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• Laws of Computer Science and Programming

  - by Jonas

  We have Amdahl's law that basically states that if your program is 10% sequential you can get a maximum 10x performance boost by parallelizing your application. Another one is Wadler's law which states that In any language design, the total time spent discussing a feature in this list is proportional to two raised to the power of its position. 0. Semantics 1. Syntax 2. Lexical syntax 3. Lexical syntax of comments My question is this: What are the most important (or at least significant / funny but true / sad but true) laws of Computer Science and programming? I want named laws, and not random theorems, So an answer should look something like Surname's (law|theorem|conjecture|corollary...) Please state the law in your answer, and not only a link. Edit: The name of the law does not need to contain it's inventors surname. But I do want to know who stated (and perhaps proved) the law

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• How to recognize touch events and control a script object inside UIWebView?

  - by Markus S.

  Situation: I have an UIView with an UIWebView in it. When the viewDidLoad the Javascript Object inside the UIWebView is called (Microsoft Seadragon AJAX JS). For your Understanding: Seadragon loads a specified megapixel image(JPEG) and in a Desktop Browser like Firefox i can Zoom into the image and I can drag the crop for example from the middle to the left. In the iPhone Simulator (for iPad) only the Zooming Function is working on one single tap but when i try to drag the crop (with left mouse button click and holding it) I'm dragging the whole UIWebView but not the crop of course! Is that feature which the simulator isn't able to handle or what's yout solutin guys? Special Thanks!! P.S.: It's a bit jiggling when the zooming function of Seadragon is called. Is that authentic to the real performance of the iPad or does the simulator not have the power as the iPad has?

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• Filtering in E4X

  - by FB55

  This is just a simple question. I'm currently using Mozilla's Rhino to develop a little webapp. As one step, I need to get a webpage and filter all of it's nodes. For doing that, I use E4X. I thought I could do this like that: var pnodes = doc..*(p); But that produces an error. How is it done right? (BTW: this is just a step for increasing performance. The code already does well, it's just a bit slow.)

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• iPhone - Is it ok to override UITableViewCell setSelected:animated

  - by Brian

  I am drawing custom UITableViewCells. My cells are opaque and are completely drawn in the drawRect of the cell to help with performance. I want to handle the look of a selected cell myself. If I don't, then the contents of my cell is covered up by the selectedBackgroundView that is added. Is it common or acceptable to override the setSelected:animated method of my cell so this is done properly. I guess if I did that, then I would not call the super's setSelected method since I would be handling how the cell will show that its selected. I would also have to set the selected property of the cell. Any help would be great. Thanks.

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• Cocos2D SpriteSheet animation problem, my number of frames is much larger.

  - by vaibhav-tekam

  Hello, I am trying to use SpriteSheet to run an animation. My frames are of 320x480 in size each, So I am able to put max 6 frames on the texture image. But my animation consists of frame number ranging from 50 to 200 sometimes, and all are of size 320x480. But this much number of frames cannot be added on the Texture image as the size is restricted to 1024x1024. Is there any other approach I can try out. Can I play one animation after the other.And won't it be hampering the performance. Please, I need suggestions. Best, Vaibhav Tekam.

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• Does a Collection<T> wrap an IList<T> or enumerate over the IList<T>?

  - by Brian Triplett

  If I am exposing a internal member via a Collection property via: public Collection<T> Entries { get { return new Collection<T>(this.fieldImplimentingIList<T>); } } When this property is called what happens? For example what happens when the following lines of code are called: T test = instanceOfAbove.Entries[i]; instanceOfAbove[i] = valueOfTypeT; It's clear that each time this property is called a new reference type is created but what acctually happens? Does it simply wrap the IList<T> underneath, does it enumerate over the IList<T> and to create a new Collection<T> instance? I'm concerned about performance if this property is used in a for loop.

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• Tomcat6 MySql JDBC Datasource configuration

  - by Bob

  Hi, I've always used Spring's dependency injection to get datasource objects and use them in my DAOs, but now, I have to write an app without that. With Spring I can write something like this: <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://127.0.0.1/app?characterEncoding=UTF-8" /> <property name="username" value="u" /> <property name="password" value="p" /> </bean> But how can I use datasource in my DAOs without Spring or anything? I'm using servlets and JSPs only. Performance is very important factor. Thanks in advance!

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• Hook Response.Cache to memcache

  - by dvr

  Has anyone done this before? I have a 32 bit win 2003 server running 2.0 and have read the ms engineers' blog about min(60%, 1800mb) for cache limits and our site (asp.net 2.0 / 3.5) is caching alot. It throws system outofmemory exceptions when wp is around 1.3gb (unfortunately it is the 2.0 apps) and I would like to push alot over to memcache but worried that at the moment the site is efficient using response.cache as is (though memory is an issue). I want to move most items over to memcache and have concerns on a – how to do this (implementation of response.cache to read/write from memcache) and b – what will performance be like? Before I commit to doing this and possibly spending a few days running tests I would like to hear from you if this has been done already and get some feedback. (and please don’t tell me to buy a x64 machine – I have already requested this!), by the way I ran a test requesting a single image 1000 times and response.cache was over 50% quicker than using application cache. Does response.cache bypass the page lifecycle?

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• Why does my 64-bit IIS app pool show 3 gigabytes more virtual memory than private memory?

  - by Brett

  I have an ASP.Net application that I am running on 64-bit IIS 6 on Windows XP x64. When I open performance counters after one page hit of a trivial page, I see a Private Bytes of about 88 megs, but a Virtual Bytes of about 3 Gigs. When I try the same thing with a VERY trivial ASP.Net app, I get the same result. We see something similar on Windows Server 2003 in production -- there it is an issue because we recycle when the virtual memory consumed outgrows a limit. Before we make any changes to our recycling settings, we'd like to answer the following questions: Why does the app pool grab such a large hunk of virtual memory? Is the amount of virtual memory headroom the app requests configurable? Thanks! Brett

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• Webservice or WCF for compactframework.

  - by Tan

  Hi iam making a Windows mobile application thats connects to an WCF service with basic httpbinding. The mobile device talks directly to the WCF service by tcp. But the performace is really slow. So i tried to switch the mobile device talking to a Webservice (ASMX) then the webservice talks to WCF service. The respone and performace is much faster. Why is it so. Isnt WCF suppose to be faster and have greater performance then the old webservice. please advice and help.

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• Multiple rows with a single INSERT in SQLServer 2008

  - by Todd

  I am testing the speed of inserting multiple rows with a single INSERT statement. For example: INSERT INTO [MyTable] VALUES (5, 'dog'), (6, 'cat'), (3, 'fish) This is very fast until I pass 50 rows on a single statement, then the speed drops significantly. Inserting 10000 rows with batches of 50 take 0.9 seconds. Inserting 10000 rows with batches of 51 take 5.7 seconds. My question has two parts: Why is there such a hard performance drop at 50? Can I rely on this behavior and code my application to never send batches larger than 50? My tests were done in c++ and ADO.

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• image archive VS image strip

  - by DevA

  Hi, i've noticed that plenty of games / applications (very common on mobile builds) pack numerous images into an image strip. I figured that the advantages in this are making the program more tidy (file system - wise) and reducing (un)installation time. During the runtime of the application, the entire image strip is allocated and copied from FS to RAM. On the contrary, images can be stored in an image archive and unpacked during runtime to a number of image structures in RAM. The way I see it, the image strip approach is less efficient because of worse caching performance and because that even if the optimal rectangle packing algorithm is used, there will be empty spaces between the stored images in the strip, causing a waste of RAM. What are the advantages in using an image strip over using an image archive file?

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• Repeated Scene Trees (Java3d / OpenGL)

  - by Jim

  Hello, I want to make a 3d scene that loops around on its self. That is to say, if you keep going in any direction, you will loop back to the other side. My current implementation is so bad, it's embarrassing to admit to it. I redraw the each change twenty-seven times, to make a 3x3x3 scene cube. When the user reaches the end of the middle cube, I jump them over to the other side. Maintaining consistency (let alone performance) is a nightmare. Total Disaster. This doesn't seem like it would be an unusual request, so I'm wondering if anyone knows of a more legit solution. Thanks!

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• use ngen and bundle .NET dlls to run application in .NET-less machine?

  - by Camilo Martin

  AFAIK, ngen turns MSIL into native code (also reffered to as pre-JIT), however I never payed too much attention at it's startup performance impact. Ngen'd applications still require the .NET base class libraries (the runtime). Since the base class libraries have everything our .NET assemblies need (correct?) would it be possible to ship the framework's DLLs with my ngen'd application so that it does not require the runtime to be installed? (e.g., the scenario for most Windows XP machines) Oh, and please don't bother mentioning Remotesoft's Salamander Linker or Xenocode's Postbuild. They are not for my (and many's) current budget (and they seem to simply bundle the framework in a virtualized enviroinment, which means big download sizes and slow startup times I believe)

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• Generate HTML To PDF Control for the .NET application

  - by Karan

  Has anyone used any open source or paid .NET Control which does the conversion job from html to pdf file? At the moment, i am using Winnovative convertor control. But it has a performance limitation during the generation of bulk pages (like more than 1000) in the pdf. The limitation comes when we use bigger images in the html content. From last 4 months i've been working on the winnovative control and found plenty of major bugs in it. For a small application and usage. winnovative is good but not for the level where application will be used by thousands of clients. Please suggest.

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• What's the difference between !col and col=false in MySQL?

  - by Mask

  The two statements have totally different performance: mysql> explain select * from jobs where createIndexed=false; +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ | 1 | SIMPLE | jobs | ref | i_jobs_createIndexed | i_jobs_createIndexed | 1 | const | 1 | | +----+-------------+-------+------+----------------------+----------------------+---------+-------+------+-------+ 1 row in set (0.01 sec) mysql> explain select * from jobs where !createIndexed; +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | jobs | ALL | NULL | NULL | NULL | NULL | 17996 | Using where | +----+-------------+-------+------+---------------+------+---------+------+-------+-------------+ Column definition and related index for aiding analysis: createIndexed tinyint(1) NOT NULL DEFAULT 0, create index i_jobs_createIndexed on jobs(createIndexed);

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• Are there any real benefits to including javascript dynamically rather than as script tags at the bo

  - by SB

  I've read that including the scripts dynamically may provide some better performance, however i'm not really seeing that on the small local tests I'm doing. I created a jquery plugin to dynamically load other plugins as necessary and am curious as to if this is actually a good idea. The following would be called onready or at the bottom of the page(I can provide the source for the plugin if anyone is interested): $.fn.executePlugin( 'qtip', // looks in default folder { required: '/javascript/plugin/easing.js', // not really required for qtip just testing it version: 1, //used for versioning and caching checkelement: '#thumbnail', // will not include plugin if $(element).length==0 css: 'page.css', // include this css file as well with plugin cache:true, // $.ajax will use cache:true success:function() { // success function to be called after the plugin loads - apply qtip to an element $('#thumbnail').qtip( { content: 'Some basic content for the tooltip', // Give it some content, in this case a simple string style: {name:'cream'}, }); } });

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• What's the easiest way to parse numbers in clojure?

  - by Rob Lachlan

  I've been using java to parse numbers, e.g. (. Integer parseInt numberString) Is there a more clojuriffic way that would handle both integers and floats, and return clojure numbers? I'm not especially worried about performance here, I just want to process a bunch of white space delimited numbers in a file and do something with them, in the most straightforward way possible. So a file might have lines like: 5 10 0.0002 4 12 0.003 And I'd like to be able to transform the lines into vectors of numbers.

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• SQL to retrieve aggregated data with computed columns

  - by Remnant

  I have a table that looks like this for about ~30 students: StudentID Course* CourseStatus 1 Math Pass 1 English Fail 1 Science Pass 2 Math Fail 2 English Pass 2 Science Fail etc. *In my actual database the 'Course' column is a CourseID e.g. (1 = Math; 2 = English etc.) which references a 'CourseName' table. I amended the table above just to make it clear the nature of the problem. I want to write a query (stored procedure) in SQL that summarises performance for a given course and returns the following: EXEC usp_GetCourseSummary 'Math' Total Students Total Pass % Pass Total Fail % Fail 25 15 60 10 40 Have been scratching my head on this one for some time. Any ideas?

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• Is it Possible to Query Multiple Databases with WCF Data Services?

  - by Mas

  I have data being inserted into multiple databases with the same schema. The multiple databases exist for performance reasons. I need to create a WCF service that a client can use to query the databases. However from the client's point of view, there is only 1 database. By this I mean when a client performs a query, it should query all databases and return the combined results. I also need to provide the flexibility for the client to define its own queries. Therefore I am looking into WCF Data Services, which provides the very nice functionality for client specified queries. So far, it seems that a DataService can only make a query to a single database. I found no override that would allow me to dispatch queries to multiple databases. Does anyone know if it is possible for a WCF Data Service to query against multiple databases with the same schema?

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• Shark was unable to find symbol information for this address range - iPhone

  - by Elliot

  I'm trying to use Shark to determine which method(s) are taking the most time in my iPhone app. After sampling, I get this: Clicking the "!" button yields: Shark was unable to find symbol information for this address range. Typically this happens because the application was compiled without symbols or they have been subsequently stripped away. In Xcode, make sure the "Generate Debug Symbols" checkbox is selected (passes the -g flag to the compiler). Note that this does not affect code optimization, and does not typically alter performance significantly. However, the extra symbol information does consume significantly more space and may bloat the size of the executable. But I AM using the Debug option, and I am running on my Device. And Generate Debug Symbols IS checked. So what's wrong?

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• opengl invert framebuffer pixels

  - by ToxIk

  I was wondering was the best way to invert the color pixels in the frame buffer is. I know it's possible to do with glReadPixels() and glDrawPixels() but the performance hit of those calls is pretty big. Basically, what I'm trying to do is have an inverted color cross-hair which is always visible no matter what's behind it. For instance, I'd have an arbitrary alpha mask bitmap or texture, have it render without depth test after the scene is drawn, and all the frame buffer pixels under the masked (full alpha) pixels of the texture would be inverted. I've been trying to do this with a texture, but I'm getting some strange results, also all the blending options I still find confusing.

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• SqlServer / MySql Connection pool: is it really important ?

  - by stighy

  Hy guys, after a lot of problem with my hoster, i decided to disable connection pooling of my application. The problem was related to the number of concurrent connections : only five. So i decided to disable connection pooling: the result is that my web app don't crash. So i'm asking you: are there some "collateral" effect disabling connection pooling ? Is it so important ? I didn't noticed bad performance after disabling it. Thank you for your (i'm sure) precious advice!

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• Retrieve input and output parameters for SQL stored procs and functions?

  - by Darth Continent

  For a given SQL stored proc or function, I'm trying to obtain its input and output parameters, where applicable, in a Winforms app I'm creating to browse objects and display their parameters and other attributes. So far I've discovered the SQL system function object_definition, which takes a given sysobjects.id and returns the text of that object; also discovered via search this post which describes extracting the parameters in the context of a app using the ADO.NET method DeriveParameters in conjunction with some caching for better performance; and for good measure found some helpful system stored procs from this earlier post on Hidden Features of SQL Server. I'm leaning towards implementing the DeriveParameters method in my C# app, since parsing the output of object_definition seems messy, and I haven't found a hidden feature in that post so far that would do the trick. Is DeriveParameters applicable to both functions and stored procs for purposes of retreiving their parameters, and if so, could someone please provide an example?

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• How to setup RAM disk drive using python or WMI?

  - by Ming Xie

  Hi, The background of my question is associated with Tesseract, the free OCR engine (1985-1995 by HP, now hosting in Google). It specifically requires an input file and an output file; the argument only takes filename (not stream / binary string), so in order to use the wrapper API such as pytesser and / or python-tesser.py, the OCR temp files must be created. I, however, have a lot of images need to OCR; frequent disk write and remove is inevitable (and of course the performance hit). The only choice I could think about is changing the wrapper class and point the temp file to RAM disk, which bring this problem up. If you have better solution, please let me know. Thanks a lot. -M

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