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• Is referencing a selector faster in jquery than actually calling the selector? if so, how much does it make a difference?

  - by anthonypliu

  Hi, I have this code: $(preview-button).click(...) $(preview-button).slide(...) $(preview-button).whatever(...) Is it a better practice to do this: var preview-button = $(preview-button); preview-button.click(...); preview-button.click(...); preview-button).slide(...); preview-button.whatever(...); It probably would be better practice to do this for the sake of keeping code clean and modular, BUT does it make a difference performance wise? Does one take longer to process than the other? Thanks guys.

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• Selecting a value from multiple dictionaries inside an enumeration

  - by johaanfaust

  If I have an enumeration of dictionaries IEnumerable<IDictionary<string, float>> enumeration can I perform a Linq query on it so that I can select by a value from each dictionary in the enumeration using the same key? I can do this in a loop: float f; foreach (var dictionary in enumeration) { if (dictionary.TryGetValue("some key", out f)) { Console.WriteLine(f); } } (The eventual plan is to compare the performance of the query verses the equivalent nested looping statements (the enumeration itself is formed from either another query or an equivalent set of loops).)

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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• Which is more efficent PHP: array_intersect() OR array_intersect_key()

  - by Jordan Rutty

  Is it more efficient to use the key intersect or the value intersect if both key and value have the same contents for example: Array ( [743] => 743 [744] => 744 [745] => 745 [746] => 746 [747] => 747 [748] => 748 ) Is there any difference in performance in using one or the other with the same values. Similar to the difference of using double or single quotes?

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• Can I replicate some of the optimisations done by the JVM by hand?

  - by Subb

  I'm working on a Sudoku solver at school and we're having a little performance contest. Right now, my algorithm is pretty fast on the first run (about 2.5ms), but even faster when I solve the same puzzle 10 000 times (about 0.5ms for each run). Those timing are, of course, depend of the puzzle being solved. I know the JVM do some optimization when a method is called multiple time, and this is what I suspect is happening. I don't think I can further optimize the algorithm itself (though I'll keep looking), so I was wondering if I could replicate some of the optimizations done by the JVM. Note : compiling to native code is not an option Thanks!

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• C++ Vector at/[] operator speed

  - by sub

  In order to give functions the option to modify the vector I can't do curr = myvec.at( i ); doThis( curr ); doThat( curr ); doStuffWith( curr ); But I have to do: doThis( myvec.at( i ) ); doThat( myvec.at( i ) ); doStuffWith( myvec.at( i ) ); (as the answers of my other question pointed out) I'm going to make a hell lot of calls to myvec.at() then. How fast is it, compared to the first example using a variable to store the result? Is there a different option for me? Can I somehow use pointers? When it's getting serious there will be thousands of calls to myvec.at() per second. So every little performance-eater is important.

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• Filtering with joined tables

  - by viraptor

  I'm trying to get some query performance improved, but the generated query does not look the way I expect it to. The results are retrieved using: query = session.query(SomeModel). options(joinedload_all('foo.bar')). options(joinedload_all('foo.baz')). options(joinedload('quux.other')) What I want to do is filter on the table joined via 'first', but this way doesn't work: query = query.filter(FooModel.address == '1.2.3.4') It results in a clause like this attached to the query: WHERE foos.address = '1.2.3.4' Which doesn't do the filtering in a proper way, since the generated joins attach tables foos_1 and foos_2. If I try that query manually but change the filtering clause to: WHERE foos_1.address = '1.2.3.4' AND foos_2.address = '1.2.3.4' It works fine. The question is of course - how can I achieve this with sqlalchemy itself?

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• How do I change the class of an object to a subclass of its current class in C++?

  - by Jared P

  I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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• Why is 'using namespace std;' considered a bad practice in C++?

  - by Mana

  Okay, sorry for the simplistic question, but this has been bugging me ever since I finished high school C++ last year. I've been told by others on numerous occasions that my teacher was wrong in saying that we should have "using namespace std;" in our programs, and that std::cout and std::cin are more proper. However, they would always be vague as to why this is a bad practice. So, I'm asking now: Why is "using namespace std;" considered bad? Is it really that inefficient, or risk declaring ambiguous vars(variables that share the same name as a function in std namespace) that much? Or does this impact program performance noticeably as you get into writing larger applications? I'm sorry if this is something I should have googled to solve; I figured it would be nice to have this question on here regardless in case anyone else was wondering.

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• Design guidelines for cache mechanism

  - by Delashmate

  Hi All, I got assignment to write design for cache mechanism (this is work assignment, not homework), This is my first time writing a design document, Our program display images for doctors, and we want to reduce the parsing time of the images So we want to save the parsed data in advance (in files or inside database) Currently I have several design key ideas: Handle locks - each shared data structure should be handled, also files Test - add test to verify the data from the cache is equal to the data from the files To decouple the connection to the database- not to call directly to the database Cleanup mechanisem- to delete old files if the cahce directory exceed configurable threshold Support config file Support performance tool in the feature I will also add class diagram, data flow charts, and workflow What do you think I should add to the key ideas? Do you know good link to atricales about design? Thanks in advance, Dan

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• Is there a way to ignore Cache errors in Django?

  - by Josh Smeaton

  I've just set our development Django site to use redis for a cache backend and it was all working fine. I brought down redis to see what would happen, and sure enough Django 404's due to cache backend behaviour. Either the Connection was refused, or various other errors. Is there any way to instruct Django to ignore Cache errors, and continue processing the normal way? It seems weird that caching is a performance optimization, but can bring down an entire site if it fails. I tried to write a wrapper around the backend like so: class CacheClass(redis_backend.CacheClass): """ Wraps the desired Cache, and falls back to global_settings default on init failure """ def __init__(self, server, params): try: super(CacheClass, self).__init__(server, params) except Exception: from django.core import cache as _ _.cache = _.get_cache('locmem://') But that won't work, since I'm trying to set the cache type in the call that sets the cache type. It's all a very big mess. So, is there any easy way to swallow cache errors? Or to set the default cache backend on failure?

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• Oracle spatial search within distance

  - by KA_lin

  I have the following table Cities: ID(int),City(char),latitude(float),longitude(float). Now based on a user`s longitude(ex:44.8) and latitude(ex:46.3) I want to search for all the cities near him within 100 miles/KM. I have found some examples but don`t know how to adapt them to my case select * from GEO.Cities a where SDO_WITHIN_DISTANCE([I don`t know], MDSYS.SDO_GEOMETRY(2001, 8307, MDSYS.SDO_POINT_TYPE(44.8,46.3, NULL) ,NULL, NULL), 'distance = 1000') = 'TRUE'; Any help would be appreciated. P.S: If it is possible to have the distance and to be sorted P.P.S: I want to do it in this way due to performance issues, I have done this in this way http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL but it takes too long...

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• Which are the current/emerging desktop development technologies worth looking into?

  - by heeboir

  Greetings, With all the existing development towards web development and emerging technologies in that area, I'm left wondering; what is a state of the art way to implement desktop applications in this day and age? If you were to start a new application of considerable size from scratch what technology would you invest your efforts in (focusing on cross platform portability, decent performance and interoperability with existing standards)? I've looked into the Adobe Air platform which appears quite impressive but seems rather limited to support a large application. Would something like Java/SWT still be the sensible choice? Do things like GWT fit the bill? Thanks P.S. I'm leaving my question a bit open-ended in an effort to gather diverse answers. Surely this a subjective matter and there is no right and wrong answer.

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• matrix = *((fxMatrix*)&d3dMatrix); //Evil?

  - by Xilliah

  I've been using matrix = *((fxMatrix*)&d3dMatrix); for quite a while. It worked fine until my screen turned black and received a bucket of frustration on my desk. fxMatrix contains 4 fxVectors. fxVector used to be 16 bytes, but now it was suddenly 20. This was because it inherited fxStreamable, which added the vTable. So one solution is of course just to not inherit fxStreamable, and leave a comment saying that it must always be 16 bytes and never more. Another solution would be to make conversion functions, and copy the matrix completely. This makes it more secure, but has an impact on the performance. I suppose this is the best idea. Another solution is to not convert at all, and stick to D3DXMATRIX, but this makes the engine inconsistent and I personally really dislike this idea. What is your opinion?

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• Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

  - by Personman

  I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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• Why is this loop over mysql resultset slow? (1.4ms per cycle)

  - by pawpro

  The $res contains around 488k rows the whole loop takes 61s! that's over 1.25ms per cycle! What is taking all that time? while($row = $res->fetch_assoc()) { $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['std'] = $row['cost_std']; $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['ecn'] = $row['cost_ecn']; $clist[$row['upload_id']][$row['dialcode_id']][$row['carrier_id']]['wnd'] = $row['cost_wnd']; $dialcode_destination[$row['upload_id']][$row['carrier_id']][$row['dialcode_id']]['other_destination'] = $row['destination_id']; $dialcode_destination[$row['upload_id']][$row['carrier_id']][$row['dialcode_id']]['carrier_destination'] = $row['carrier_destination_id']; } Now resultset of 10 rows, smaller arrays and performance 30 times higher (0.041ms) not the fastest still but better. while($row = $res->fetch_assoc()) { $customer[$row['id']]['name'] = $row['name']; $customer[$row['id']]['code'] = $row['customer']; }

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• How to pass a reference to a string in JavaScript?

  - by ijjo

  Maybe a closure is my solution? Not exactly sure how to pull it off though. The code is set up like so: var globalVar = ''; var globalVar2 = ''; function func() { if (condition) func2(globalVar) else func2(globalVar2) } In func2() I cache some HTML in a main container into the appropriate global variable that I pass to it. Basically I have a main container that holds different pages depending on what tab they choose. For performance I want to cache the page into global vars so I need to know what tab is active to figure out which global var to assign the HTML to.

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• Can Silverlight be linked with a C++ static library ?

  - by Niklaos

  Hi, I'm currently doing research to start a new project. This project will be in 2 parts a light Client (probably console) and an heavy one using silverlight. The light client must be cross-platform. However, they will both use the same Core (by the way, the core will need to use the sockets). I'd like to use C++ to build the light client but given that the core is common to both applications, it would be much appreciated if it's could be the same code. So the question is quite simple : Can Silverlight be compilated with a C++ static library ? And if it's possible, what about cross-platform issues (with moonlight) ? If it's not possible. Which language can i use to work with silverlight while being cross-platform ? Because of performance, a compilated language will be better ! Thanks for your expertise :)

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• Using pthread condition variable with rwlock

  - by Doomsday

  Hello, I'm looking for a way to use pthread rwlock structure with conditions routines in C++. I have two questions: First: How is it possible and if we can't, why ? Second: Why current POSIX pthread have not implemented this behaviour ? To understand my purpose, I explain what will be my use: I've a producer-consumer model dealing with one shared array. The consumer will cond_wait when the array is empty, but rdlock when reading some elems. The producer will wrlock when adding(+signal) or removing elems from the array. The benefit of using rdlock instead of mutex_lock is to improve performance: when using mutex_lock, several readers would block, whereas using rdlock several readers would not block.

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• Using function arguments as local variables

  - by Rubys

  Something like this (yes, this doesn't deal with some edge cases - that's not the point): int CountDigits(int num) { int count = 1; while (num >= 10) { count++; num /= 10; } return count; } What's your opinion about this? That is, using function arguments as local variables. Both are placed on the stack, and pretty much identical performance wise, I'm wondering about the best-practices aspects of this. I feel like an idiot when I add an additional and quite redundant line to that function consisting of int numCopy = num, however it does bug me. What do you think? Should this be avoided?

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• What is the best platform/language for a 3D game in a web browser?

  - by CodeJustin.com

  I have enjoyed making 2D games in various langues (actionscript 3.0, java, python, others) but now I'm ready to move into 3D and to really get me amped up while learning 3D development I'm going to attempt to make a 3D multiplayer game (I already have server written in python). I'm looking for a platform that will run a 3D game well in the browser on low end computers with low end internet. What first came to mind was try Java or use flash/silver light with a 3D framework but I wanted to ask the good people of stackoverflow since performance is a big part of my needs and also good documentation is a plus since I'm just starting 3D development. (the programming language does not matter)

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• Help choosing the right data structure

  - by devoured elysium

  I need a data structure with the following requirements: Needs to be able to get elements by index (like a List). I will always just add / remove elements from the end of the structure. I am inclined to use an ArrayList. In this situation, it seems to be O(1) both to read elements (they always are?), remove elements (I only need to remove them at the end of the list) and to add(I only add to the end of the list). There is only the problem that time to time the ArrayList will have a performance penalty when it's completly full and I need to add more elements to it. Is there any other better idea? I don't think of a data structure that'd beat the ArrayList here. Thanks

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• Java : VolatileImage slower than BufferedImage.

  - by Norswap

  I'm making a game in java and in used BufferedImages to render content to the screen. I had performance issues on low end machines where the game is supposed to run, so I switched to VolatileImage which are normally faster. Except they actually slow the whole thing down. The images are created with GraphicsConfiguration.createCompatibleVolatileImage(...) and are drawn to the screen with Graphics.drawImage(...) (follow link to see which one specifically). They are drawn upon a Canvas using double buffering. Does someone has an idea of what is going wrong here ?

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• ASP.NET Session StateServer - is it possible to extract info about current sessions?

  - by Moe Sisko

  I'm looking into changing the ASP.NET session state mode of our application from SQLServer to StateServer (for performance reasons). In SQLServer mode, it is easy to extract information about the current sessions by querying SQL Server tables like ASPStateTempSessions. e.g. things like when each session was created, when it is due to expire, etc. You could even query the session state blob data to extract further application specific info (e.g. like the UserID, if it was saved in session state). This info was useful for administrators. Just wondering if anyone has managed to do something similar for StateServer mode.

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• Create empty C# event handlers automatically

  - by TomA

  It is not possible to fire an event in C# that has no handlers attached to it. So before each call it is necessary to check if the event is null. if ( MyEvent != null ) { MyEvent( param1, param2 ); } I would like to keep my code as clean as possible and get rid of those null checks. I don't think it will affect performance very much, at least not in my case. MyEvent( param1, param2 ); Right now I solve this by adding an empty inline handler to each event manually. This is error prone, since I need to remember to do that etc. void Initialize() { MyEvent += new MyEvent( (p1,p2) => { } ); } Is there a way to generate empty handlers for all events of a given class automatically using reflection and some CLR magic?

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