When running Visual Studio's memory profiler (Memory Usage Analysis) on my Windows Store app it shows me that there are many objects of type System.Signature (mscorlib.dll) on the heap.
I can't find System.Signature in the Object Browser, so I assume that it is some internal class only used and only usable by the Framework.
Does anyone have more information about this class?
When or why are System.Signature objects created and what are they used for internally?
According to the memory profiler, the number of System.Signature objects raises constantly while the app is used. This looks like a memory leak to me, but where do these objects come from or what creates these objects? To answer this question, I first need to know what System.Signature actually is.
Related
I have written a windows service using .NET technologies. I am using `JetBrains dotMemory' tool to understand the memory leak.
I am getting below report but as a new bee I am not sure how to read this.
System namespace is showing more survived bytes. But how do I know which code is the root cause of memory leak?
At the first your should decide which kind of memory issue you are going to find
Constantly growing memory consumption - get base snaphsot, get another after memory consumption is increased, open snapshots comparison, open new objects created after first snapshot, look at them to understand which should be collected.
Ensure that some key object doesn't leak - set your app in a state when some object should not be presented in memory (e.g. close some view), get snapshot, using filter on "Group by type" view to ensure that this object is not presented in memory.
Memory traffic - get base snapshot if needed, run action/algorithm in your app which you want to check, get snapshot. Open "Memory Traffic" view, look if it looks as you implemented or more objects then you expected were allocated during the action.
Grab this free book for other possible memory issues.
P.S. Only you as an app author can answer the question, is it a problem or it is as designed.
You should look at the survived bytes / retained bytes which will point you to the base instance or the root object of the creation. It depends on your application design and implementation to decide whether the specified object in the memory should be retained or not.
If you identify the root object of the creation, you should try to separate the linkage and make the .net garbage collector to automatically collect the unwanted objects.
There is no fixed flag points to identify memory leaks.
Using ANTS Memory Profiler
Using Windbg or here
One source of memory leaks are the event handlers that are not being de-referenced.
Example:
myClass.DoSomething += Event_DoSomething
You need to make sure the resources are being clearead like below:
myClass.DoSomething -= Event_DoSomething
I am doing memory profiling for my application using Visual Studio diagnostic tool. I find that there is Node takes up a lot of memory (based on Inclusive Size Diff. (bytes). (see below #1). And when I click on the first instance of Node, 'Referenced Objects', I see Node is referencing other Node. And I see something like 'Overlapped data' in the attribute.
How can I find out where is creating these Node as they are from mscorlib.ni.dll.
The weapon of choice when you are rooting through these .NET Framework objects is a good decompiler. I use Reflector, there are others.
You see an opaque Node<T> object back. Just type it into the Search box, out pops but a few types that use it. Most are in the System.Collections.Concurrent namespace. Well, look no further, the profiler already told you about that one. Clearly it is the Stack<T> class in the System.Collections.Concurrent namespace that's storing Nodes.
Your profiler told you there is just one Stack<> class object that owns these objects. Well good, that narrows it down to just a single object. It just happens to have 208 elements. Hmm, well, not that much, is it?
That's not where you have to stop, the Stack<> class is a pretty useless class, nobody ever actually uses it in their code. Keep using the decompiler and let it search for usages of that class.
Ah, nice, that's a very short list as well. You see System.Data.ProviderBase show up several times, hmm, this question probably isn't related to querying dbases. Only other set of references is System.PinnableBufferCache.
"Pinnable buffers", whoa, that's a match. Pinning a buffer is important when you ask native code to get a job done to fill a managed array. With BeginRead(), the universal asynchronous I/O call. The driver needs a stable reference to the array while it is working on the async I/O request. Getting a stable buffer requires pinning in .NET. And big bingo in the profiler data, you see OverlappedData, the core data-structure in Windows to do async I/O.
Long story short, you found this guy's project. Programmers noticed, not very often.
Knowing when the stop profiling is very important. You cannot change code written by another programmer. And nobody at Microsoft thinks that guy did anything wrong. He didn't, caches are Good Things.
You are most definitely done. Congratulations.
I would like to ask a very general question about a technical concept of which I do not know whether it exists or whether it is feasible at all.
The idea is the following:
I have an object in Garbage Collected language (e.g. C# or Java). The objects may itself contain several objects but there is no reference to any other objects that are not sub-element of the objects (or the object itself).
Theoretically it would be possible to get the memory used by this object which is most likely not a connected piece. Because I have some knowledge about the objects I can find all reference variables/properties and pointers that at the end point to another piece of the memory (probably indirectly, depending on the implementation of the programming language and virtual machine). I can take this pieces of memory combining them to a bigger piece of memory (correcting the references/pointers so that they are still intact). This piece of memory, basically bytes, could be written to a storage for example a database or a redis cache. On another machine I could theoretically load this object again an put it into the memory of the virtual machine (maybe again correct the references/pointers if they are absolute and not relative). Then I should have the same object on the other VM. The object can as complicated as I want, may also contain events or whatever and I would be able to get the state of the object transfered to anther VM (running on another computer). The only condition is that it would not contain references to something outside the objects. And of course I have to know the class type of the object on the other VM.
I ask this question because I want to share the state of an object and I think all this serialization work is just an overhead and it would be very simple if I could just freeze the memory and transport to another VM.
Is something like this possible, I'd say yes, though it might be complicated. maybe it is not possible with some VM's due to their architecture. Does something like this exist in any programming language? Maybe even in non garbage collected languages?
NOTE: I am not sure what tags should be added to this question except from programming-language, also I am not sure if there might be a better place for such a question. So please forgive me.
EDIT:
Maybe the concept can be compared to the initrd on Linux or hibernation in general.
you will have to collect all references to other objects. including graphs of objects (cycles) without duplications. it would require some kind of 'stop the world' at least for the serializing thread. it's complicated to do effectively but possible - native serialization mechanisms in many languages (java) are doing it for the developer.
you will need some kind of VM to abstract from the byte order in different hardware architectures.
you will have to detach object from any kind of environment. you can't pass objects representing threads, files handles, sockets etc. how will you detect it?
in nowadays systems memory is virtual so it will be impossible to simply copy addresses from one machine to another - you will have to translate them
objects are not only data visible to developer, it's also structure, information of sandboxing, permissions, superclasses, what method/types were already loaded and which are still not loaded because of optimalizations and lazy loading, garbage collector metadata etc
version of your object/class. on one machine class A can be created from source ver 1 but on another machine there allready might be objects of class A built from source of version 2
take performacne into consideration. will it be faster then old-school serialization? what benefits will it have?
and probably many more things none of us thought about
so: i've never heard of such solution. it seems theoretically doable but for some reason no one have ever done that. everyone offers plain old programmatic serialization. maybe you discover new, better way but keep in mind you'll be going against the crowd
I am developing a windows application using C# .Net. This is in fact a plug-in which is installed in to a DBMS. The purpose of this plug-in is to read all the records (a record is an object) in DBMS, matching the provided criteria and transfer them across to my local file system as XML files. My problem is related to usage of memory. Everything is working fine. But, each time I read a record, it occupies the memory and after a certain limit the plug in stops working, because of out of memory.
I am dealing with around 10k-20k of records (objects). Is there any memory related methods in C# to clear the memory of each record as soon as they are written to the XML file. I tried all the basic memory handling methods like clear(), flush(), gc(), & finalize()/ But no use.
Please consider he following:
Record is an object, I cannot change this & use other efficient data
structures.
Each time I read a record I write them to XML. and repeat this
again & again.
C# is a garbage collected language. Therefore, to reclaim memory used by an object, you need to make sure all references to that object are removed so that it is eligible for collection. Specifically, this means you should remove the objects from any data structures that are holding references to them after you're done doing whatever you need to do with them.
If you get a little more specific about what type of data structures you're using we can probably give a more specific answer.
What is this thing called a KGL SIMULATOR and how can its memory utilisation be managed by application developers?
The background to the question is that I'm occasionally getting errors like the following and would like to get a general understanding of what is using this heap-space?
ORA-04031: unable to allocate 4032 bytes of shared memory ("shared pool","select text from > view$ where...","sga heap(3,0)","kglsim heap")
I've read forum posts through Google suggesting that the kglsim is related to the KGL SIMULATOR, but there is no definition of that component, or any tips for developers.
KGL=Kernel General Library cache manager, as the name says it deals with library objects such cursors, cached stored object definitions (PL/SQL stored procs, table definitions etc).
KGL simulator is used for estimating the benefit of caching if the cache was larger than currently. The general idea is that when flushing out a library cache object, it's hash value (and few other bits of info) are still kept in the KGL simulator hash table. This stores a history of objects which were in memory but flushed out.
When loading a library cache object (which means that no existing such object is in library cache), Oracle goes and checks the KGL simulator hash table to see whether an object with matching hash value is in there. If a matching object is found, that means that the required object had been in cache in past, but flushed out due space pressure.
Using that information of how many library cache object (re)loads could have been been avoided if cache had been bigger (thanks to KGL simulator history) and knowing how much time the object reloads took, Oracle can predict how much response time would have been saved instancewide if shared pool was bigger. This is seen from v$library_cache_advice.
Anyway, this error was probably raised by a victim session due running out of shared pool space. In other words, someone else may have used up all the memory (or all the large enough chunks) and this allocation for KGL sim failed because of that.
v$sgastat would be the first point for troubleshooting ORA-4031 errors, you need to identify how much free memory you have in shared pool (and who's using up most of the memory).
--
Tanel Poder
http://blog.tanelpoder.com
I've found that KGL stands for "Kernel Generic Library".
Your issue could be a memory leak within Oracle. You probably should open a case with Oracle support.