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  • C++ Performance/memory optimization guidelines

    - by ML
    Hi All, Does anyone have a resource for C++ memory optimization guidelines? Best practices, tuning, etc? As an example: Class xxx { public: xxx(); virtual ~xxx(); protected: private: }; Would there be ANY benefit on the compiler or memory allocation to get rid of protected and private since there there are no items that are protected and private in this class?

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  • Any Javascript optimization benchmarks?

    - by int3
    I watched Nicholas Zakas' talk, Speed up your Javascript, with some interest. I liked how he benchmarked the various performance improvements created by various optimization techniques, e.g. reducing calls to deeply nested objects, changing loops to count down instead of up, etc. I would like to run these benchmarks myself though, to see exactly how our current browsers are faring. I guess it wouldn't be too difficult to cook up some timed loops, but I'd like to know if there are any existing implementations out there.

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  • Java code optimization leads to numerical inaccuracies and errors

    - by rano
    I'm trying to implement a version of the Fuzzy C-Means algorithm in Java and I'm trying to do some optimization by computing just once everything that can be computed just once. This is an iterative algorithm and regarding the updating of a matrix, the clusters x pixels membership matrix U, this is the update rule I want to optimize: where the x are the element of a matrix X (pixels x features) and v belongs to the matrix V (clusters x features). And m is a parameter that ranges from 1.1 to infinity. The distance used is the euclidean norm. If I had to implement this formula in a banal way I'd do: for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < V.length; j++) { double num = D[i][j]; double sumTerms = 0; for(int k = 0; k < V.length; k++) { double thisDistance = D[i][k]; sumTerms += Math.pow(num / thisDistance, (1.0 / (m - 1.0))); } U[i][j] = (float) (1f / sumTerms); } } In this way some optimization is already done, I precomputed all the possible squared distances between X and V and stored them in a matrix D but that is not enough, since I'm cycling througn the elements of V two times resulting in two nested loops. Looking at the formula the numerator of the fraction is independent of the sum so I can compute numerator and denominator independently and the denominator can be computed just once for each pixel. So I came to a solution like this: int nClusters = V.length; double exp = (1.0 / (m - 1.0)); for(int i = 0; i < X.length; i++) { int count = 0; for(int j = 0; j < nClusters; j++) { double distance = D[i][j]; double denominator = D[i][nClusters]; double numerator = Math.pow(distance, exp); U[i][j] = (float) (1f / (numerator * denominator)); } } Where I precomputed the denominator into an additional column of the matrix D while I was computing the distances: for (int i = 0; i < X.length; i++) { for (int j = 0; j < V.length; j++) { double sum = 0; for (int k = 0; k < nDims; k++) { final double d = X[i][k] - V[j][k]; sum += d * d; } D[i][j] = sum; D[i][B.length] += Math.pow(1 / D[i][j], exp); } } By doing so I encounter numerical differences between the 'banal' computation and the second one that leads to different numerical value in U (not in the first iterates but soon enough). I guess that the problem is that exponentiate very small numbers to high values (the elements of U can range from 0.0 to 1.0 and exp , for m = 1.1, is 10) leads to ver y small values, whereas by dividing the numerator and the denominator and THEN exponentiating the result seems to be better numerically. The problem is it involves much more operations. Am I doing something wrong? Is there a possible solution to get both the code optimized and numerically stable? Any suggestion or criticism will be appreciated.

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  • PHP website Optimization

    - by ana
    I have a high traffic website and I need make sure my site is fast enough to display my pages to everyone rapidly. I searched on Google many articles about speed and optimization and here's what I found: Cache the page Save it to the disk Caching the page in memory: This is very fast but if I need to change the content of my page I have to remove it from cache and then re-save the file on the disk. Save it to disk This is very easy to maintain but every time the page is accessed I have to read on the disk. Which method should I go with? Thanks

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  • Performance optimization strategies of last resort?

    - by jerryjvl
    There are plenty of performance questions on this site already, but it occurs to me that almost all are very problem-specific and fairly narrow. And almost all repeat the advice to avoid premature optimization. Let's assume: the code already is working correctly the algorithms chosen are already optimal for the circumstances of the problem the code has been measured, and the offending routines have been isolated all attempts to optimize will also be measured to ensure they do not make matters worse What I am looking for here is strategies and tricks to squeeze out up to the last few percent in a critical algorithm when there is nothing else left to do but whatever it takes. Ideally, try to make answers language agnostic, and indicate any down-sides to the suggested strategies where applicable. I'll add a reply with my own initial suggestions, and look forward to whatever else the SO community can think of.

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  • Does MATLAB perform tail call optimization?

    - by Shea Levy
    I've recently learned Haskell, and am trying to carry the pure functional style over to my other code when possible. An important aspect of this is treating all variables as immutable, i.e. constants. In order to do so, many computations that would be implemented using loops in an imperative style have to be performed using recursion, which typically incurs a memory penalty due to the allocation a new stack frame for each function call. In the special case of a tail call (where the return value of a called function is immediately returned to the callee's caller), however, this penalty can be bypassed by a process called tail call optimization (in one method, this can be done by essentially replacing a call with a jmp after setting up the stack properly). Does MATLAB perform TCO by default, or is there a way to tell it to?

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  • Including associations optimization in Rails

    - by Vitaly
    Hey, I'm looking for help with Ruby optimization regarding loading of associations on demand. This is simplified example. I have 3 models: Post, Comment, User. References are: Post has many comments and Comment has reference to User (:author). Now when I go to the post page, I expect to see post body + all comments (and their respective authors names). This requires following 2 queries: select * from Post -- to get post data (1 row) select * from Comment inner join User -- to get comment + usernames (N rows) In the code I have: Post.find(params[:id], :include => { :comments => [:author] } But it doesn't work as expected: as I see in the back end, there're still N+1 hits (some of them are cached though). How can I optimize that?

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  • why optimization does not happen?

    - by aaa
    hi. I have C/C++ code, that looks like this: static int function(double *I) { int n = 0; // more instructions, loops, for (int i; ...; ++i) n += fabs(I[i] > tolerance); return n; } function(I); // return value is not used. compiler inlines function, however it does not optimize out n manipulations. I would expect compiler is able to recognize that value is never used as rhs only. Is there some side effect, which prevents optimization? Thanks

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  • Static variable for optimization

    - by keithjgrant
    I'm wondering if I can use a static variable for optimization: public function Bar() { static $i = moderatelyExpensiveFunctionCall(); if ($i) { return something(); } else { return somethingElse(); } } I know that once $i is initialized, it won't be changed by by that line of code on successive calls to Bar(). I assume this means that moderatelyExpensiveFunctionCall() won't be evaluated every time I call, but I'd like to know for certain. Once PHP sees a static variable that has been initialized, does it skip over that line of code? In other words, is this going to optimize my execution time if I make a lot of calls to Bar(), or am I wasting my time?

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  • Copy method optimization in compilers

    - by Dženan
    Hi All! I have the following code: void Stack::operator =(Stack &rhs) { //do the actual copying } Stack::Stack(Stack &rhs) //copy-constructor { top=NULL; //initialize this as an empty stack (which it is) *this=rhs; //invoke assignment operator } Stack& Stack::CopyStack() { return *this; //this statement will invoke copy contructor } It is being used like this: unsigned Stack::count() { unsigned c=0; Stack copy=CopyStack(); while (!copy.empty()) { copy.pop(); c++; } return c; } Removing reference symbol from declaration of CopyStack (returning a copy instead of reference) makes no difference in visual studio 2008 (with respect to number of times copying is invoked). I guess it gets optimized away - normally it should first make a copy for the return value, then call assignment operator once more to assign it to variable sc. What is your experience with this sort of optimization in different compilers? Regards, Dženan

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  • Common optimization rules

    - by mafutrct
    This is a dangerous question, so let me try to phrase it correctly. Premature optimization is the root of all evil, but if you know you need it, there is a basic set of rules that should be considered. This set is what I'm wondering about. For instance, imagine you got a list of a few thousand items. How do you look up an item with a specific, unique ID? Of course, you simply use a Dictionary to map the ID to the item. And if you know that there is a setting stored in a database that is required all the time, you simply cache it instead of issuing a database request hundred times a second. I guess there are a few even more basic ideas. I am specifically not looking for "don't do it, for experts: don't do it yet" or "use a profiler" answers, but for really simple, general hints. If you feel this is an argumentative question, you probably misunderstood my intention.

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  • My VB crushes for a pre-header non recognized

    - by Newben
    I have a great problem to deal : no access anymore to Ubuntu through my VirtualBox. I always have the same message Session failed to Open Could not open the medium '/Users/me/VirtualBox VMs/Ubuntu/Ubuntu.vdi'. VDI: error reading pre-header in '/Users/me/VirtualBox VMs/Ubuntu/Ubuntu.vdi' (VERR_DEV_IO_ERROR). VD: error VERR_VD_VDI_INVALID_HEADER opening image file '/Users/me/VirtualBox VMs/Ubuntu/Ubuntu.vdi' (VERR_VD_VDI_INVALID_HEADER). Code d'erreur : NS_ERROR_FAILURE (0x80004005) Composant : Medium Interface : IMedium {53f9cc0c-e0fd-40a5-a404-a7a5272082cd} I tried to follow this post explaining how to mount manually the vdi file. But I can't open my 6go sized file nor with HexFiend, nor with 0exED... And if I did, how do I find the pre-header ?

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  • SQL Pre-Con…at the Beach

    - by Argenis
      Building upon the success of SQL Rally 2012 (where we packed a room full of DBAs), my friend Robert Davis [Twitter|Blog] and yours truly will be again delivering our day-long Pre-Conference “Demystifying Database Administration Best Practices” this Friday (6/8/2012) – right before SQLSaturday #132 in Pensacola, FL. If you are in the vicinity of Pensacola, come join us! We had tons of fun at Rally. Robert and I love sharing tips and stories that will help you on your day to day duties as a DBA. Some of the topics that we’ll touch on (this is by no means a comprehensive list) Active Directory configuration for SQL Server Deployments Windows Server Deployments Storage and I/O High Availability / Disaster Recovery / Business Continuity Replication Day-To-Day Operations Maintenance TempDB Code Reviews Other Database and Server Settings   Follow this link to sign up for the Pre-Con at Pensacola: http://demystifyingdba.eventbrite.com/ Here’s a blog post that Robert made on the subject of Best Practices.  Hope to see you there!

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  • SQL Pre-Con…at the Beach

    - by Argenis
      Building upon the success of SQL Rally 2012 (where we packed a room full of DBAs), my friend Robert Davis [Twitter|Blog] and yours truly will be again delivering our day-long Pre-Conference “Demystifying Database Administration Best Practices” this Friday (6/8/2012) – right before SQLSaturday #132 in Pensacola, FL. If you are in the vicinity of Pensacola, come join us! We had tons of fun at Rally. Robert and I love sharing tips and stories that will help you on your day to day duties as a DBA. Some of the topics that we’ll touch on (this is by no means a comprehensive list) Active Directory configuration for SQL Server Deployments Windows Server Deployments Storage and I/O High Availability / Disaster Recovery / Business Continuity Replication Day-To-Day Operations Maintenance TempDB Code Reviews Other Database and Server Settings   Follow this link to sign up for the Pre-Con at Pensacola: http://demystifyingdba.eventbrite.com/ Here’s a blog post that Robert made on the subject of Best Practices.  Hope to see you there!

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  • SQL Saturday #220 - Atlanta - Pre-Con Scholarship Winners!

    - by Most Valuable Yak (Rob Volk)
    A few weeks ago, AtlantaMDF offered scholarships for each of our upcoming Pre-conference sessions at SQL Saturday #220. We would like to congratulate the winners! David Thomas SQL Server Security http://sqlsecurity.eventbrite.com/ Vince Bible Surfing the Multicore Wave: Processors, Parallelism, and Performance http://surfmulticore.eventbrite.com/ Mostafa Maged Languages of BI http://languagesofbi.eventbrite.com/ Daphne Adams Practical Self-Service BI with PowerPivot for Excel http://selfservicebi.eventbrite.com/ Tim Lawrence The DBA Skills Upgrade Toolkit http://dbatoolkit.eventbrite.com/ Thanks to everyone who applied! And once again we must thank Idera's generous sponsorship, and the time and effort made by Bobby Dimmick (w|t) and Brian Kelley (w|t) of Midlands PASS for judging all the applicants. Don't forget, there's still time to attend the Pre-Cons on May 17, 2013! Click on the EventBrite links for more details and to register!

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  • Pre order Nokia Lumia 900 from AT&T for $99.99 and Walmart for $49.99

    - by Gopinath
    Nokia Lumia 900, the flagship Windows Phone OS smartphone from Nokia is available for pre-order from AT&T Stores. With a two year contract, you can grab the phone by paying $99.99 online and they are expected to ship a day or two earlier than their official launch in AT&T stores across US. Walmart in an aggressive move, is selling Nokia Lumia 900 for just $49.99 with a two year contract. So you save $50 more. Earlier in January of this year, Nokia unveiled its plans of Lumia 900 launch exclusively for American market. Nokia Lumia 900 features a 4.3 inch Clear Black display, sporting a resolution of 800 x 480 pixels, 1.4 GHz Snapdragon processor, Windows Phone 7.5 (Mango) OS, 8 megapixel rear camera with f2.2/28mm Carl Zeiss lens and dual LED flash, auto-focus and HD (720p) video recording, 1 megapixel front-facing camera for video calls, 512 MB RAM, 16 GB internal memory, 14.5 GB user memory and more. Pre-order Nokia Lumia 900 from AT&T and Walmart

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  • Pre-Loading von Tabellen in 11g

    - by Ulrike Schwinn (DBA Community)
    Tabellen und Indizes in den Cache zu laden, damit möglichst wenig I/O durchgeführt wird, ist eine häufig anzutreffende Anforderung. Diese Technik nennt man auch Pre-Loading oder Pre-Caching von Datenbank Objekten. Die Durchführung ist dabei sehr einfach. Gleich zu Beginn werden spezielle SQL Statements wie SELECT Statements mit Full Table Scan oder Index Scan durchgeführt, damit die entsprechenden Objekte vollständig in den Cache geladen werden können. Besonders interessant ist dieser Aspekt auch im Zusammenhang mit der Erstellung von Testumgebungen. Falls beispielsweise kein Warmup möglich ist, kann man bevor der eigentliche Test durchgeführt wird, bestimmte Tabellen und Indizes mit dieser Technik vorab in den Buffer Cache laden.  Der folgende Artikel zeigt wie man eine Tabelle in 11g in den Buffer Cache laden kann und gibt Tipps zur Durchführung.

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  • Les pré-commandes de l'iPad ouvertes en France, pour Apple 1 Euro = 1 $

    Mise à jour du 11.05.2010 par Katleen Les pré-commandes de l'iPad ouvertes en France, pour Apple 1 € = 1 $ Les pré-commandes d'iPad sont possible depuis quelques heures sur l'Apple Store français. Toute la gamme y est présente : la version simple, mais aussi celles incluant le wi-fi et la 3G, dans toutes les capacités de stockage, et livrables à la date du 28 mai. Du bonheur ? Presque, jusqu'à ce que l'on parle des tarifs. En effet, les prix européens sont sensiblement les mêmes que ceux affichés aux USA. Oui mais voilà, le dollar vaut beaucoup moins que l'euro. Autrement dit, le même appareil coutera plus cher à un français qu'à un américain. Un consommateur s'est ainsi plaint à ...

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  • Oracle 2012 Pre-Placement Talk Schedule

    - by user769227
    As we get closer to October, we are working to prepare for our upcoming Pre-Placements Talks at the IIT's across India.We now have confirmation from each IIT on our Pre-Placement Talk dates. For IIT students who are interested in graduate opportunities with Oracle and want to attend our Information Sessions please find the dates we will be visiting your respective colleges below. IIT  Date  IIT Kanpur October 5th 2012   IIT Mumbai October 13th 2012  IIT Delhi October 14th 2012  IIT Roorkee  October 19th 2012  IIT Guwahati  October 29th 2012  IIT Madras  October 30th 2012  IIT Kharagpur  October 30th 2012  We will make our presentations publicly available online after October 30th, however if you have any questions at all please feel free to email us at [email protected] and we will help where we can. We are looking forward to seeing you in October. 

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  • Which isometric angles can be mirrored (and otherwise transformed) for optimization?

    - by Tom
    I am working on a basic isometric game, and am struggling to find the correct mirrors. Mirror can be any form of transform. I have managed to get SE out of SW, by scaling the sprite on X axis by -1. Same applies for NE angle. Something is bugging me, that I should be able to also mirror N to S, but I cannot manage to pull this one off. Am I just too sleepy and trying to do the impossible, or a basic -1 scale on Y axis is not enough? What are the common used mirror table for optimizing 8 angle (N, NE, E, SE, S, SW, W, NW) isometric sprites?

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  • When should an API favour optimization over readability and ease-of-use?

    - by jmlane
    I am in the process of designing a small library, where one of my design goals is to use as much of the native domain language as possible in the API. While doing so, I've noticed that there are some cases in the API outline where a more intuitive, readable attribute/method call requires some functionally unnecessary encapsulation. Since the final product will not necessarily require high performance, I am unconcerned about making the decision to favour ease-of-use in my current project over the most efficient implementation of the code in question. I know not to assume readability and ease-of-use are paramount in all expected use-cases, such as when performance is required. I would like to know if there are more general reasons that argue for an API design preferring (marginally) more efficient implementations?

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  • When should code favour optimization over readability and ease-of-use?

    - by jmlane
    I am in the process of designing a small library, where one of my design goals is that the API should be as close to the domain language as possible. While working on the design, I've noticed that there are some cases in the code where a more intuitive, readable attribute/method call requires some functionally unnecessary encapsulation. Since the final product will not necessarily require high performance, I am unconcerned about making the decision to favour ease-of-use in my current project over the most efficient implementation of the code in question. I know not to assume readability and ease-of-use are paramount in all expected use-cases, such as when performance is required. I would like to know if there are more general reasons that argue for a design preferring more efficient implementations—even if only marginally so?

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  • exchange live feed with pre-recorded video for wireless internet camera to router

    - by nate
    I wasn't sure if this should be asked in Web Applications, or Network Engineering, or what... Long story short, I have a video camera with mic that is wirelessly connected to a router (NETGEAR R6200), which can then be viewed through an online service. I would like to be able to somehow exchange the live feed with a pre-recorded video, or image, preferably with pre-recorded sound (the sound of silence would be easiest). Can I place this inbetween the camera and the router, do I need to redirect the camera feed to my laptop first, and then push out the fake video/audio onto the router, without the service knowing the difference? Thanks much and I hope this is well understood!

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  • Personalized URL with pre-populated data

    - by AttackingHobo
    I think I am going to use Google spreadsheets and an embedded form. I see that it is possible to pre-populate the fields with URL parameters. So I think I just need a way to redirect with the correct data from a database when a user goes to their Personalized URL. I have no idea how to do the second part. Or if it is even the best way to do it. How do I set up Personalized URLS? How do I redirect from those URLS to the spreadsheets? Is this even the best method for pre-filled forms?

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  • SAP annonce des pré-résultats records pour ses ventes de logiciels au 4ème trimestre 2010

    SAP annonce des pré-résultats records Pour ses ventes de logiciels au 4ème trimestre 2010 Malgré le départ de son PDG pour HP et l'affaire TomorrowNow qui l'oppose à Oracle, l'éditeur allemand de solutions professionnelles SAP se porte bien. La société vient d'annoncer des pré-résultats records pour le le 4ème trimestre de son année fiscale 2010, qui se terminait le 31 décembre 2010. . Ses revenus liés à la vente de logiciels s'élèvent à 1,5 milliards d'Euros, soit une progression de + 34 % (+ 24 à taux de change constant). SAP s'en félicite. « Nous sommes heureux d'annoncer le meilleur trimestre de ventes de logiciels de l'histoire de SAP. Nous avons réalisé une...

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