Are there any methods to trace how much memory is allocated, de-allocated and retrieved by GC for a particular module in C# .net ?
I want to trace out the possible memmory leaks in my module. I am getting occasional System out of memory exceptions in production.
You should use a memory profiler to profile memory allocations.
I've used JetBrains dotTrace, which has a nice mode of taking two snapshots at different times and showing which objects were allocated but not collected between those two snapshots. Allows for easy finding for memory leaks, where you keep allocating new instances and not collect them.
To view the difference between two application memory states, you can
mark the start and the end of a time interval, then capture a
difference snapshot which shows how much memory was allocated and
released during the marked time interval. The view can be filtered to
show only live, new, or dead objects, or the difference between new
and dead objects.
A memory profiler is a good idea. You can also get a rough sketch using the PerformanceCounters See the msdn. You could then gather some stats on your prod environment if it's hard to reproduce locally.
you can try .NET Memory Allocation Profiling with Visual Studio.
try this msdn article to show you how http://blogs.msdn.com/b/dotnet/archive/2013/04/04/net-memory-allocation-profiling-with-visual-studio-2012.aspx.
About 1/3 of the way through the article it shows how to Run the .NET memory allocation profiler.
JetBrains, as mentioned, as well as .NET Memory profiler has helped me several times. If you have a memory leakage problem in WPF there are some good advice in this post (old but a lot is still valid):
http://blogs.msdn.com/b/jgoldb/archive/2008/02/04/finding-memory-leaks-in-wpf-based-applications.aspx
Related
I am using C# 2.0 for a multi-threaded application that receives atleast thousand callbacks per second from an unmanaged dll and periodically send messages out of socket. GUI remains on main thread.
My application mostly creates object at the startup and periodically during the execution for a short lived period.
The problem I am experiencing is periodic latency spike (measured by time stamping a function at start and end) which I suppose happen when GC run.
I ran perfmon and here are my observations...
Gen0 Heap Size is flat with a spike every few seconds with periodic spike.
Gen1 Heap Size is always on the roll. Up and down
Gen2 Heap Size follows a cycle. It keep increasing till it becomes flat for a while and then drops.
Gen 0 and 1 Collections are always increasing in a range of 1 to 5 units.
Gen 2 collections is constant.
I recommend using a memory profiler in order to know if you have a real memory leak or not. There are many available and they will allow you to quickly isolate any issue.
The garbage collector is adaptive and will modify how often it runs in response to the way your application is using memory. Just looking at the generation heap sizes is going to tell you very little in terms of isolating the source of any problem. Second quessing how it works is a bad idea.
RedGate Ants Memory Profiler
SciTech .NET Memory Profiler
EQATEC .NET Profiler
CLR Profiler (Free)
So as #Jalf says, there's no evidence of a memory "leak" as such: what you discuss is closer to latency caused by garbage collection.
Others may disagree but I'd suggest anything above a few hundred callbacks per second is going to stretch a general purpose language like C#, especially one that manages memory on your behalf. So you're going to have to get smart with your memory allocation and give the runtime some help.
First, get a real profiler. Perfmon has its uses but even the profiler in later versions of Visual Studio can give you much more information. I like the SciTech profiler best (http://memprofiler.com/); there are others including a well respected one from RedGate reviewed here: http://devlicio.us/blogs/scott_seely/archive/2009/08/23/review-of-ants-memory-profiler.aspx
Once you know your baseline, aim to eliminate gen2 collections. They'll be the really slow ones. Work hard in any tight loops to eliminate as much memory allocation as you can -- strings are the usual offenders.
Some useful tips are in an old but still relevant MSDN article here: http://msdn.microsoft.com/en-us/library/ms973837.aspx.
It's also good to read Tess Ferrandez's (outstanding) blog series on debugging ASP.NET applications - book a day out of the office and start here: http://blogs.msdn.com/b/tess/archive/2008/02/04/net-debugging-demos-information-and-setup-instructions.aspx.
I remember reading a blog post about memory performance in .NET (specifically, XNA on the XBox 360) a while ago (unfortunately I can't find said link anymore).
The nutshell of achieving low latency memory performance was to make sure you never run gen 2 GC's at a performance critical time (although it is OK to run them when latency is not important; there are a bunch of notification callback functions on the GC class in more recent versions of the framework which may help with this). There are two ways to make sure this happens:
Don't allocate anything that escapes to gen 2. It's alarmingly easy for objects to escape to gen 2 when you don't realise it, so this often translates into: don't allocate anything in performance critical code. Because no objects escape to gen 2, the GC doesn't need to collect.
Allocate everything you need upfront and use object pooling. Your gen 2 heap will be big but because nothing is being added to it, the GC doesn't need to collect it.
It may be helpful to look into some XNA or Silverlight related performance articles because
games and resource constrained devices are often very latency sensitive. (Note that you have it easy because the XBox 360 and, until Mango, Windows Phone only had a single generation GC (mark-and-sweep collector)).
I'm trying to see how feasible it is to attempt to accurately determine that there is a potential memory leak in a block of managed .NET code programmatically. The reason to do this would be to isolate some block of code that appears to be leaking memory, and to then use a standard profiler to further determine the actual cause of the leak. In my particular business case, I would be loading a 3rd party class that extends one of mine to check it for leaks.
The approach that first comes to mind is something like this:
Wait for GC to run.
Get the current allocated memory from the GC.
[Run block of managed code.]
Wait for GC to run.
Get the current allocated memory from the GC and subtract from the allocated memory recorded before running the block of code. Is it correct that the difference should theoretically be (near) 0 if all objects allocated in the block of code that was run were dereferenced appropriately and collected?
Certainly the immediate issue with this is that there will likely be waiting...and waiting...and waiting for the non-deterministic GC to run. If we skip that aspect, the calculation for determining if the block of code leaked any memory however can vary wildly, and would not necessarily be accurate, as some items may not have been collected at the time.
Does the above seem like my best option of attempting to determine somewhat accurately if a block of code is leaking memory? Or are there other working methods that are used in real-life? Thanks.
Personally, I would never dare to do memory profiling on my own. I'll fear that I either do not have the full knowledge and that it would take endless time to do so.
Instead I used successfully memory profilers like Red Gate's ANTS Memory Profiler.
While using ANTS Profiler is awesome it doesn't help if your problem is only seen in production.
Tess Ferrandez has a series of Labs that demonstrate how to debug production problems, including memory leaks. They focus on ASP.NET but it can be use for other types of applications as well.
You really need a Memory Profiler like this one: With that, you can:
start your application, take a memory snapshot (manually or from your code)
[Run block of managed code]
take another memory snapshot
compare the two snapshots and see which new objects are now on the managed heap
I believe it does exactly what you want to do, only far less painful. It also has some helpful filters like "show objects that are kept alive by delegates". It can also analyze memory dumps from a production system.
I understand there are many questions related to this, so I'll be very specific.
I create Console application with two instructions. Create a List with some large capacity and fill it with sample data, and then clear that List or make it equal to null.
What I want to know is if there is a way for me to know/measure/profile while debugging or not, if the actual memory used by the application after the list was cleared and null-ed is about the same as before the list was created and populated. I know for sure that the application has disposed of the information and the GC has finished collecting, but can I know for sure how much memory my application would consume after this?
I understand that during the process of filling the list, a lot of memory is allocated and after it's been cleared that memory may become available to other process if it needs it, but is it possible to measure the real memory consumed by the application at the end?
Thanks
Edit: OK, here is my real scenario and objective. I work on a WPF application that works with large amounts of data read through USB device. At some point, the application allocates about 700+ MB of memory to store all the List data, which it parses, analyzes and then writes to the filesystem. When I write the data to the filesystem, I clear all the Lists and dispose all collections that previously held the large data, so I can do another data processing. I want to know that I won't run into performance issues or eventually use up all memory. I'm fine with my program using a lot of memory, but I'm not fine with it using it all after few USB processings.
How can I go around controlling this? Are memory or process profilers used in case like this? Simply using Task Manager, I see my application taking up 800 MB of memory, but after I clear the collections, the memory stays the same. I understand this won't go down unless windows needs it, so I was wondering if I can know for sure that the memory is cleared and free to be used (by my application or windows)
It is very hard to measure "real memory" usage on Windows if you mean physical memory. Most likley you want something else like:
Amount of memory allocated for the process (see Zooba's answer)
Amount of Managed memory allocated - CLR Profiler, or any other profiler listed in this one - Best .NET memory and performance profiler?
What Task Manager reports for your application
Note that it is not necessary that after garbage collection is finished amount of memory allocated for your process (1) changes - GC may keep allocated memory for future managed allocations (this behavior is not specific to CLR for memory allcation - most memory allocators keep free blocks for later usage unless forced to release it by some means). The http://blogs.msdn.com/b/maoni/ blog is excelent source for details on GC/memory.
Process Explorer will give you all the information you need. Specifically, you will probably be most interested in the "private bytes history" graph for your process.
Alternatively, it is possible to use Window's Performance Monitor to track your specific application. This should give identical information to Process Explorer, though it will let you write the actual numbers out to a separate file.
(A picture because I can...)
I personaly use SciTech Memory Profiler
It has a real time option that you can use to see your memory usage. It has help me find a number of problems with leaking memory.
Try ANTS Profiler. Its not free but you can try the trial version.
http://www.red-gate.com/products/dotnet-development/ants-performance-profiler/
How I can get the actual memory used in my C# application?
Task Manager shows different metrics.
Process Explorer shows increased usage of private bytes.
Performance counter (perfmon.msc) showed different metrics
when I used .NET memory profiler, it showed most of the memory is garbage collected and only few Live bytes.
I do not know which to believe.
Memory usage is somewhat more complicated than displaying a single number or two. I suggest you take a look at Mark Russinovich's excellent post on the different kinds of counters in Windows.
.NET only complicates matters further. A .NET process is just another Windows process, so obviously it will have all the regular metrics, but in addition to that the CLR acts as a memory manager for the managed application. So depending on the point of view these numbers will vary.
The CLR effectively allocates and frees virtual memory in big chunks on behalf of the .NET application and then hands out bits of memory to the application as needed. So while your application may use very little memory at a given point in time this memory may or may not have been released to the OS.
On top of that the CLR itself uses memory to load IL, compile IL to native code, store all the type information and so forth. All of this adds to the memory footprint of the process.
If you want to know how much memory your managed application uses for data, the Bytes in all heaps counter is useful. Private bytes may be used as a somewhat rough estimate for the application's memory usage on the process level.
You may also want to check out these related questions:
Reducing memory usage of .NET applications?
How to detect where a Memory Leak is?
If you are using VS 2010 you can use Visual Studio 2010 Profiler.
This tool can create very informative reports for you.
If you want to know approximately how many bytes are allocated on the GC heap (ignoring memory used by the runtime, the JIT compiler, etc.), you can call GC.GetTotalMemory. We've used this when tracking down memory leaks.
Download VADump (If you do not have it yet)
Usage: VADUMP.EXE -sop [PID]
Well, what is "actual memory used in my C# application" ?
Thanks to Virtual memory and (several) Memory management layers in Windows and the CLR, this is a rather complicated question.
From the sources you mention the CLR profiler will give you the most detailed breakdown, I would call that the most accurate.
But there is no 'single number' answer, the question whether Application A use more or less memory than B can be impossible to answer.
So what do you actually want to know? Do you have a concrete performance problem to solve?
I have a large website that seems to be sucking up all the memory that is being allocated. There is nothing else on the server beside this site. Within a week it eats away the 2 gigs and requires a restart. Currently this is server 2008 32 bit using IIS 7. We are reinstalling to use 64bit and add more memory. It would be nice to be able to track down where the leaks are occurring.
So what is the best practice to tracking memory leaks?
Memory leaks in .NET are not that common, but when they happen it is most commonly due to unattached event handlers. Make sure you detach handlers, before the listeners go out of scope.
Another option is if you forget to call Dispose() on IDisposable resources. This may prevent cleanup of unmanaged resources (which are not handled by GC).
And yet another possible reason is a deadlocked finalizer. That will prevent all remaining objects in the finalizer queue from being collected.
I use WinDbg + Sos to track down leaks. The steps are as follows
Dump the heap and look for suspects
Use !gcroot to find out what is keeping the suspects alive
Repeat as necessary
Be aware that large memory usage may also be due to heap fragmentation. The regular heaps are compacted, but pinned objects can cause fragmentation. Also, the LOH is not compacted so fragmentation is not uncommon for LOH.
Excellent tutorials on WinDbg + sos here: http://blogs.msdn.com/tess/
Run a profiler on your code.
Here are two good options:
RedGate's memory profiler
Jetbrains dotTrace
I believe both products have a free trial.
Run, don't walk, over to Tess
Ferrandez's blog, If broken it is,
fix it you should, which has well
scripted labs dedicated to learning
how to diagnose and debug crash, hang
and memory issues with .NET code. She
has some of the best material I've
found to date to help get you started.
Commercial memory profilers such as ANTS and SciTech are excellent resources that will show what objects are in the heap, and how they are rooted. Most commercial memory profilers have the ability to load a memory 'snap' of a process (say from your production environment).
You can capture a memory 'snap' (see Snap v. Dump) using adplus.vbs or DebugDiag. Adplus is available as part of the Debugging Tools for Windows. DebugDiag will also have some rudimentary analysis (but seems to be more reliable on unmanaged code) automagically.
Monitor the Application
For an idea on what to monitor, see Improving .NET Performance and Scalability, specifically Chapter 15.
As to how to monitor, there are commercial tools available for that as well, however, every Windows machine also comes with Perfmon.exe, which can be used to record relevant performance counters.
Test the Application
For an idea on how to perform load, or stress, tests, check out the Patterns and Practices Performance Testing Guidance for Web Applications.
Debug the Application
Once you've identified you've got a problem (monitoring) and your able to reproduce the problem (testing) you can get down to debugging the problem. See the links for Tess - that information will carry you a long way.
Then rinse and repeat! :)
Good luck!
Z
In performance monitor, add counters for Process/Private Bytes and .NET CLR Memory/# Bytes in All Heaps. Private bytes is all memory and CLR memory is just managed. So if the CLR memory remains fairly even but the private bytes continues to grow over time, this means that the leak is in unmanaged resource. That usually means that you are not disposing of native resources properly. A good thing to look at is stuff like COM or IO (streams and files). Make sure all of that stuff gets disposed when you are done with it.
You can try using profilers such as dotTrace -- set it into a memory trace and run your application.
This should give you clues in which assemblies and areas of the application that eat up too much memory on the get go.
This is probably prevention rather then detection, but at the c# code level, you should check that any classes that use large resources such as images and other files are correctly implementing the dispose pattern. If needed you may also need to override the finalizer.
MSDN has good guidance on this subject.
If you have any classes in your application that you know make use of large resources, these are the first places to look for memory issues.
I've found that the EQATEC Profiler is pretty good, plus it's free!
Check out the Memory and Memory Leak labs on this blog post:
.NET Debugging Demos
They may be of some help. Basically, you can use WinDBG to analyze a memory dump and help determine what is eating up all of your memory.
We used a similar approach to determine that Regex was chewing up all of our memory, but only when the product was run on 64-bit machines. The learning curve is kind of steep, but WinDBG is a very powerful tool.
This new article of mine maybe useful: How to detect and avoid memory and resources leaks in .NET applications
Do you do any Office interop? If so, make sure you clean up your application objects. That's one possible culprit.
Another is global objects, such as anything that's static.
Do you have lots of dynamic pages on your site?
You can also try IBM's Purify
I suggest you try with a small set of dynamic pages disabling all others for the meantime. I hate to say this but it's very much possible that IIS 7 may also have leaks.
Look at this article on detecting .NET application memory leaks and related articles mentioned at the bottom of the page and hopefully you will find a solution or at least an idea to resolve it.
Thanks