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• Data Structures usage and motivational aspects

  - by Aubergine

  For long student life I was always wondering why there are so many of them yet there seems to be lack of usage at all in many of them. The opinion didn't really change when I got a job. We have brilliant books on what they are and their complexities, but I never encounter resources which would actually give a good hint of practical usage. I perfectly understand that I have to look at problem , analyse required operations, look for data structure that does them efficiently. However in practice I never do that, not because of human laziness syndrome, but because when it comes to work I acknowledge time priority over self-development. Over time I thought that when I would be better developer I will automatically use more of them - that didn't happen at all or maybe I just didn't. Then I found that the colleagues usually in the same plate as me - knowing more or less some three of data structures and being totally happy about it and refusing to discuss this matter further with me, coming back to conversations about 'cool new languages' 'libraries that do jobs for you' and the joy to work under scrumban etc. I am stuck with ArrayLists, Arrays and SortedMap , which no matter what I do always suffice or either I tweak them to be capable of fulfilling my task. Yes, it might be inefficient but do we really have to care if Intel increases performance over years no matter if we improve our skills? Does new Xeon or IBM machines really care what we use? What if I like build things, but I am not particularly excited whether it is n log(n) or just n? Over twenty years the processing power increased enormously, which gives us freedom of not being critical about which one to use? On top of that new more optimized languages appear which support multiple cores more efficiently. To be more specific: I would like to find motivational material on complex real areas/cases of possible effective usages of data structures. I would be really grateful if you would provide relevant resources. There is similar question ,but in the end the links again mostly describe or do dumb example(vehicles, students or holy grail quest - yes, very relevant) them and people keep referring to the "scenario decides the data structure to use". I want to know these complex scenarios to be able to identify similarities to my scenario and then use them. The complex scenarios where it really matters and not necessarily of quantitive nature. It seems that data structures only concern is efficiency and nothing else? There seems to be no particular convenience for developer in use one over another. (only when I found scientific resources on why exactly simple carbohydrates are evil I stopped eating sugar and candies completely replacing it with less harmful fruits - I hope you can see the analogy)

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• Domain Models (PHP)

  - by Calum Bulmer

  I have been programming in PHP for several years and have, in the past, adopted methods of my own to handle data within my applications. I have built my own MVC, in the past, and have a reasonable understanding of OOP within php but I know my implementation needs some serious work. In the past I have used an is-a relationship between a model and a database table. I now know after doing some research that this is not really the best way forward. As far as I understand it I should create models that don't really care about the underlying database (or whatever storage mechanism is to be used) but only care about their actions and their data. From this I have established that I can create models of lets say for example a Person an this person object could have some Children (human children) that are also Person objects held in an array (with addPerson and removePerson methods, accepting a Person object). I could then create a PersonMapper that I could use to get a Person with a specific 'id', or to save a Person. This could then lookup the relationship data in a lookup table and create the associated child objects for the Person that has been requested (if there are any) and likewise save the data in the lookup table on the save command. This is now pushing the limits to my knowledge..... What if I wanted to model a building with different levels and different rooms within those levels? What if I wanted to place some items in those rooms? Would I create a class for building, level, room and item with the following structure. building can have 1 or many level objects held in an array level can have 1 or many room objects held in an array room can have 1 or many item objects held in an array and mappers for each class with higher level mappers using the child mappers to populate the arrays (either on request of the top level object or lazy load on request) This seems to tightly couple the different objects albeit in one direction (ie. a floor does not need to be in a building but a building can have levels) Is this the correct way to go about things? Within the view I am wanting to show a building with an option to select a level and then show the level with an option to select a room etc.. but I may also want to show a tree like structure of items in the building and what level and room they are in. I hope this makes sense. I am just struggling with the concept of nesting objects within each other when the general concept of oop seems to be to separate things. If someone can help it would be really useful. Many thanks

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• Making A Photo-Sharing App For Android In Eclipse [on hold]

  - by user3694394

  I've only just started developing mobile apps, which is something that I've been wanting to learn for a while now. I'm from an indie games studio, making PC games for around the last 3 years, and I finally decided to move into android app development. The only problem I'm having is that I don't know where to start. The project which I'm aiming to create will be something similar to Instagram, basically a photo-sharing app which allows users to take new photos, or pull them from their device, and add filters to them, before posting them. I have a rough idea of how I could go about doing this, but I need pointing towards any tutorials available for each specific step. So, here's my idea: Create a UI in eclipse (this wont be a problem for me, I should be able to do this fine through xml files) Setup a server-side database to store all user info and uploaded images (the images will need to be converted into byte arrays, and I have no idea how to do this through a database). My best idea would be to use a MySQL database to do this. Add user interactions (likes, favourites, reposts, etc.). This would, again, have to be stored in the database (or, at least, i think it would). Add the ability to take new photos using the phone's camera (I can probably do this anyway, using the Camera API). Add the ability to pull existing photos from the device (again, pretty simple to do). Add the ability to add filters to any photos (I had a look around, and there are some repos and resources which allow you to do this, but they're mainly for iOS development). Add facebook/twitter integration (possibly) to allow phots to be shared to other social networks. Create a news feed which shows users all of the latest photos from their friends, and allows them to post their own images to it. Give all registered users their own wall/page which has their latest posts/images displayed on it. Add the ability to allow users to follow other users, and display their followed users posts on their news feed. Yep. It's not going to be easy, and I don't even know if it's possible for me to do alone in Eclipse. However, this is the plan, and I'm going to do my best to learn everything I need to know to do this successfully. My actual question would be how should I start doing this- where do I begin learning how to do all of this? I've had a look at snapify, which can be edited via Parse, but I won't be spending hundreds of dollars (since I'm 15 and just don't have the available funds) on software. I have extensive knowledge of Java (again, I've been making games for around 3 years, mainly in Java), and various scripting languages. So, hopefully, this will be of some use here. Thanks in advance, Josh.

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• 2D Animation Smoothness - Delta time vs. Kinematics

  - by viperld002

  I'm animating a sprite in 2D with key frames of rotation and xy-positions. I've recently had a discussion with someone saying that when the device (happens to be an iPad using cocos2D) hits a performance bump due to whatever else the user may be doing, lag will arise and that the best way to fight it is to not use actual positions, but velocities, accelerations and torques with kinematics. His message is to evaluate the positions and rotations from these speeds at the current point in time. I've never experienced a situation where I've heard of using kinematics to stem lag in 2D animations and am not sure of how effective it could be. Also, it seems to be overkill. The application is not networked so it's all running on a local device. The desired effect is that the animation always plays as closely as it can to the target frame rate. Wouldn't the technique suffer the same problems as just using the time since the last frame or a fixed time step since the kinematics would also require some time value to perform the calculation? What techniques could you suggest to best achieve the desired effect? EDIT 1 Thank you for your responses, they are very illuminating. I want to clarify my question before choosing an answer however, to make sure that this post really serves it's purpose. I have a sprite of a ball, and a text file with 3 arrays worth of information (rotation,translations x, translations y) with each unit of information existing as a key frame to be stepped through (0 to 49 and back to 0 to replay it again). I have this playing by interpolating from the current key frame to the next, every n-units of time. The animation is visibly correct when compared to a video I was given of it, and it is smooth because of the interpolations between the key frames. This is the existing state of the project. There are no physics simulated, only a static animation of a ball moving in a way an artist specifically designed. Should I, instead of rotation in degrees and translations by positions in space, derive velocities, accelerations and torques to express this static animation as a function of time? As in, position now = foo(time now), where foo uses kinematics.

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• SQL 2014 does data the way developers want

  - by Rob Farley

  A post I’ve been meaning to write for a while, good that it fits with this month’s T-SQL Tuesday, hosted by Joey D’Antoni (@jdanton) Ever since I got into databases, I’ve been a fan. I studied Pure Maths at university (as well as Computer Science), and am very comfortable with Set Theory, which undergirds relational database concepts. But I’ve also spent a long time as a developer, and appreciate that that databases don’t exactly fit within the stuff I learned in my first year of uni, particularly the “Algorithms and Data Structures” subject, in which we studied concepts like linked lists. Writing in languages like C, we used pointers to quickly move around data, without a database in sight. Of course, if we had a power failure all this data was lost, as it was only persisted in RAM. Perhaps it’s why I’m a fan of database internals, of indexes, latches, execution plans, and so on – the developer in me wants to be reassured that we’re getting to the data as efficiently as possible. Back when SQL Server 2005 was approaching, one of the big stories was around CLR. Many were saying that T-SQL stored procedures would be a thing of the past because we now had CLR, and that obviously going to be much faster than using the abstracted T-SQL. Around the same time, we were seeing technologies like Linq-to-SQL produce poor T-SQL equivalents, and developers had had a gutful. They wanted to move away from T-SQL, having lost trust in it. I was never one of those developers, because I’d looked under the covers and knew that despite being abstracted, T-SQL was still a good way of getting to data. It worked for me, appealing to both my Set Theory side and my Developer side. CLR hasn’t exactly become the default option for stored procedures, although there are plenty of situations where it can be useful for getting faster performance. SQL Server 2014 is different though, through Hekaton – its In-Memory OLTP environment. When you create a table using Hekaton (that is, a memory-optimized one), the table you create is the kind of thing you’d’ve made as a developer. It creates code in C leveraging structs and pointers and arrays, which it compiles into fast code. When you insert data into it, it creates a new instance of a struct in memory, and adds it to an array. When the insert is committed, a small write is made to the transaction to make sure it’s durable, but none of the locking and latching behaviour that typifies transactional systems is needed. Indexes are done using hashes and using bw-trees (which avoid locking through the use of pointers) and by handling each updates as a delete-and-insert. This is data the way that developers do it when they’re coding for performance – the way I was taught at university before I learned about databases. Being done in C, it compiles to very quick code, and although these tables don’t support every feature that regular SQL tables do, this is still an excellent direction that has been taken. @rob_farley

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• Witchcraft! Php [migrated]

  - by Steve Green

  This is madness, hoping someone can explain. $dir = getcwd(); $a = "/bla/httpdocs/ble"; $b = "/bla/httpdocs/meh"; if( ($dir == $a) || ($dir == $b) ){ $dirlist = glob("../images2/spinner/*.jpg"); }else{ $dirlist = glob("images2/spinner/*.jpg"); } works fine but $dir = getcwd(); if( ($dir == "/bla/httpdocs/ble") || ($dir == "/bla/httpdocs/meh") ){ $dirlist = glob("../images2/spinner/*.jpg"); }else{ $dirlist = glob("images2/spinner/*.jpg"); } doesn't. (By doesn't work I mean it returns false, I also tried === ) Wondered if strings were being null terminated so tried: print_r(str_split($a)); //$a has been set to the string below for this. print_r(str_split("/bla/httpdocs/ble")); they returned identical arrays Array ( [0] => / [1] => b [2] => l [3] => a [4] => / [5] => h [6] => t [7] => t [8] => p [9] => d [10] => o [11] => c [12] => s [13] => / [14] => b [15] => l [16] => e ) Array ( [0] => / [1] => b [2] => l [3] => a [4] => / [5] => h [6] => t [7] => t [8] => p [9] => d [10] => o [11] => c [12] => s [13] => / [14] => b [15] => l [16] => e ) Anyone?

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• Rendering Texture Quad to Screen or FBO (OpenGL ES)

  - by Usman.3D

  I need to render the texture on the iOS device's screen or a render-to-texture frame buffer object. But it does not show any texture. It's all black. (I am loading texture with image myself for testing purpose) //Load texture data UIImage *image=[UIImage imageNamed:@"textureImage.png"]; GLuint width = FRAME_WIDTH; GLuint height = FRAME_HEIGHT; //Create context void *imageData = malloc(height * width * 4); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); CGContextRef context = CGBitmapContextCreate(imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); CGColorSpaceRelease(colorSpace); //Prepare image CGContextClearRect(context, CGRectMake(0, 0, width, height)); CGContextDrawImage(context, CGRectMake(0, 0, width, height), image.CGImage); glGenTextures(1, &texture); glBindTexture(GL_TEXTURE_2D, texture); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); Simple Texture Quad drawing code mentioned here //Bind Texture, Bind render-to-texture FBO and then draw the quad const float quadPositions[] = { 1.0, 1.0, 0.0, -1.0, 1.0, 0.0, -1.0, -1.0, 0.0, -1.0, -1.0, 0.0, 1.0, -1.0, 0.0, 1.0, 1.0, 0.0 }; const float quadTexcoords[] = { 1.0, 1.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 1.0, 1.0 }; // stop using VBO glBindBuffer(GL_ARRAY_BUFFER, 0); // setup buffer offsets glVertexAttribPointer(ATTRIB_VERTEX, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), quadPositions); glVertexAttribPointer(ATTRIB_TEXCOORD0, 2, GL_FLOAT, GL_FALSE, 2*sizeof(float), quadTexcoords); // ensure the proper arrays are enabled glEnableVertexAttribArray(ATTRIB_VERTEX); glEnableVertexAttribArray(ATTRIB_TEXCOORD0); //Bind Texture and render-to-texture FBO. glBindTexture(GL_TEXTURE_2D, GLid); //Actually wanted to render it to render-to-texture FBO, but now testing directly on default FBO. //glBindFramebuffer(GL_FRAMEBUFFER, textureFBO[pixelBuffernum]); // draw glDrawArrays(GL_TRIANGLES, 0, 2*3); What am I doing wrong in this code? P.S. I'm not familiar with shaders yet, so it is difficult for me to make use of them right now.

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• How do I randomly generate a top-down 2D level with separate sections and is infinite?

  - by Bagofsheep

  I've read many other questions/answers about random level generation but most of them deal with either randomly/proceduraly generating 2D levels viewed from the side or 3D levels. What I'm trying to achieve is sort of like you were looking straight down on a Minecraft map. There is no height, but the borders of each "biome" or "section" of the map are random and varied. I already have basic code that can generate a perfectly square level with the same tileset (randomly picking segments from the tileset image), but I've encountered a major issue for wanting the level to be infinite: Beyond a certain point, the tiles' positions become negative on one or both of the axis. The code I use to only draw tiles the player can see relies on taking the tiles position and converting it to the index number that represents it in the array. As you well know, arrays cannot have a negative index. Here is some of my code: This generates the square (or rectangle) of tiles: //Scale is in tiles public void Generate(int sX, int sY) { scaleX = sX; scaleY = sY; for (int y = 0; y <= scaleY; y++) { tiles.Add(new List<Tile>()); for (int x = 0; x <= scaleX; x++) { tiles[tiles.Count - 1].Add(tileset.randomTile(x * tileset.TileSize, y * tileset.TileSize)); } } } Before I changed the code after realizing an array index couldn't be negative my for loops looked something like this to center the map around (0, 0): for (int y = -scaleY / 2; y <= scaleY / 2; y++) for (int x = -scaleX / 2; x <= scaleX / 2; x++) Here is the code that draws the tiles: int startX = (int)Math.Floor((player.Position.X - (graphics.Viewport.Width) - tileset.TileSize) / tileset.TileSize); int endX = (int)Math.Ceiling((player.Position.X + (graphics.Viewport.Width) + tileset.TileSize) / tileset.TileSize); int startY = (int)Math.Floor((player.Position.Y - (graphics.Viewport.Height) - tileset.TileSize) / tileset.TileSize); int endY = (int)Math.Ceiling((player.Position.Y + (graphics.Viewport.Height) + tileset.TileSize) / tileset.TileSize); for (int y = startY; y < endY; y++) { for (int x = startX; x < endX; x++) { if (x >= 0 && y >= 0 && x <= scaleX && y <= scaleY) tiles[y][x].Draw(spriteBatch); } } So to summarize what I'm asking: First, how do I randomly generate a top-down 2D map with different sections (not chunks per se, but areas with different tile sets) and second, how do I get past this negative array index issue?

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• PHP - Internal APIs/Libraries - What makes sense?

  - by Mark Locker

  I've been having a discussion lately with some colleagues about the best way to approach a new project, and thought it'd be interesting to get some external thoughts thrown into the mix. Basically, we're redeveloping a fairly large site (written in PHP) and have differing opinions on how the platform should be setup. Requirements: The platform will need to support multiple internal websites, as well as external (non-PHP) projects which at the moment consist of a mobile app and a toolbar. We have no plans/need in the foreseeable future to open up an API externally (for use in products other than our own). My opinion: We should have a library of well documented native model classes which can be shared between projects. These models will represent everything in our database and can take advantage of object orientated features such as inheritance, traits, magic methods, etc. etc. As well as employing ORM. We can then add an API layer on top of these models which can basically accept requests and route them to the appropriate methods, translating the response so that it can be used platform independently. This routing for each method can be setup as and when it's required. Their opinion: We should have a single HTTP API which is used by all projects (internal PHP ones or otherwise). My thoughts: To me, there are a number of issues with using the sole HTTP API approach: It will be very expensive performance wise. One page request will result in several additional http requests (which although local, are still ones that Apache will need to handle). You'll lose all of the best features PHP has for OO development. From simple inheritance, to employing the likes of ORM which can save you writing a lot of code. For internal projects, the actual process makes me cringe. To get a users name, for example, a request would go out of our box, over the LAN, back in, then run through a script which calls a method, JSON encodes the output and feeds that back. That would then need to be JSON decoded, and be presented as an array ready to use. Working with arrays, as appose to objects, makes me sad in a modern PHP framework. Their thoughts (and my responses): Having one method of doing thing keeps things simple. - You'd only do things differently if you were using a different language anyway. It will become robust. - Seeing as the API will run off the library of models, I think my option would be just as robust. What do you think? I'd be really interested to hear the thoughts of others on this, especially as opinions on both sides are not founded on any past experience.

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• Is this a pattern? Should it be?

  - by Arkadiy

  The following is more of a statement than a question - it describes something that may be a pattern. The question is: is this a known pattern? Or, if it's not, should it be? I've had a situation where I had to iterate over two dissimilar multi-layer data structures and copy information from one to the other. Depending on particular use case, I had around eight different kinds of layers, combined in about eight different combinations: A-B-C B-C A-C D-E A-D-E and so on After a few unsuccessful attempts to factor out the repetition of per-layer iteration code, I realized that the key difficulty in this refactoring was the fact that the bottom level needed access to data gathered at higher levels. To explicitly accommodate this requirement, I introduced IterationContext class with a number of get() and set() methods for accumulating the necessary information. In the end, I had the following class structure: class Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const = 0; }; class RecursingIterator : public Iterator { RecursingIterator(const Iterator &below); }; class IterateOverA : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // Iterate over members in dataStructure1 // locate corresponding item in dataStructure2 (passed via context) // and set it in the context // invoke the sub-iterator }; class IterateOverB : public RecursingIterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // iterate over members dataStructure2 (form context) // set dataStructure2's item in the context // locate corresponding item in dataStructure2 (passed via context) // invoke the sub-iterator }; void main() { class FinalCopy : public Iterator { virtual void iterateOver(const Structure &dataStructure1, IterationContext &ctx) const { // copy data from structure 1 to structure 2 in the context, // using some data from higher levels as needed } } IterationContext ctx(dateStructure2); IterateOverA(IterateOverB(FinalCopy())).iterate(dataStructure1, ctx); } It so happens that dataStructure1 is a uniform data structure, similar to XML DOM in that respect, while dataStructure2 is a legacy data structure made of various structs and arrays. This allows me to pass dataStructure1 outside of the context for convenience. In general, either side of the iteration or both sides may be passed via context, as convenient. The key situation points are: complicated code that needs to be invoked in "layers", with multiple combinations of layer types possible at the bottom layer, the information from top layers needs to be visible. The key implementation points are: use of context class to access the data from all levels of iteration complicated iteration code encapsulated in implementation of pure virtual function two interfaces - one aware of underlying iterator, one not aware of it. use of const & to simplify the usage syntax.

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• Zelda-style top-down RPG. How to store tile and collision data?

  - by Delerat

  I'm looking to build a Zelda: LTTP style top-down RPG. I've read a lot on the subject and am currently going back and forth on a few solutions. I'm using C#, MonoGame, and Tiled. For my tile maps, these are the choices I can see in front of me: Store each tile as its own array. Each one having 3-4 layers, texture/animation, depth, flags, and maybe collision(depending on how I do it). I've read warning about memory issues going this route, and my biggest map will probably be 160x120 tiles. My average map however will be about 40x30. The number of tiles might cut in half if I decide to double my tile size, which is currently 16x16. This is the most appealing approach for me, as I feel like I would know how to save maps, make changes, and separate it into chunks for collision checks. Store the static parts of my tile map in multiple arrays acting as the different layers. Then I would just use entities for anything that wasn't static. All of the other tile data such as collisions, depth, etc., would be stored in their own layers as well I guess? This way just seems messy to me though. Regardless of which one I choose, I'm also unsure how to plan all of that other tile data. I could write a bunch of code that would know which integer represents what tile and it's data, but if I changed a tileset in Tiled and exported it again, all of those integers could potentially change and I'd have to adjust a whole bunch of code. My other issue is about how I could do collision. I want to at least support angled collision that slides you around the corners of objects like LTTP does, if not more oddball shapes as well. So do I: Store collision as a flag for binary collision. Could I get this to support angles? Would it be fine to store collision as an integer and have each number represent a certain angle of collision? Store a list of rectangles or other shapes and do collision that way? Sorry for the large two-part(three-part?) question. I felt like these needed to be asked together as I believe each choice influences the other.

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• Make c# matrix code faster

  - by Wam

  Hi all, Working on some matrix code, I'm concerned of performance issues. here's how it works : I've a IMatrix abstract class (with all matrices operations etc), implemented by a ColumnMatrix class. abstract class IMatrix { public int Rows {get;set;} public int Columns {get;set;} public abstract float At(int row, int column); } class ColumnMatrix : IMatrix { private data[]; public override float At(int row, int column) { return data[row + columns * this.Rows]; } } This class is used a lot across my application, but I'm concerned with performance issues. Testing only read for a 2000000x15 matrix against a jagged array of the same size, I get 1359ms for array access agains 9234ms for matrix access : public void TestAccess() { int iterations = 10; int rows = 2000000; int columns = 15; ColumnMatrix matrix = new ColumnMatrix(rows, columns); for (int i = 0; i < rows; i++) for (int j = 0; j < columns; j++) matrix[i, j] = i + j; float[][] equivalentArray = matrix.ToRowsArray(); TimeSpan totalMatrix = new TimeSpan(0); TimeSpan totalArray = new TimeSpan(0); float total = 0f; for (int iteration = 0; iteration < iterations; iteration++) { total = 0f; DateTime start = DateTime.Now; for (int i = 0; i < rows; i++) for (int j = 0; j < columns; j++) total = matrix.At(i, j); totalMatrix += (DateTime.Now - start); total += 1f; //Ensure total is read at least once. total = total > 0 ? 0f : 0f; start = DateTime.Now; for (int i = 0; i < rows; i++) for (int j = 0; j < columns; j++) total = equivalentArray[i][j]; totalArray += (DateTime.Now - start); } if (total < 0f) logger.Info("Nothing here, just make sure we read total at least once."); logger.InfoFormat("Average time for a {0}x{1} access, matrix : {2}ms", rows, columns, totalMatrix.TotalMilliseconds); logger.InfoFormat("Average time for a {0}x{1} access, array : {2}ms", rows, columns, totalArray.TotalMilliseconds); Assert.IsTrue(true); } So my question : how can I make this thing faster ? Is there any way I can make my ColumnMatrix.At faster ? Cheers !

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• Self-updating collection concurrency issues

  - by DEHAAS

  I am trying to build a self-updating collection. Each item in the collection has a position (x,y). When the position is changed, an event is fired, and the collection will relocate the item. Internally the collection is using a “jagged dictionary”. The outer dictionary uses the x-coordinate a key, while the nested dictionary uses the y-coordinate a key. The nested dictionary then has a list of items as value. The collection also maintains a dictionary to store the items position as stored in the nested dictionaries – item to stored location lookup. I am having some trouble making the collection thread safe, which I really need. Source code for the collection: public class PositionCollection<TItem, TCoordinate> : ICollection<TItem> where TItem : IPositionable<TCoordinate> where TCoordinate : struct, IConvertible { private readonly object itemsLock = new object(); private readonly Dictionary<TCoordinate, Dictionary<TCoordinate, List<TItem>>> items; private readonly Dictionary<TItem, Vector<TCoordinate>> storedPositionLookup; public PositionCollection() { this.items = new Dictionary<TCoordinate, Dictionary<TCoordinate, List<TItem>>>(); this.storedPositionLookup = new Dictionary<TItem, Vector<TCoordinate>>(); } public void Add(TItem item) { if (item.Position == null) { throw new ArgumentException("Item must have a valid position."); } lock (this.itemsLock) { if (!this.items.ContainsKey(item.Position.X)) { this.items.Add(item.Position.X, new Dictionary<TCoordinate, List<TItem>>()); } Dictionary<TCoordinate, List<TItem>> xRow = this.items[item.Position.X]; if (!xRow.ContainsKey(item.Position.Y)) { xRow.Add(item.Position.Y, new List<TItem>()); } xRow[item.Position.Y].Add(item); if (this.storedPositionLookup.ContainsKey(item)) { this.storedPositionLookup[item] = new Vector<TCoordinate>(item.Position); } else { this.storedPositionLookup.Add(item, new Vector<TCoordinate>(item.Position)); // Store a copy of the original position } item.Position.PropertyChanged += (object sender, PropertyChangedEventArgs eventArgs) => this.UpdatePosition(item, eventArgs.PropertyName); } } private void UpdatePosition(TItem item, string propertyName) { lock (this.itemsLock) { Vector<TCoordinate> storedPosition = this.storedPositionLookup[item]; this.RemoveAt(storedPosition, item); this.storedPositionLookup.Remove(item); } } } I have written a simple unit test to check for concurrency issues: [TestMethod] public void TestThreadedPositionChange() { PositionCollection<Crate, int> collection = new PositionCollection<Crate, int>(); Crate crate = new Crate(new Vector<int>(5, 5)); collection.Add(crate); Parallel.For(0, 100, new Action<int>((i) => crate.Position.X += 1)); Crate same = collection[105, 5].First(); Assert.AreEqual(crate, same); } The actual stored position varies every time I run the test. I appreciate any feedback you may have.

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• Problem with the output of Jquery function .offset in IE

  - by vandalk

  Hello! I'm new to jquery and javascript, and to web site developing overall, and I'm having a problem with the .offset function. I have the following code working fine on chrome and FF but not working on IE: $(document).keydown(function(k){ var keycode=k.which; var posk=$('html').offset(); var centeryk=screen.availHeight*0.4; var centerxk=screen.availWidth*0.4; $("span").text(k.which+","+posk.top+","+posk.left); if (keycode==37){ k.preventDefault(); $("html,body").stop().animate({scrollLeft:-1*posk.left-centerxk}) }; if (keycode==38){ k.preventDefault(); $("html,body").stop().animate({scrollTop:-1*posk.top-centeryk}) }; if (keycode==39){ k.preventDefault(); $("html,body").stop().animate({scrollLeft:-1*posk.left+centerxk}) }; if (keycode==40){ k.preventDefault(); $("html,body").stop().animate({scrollTop:-1*posk.top+centeryk}) }; }); hat I want it to do is to scroll the window a set percentage using the arrow keys, so my thought was to find the current coordinates of the top left corner of the document and add a percentage relative to the user screen to it and animate the scroll so that the content don't jump and the user looses focus from where he was. The $("span").text are just so I know what's happening and will be turned into comments when the code is complete. So here is what happens, on Chrome and Firefox the output of the $("span").text for the position variables is correct, starting at 0,0 and always showing how much of the content was scrolled in coordinates, but on IE it starts on -2,-2 and never gets out of it, even if I manually scroll the window until the end of it and try using the right arrow key it will still return the initial value of -2,-2 and scroll back to the beggining. I tried substituting the offset for document.body.scrollLetf and scrollTop but the result is the same, only this time the coordinates are 0,0. Am I doing something wrong? Or is this some IE bug? Is there a way around it or some other function I can use and achieve the same results? On another note, I did other two navigating options for the user in this section of the site, one is to click and drag anywhere on the screen to move it: $("html").mousedown(function(e) { var initx=e.pageX var inity=e.pageY $(document).mousemove(function(n) { var x_inc= initx-n.pageX; var y_inc= inity-n.pageY; window.scrollBy(x_inc*0.7,y_inc*0.7); initx=n.pageX; inity=n.pageY //$("span").text(initx+ "," +inity+ "," +x_inc+ "," +y_inc+ "," +e.pageX+ "," +e.pageY+ "," +n.pageX+ "," +n.pageY); // cancel out any text selections document.body.focus(); // prevent text selection in IE document.onselectstart = function () { return false; }; // prevent IE from trying to drag an image document.ondragstart = function() { return false; }; // prevent text selection (except IE) return false; }); }); $("html").mouseup(function() { $(document).unbind('mousemove'); }); The only part of this code I didn't write was the preventing text selection lines, these ones I found in a tutorial about clicking and draging objects, anyway, this code works fine on Chrome, FireFox and IE, though on Firefox and IE it's more often to happen some moviment glitches while you drag, sometimes it seems the "scrolling" is a litlle jagged, it's only a visual thing and not that much significant but if there's a way to prevent it I would like to know.

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• How to set shmall, shmmax, shmni, etc ... in general and for postgresql

  - by jpic

  I've used the documentation from PostgreSQL to set it for example this config: >>> cat /proc/meminfo MemTotal: 16345480 kB MemFree: 1770128 kB Buffers: 382184 kB Cached: 10432632 kB SwapCached: 0 kB Active: 9228324 kB Inactive: 4621264 kB Active(anon): 7019996 kB Inactive(anon): 548528 kB Active(file): 2208328 kB Inactive(file): 4072736 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 3432 kB Writeback: 0 kB AnonPages: 3034588 kB Mapped: 4243720 kB Shmem: 4533752 kB Slab: 481728 kB SReclaimable: 440712 kB SUnreclaim: 41016 kB KernelStack: 1776 kB PageTables: 39208 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 8172740 kB Committed_AS: 14935216 kB VmallocTotal: 34359738367 kB VmallocUsed: 399340 kB VmallocChunk: 34359334908 kB HardwareCorrupted: 0 kB AnonHugePages: 456704 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 12288 kB DirectMap2M: 16680960 kB >>> ipcs -l ------ Shared Memory Limits -------- max number of segments = 4096 max seg size (kbytes) = 4316816 max total shared memory (kbytes) = 4316816 min seg size (bytes) = 1 ------ Semaphore Limits -------- max number of arrays = 128 max semaphores per array = 250 max semaphores system wide = 32000 max ops per semop call = 32 semaphore max value = 32767 ------ Messages Limits -------- max queues system wide = 31918 max size of message (bytes) = 8192 default max size of queue (bytes) = 16384 sysctl.conf extract: kernel.shmall = 1079204 kernel.shmmax = 4420419584 postgresql.conf non defaults: max_connections = 60 # (change requires restart) shared_buffers = 4GB # min 128kB work_mem = 4MB # min 64kB wal_sync_method = open_sync # the default is the first option checkpoint_segments = 16 # in logfile segments, min 1, 16MB each checkpoint_completion_target = 0.9 # checkpoint target duration, 0.0 - 1.0 effective_cache_size = 6GB Is this appropriate ? If not (or not necessarily), in which case would it be appropriate ? We did note nice performance improvements with this config, how would you improve it ? How should kernel memory management parameters be set ? Can anybody explain how to really set them from the ground up ?

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• mdadm cron job sends email that cron has run

  - by Andrew

  I've got an Ubuntu 8.04 server using mdadm to create several RAID1 arrays. I created /etc/cron.hourly/mdadm as follows: #! /bin/sh set -e mdadm --monitor /dev/md0 /dev/md3 /dev/md4 --oneshot (Yes, the array numbers are not sequential, and I'm not using --scan beacuse I have a degraded array that may or may not have been used as swap and I can't delete, but I think that's a separate issue. If it's the underlying cause of this, I need to fix it.) mdadm sends me email (configured in the /etc/mdadm/mdadm.conf) on DegradedArray etc. events. This is the desired behaviour. What is not desired, and I can't work out, is why cron is sending me (relatively pointless) emails, via an alias in /etc/aliases: From: root@<hostname> (Cron Daemon) To: root@<hostname> Subject: Cron <root@<hostname>> cd / && run-parts --report /etc/cron.hourly Content-Type: text/plain; charset=ANSI_X3.4-1968 X-Cron-Env: <SHELL=/bin/sh> X-Cron-Env: <PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin> X-Cron-Env: <HOME=/root> X-Cron-Env: <LOGNAME=root> Message-Id: <id@hostname> Date: Fri, 7 May 2010 13:17:01 +0930 (CST) /etc/cron.hourly/mdadm: mdadm: Monitor using email address "<root_alias@domain>" from config file I've got a dozen other servers behaving correctly (mdadm sends email, cron doesnt') with identical /etc/crontab files: # /etc/crontab: system-wide crontab # <snip comments> SHELL=/bin/sh PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin # m h dom mon dow user command 17 * * * * root cd / && run-parts --report /etc/cron.hourly <snip anacron jobs> Should I simply remove the --report, or is there something else in my cron config somewhere causing this?

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• Puppet: array in parameterized classes VS using resources

  - by Luke404

  I have some use cases where I want to define multiple similar resources that should end up in a single file (via a template). As an example I'm trying to write a puppet module that will let me manage the mapping between MAC addresses and network interface names (writing udev's persistent-net-rules file from puppet), but there are also many other similar usage cases. I searched around and found that it could be done with the new parameterised classes syntax: if implemented that way it should end up being used like this: node { "myserver.example.com": class { "network::iftab": interfaces => { "eth0" => { "mac" => "ab:cd:ef:98:76:54" } "eth1" => { "mac" => "98:76:de:ad:be:ef" } } } } Not too bad, I agree, but it would rapidly explode when you manage more complex stuff (think network configurations like in this module or any other multiple-complex-resources-in-a-single-config-file stuff). In a similar question on SF someone suggested using Pienaar's puppet-concat module but I doubt it could get any better than parameterised classes. What would be really cool and clean in the configuration definition would be something like the included host type, it's usage is simple, pretty and clean and naturally maps to multiple resources that will end up being configured in a single place. Transposed to my example it would be like: node { "myserver.example.com": interface { "eth0": "mac" => "ab:cd:ef:98:76:54", "foo" => "bar", "asd" => "lol", "eth1": "mac" => "98:76:de:ad:be:ef", "foo" => "rab", "asd" => "olo", } } ...that looks much better to my eyes, even with 3x options to each resource. Should I really be passing arrays to parameterised classes, or there is a better way to do this kind of stuff? Is there some accepted consensus in the puppet [users|developers] community? By the way, I'm referring to the latest stable release of the 2.7 branch and I am not interested in compatibility with older versions.

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• ZFS: Mirror vs. RAID-Z

  - by John Clayton

  I'm planning on building a file server using OpenSolaris and ZFS that will provide two primary services - be an iSCSI target for XenServer virtual machines & be a general home file server. The hardware I'm looking at includes 2x 4-port SATA controllers, 2x small boot drives (one on each controller), and 4x big drives for storage. This allows one free port per controller for upgrading the array down the road. Where I'm a little confused is how to setup the storage drives. For performance, mirroring appears to be king. I'm having a hard time seeing what the benefit would be of using RAIDZ over mirroring would be. With this setup I can see two options - two mirrored pools in one stripe, or RAIDZ2. Both should protect against 2 drive failures, and/or one controller failure...the only benefit of RAIDZ2 would be that any 2 drives could fail. The storage should be 50% of capacity in both cases, but the first should have much better performance, right? The other thing I'm trying to wrap my mind around is the benefit of mirrored arrays with more than two devices. For data integrity what, if any, would be the benefit of a RAIDZ over a three-way mirror? Since ZFS maintains file integrity what does RAIDZ bring to the table...doesn't ZFS's integrity checks negate the value of RAIDZ's parity?

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• Using mixed disks and OpenFiler to create RAID storage

  - by Cylindric

  I need to improve my home storage to add some resilience. I currently have four disks, as follows: D0: 500Gb (System, Boot) D1: 1Tb D2: 500Gb D3: 250Gb There's a mix of partitions on there, so it's not JBOD, but data is pretty spread out and not redundant. As this is my primary PC and I don't want to give up the entire OS to storage, my plan is to use OpenFiler in a VM to create a virtual SAN. I will also use Windows Software RAID to mirror the OS. Partitions will be created as follows: D0 P1: 100Mb: System-Reserved Boot D0 P2: 50Gb: Virtual Machine VMDKs for OS D0 P3: 350Gb: Data D1 P1: 100Mb: System-Reserved Boot D1 P2: 50Gb: Virtual Machine VMDKs for OS D1 P3: 800Gb: Data D2 P1: 450Gb: Data D3 P1: 200Gb: Data This will result in: Mirrored boot partition Mirrored Operating system Mirrored Virtual machine O/S disks Four partitions for data In the four data partitions I will create several large VMDK files, which I will "mount" into OpenFiler as block-storage devices, combined into three RAID arrays (due to the differing disk sizes) In effect, I'll end up with the following usable partitions SYSTEM 100Mb the small boot partition created by the Windows 7 installer (RAID-1) HOST 50Gb the Windows 7 partition (RAID-1) GUESTS 50Gb Virtual machine Guest VMDK's (RAID-1) VG1 900Gb Volume group consisting of a RAID-5 and two RAID-1 VG2 300Gb Volume group consisting of a single disk On VG1 I can dynamically assign storage for my media, photographs, documents, whatever, and it will be safe. On VG2 I can dynamically assign storage for my data that is not critical, and easily recoverable, as it is not safe. Are there any particular 'gotchas' when implementing a virtual OpenFiler like this? Is the recovery process for a failing disk going to be very problematic? Thanks.

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• 24TB RAID 6 configuration

  - by Phil

  I am in charge of a new website in a niche industry that stores lots of data (10+ TB per client, growing to 2 or 3 clients soon). We are considering ordering about $5000 worth of 3TB drives (10 in a RAID 6 configuration and 10 for backup), which will give us approximately 24 TB of production storage. The data will be written once and remain unmodified for the lifetime of the website, so we only need to do a backup one time. I understand basic RAID theory, however I am not experienced with it. My question is, does this sound like a good configuration? What potential problems could this setup cause? Also, what is the best way to do a one-time backup? Have two RAID 6 arrays, one for offsite backup and one for production? Or should I backup the RAID 6 production array to a JBOD? EDIT: The data server is running Windows 2008 Server x64. EDIT 2: To reduce rebuild time, what would you think about using two RAID 5's instead of one RAID 6?

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• Ubuntu 10.04 - Add RAID 1 Array?

  - by N Rahl

  I have an existing Ubuntu 10.04 desktop system setup and running on a hard drive (Drive A). I'd like to add 2 more hard drives (Drives B & C, same size) to the system and mount them as a RAID 1 array. How do I do that? I know how to create RAID arrays during the installation, but I don't want to reinstall my system, and I shouldn't have to since my system files will stay on their own drive separate from the RAID array. I've physically added both drives to the system, and formatted them as EXT3 with gparted. Ubuntu's disk utility has a "create raid" option, but it won't let me select any of my drives (it thinks they're all full). I don't mind using mdadm, but I've found several guides that are old, and give conflicting advice. Some say I have to edit an /etc/raidtab file, some say this is done automatically. So what's the current (Ubuntu 10.04) preferred way of adding a RAID 1 to an existing system? It should turn into a raid at boot, and mount itself in /home/myname/files/. Thanks!

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• Is basing storage requirements based on IOPS sufficient?

  - by Boden

  The current system in question is running SBS 2003, and is going to be migrated on new hardware to SBS 2008. Currently I'm seeing on average 200-300 disk transfers per second total across all the arrays in the system. The array seeing the bulk of activity is a 6 disk 7200RPM RAID 6 and it struggles to keep up during high traffic times (idle time often only 10-20%; response times peaking 20-50+ ms). Based on some rough calculations this makes sense (avg ~245 IOPS on this array at 70/30 read to write ratio). I'm considering using a much simpler disk configuration using a single RAID 10 array of 10K disks. Using the same parameters for my calculations above, I'm getting 583 average random IOPS / sec. Granted SBS 2008 is not the same beast as 2003, but I'd like to make the assumption that it'll be similar in terms of disk performance, if not better (Exchange 2007 is easier on the disk and there's no ISA server). Am I correct in believing that the proposed system will be sufficient in terms of performance, or am I missing something? I've read so much about recommended disk configurations for various products like Exchange, and they often mention things like dedicating spindles to logs, etc. I understand the reasoning behind this, but if I've got more than enough random I/O overhead, does it really matter? I've always at the very least had separate spindles for the OS, but I could really reduce cost and complexity if I just had a single, good performing array. So as not to make you guys do my job for me, the generic version of this question is: if I have a projected IOPS figure for a new system, is it sufficient to use this value alone to spec the storage, ignoring "best practice" configurations? (given similar technology, not going from DAS to SAN or anything)

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• Recovering Data from a Linkstation LS-WXL/R1

  - by kingkool68

  I've been running a Buffalo Linkstation LS-WXL/R1 in RAID1 for a few weeks. Two nights ago we had a brief power outage. Yesterday when I tried to mount the disk it couldn't be found. I logged in to the web admin and it couldn't see any storage attached and no arrays available. Well this sucks. I ended up taking the disks out and mounting them to an Ubuntu virtual machine. They how up as an Array but I can't start the Array to the best of my limited knowledge. I could still see the 6 partitions, so I'm confident the data is there. I can use Photorec (http://www.cgsecurity.org/wiki/PhotoRec) to recover most of the files I want, it just takes some time. Could I make an image of the data partition and mount that in Ubuntu so I can get at the data I want through the file system? 95% of the data on my Linkstation LS-WXL/R1 is backup. I just put a few folders of images on there that I need to get back. I'm already preparing to format the disks when I'm done and re-building the RAID1 array from scratch. Any advice would be appreciated.

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• Dell PERC 5 - RAID-10 keeps rebuilding drive 2 every day

  - by raid question

  I have a Dell PowerEdge 2950 with this card: RAID bus controller [0104]: Dell PowerEdge Expandable RAID controller 5 [1028:0015] and six disks in a RAID-10. I replaced drive 2, because it didn't show up, and then it started to rebuild itself: root@backup01:~# megaraidsas-status -- Arrays informations -- -- ID | Type | Size | Status a0d0 | RAID 10 | 5587GiB | DEGRADED -- Disks informations -- ID | Model | Status | Warnings a0e8s0 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s1 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5394 a0e8s2 | ATA ST2000DM001-1E61 1863GiB | rebuild | errs: media:0 other:99 a0e8s3 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s4 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 a0e8s5 | ATA ST2000DM001-9YN1 1863GiB | online | errs: media:0 other:5393 The rebuild finishes, then the virtual drive becomes optimal, and drive 2 goes online. Then once a day, drive 2 acts like it's been removed, and the rebuild starts all over again. How do I make this once a day rebuild stop? Event Description: Removed: PD 02(e1/s2) Event Description: Removed: PD 02(e1/s2) Info: enclPd=08, scsiType=0, portMap=04, sasAddr=1221000002000000,0000000000000000 Event Description: State change on VD 00/0 from OPTIMAL(3) to DEGRADED(2) Event Description: VD 00/0 is now DEGRADED1 Event Description: State change on PD 02(e1/s2) from ONLINE(18) to FAILED(11) Event Description: State change on PD 02(e1/s2) from FAILED(11) to UNCONFIGURED_BAD(1) Event Description: Background Initialization failed on VD 00/0 Event Description: Inserted: PD 02(e1/s2) Event Description: Inserted: PD 02(e1/s2) Info: enclPd=08, scsiType=0, portMap=04, sasAddr=1221000002000000,0000000000000000 Event Description: PD 02(e1/s2) is not a certified drive Event Description: State change on PD 02(e1/s2) Event Description: State change on PD 02(e1/s2) from UNCONFIGURED_GOOD(0) to OFFLINE(10) from UNCONFIGURED_BAD(1) to UNCONFIGURED_GOOD(0) Event Description: Rebuild automatically started on PD 02(e1/s2) Event Description: State change on PD 02(e1/s2) from OFFLINE(10) to REBUILD(14)

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• Win 2008 R2 - copying TO disk is very slow, copying FROM is more or less okay

  - by avs099

  I have Windows 2008 R2 SP1 with 4 identical SATA disks (Seagate Barracude 7200) in RAID 5 array. It has 4Gb of memory; all recent updates are installed. Problem: when I copy large file from one folder to another, I get about 10MB/s average speed. When I read this file from network share via 1Gbps connection - I get about 25-30 MB/s. Both numbers seems to be low for me - but specifically I'm very frustrated with low write speed. there is no antivirus, no hyper-v, it's just a fileserver - i when i do my tests nobody else reads/write from it (we have only 4 people in a team, so I'm sure). Not sure if that matters, but there is only 1 logic disk "C" with all available space (1400 GB). I'm not an admin at all, so I have no idea where to look and what other information to provide. I did run performance monitor with "% idle time", "avg bytes read", "avg byte write" - here is the screenshot: I'm not sure why there are such obvious spikes. Any idea? Please let me know if you need me to provide more information - what counters should I check, etc. I'm very eager to get this solved. Thank you. UPDATE: we have another Windows 2008 R2 SP1 server with 2 RAID1 arrays - one is disk C (where windows is installed, another one is disk E). It is running Hyper-V and does not have antivirus. I noticed the following behavior when I copy large file (few GBs): C - C: about 50MB/sec C - E: about 55MB/sec E - E: 8MB/sec!!! E - C: 8MB/sec!!! what could cause this?? E drive is RAID1 array from same Seagate Barracuda 1TB drives..

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