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.NET Forum / .NET Framework / Performance / January 2007Generic collections vs. arrays on structs vs. class
I started working on a performance demanding app. I created structures that I put into an Array. Then I realized that arrays are byref objects, while struct is byval. Now, I presumed, that managing these objects would be faster if I would use class instead of structure, cause I can send a reference, not the whole object as an procedure parameter. Am I right? but.... I realized that it would be very good to use generic collections instead of array (that keeps classes). Would it be faster than structs on arrays? (or even classes put in arrays). Also, wich kind of generic collections would be the best for it? These objects have one primary key (because of it Dictionary is one possibility), but that object has 2-3 index keys wich are often used, but they're not unique. Wich way you recomend? Hello, generic classes (List<T> for example) internally use an array of type T, so access is relative fast. But List<T> (as well as Dictionary<TKey, TValue> are not extensible (no virtual methods). Your option here is either to create a decorator for Dictionary<TKey, TValue> which implements the Add, Remove methods and handles those additional indizes. The other method is to inherit from KeyedCollection. This class has some extension points which allow you to maintain your special indexes. If you stick with your array of structs, you end up having one large object in memory. If this object grows beyond ~85kbytes, it will end up on the LargeObjectHeap, which will never be defragmented and only garbage-collected when a full garbage collection is performed (which hopefully doesn't happen very often). So, I would go for a collection of classes. Best regards, Henning Krause >I started working on a performance demanding app. I created structures that >I put into an Array. Then I realized that arrays are byref objects, while [quoted text clipped - 12 lines] > they're not unique. > Wich way you recomend? Hi buu, may be this article help for you: http://blogs.msdn.com/ricom/archive/2006/03/09/548097.aspx > I started working on a performance demanding app. I created structures that > I put into an Array. Then I realized that arrays are byref objects, while [quoted text clipped - 12 lines] > they're not unique. > Wich way you recomend? >I started working on a performance demanding app. I created structures that >I put into an Array. Then I realized that arrays are byref objects, while [quoted text clipped - 6 lines] > instead of array (that keeps classes). Would it be faster than structs on > arrays? (or even classes put in arrays). It depends on whether you ever resize the array, use random or sequential access, etc. It's really hard to beat an array of structs for fixed-size random access. For one thing, it's a single large memory area passed by reference. As others have said, it will probably end up on the Large Object Heap which means the garbage collector can pretty much ignore it. Another thing is that since it is stored sequentially, locality of reference is extremely good so you get maximum benefit from your CPU cache. You can of course still pass individual elements by reference, either using the ref keyword, or by passing the array and an index. > Also, wich kind of generic collections would be the best for it? > These objects have one primary key (because of it Dictionary is one > possibility), but that object has 2-3 index keys wich are often used, but > they're not unique. > Wich way you recomend? Does the primary key change? (Often, Rarely, Never) If never, then you can fill the array in sorted order and use the extremely fast+scalable binary search algorithm. Again, if objects don't move around, then an index (meaning offset) is as good as a tracking reference, but without the GC overhead, so you could store indexes (meaning offset) in your index (meaning key) structures. If you add, remove, and move elements frequently, then a Dictionary of instances will be far better than an array. Hi I have lately written an app to measure exactly this. I came to the result, that an array of classes is the fastest, but structs are much less memory consuming. About the idea of generic collections: their performance is extremely bad (i got a 4x better performance with arrays).  SignatureYours, Lukas Cavigelli http://www.cavigelli.net >I started working on a performance demanding app. I created structures that >I put into an Array. Then I realized that arrays are byref objects, while [quoted text clipped - 12 lines] > they're not unique. > Wich way you recomend? I have forgotten to say something that might be important as well: Memory consumption and performance depends on the language you are using. Although c# and vb are both .net languages vb needs more memory (and therefore has to read and write more) because of its compatibility to vb6. Yours, Lukas Cavigelli http://www.cavigelli.net > Hi > [quoted text clipped - 20 lines] >> they're not unique. >> Wich way you recomend? Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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