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  • Junior software developer - How to understand web applications in depth?

    - by nat_gr
    I am currently a junior developer in web applications and specifically in ASP.NET MVC technology. My problem is that the C# senior developer in the company has no experience with this technology and I try to learn without any guidance. I went through all tutorials (e.g music store), codeplex projects and also read Pro ASP.NET MVC 4. However, most of the examples are about CRUD and e-commerce applications. What I don't understand is how dependency injection fits in web applications (I have realized that is not only used for facilitating unit testing) or when I should use a custom model binder or how to model the business logic when there is already a database schema in place. I read the forum quite often and it would very helpful if some experienced developer could give me an insight about how to proceed. Do I need to read some books to understand the overall idea behind web applications? And what kind of application should I start building myself - I don't think it would be useful to create similar examples with the tutorials.

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  • Differences between software testing processes and techniques?

    - by Aptos
    I get confused between these terms. For examples, should Unit testing be listed as a software testing process or technique? I think unit testing is a software testing technique. And how about Test driven development? Can you give me some examples for software testing processes and techniques? In my opinion, software testing process is a part of the software development life cycle. For example, if we use V-Model, the software testing process will be System test, Acceptance test, Integration Test... Thank you.

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  • Orthographic Zooming with 0,0 at top/left

    - by Sean M.
    I'm trying to implement zooming on my 2D game. Since it's using orthographic projection, I thought it would be easy to implement zooming. After looking around the internet, I found a bunch of explanations and samples on how to do this if (0,0) is the center of the screen with the orthographic projection. The problem is, my ortho projection has (0,0) at the top-left (similar to XNA/Monogame, and a couple others). I could not find any examples about how to implement zooming to the center of the screen when the center is not (0,0). And help/links/code examples would be greatly appreciated.

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  • How to teach computer science ?

    - by proferikson
    I am just starting to teach computer science. It's just the basic level. I'm finding that I sometimes don't know how to approach topics in a way that lets students easily understand. I've found that the best thing is to use analogies. A terrible one, that worked well, was presenting recursion by using the process of eating a burger. (You eat one bite, then you eat the rest). Interesting real world examples do wonders here. I'd like to know the techniques you have used for teaching, or teachers you've had have used that proved particularly effective. I'd also like to know your best analogies and examples for topics in CS101, especially for those harder to grasp topics. I'm teaching the class in Java (as required).

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  • Using lookahead assertions in regular expressions

    - by Greg Jackson
    I use regular expressions on a daily basis, as my daily work is 90% in Perl (legacy codebase, but that's a different issue). Despite this, I still find lookahead and lookbehind to be terribly confusing and often unreadable. Right now, if I were to get a code review with a lookahead or lookbehind, I would immediately send it back to see if the problem can be solved by using multiple regular expressions or a different approach. The following are the main reasons I tend not to like them: They can be terribly unreadable. Lookahead assertions, for example, start from the beginning of the string no matter where they are placed. That, among other things, can cause some very "interesting" and non-obvious behaviors. It used to be the case that many languages didn't support lookahead/lookbehind (or supported them as "experimental features"). This isn't the case quite as much, but there's still always the question as to how well it's supported. Quite frankly, they feel like a dirty hack. Regexps often already are, but they can also be quite elegant, and have gained widespread acceptance. I've gotten by without any need for them at all... sometimes I think that they're extraneous. Now, I'll freely admit that especially the last two reasons aren't really good ones, but I felt that I should enumerate what goes through my mind when I see one. I'm more than willing to change my mind about them, but I feel that they violate some of my core tenets of programming, including: Code should be as readable as possible without sacrificing functionality -- this may include doing something in a less efficient, but clearer was as long as the difference is negligible or unimportant to the application as a whole. Code should be maintainable -- if another programmer comes along to fix my code, non-obvious behavior can hide bugs or make functional code appear buggy (see readability) "The right tool for the right job" -- I'm sure you can come up with contrived examples that could use lookahead, but I've never come across something that really needs them in my real-world development work. Is there anything that they're really the best tool for, as opposed to, say, multiple regexps (or, alternatively, are they the best tool for most cases they're used for today). My question is this: Is it good practice to use lookahead/lookbehind in regular expressions, or are they simply a hack that have found their way into modern production code? I'd be perfectly happy to be convinced that I'm wrong about this, and simple examples are useful for examples or illustration, but by themselves, won't be enough to convince me.

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  • Aptronyms: fitting the profession to the name

    - by Tony Davis
    Writing a recent piece on the pains of index fragmentation, I found myself wondering why, in SQL Server, you can’t set the equivalent of a fill factor, on a heap table. I scratched my head…who might know? Phil Factor, of course! I approached him with a due sense of optimism only to find that not only did he not know, he also didn’t seem to care much either. I skulked off thinking how this may be the final nail in the coffin of nominative determinism. I’ve always wondered if there was anything in it, though. If your surname is Plumb or Leeks, is there even a tiny, extra percentage chance that you’ll end up fitting bathrooms? Some examples are quite common. I’m sure we’ve all met teachers called English or French, or lawyers called Judge or Laws. I’ve also known a Doctor called Coffin, a Urologist called Waterfall, and a Dentist called Dentith. Two personal favorites are Wolfgang Wolf who ended up managing the German Soccer team, Wolfsburg, and Edmund Akenhead, a Crossword Editor for The Times newspaper. Having forgiven Phil his earlier offhandedness, I asked him for if he knew of any notable examples. He had met the famous Dr. Batty and Dr. Nutter, both Psychiatrists, knew undertakers called Death and Stiff, had read a book by Frederick Page-Turner, and suppressed a giggle at the idea of a feminist called Gurley-Brown. He even managed to better my Urologist example, citing the article on incontinence in the British Journal of Urology (vol.49, pp.173-176, 1977) by A. J. Splatt and D. Weedon. What, however, if you were keen to gently nudge your child down the path to a career in IT? What name would you choose? Subtlety probably doesn’t really work, although in a recent interview, Rodney Landrum did congratulate PowerShell MVP Max Trinidad on being named after a SQL function. Grant “The Memory” Fritchey (OK, I made up that nickname) doesn’t do badly either. Some surnames, seem to offer a natural head start, although I know of no members of the Page-Reid clan in the profession. There are certainly families with the Table surname, although sadly, Little Bobby Tables was merely a legend by xkcd. A member of the well-known Key family would need to name their son Primary, or maybe live abroad, to make their mark. Nominate your examples of people seemingly destined, by name, for their chosen profession (extra points for IT). The best three will receive a prize. Cheers, Tony.

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  • Resources for up-to-date Delphi programming

    - by Dan Kelly
    I'm a developer in a small department and have been using Delphi for the last 10 years. Whilst I've tried to keep up-to-date with movements there are a lot of changes that have occurred between Delphi 7 and (current for us) 2010. Stack Exchange and here have been great for answering the "how do you" questions, but what I'd like is a resource that shows great examples of larger scale programming. For example is there anywhere that hosts examples of well written, multi form applications? Something that can be looked at as a whole to illustrate why things should be done a certain way?

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  • Junior software developer - How to understand web aplications in depth?

    - by nat_gr
    I am currently a junior developer in web applications and specifically in asp.net mvc technology. My problem is that the c# senior developer in the company has no experience with this technology and I try to learn without any guidance. I went through all tutorials (e.g music store), codeplex projects and also read pro asp.net mvc 4. However, most of the examples are about crud and e-commerce applications. What I don't understand is how dependency injection fits in web applications (I have realized that is not only used for facilitating unit testing) or when i should use a custom model binder or how to model the business logic when there is already a database schema in place. I read the forum quite often and it would very helpful if some experienced developers could give me an insight about how to proceed. Do I need to read some books to understand the overall idea behind web applications? And what kind of application should I start building myself - I don't think it would be useful to create similar examples with the tutorials.

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  • Books are Dead! Long Live the Books!

    - by smisner
    We live in interesting times with regard to the availability of technical material. We have lots of free written material online in the form of vendor documentation online, forums, blogs, and Twitter. And we have written material that we can buy in the form of books, magazines, and training materials. Online videos and training – some free and some not free – are also an option. All of these formats are useful for one need or another. As an author, I pay particular attention to the demand for books, and for now I see no reason to stop authoring books. I assure you that I don’t get rich from the effort, and fortunately that is not my motivation. As someone who likes to refer to books frequently, I am still a big believer in books and have evidence from book sales that there are others like me. If I can do my part to help others learn about the technologies I work with, I will continue to produce content in a variety of formats, including books. (You can view a list of all of my books on the Publications page of my site and my online training videos at Pluralsight.) As a consumer of technical information, I prefer books because a book typically can get into a topic much more deeply than a blog post, and can provide more context than vendor documentation. It comes with a table of contents and a (hopefully accurate) index that helps me zero in on a topic of interest, and of course I can use the Search feature in digital form. Some people suggest that technology books are outdated as soon as they get published. I guess it depends on where you are with technology. Not everyone is able to upgrade to the latest and greatest version at release. I do assume, however, that the SQL Server 7.0 titles in my library have little value for me now, but I’m certain that the minute I discard the book, I’m going to want it for some reason! Meanwhile, as electronic books overtake physical books in sales, my husband is grateful that I can continue to build my collection digitally rather than physically as the books have a way of taking over significant square footage in our house! Blog posts, on the other hand, are useful for describing the scenarios that come up in real-life implementations that wouldn’t fit neatly into a book. As many years that I have working with the Microsoft BI stack, I still run into new problems that require creative thinking. Likewise, people who work with BI and other technologies that I use share what they learn through their blogs. Internet search engines help us find information in blogs that simply isn’t available anywhere else. Another great thing about blogs, also, is the connection to community and the dialog that can ensue between people with common interests. With the trend towards electronic formats for books, I imagine that we’ll see books continue to adapt to incorporate different forms of media and better ways to keep the information current. At the moment, I wish I had a better way to help readers with my last two Reporting Services books. In the case of the Microsoft® SQL Server™ 2005 Reporting Services Step by Step book, I have heard many cases of readers having problems with the sample database that shipped on CD – either the database was missing or it was corrupt. So I’ve provided a copy of the database on my site for download from http://datainspirations.com/uploads/rs2005sbsDW.zip. Then for the Microsoft® SQL Server™ 2008 Reporting Services Step by Step book, we decided to avoid the database problem by using the AdventureWorks2008 samples that Microsoft published on Codeplex (although code samples are still available on CD). We had this silly idea that the URL for the download would remain constant, but it seems that expectation was ill-founded. Currently, the sample database is found at http://msftdbprodsamples.codeplex.com/releases/view/37109 but I have no idea how long that will remain valid. My latest books (#9 and #10 which are milestones I never anticipated), Building Integrated Business Intelligence Solutions with SQL Server 2008 R2 and Office 2010 (McGraw Hill, 2011) and Business Intelligence in Microsoft SharePoint 2010 (Microsoft Press, 2011), will not ship with a CD, but will provide all code samples for download at a site maintained by the respective publishers. I expect that the URLs for the downloads for the book will remain valid, but there are lots of references to other sites that can change or disappear over time. Does that mean authors shouldn’t make reference to such sites? Personally, I think the benefits to be gained from including links are greater than the risks of the links becoming invalid at some point. Do you think the time for technology books has come to an end? Is the delivery of books in electronic format enough to keep them alive? If technological barriers were no object, what would make a book more valuable to you than other formats through which you can obtain information?

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  • Best Method For Evaluating Existing Software or New Software

    How many of us have been faced with having to decide on an off-the-self or a custom built component, application, or solution to integrate in to an existing system or to be the core foundation of a new system? What is the best method for evaluating existing software or new software still in the design phase? One of the industry preferred methodologies to use is the Active Reviews for Intermediate Designs (ARID) evaluation process.  ARID is a hybrid mixture of the Active Design Review (ADR) methodology and the Architectural Tradeoff Analysis Method (ATAM). So what is ARID? ARD’s main goal is to ensure quality, detailed designs in software. One way in which it does this is by empowering reviewers by assigning generic open ended survey questions. This approach attempts to remove the possibility for allowing the standard answers such as “Yes” or “No”. The ADR process ignores the “Yes”/”No” questions due to the fact that they can be leading based on how the question is asked. Additionally these questions tend to receive less thought in comparison to more open ended questions. Common Active Design Review Questions What possible exceptions can occur in this component, application, or solution? How should exceptions be handled in this component, application, or solution? Where should exceptions be handled in this component, application, or solution? How should the component, application, or solution flow based on the design? What is the maximum execution time for every component, application, or solution? What environments can this component, application, or solution? What data dependencies does this component, application, or solution have? What kind of data does this component, application, or solution require? Ok, now I know what ARID is, how can I apply? Let’s imagine that your organization is going to purchase an off-the-shelf (OTS) solution for its customer-relationship management software. What process would we use to ensure that the correct purchase is made? If we use ARID, then we will have a series of 9 steps broken up by 2 phases in order to ensure that the correct OTS solution is purchases. Phase 1 Identify the Reviewers Prepare the Design Briefing Prepare the Seed Scenarios Prepare the Materials When identifying reviewers for a design it is preferred that they be pulled from a candidate pool comprised of developers that are going to implement the design. The believe is that developers actually implementing the design will have more a vested interest in ensuring that the design is correct prior to the start of code. Design debriefing consist of a summary of the design, examples of the design solving real world examples put in to use and should be no longer than two hours typically. The primary goal of this briefing is to adequately summarize the design so that the review members could actually implement the design. In the example of purchasing an OTS product I would attempt to review my briefing prior to its distribution with the review facilitator to ensure that nothing was excluded that should have not been. This practice will also allow me to test the length of the briefing to ensure that can be delivered in an appropriate about of time. Seed Scenarios are designed to illustrate conceptualized scenarios when applied with a set of sample data. These scenarios can then be used by the reviewers in the actual evaluation of the software, All materials needed for the evaluation should be prepared ahead of time so that they can be reviewed prior to and during the meeting. Materials Included: Presentation Seed Scenarios Review Agenda Phase 2 Present ARID Present Design Brainstorm and prioritize scenarios Apply scenarios Summarize Prior to the start of any ARID review meeting the Facilitator should define the remaining steps of ARID so that all the participants know exactly what they are doing prior to the start of the review process. Once the ARID rules have been laid out, then the lead designer presents an overview of the design which typically takes about two hours. During this time no questions about the design or rational are allowed to be asked by the review panel as a standard, but they are written down for use latter in the process. After the presentation the list of compiled questions is then summarized and sent back to the lead designer as areas that need to be addressed further. In the example of purchasing an OTS product issues could arise regarding security, the implementation needed or even if this is this the correct product to solve the needed solution. After the Design presentation a brainstorming and prioritize scenarios process begins by reducing the seed scenarios down to just the highest priority scenarios.  These will then be used to test the design for suitability. Once the selected scenarios have been defined the reviewers apply the examples provided in the presentation to the scenarios. The intended output of this process is to provide code or pseudo code that makes use of the examples provided while solving the selected seed scenarios. As a standard rule, the designers of the systems are not allowed to help the review board unless they all become stuck. When this occurs it is documented and along with the reason why the designer needed to help the review panel back on track. Once all of the scenarios have been completed the review facilitator reviews with the group issues that arise during the process. Then the reviewers will be polled as to efficacy of the review experience. References: Clements, Paul., Kazman, Rick., Klien, Mark. (2002). Evaluating Software Architectures: Methods and Case Studies Indianapolis, IN: Addison-Wesley

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  • Why should ViewModel route actions to Controller when using the MVCVM pattern?

    - by Lea Hayes
    When reading examples across the Internet (including the MSDN reference) I have found that code examples are all doing the following type of thing: public class FooViewModel : BaseViewModel { public FooViewModel(FooController controller) { Controller = controller; } protected FooController Controller { get; private set; } public void PerformSuperAction() { // This just routes action to controller... Controller.SuperAction(); } ... } and then for the view: public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.PerformSuperAction(); } } Why do we not just do the following? public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.Controller.SuperAction(); // or, even just use a shortcut property: Controller.SuperAction(); } }

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  • OpenGL ES 2.0 example for JOGL

    - by fjdutoit
    I've scoured the internet for the last few hours looking for an example of how to run even the most basic OpenGL ES 2 example using JOGL but "by Jupiter!" it has been a total fail. I tried converting the android example from the OpenGL ES 2.0 Programming Guide examples (and at the same time looking at the WebGL example -- which worked fine) yet without any success. Are there any examples out there? If anyone else wants some extra help regarding this question see this thread on the official Jogamp forum.

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  • Real life example of an agile game development process

    - by Ken
    I'm trying to learn about applying agile methodologies to game development. But seems to be impossible to find real life examples. What I am looking for are things like; Initial user stories Final user stories (complete, covering the entire game requirements) Acceptance criteria Task list Sprint backlogs (before and after each sprint) The agile books seem to have some limited examples, many of which seem contrived. In this era of open source software, there must be an documented example of the process applied to a game that is publicly available. I am asking specifically about games because they are so different from normal applications. Regular applications are built to all users to complete specific tasks in order to get stuff done(book a room, print a report etc). People play games for much less tangible reasons, so I think the process is significantly different. [it doesn't have to be scrum, it could be any process, just needs to be a real life example game and be reasonably complete]

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  • io Exception error in wordcount example

    - by Anitha
    I have installed Hadoop 1.0.3 in Ubuntu 12.04 version (64bit) based on michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/ . I am trying to run a mapreduce job using the wordcount example. Running the command hduser@ubuntu: $/usr/local/hadoop/bin/hadoop jar hadoop-examples-1.0.3.jar wordcount /user/hduser/gutenberg /user/hduser/gutenberg-output gives the following error: Warning: $HADOOP_HOME is deprecated. Exception in thread "main" java.io.IOException: Error opening job jar: hadoop-examples-1.0.3.jar at org.apache.hadoop.util.RunJar.main(RunJar.java:90) Caused by: java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.<init>(ZipFile.java:131) at java.util.jar.JarFile.<init>(JarFile.java:150) at java.util.jar.JarFile.<init>(JarFile.java:87) at org.apache.hadoop.util.RunJar.main(RunJar.java:88) Thanks in advance.

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  • Android frame by frame PNG animation

    - by Trick
    I am new at Android game development. I have done some apps before, but none of them are games :) So, I wanted to do a frame-by-frame animation of PNGs. I tried with AnimationDrawable, but OutOfMemory error comes quickly (I have a lot of PNGs). So I came upon SurfaceView. But I am stuck, because I really don't find any useful tutoirals/examples. What is the best way to make an animation like this? Here there already is a great answer to almost the same question, but all the links there don't work anymore. I would really like to here suggestions how to make an animation frame-by-frame with PNGs in Android and if you have any tutorials or examples, I will be really happy :)

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  • Naming conventions used for variables and functions in C

    - by Zel
    While coding a large project in C I came upon a problem. If I keep on writing more code then there will be a time when it will be difficult for me to organize the code. I mean that the naming for functions and variables for different parts of the program may seem to be mixed up. So I was thinking whether there are useful naming conventions that I can use for C variables and functions? Most languages suggest a naming convention. But for C the only thing I have read so far is the names should be descriptive for code readability. EDIT: Examples of some examples of suggested naming conventions: Python's PEP 8 Java Tutorial I read some more naming conventions for java somewhere but couldn't remember where.

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  • What can procs and lambdas do that functions can't in ruby

    - by SecurityGate
    I've been working in Ruby for the last couple weeks, and I've come to the subject of procs, lambdas and blocks. After reading a fair share of examples from a variety of sources, I don't how they're much different from small, specialized functions. It's entirely possible that the examples I've read aren't showing the power behind procs and lambdas. def zero_function(x) x = x.to_s if x.length == 1 return x = "0" + x else return x end end zero_lambda = lambda {|x| x = x.to_s if x.length == 1 return x = "0" + x else return x end } zero_proc = Proc.new {|x| x = x.to_s if x.length == 1 puts x = "0" + x else puts x end } puts zero_function(4) puts zero_lambda.call(3) zero_proc.call(2) This function, proc, and lambda do the exact same thing, just slightly different. Is there any reason to choose one over another?

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  • Crypted partition in clear, how crypt?

    - by bux
    I've crypted my home partition like that: root@mycomputer:# ecryptfs-migrate-home -u bux After 1 hour ecryptfs done his work. fine. To check it, i connect with root on TTY1 just after boot. I seen my files in /home/bux.HfooOU2x was not crypted ! cat /home/bux.HfooOU2x/.bashrc # ~/.bashrc: executed by bash(1) for non-login shells. # see /usr/share/doc/bash/examples/startup-files (in the package bash-doc) # for examples Error is mine ? How crypt this home folder ? Thank's ;)

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  • Randomly generate directed graph on a grid

    - by Talon876
    I am trying to randomly generate a directed graph for the purpose of making a puzzle game similar to the ice sliding puzzles from Pokemon. This is essentially what I want to be able to randomly generate: http://bulbanews.bulbagarden.net/wiki/Crunching_the_numbers:_Graph_theory. I need to be able to limit the size of the graph in an x and y dimension. In the example given in the link, it would be restricted to an 8x4 grid. The problem I am running into is not randomly generating the graph, but randomly generating a graph, which I can properly map out in a 2d space, since I need something (like a rock) on the opposite side of a node, to make it visually make sense when you stop sliding. The problem with this is that sometimes the rock ends up in the path between two other nodes or possibly on another node itself, which causes the entire graph to become broken. After discussing the problem with a few people I know, we came to a couple of conclusions that may lead to a solution. Including the obstacles in the grid as part of the graph when constructing it. Start out with a fully filled grid and just draw a random path and delete out blocks that will make that path work. The problem then becomes figuring out which ones to delete to avoid introducing an additional, shorter path. We were also thinking a dynamic programming algorithm may be beneficial, though none of us are too skilled with creating dynamic programming algorithms from nothing. Any ideas or references about what this problem is officially called (if it's an official graph problem) would be most helpful. Here are some examples of what I have accomplished so far by just randomly placing blocks and generating the navigation graph from the chosen start/finish. The idea (as described in the previous link) is you start at the green S and want to get to the green F. You do this by moving up/down/left/right and you continue moving in the direction chosen until you hit a wall. In these pictures, grey is a wall, white is the floor, and the purple line is the minimum length from start to finish, and the black lines and grey dots represented possible paths. Here are some bad examples of randomly generated graphs: http://i.stack.imgur.com/9uaM6.png Here are some good examples of randomly generated (or hand tweaked) graphs: i.stack.imgur.com/uUGeL.png (can't post another link, sorry) I've also seemed to notice the more challenging ones when actually playing this as a puzzle are ones which have lots of high degree nodes along the minimum path.

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  • Has test driven development (TDD) actually benefited a real world project?

    - by James
    I am not new to coding. I have been coding (seriously) for over 15 years now. I have always had some testing for my code. However, over the last few months I have been learning test driven design/development (TDD) using Ruby on Rails. So far, I'm not seeing the benefit. I see some benefit to writing tests for some things, but very few. And while I like the idea of writing the test first, I find I spend substantially more time trying to debug my tests to get them to say what I really mean than I do debugging actual code. This is probably because the test code is often substantially more complicated than the code it tests. I hope this is just inexperience with the available tools (RSpec in this case). I must say though, at this point, the level of frustration mixed with the disappointing lack of performance is beyond unacceptable. So far, the only value I'm seeing from TDD is a growing library of RSpec files that serve as templates for other projects/files. Which is not much more useful, maybe less useful, than the actual project code files. In reading the available literature, I notice that TDD seems to be a massive time sink up front, but pays off in the end. I'm just wondering, are there any real world examples? Does this massive frustration ever pay off in the real world? I really hope I did not miss this question somewhere else on here. I searched, but all the questions/answers are several years old at this point. It was a rare occasion when I found a developer who would say anything bad about TDD, which is why I have spent as much time on this as I have. However, I noticed that nobody seems to point to specific real-world examples. I did read one answer that said the guy debugging the code in 2011 would thank you for have a complete unit testing suite (I think that comment was made in 2008). So, I'm just wondering, after all these years, do we finally have any examples showing the payoff is real? Has anybody actually inherited or gone back to code that was designed/developed with TDD and has a complete set of unit tests and actually felt a payoff? Or did you find that you were spending so much time trying to figure out what the test was testing (and why it was important) that you just tossed out the whole mess and dug into the code?

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  • Performance triage

    - by Dave
    Folks often ask me how to approach a suspected performance issue. My personal strategy is informed by the fact that I work on concurrency issues. (When you have a hammer everything looks like a nail, but I'll try to keep this general). A good starting point is to ask yourself if the observed performance matches your expectations. Expectations might be derived from known system performance limits, prototypes, and other software or environments that are comparable to your particular system-under-test. Some simple comparisons and microbenchmarks can be useful at this stage. It's also useful to write some very simple programs to validate some of the reported or expected system limits. Can that disk controller really tolerate and sustain 500 reads per second? To reduce the number of confounding factors it's better to try to answer that question with a very simple targeted program. And finally, nothing beats having familiarity with the technologies that underlying your particular layer. On the topic of confounding factors, as our technology stacks become deeper and less transparent, we often find our own technology working against us in some unexpected way to choke performance rather than simply running into some fundamental system limit. A good example is the warm-up time needed by just-in-time compilers in Java Virtual Machines. I won't delve too far into that particular hole except to say that it's rare to find good benchmarks and methodology for java code. Another example is power management on x86. Power management is great, but it can take a while for the CPUs to throttle up from low(er) frequencies to full throttle. And while I love "turbo" mode, it makes benchmarking applications with multiple threads a chore as you have to remember to turn it off and then back on otherwise short single-threaded runs may look abnormally fast compared to runs with higher thread counts. In general for performance characterization I disable turbo mode and fix the power governor at "performance" state. Another source of complexity is the scheduler, which I've discussed in prior blog entries. Lets say I have a running application and I want to better understand its behavior and performance. We'll presume it's warmed up, is under load, and is an execution mode representative of what we think the norm would be. It should be in steady-state, if a steady-state mode even exists. On Solaris the very first thing I'll do is take a set of "pstack" samples. Pstack briefly stops the process and walks each of the stacks, reporting symbolic information (if available) for each frame. For Java, pstack has been augmented to understand java frames, and even report inlining. A few pstack samples can provide powerful insight into what's actually going on inside the program. You'll be able to see calling patterns, which threads are blocked on what system calls or synchronization constructs, memory allocation, etc. If your code is CPU-bound then you'll get a good sense where the cycles are being spent. (I should caution that normal C/C++ inlining can diffuse an otherwise "hot" method into other methods. This is a rare instance where pstack sampling might not immediately point to the key problem). At this point you'll need to reconcile what you're seeing with pstack and your mental model of what you think the program should be doing. They're often rather different. And generally if there's a key performance issue, you'll spot it with a moderate number of samples. I'll also use OS-level observability tools to lock for the existence of bottlenecks where threads contend for locks; other situations where threads are blocked; and the distribution of threads over the system. On Solaris some good tools are mpstat and too a lesser degree, vmstat. Try running "mpstat -a 5" in one window while the application program runs concurrently. One key measure is the voluntary context switch rate "vctx" or "csw" which reflects threads descheduling themselves. It's also good to look at the user; system; and idle CPU percentages. This can give a broad but useful understanding if your threads are mostly parked or mostly running. For instance if your program makes heavy use of malloc/free, then it might be the case you're contending on the central malloc lock in the default allocator. In that case you'd see malloc calling lock in the stack traces, observe a high csw/vctx rate as threads block for the malloc lock, and your "usr" time would be less than expected. Solaris dtrace is a wonderful and invaluable performance tool as well, but in a sense you have to frame and articulate a meaningful and specific question to get a useful answer, so I tend not to use it for first-order screening of problems. It's also most effective for OS and software-level performance issues as opposed to HW-level issues. For that reason I recommend mpstat & pstack as my the 1st step in performance triage. If some other OS-level issue is evident then it's good to switch to dtrace to drill more deeply into the problem. Only after I've ruled out OS-level issues do I switch to using hardware performance counters to look for architectural impediments.

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  • need example sql transaction procedures for sales tracking or financial database [closed]

    - by fa1c0n3r
    hi, i am making a database for an accounting/sales type system similar to a car sales database and would like to make some transactions for the following real world actions salesman creates new product shipped onto floor (itempk, car make, year, price).   salesman changes price.   salesman creates sale entry for product sold (salespk, itemforeignkey, price sold, salesman).   salesman cancels item for removed product.   salesman cancels sale for cancelled sale    the examples i have found online are too generic...like this is a transaction... i would like something resembling what i am trying to do to understand it.  anybody have some good similar or related sql examples i can look at to design these? do people use transactions for sales databases?  or if you have done this kind of sql transaction before could you make an outline for how these could be made?  thanks  my thread so far on stack overflow... http://stackoverflow.com/q/4975484/613799

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  • What the best way to wire up Entity Framework database context (model) to ViewModel in MVVM WPF?

    - by hal9k2
    As in the question above: What the best way to wire up Entity Framework database model (context) to viewModel in MVVM (WPF)? I am learning MVVM pattern in WPF, alot of examples shows how to implement model to viewModel, but models in that examples are just simple classes, I want to use MVVM together with entity framework model (base first approach). Whats the best way to wire model to viewModel. Thanks for answers. //ctor of ViewModel public ViewModel() { db = new PackageShipmentDBEntities(); // Entity Framework generated class ListaZBazy = new ObservableCollection<Pack>(db.Packs.Where(w => w.IsSent == false)); } This is my usual ctor of ViewModel, think there is a better way, I was reading about repository pattern, not sure if I can adapt this to WPF MVVM

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  • 2D vector graphic html5 framework

    - by Yury
    I trying to find html5 game framework by following criteria: 1)Real good performance. 2)Good support of vector graphic( objects which contains canvas elements -line, rec,bezierCurve etc.) 3)Easy port to mobile. Optional- Physics Engine. I found 1)Pixi.js- it looks like real good, but i didn't find any info about "vector objects" support. 2) i found "vector objects" support in paper.js I need something like these: http://paperjs.org/examples/chain/ and http://paperjs.org/examples/path-intersections/. But it looks like paper.js- not so good performance as pixi.js. And it is not game engine. Is there any good framework meets these requirements? P.S. I found similar question here Which free HTML5-based game engine meets these requirements?. But it was a long time ago. A lot of new things were created since 2011.

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