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  • Arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • C# arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • Even lighter than SQLite

    - by Richard Fabian
    I've been looking for a C++ SQL library implementation that is simple to hook in like SQLite, but faster and smaller. My projects are in games development and there's definitely a cutoff point between needing to pass the ACID test and wanting some extreme performance. I'm willing to move away from SQL string style queries, allowing it to be code driven, but I haven't found anything out there that provides SQL like flexibility while also preferring performance over the ACID test. I don't want to go reinventing the wheel, and the idea of implementing an SQL library on my own is quite daunting, even if it's only going to be simple subset of all the calls you could make. I need the basic commands (SELECT, MODIFY, DELETE, INSERT, with JOIN, and WHERE), not data operations (like sorting, min, max, count) and don't need the database to be atomic, or even enforce consistency (I can use a real SQL service while I'm testing and debugging).

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  • What is the easiest straightforward way of telling which version performs better?

    - by Peter Perhác
    I have an application, which I have re-factored so that I believe it is now faster. One can't possibly feel the difference, but in theory, the application should run faster. Normally I would not care, but as this is part of my project for my master's degree, I would like to support my claim that the re-factoring did not only lead to improved design and 'higher quality', but also an increase in performance of the application (a small toy-thing - a train set simulation). I have toyed with the latest VisualVM thing today for about four hours but I couldn't get anything helpful out of it. There isn't (or I haven't found it) a way to simply compare the profiling results taken from the two versions (pre- and post- refactoring). What would be the easiest, the most straightforward way of simply telling the slower from the faster version of the application. The difference of the two must have had an impact on the performance. Thank you.

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  • Proper usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something?

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  • List comprehension, map, and numpy.vectorize performance

    - by mcstrother
    I have a function foo(i) that takes an integer and takes a significant amount of time to execute. Will there be a significant performance difference between any of the following ways of initializing a: a = [foo(i) for i in xrange(100)] a = map(foo, range(100)) vfoo = numpy.vectorize(foo) a = vfoo(range(100)) (I don't care whether the output is a list or a numpy array.) Is there a better way?

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  • Does allocation speed depend on the garbage collector being used?

    - by jkff
    My app is allocating a ton of objects (1mln per second; most objects are byte arrays of size ~80-100 and strings of the same size) and I think it might be the source of its poor performance. The app's working set is only tens of megabytes. Profiling the app shows that GC time is negligibly small. However, I suspect that perhaps the allocation procedure depends on which GC is being used, and some settings might make allocation faster or perhaps make a positive influence on cache hit rate, etc. Is that so? Or is allocation performance independent on GC settings under the assumption that garbage collection itself takes little time?

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  • NULL pointer dereference in swiotlb_unmap_sg_attrs() on disk IO

    - by Inductiveload
    I'm getting an error I really don't understand when reading or writing files using a PCIe block device driver. I seem to be hitting an issue in swiotlb_unmap_sg_attrs(), which appears to be doing a NULL dereference of the sg pointer, but I don't know where this is coming from, as the only scatterlist I use myself is allocated as part of the device info structure and persists as long as the driver does. There is a stacktrace to go with the problem. It tends to vary a bit in exact details, but it always crashes in swiotlb_unmap_sq_attrs(). I think it's likely I have a locking issue, as I am not sure how to handle the locks around the IO functions. The lock is already held when the request function is called, I release it before the IO functions themselves are called, as they need an (MSI) IRQ to complete. The IRQ handler updates a "status" value, which the IO function is waiting for. When the IO function returns, I then take the lock back up and return to request queue handling. The crash happens in blk_fetch_request() during the following: if (!__blk_end_request(req, res, bytes)){ printk(KERN_ERR "%s next request\n", DRIVER_NAME); req = blk_fetch_request(q); } else { printk(KERN_ERR "%s same request\n", DRIVER_NAME); } where bytes is updated by the request handler to be the total length of IO (summed length of each scatter-gather segment).

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  • iPhone. Particle system performance

    - by e40pud
    I try to draw rain and snow as particle system using Core Graphics. In simulator rendering proceeded fine but when I run my app on real device rendering is slow down. So, advise me please approaches to increase particle system drawing performance on iPhone. May be I should use OpenGL for this or CoreAnimation?

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  • Can you get a Func<T> (or similar) from a MethodInfo object?

    - by Dan Tao
    I realize that, generally speaking, there are performance implications of using reflection. (I myself am not a fan of reflection at all, actually; this is a purely academic question.) Suppose there exists some class that looks like this: public class MyClass { public string GetName() { return "My Name"; } } Bear with me here. I know that if I have an instance of MyClass called x, I can call x.GetName(). Furthermore, I could set a Func<string> variable to x.GetName. Now here's my question. Let's say I don't know the above class is called MyClass; I've got some object, x, but I have no idea what it is. I could check to see if that object has a GetName method by doing this: MethodInfo getName = x.GetType().GetMethod("GetName"); Suppose getName is not null. Then couldn't I furthermore check if getName.ReturnType == typeof(string) and getName.GetParameters().Length == 0, and at this point, wouldn't I be quite certain that the method represented by my getName object could definitely be cast to a Func<string>, somehow? I realize there's a MethodInfo.Invoke, and I also realize I could always create a Func<string> like: Func<string> getNameFunc = () => getName.Invoke(x, null); I guess what I'm asking is if there's any way to go from a MethodInfo object to the actual method it represents, incurring the performance cost of reflection in the process, but after that point being able to call the method directly (via, e.g., a Func<string> or something similar) without a performance penalty. What I'm envisioning might look something like this: // obviously this would throw an exception if GetActualInstanceMethod returned // something that couldn't be cast to a Func<string> Func<string> getNameFunc = (Func<string>)getName.GetActualInstanceMethod(x); (I realize that doesn't exist; I'm wondering if there's anything like it.) If what I'm asking doesn't make sense, or if I'm being unclear, I'll be happy to attempt to clarify.

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  • Performance impact using culture invariant resources

    - by Praveen S
    I would like to know the performance impact of using the culture invariant resources instead of culture specific ones. For example, we plan to deploy a website and not have any en-US resources. This is because our culture invariant resources are always identical to the en-US resources. Is this a good idea ? What are the cons?

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  • PHP debugging or performance Hook

    - by Joshua
    In an interpreted language like PHP it is possible in theory to set up some sort of callback function that would be run indiscriminately after every line of code. I am wondering if such a thing exists in PHP or if such a thing could be accomplished in any way? Such a feature could be useful for diagnostics or performance tests. Does anyone know of such a mechanism in PHP?

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  • Best data recovery tools?

    - by Nonick
    So due to a recent act of stupidity and bravado, I uttered the words "backups! who needs backups?!" and what followed was the tragic loss of 260gb of data. This scenario in particular is requiring me to recover a repartitioned hard disk, but I was wondering what tools people here use in general to recover lost data. I'm sure everyone has been there, either accidentally rewriting files, resaving an old version, computer crash, hard disk death, user deletes an important document etc. So was thinking it might be an interesting point of discussion as to what you guys use to recover lost data. I appologise if this is considered irrelevant, but considering there has been a few recovery questions, I think this might be interesting.

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  • MySQL: LOAD DATA reclaim disk space after delete

    - by Michael
    I have a DB schema composed of MYISAM tables, i am interested to delete old records from time to time from some of the tables. I know that delete does not reclaim the memory space, but as i found in a description of DELETE command, inserts may reuse the space deleted In MyISAM tables, deleted rows are maintained in a linked list and subsequent INSERT operations reuse old row positions. I am interested if LOAD DATA command also reuses the deleted space? UPDATE I am also interested how the index space reclaimed?

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  • fastest c++ file compression library available?

    - by Fabien Hure
    I have a need to find the best library to compress in memory data. I am currently using zlib but I am wondering if there is a better compression library; better in terms of performance and memory footprint. It should be able to handle multiple files in the same archive. I am looking for a C/C++ library. Performance is the key factor. The files that are being compressed are small to large XML files.

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  • function to profile / performance test PHP functions?

    - by Haroldo
    I'm not experiencing any performance issues, however I'd like to take a look at what takes how long and how much memory cpu it uses etc. I'd like to get a firsthand understanding of which things can be bottle necks etc and improve any code i might reuse or build upon... (perfectionist) I'm looking to create a litte function that i can call at the begining and end of each function that records: execution time memory used cpu demand any ideas?

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  • Are the ususal database performance-tuning tips invalide for a third-party app like Drupal

    - by Paul Strugger
    When you have a slow database app, the first suggestions that people make is to: Track the slow queries Add appropriate indexes In the case you are building your own application this is very logical, but when you use a CMS like Drupal, that are people have developed and tuned, is this approach valid? I mean, aren't Drupal tables already fine-tuned for performance? Even if I try to see which queries are the slow ones, what could I do about it? Re-write Drupal core?!?

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  • A nuts and bolts reference to C# performance and memory use

    - by phil
    I wonder if anyone could point me in the direction where I can read about the nuts and bolts of C#. What I'm interested in learning are method call costs, what it costs to create objects and such. My aim of learning this is to get a better understanding of how increase the performance of an application and get a better understanding of how the C# language works. The reference should preferable be a book, a book that I can read cover to cover.

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  • Why would SQL be very slow when doing updates?

    - by ooo
    Suddenly doing updates into a few tables have gotten 10 times slower than they used to be. What are some good recommendations to determine root cause and optimization? Could it be that indexing certain columns are causing updates to be slow? Any other recommendations? I guess more important than guesses would be help on the process of identifying the root cause or metrics around performance. Is there anything in Fluent NHibernate that you can use to help identify the root cause of performance issues?

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  • C# Dictionary Performance

    - by derek
    I am using a Dictionary to store data, and will be caching it. I would like to avoid server memory issues, and have good performance by limiting the size of the Dictionary<, either in size or number of entries. What is the best method of doing this? Is there another class I should be considering other than a Dictionary?

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