed when there is plenty of AvailablePhysicalMemory reported by the VB.NET ComputerInfo class?..

The high Current and Peak Working Set indicates that probably there is a memory leak somewhere, but i still don't get why it crashed when there was plenty of available RAM.

Upvotes: 0

Views: 1773

Answers (3)

Eric Lippert
Eric Lippert

Reputation: 660004

Your assumption that physical memory is in any way relevant is the fundamental cause of your confusion. Remember, the right way to think about memory is that process memory is disk space. Physical memory is just a fast cache on top of the disk. Again, let me emphasize this: if you run out of physical memory then your machine gets slower. It doesn't give an out of memory error.

The relevant resource is virtual address space, not memory. You only get 4GB of virtual address space per 32 bit process and 2GB of that is reserved for the use of the operating system. Suppose you have 166 MB of virtual address space left and that it is divided into four chunks of 42 MB each. If a request for 50MB comes in, that request cannot be fulfilled. Unfortunately the error you get is "out of memory" and not "out of virtual address space", which would be a more accurate error message.

The solution to your problem is either (1) allocate way less than 2GB of user memory per process, (2) implement your own system for mapping memory into and out of virtual address space, or (3) use a 64 bit process that has a far larger amount of available virtual address space.

Upvotes: 7

Dan Puzey
Dan Puzey

Reputation: 34200

An OutOfMemoryException can be caused by a number of things.

It can be caused when your application doesn't have enough space in the Gen0 managed heap or in the large object heap to process a new allocation. This is a rare case, but will typically happen when the heap is too fragmented to allow a new allocation (sometimes of quite a small size!). In Gen0 this might happen due to an excessive use of pinned objects (when handling interop with unmanaged code); in the LOH this was once a common problem but appears much less frequent in later versions of .NET. It's worth noting that SqlCe access would include unmanaged code; I've not heard of any major issues with this but it's possible that your use of the SqlCe classes is causing problems.

Alternatively, it could be a virtual memory issue - which seems quite plausible given the figures you've posted. Eric Lippert has a good blog post about this kind of issue here. If your application is trying to write pages of memory to disk so that it can keep something else in memory, you might well see the exception because your VM is so limited.

Upvotes: 1

Hamlet Hakobyan
Hamlet Hakobyan

Reputation: 33381

Each 32 bit (you have 32 bit process because TotalVirtualMemory: 2047 MB) can address only up to 2GB of memory, regardless of the available physical memory.

Upvotes: 1

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