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• How does an optimizing compiler react to a program with nested loops?

  - by D.Singh

  Say you have a bunch of nested loops. public void testMethod() { for(int i = 0; i<1203; i++){ //some computation for(int k=2; k<123; k++){ //some computation for(int j=2; j<12312; j++){ //some computation for(int l=2; l<123123; l++){ //some computation for(int p=2; p<12312; p++){ //some computation } } } } } } When the above code reaches the stage where the compiler will try to optimize it (I believe it's when the intermediate language needs to converted to machine code?), what will the compiler try to do? Is there any significant optimization that will take place? I understand that the optimizer will break up the loops by means of loop fission. But this is only per loop isn't it? What I mean with my question is will it take any action exclusively based on seeing the nested loops? Or will it just optimize the loops one by one? If the Java VM complicates the explanation then please just assume that it's C or C++ code.

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• How do i make an AJAX block crawlable?

  - by Vikas Gulati

  I have a block with a few tabs. When the user clicks the tab the content of that block get loaded. Now I would like to make it crawlable by the search engines and at the same time I want to maintain the good user-experience. I figured out a couple of alternative but each one has its own shortcomings. The approached that i could come up with. Use hashbangs and then use this. But hashbangs are not good and things of past now. Secondly it will make my content crawlable by only googlebot as yahoo and bing dont support this. Use GET PARAMETERIZED fallback incase when javascript doesn't work. This will work for all bots and also would be nice as it would work without javascript. But then this will create duplicates of my page as this block is only a very small section of my page and i have like around 5-6 tabs. So it means that many duplicates! Doing this without AJAX is not an option as it would only increase the page load time as all these blocks have heavy media content in them!

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• Problem with SLATEC routine usage with gfortran

  - by user39461

  I am trying to compute the Bessel function of the second kind (Bessel_y) using the SLATEC's Amos library available on Netlib. Here is the SLATEC code I use. Below I have pasted my test program that calls SLATEC routine CBESY. PROGRAM BESSELTEST IMPLICIT NONE REAL:: FNU INTEGER, PARAMETER :: N = 2, KODE = 1 COMPLEX,ALLOCATABLE :: CWRK (:), CY (:) COMPLEX:: Z, ci INTEGER :: NZ, IERR ALLOCATE(CWRK(N), CY(N)) ci = cmplx (0.0, 1.0) FNU = 0.0e0 Z = CMPLX(0.3e0, 0.4e0) CALL CBESY(Z, FNU, KODE, N, CY, NZ, CWRK, IERR) WRITE(*,*) 'CY: ', CY WRITE(*,*) 'IERR: ', IERR STOP END PROGRAM And here is the output of the above program: CY: ( 5.78591091E-39, 5.80327020E-39) ( 0.0000000 , 0.0000000 ) IERR: 4 Ierr = 4 meaning there is some problem with the input itself. To be precise, the IERR = 4 means the following as per the header info in CBESY.f file: ! IERR=4, CABS(Z) OR FNU+N-1 TOO LARGE - NO COMPUTA- ! TION BECAUSE OF COMPLETE LOSSES OF SIGNIFI- ! CANCE BY ARGUMENT REDUCTION Clearly, CABS(Z) (which is 0.50) or FNU + N - 1 (which is 1.0) are not too large but still the routine CBESY throws the error message number 4 as above. The CY array should have following values for the argument given in above code: CY(1) = -0.4983 + 0.6700i CY(2) = -1.0149 + 0.9485i These values are computed using Matlab. I can't figure out what's the problem when I call CBESY from SLATEC library. Any clues? Much thanks for the suggestions/help. PS: if it is of any help, I used gfortran to compile, link and then create the SLATEC library file ( the .a file ) which I keep in the same directory as my test program above. shell command to execute above code: gfortran -c BesselTest.f95 gfortran -o a *.o libslatec.a a GD.

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• Squeezing hardware

  - by [email protected]

  It's very common that high availability means duplicate hardware so costs grows up.Nowadays, CIOs and DBAs has the main challenge of reduce the money spent increasing the performance and the availability. Since Grid Infrastructure 11gR2, there is a new feature that helps them to afford this challenge: Server PoolsNow, in Grid Infrastructure 11gR2, you can define server pools across the cluster setting up the minimum number of servers, the maximum and how important is the pool.For example:Consider  that "Velasco, Boixeda & co"  has 3 apps in a 6 servers cluster.First One is the main core business appSecond one is Mid RangeAnd third it's a database not very important.We Define the following resource requirements for expected workload:1- Main App 2 servers required2- Mid Range App requires 1 server3- Is not a required app in case of disasterThe we define 3 server pools across the cluster:1- Main pool min two servers, max three servers, importance four2- Mid pool, min one server max two servers, importance two3- test pool,min zero servers, max one server, importance oneSo the initial configuration is:-Main pool has three servers-Mid pool has two servers-Test pool has one serverLogically, we can see the cluster like this:If any server fails, the following algorithm will be applied:1.-The server pool of least importance2.-IF server pools are of the same importance,   THEN then the Server Pool that has more than its defined minimum servers Is chosenHope it helps 

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• That Escalated Quickly

  - by Jesse Taber

  Originally posted on: http://geekswithblogs.net/GruffCode/archive/2014/05/17/that-escalated-quickly.aspxI have been working remotely out of my home for over 4 years now. All of my coworkers during that time have also worked remotely. Lots of folks have written about the challenges inherent in facilitating communication on remote teams and strategies for overcoming them. A popular theme around this topic is the notion of “escalating communication”. In this context “escalating” means taking a conversation from one mode of communication to a different, higher fidelity mode of communication. Here are the five modes of communication I use at work in order of increasing fidelity: Email – This is the “lowest fidelity” mode of communication that I use. I usually only check it a few times a day (and I’m trying to check it even less frequently than that) and I only keep items in my inbox if they represent an item I need to take action on that I haven’t tracked anywhere else. Forums / Message boards – Being a developer, I’ve gotten into the habit of having other people look over my code before it becomes part of the product I’m working on. These code reviews often happen in “real time” via screen sharing, but I also always have someone else give all of the changes another look using pull requests. A pull request takes my code and lets someone else see the changes I’ve made side-by-side with the existing code so they can see if I did anything dumb. Pull requests can facilitate a conversation about the code changes in an online-forum like style. Some teams I’ve worked on also liked using tools like Trello or Google Groups to have on-going conversations about a topic or task that was being worked on. Chat & Instant Messaging  - Chat and instant messaging are the real workhorses for communication on the remote teams I’ve been a part of. I know some teams that are co-located that also use it pretty extensively for quick messages that don’t warrant walking across the office to talk with someone but reqire more immediacy than an e-mail. For the purposes of this post I think it’s important to note that the terms “chat” and “instant messaging” might insinuate that the conversation is happening in real time, but that’s not always true. Modern chat and IM applications maintain a searchable history so people can easily see what might have been discussed while they were away from their computers. Voice, Video and Screen sharing – Everyone’s got a camera and microphone on their computers now, and there are an abundance of services that will let you use them to talk to other people who have cameras and microphones on their computers. I’m including screen sharing here as well because, in my experience, these discussions typically involve one or more people showing the other participants something that’s happening on their screen. Obviously, this mode of communication is much higher-fidelity than any of the ones listed above. Scheduled meetings are typically conducted using this mode of communication. In Person – No matter how great communication tools become, there’s no substitute for meeting with someone face-to-face. However, opportunities for this kind of communcation are few and far between when you work on a remote team. When a conversation gets escalated that usually means it moves up one or more positions on this list. A lot of people advocate jumping to #4 sooner than later. Like them, I used to believe that, if it was possible, organizing a call with voice and video was automatically better than any kind of text-based communication could be. Lately, however, I’m becoming less convinced that escalating is always the right move. Working Asynchronously Last year I attended a talk at our local code camp given by Drew Miller. Drew works at GitHub and was talking about how they use GitHub internally. Many of the folks at GitHub work remotely, so communication was one of the main themes in Drew’s talk. During the talk Drew used the phrase, “asynchronous communication” to describe their use of chat and pull request comments. That phrase stuck in my head because I hadn’t heard it before but I think it perfectly describes the way in which remote teams often need to communicate. You don’t always know when your co-workers are at their computers or what hours (if any) they are working that day. In order to work this way you need to assume that the person you’re talking to might not respond right away. You can’t always afford to wait until everyone required is online and available to join a voice call, so you need to use text-based, persistent forms of communication so that people can receive and respond to messages when they are available. Going back to my list from the beginning of this post for a second, I characterize items #1-3 as being “asynchronous” modes of communication while we could call items #4 and #5 “synchronous”. When communication gets escalated it’s almost always moving from an asynchronous mode of communication to a synchronous one. Now, to the point of this post: I’ve become increasingly reluctant to escalate from asynchronous to synchronous communication for two primary reasons: 1 – You can often find a higher fidelity way to convey your message without holding a synchronous conversation 2 - Asynchronous modes of communication are (usually) persistent and searchable. You Don’t Have to Broadcast Live Let’s start with the first reason I’ve listed. A lot of times you feel like you need to escalate to synchronous communication because you’re having difficulty describing something that you’re seeing in words. You want to provide the people you’re conversing with some audio-visual aids to help them understand the point that you’re trying to make and you think that getting on Skype and sharing your screen with them is the best way to do that. Firing up a screen sharing session does work well, but you can usually accomplish the same thing in an asynchronous manner. For example, you could take a screenshot and annotate it with some text and drawings to illustrate what it is you’re seeing. If a screenshot won’t work, taking a short screen recording while your narrate over it and posting the video to your forum or chat system along with a text-based description of what’s in the recording that can be searched for later can be a great way to effectively communicate with your team asynchronously. I Said What?!? Now for the second reason I listed: most asynchronous modes of communication provide a transcript of what was said and what decisions might have been made during the conversation. There have been many occasions where I’ve used the search feature of my team’s chat application to find a conversation that happened several weeks or months ago to remember what was decided. Unfortunately, I think the benefits associated with the persistence of communicating asynchronously often get overlooked when people decide to escalate to a in-person meeting or voice/video call. I’m becoming much more reluctant to suggest a voice or video call if I suspect that it might lead to codifying some kind of design decision because everyone involved is going to hang up the call and immediately forget what was decided. I recognize that you can record and archive these types of interactions, but without being able to search them the recordings aren’t terribly useful. When and How To Escalate I don’t mean to imply that communicating via voice/video or in person is never a good idea. I probably jump on a Skype call with a co-worker at least once a day to quickly hash something out or show them a bit of code that I’m working on. Also, meeting in person periodically is really important for remote teams. There’s no way around the fact that sometimes it’s easier to jump on a call and show someone my screen so they can see what I’m seeing. So when is it right to escalate? I think the simplest way to answer that is when the communication starts to feel painful. Everyone’s tolerance for that pain is different, but I think you need to let it hurt a little bit before jumping to synchronous communication. When you do escalate from asynchronous to synchronous communication, there are a couple of things you can do to maximize the effectiveness of the communication: Takes notes – This is huge and yet I’ve found that a lot of teams don’t do this. If you’re holding a meeting with  > 2 people you should have someone taking notes. Taking notes while participating in a meeting can be difficult but there are a few strategies to deal with this challenge that probably deserve a short post of their own. After the meeting, make sure the notes are posted to a place where all concerned parties (including those that might not have attended the meeting) can review and search them. Persist decisions made ASAP – If any decisions were made during the meeting, persist those decisions to a searchable medium as soon as possible following the conversation. All the teams I’ve worked on used a web-based system for tracking the on-going work and a backlog of work to be done in the future. I always try to make sure that all of the cards/stories/tasks/whatever in these systems always reflect the latest decisions that were made as the work was being planned and executed. If held a quick call with your team lead and decided that it wasn’t worth the effort to build real-time validation into that new UI you were working on, go and codify that decision in the story associated with that work immediately after you hang up. Even better, write it up in the story while you are both still on the phone. That way when the folks from your QA team pick up the story to test a few days later they’ll know why the real-time validation isn’t there without having to invoke yet another conversation about the work. Communicating Well is Hard At this point you might be thinking that communicating asynchronously is more difficult than having a live conversation. You’re right: it is more difficult. In order to communicate effectively this way you need to very carefully think about the message that you’re trying to convey and craft it in a way that’s easy for your audience to understand. This is almost always harder than just talking through a problem in real time with someone; this is why escalating communication is such a popular idea. Why wouldn’t we want to do the thing that’s easier? Easier isn’t always better. If you and your team can get in the habit of communicating effectively in an asynchronous manner you’ll find that, over time, all of your communications get less painful because you don’t need to re-iterate previously made points over and over again. If you communicate right the first time, you often don’t need to rehash old conversations because you can go back and find the decisions that were made laid out in plain language. You’ll also find that you get better at doing things like writing useful comments in your code, creating written documentation about how the feature that you just built works, or persuading your team to do things in a certain way.

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• How do you put price on your source code?

  - by deviDave

  I was asked to sell the source code of small utility app I did years ago with existing users of this app. I tried investigating how to put price on the source code and haven't come up with a good solution so far. I first tried searching the net, but information I found there are somehow far from reality. Then I found a few people how also sold their source code with users as well. But their price seems unrealistic (too high). For example, one person had an app which price was around $200 for 1 user and he had 80 users. He sold the source with users for $30k. How did he come up with this price? Is it a good price if I charge the code by formula: num_of_users x app_price + app_price x num_of_new_users_in_one_year ? This means that I count the price by selling each user for the price of the app then adding the amount of money I earn in 1 year from this app. If this is a good formula, what shall I do with sources who do not have users yet?

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• TFS 2010 Build: Dealing with the API restriction error

  - by Jakob Ehn

  Recently I’ve come across this error a couple of times when running builds that exeucte unit tests using Test containers: API restriction: The assembly 'file:///C:\Builds\<path>\myassembly.dll' has already loaded from a different location. It cannot be loaded from a new location within the same appdomain. Every time I’ve got this error, the project has been a web application, and the path to the assembly points down to the _PublishedWebsites directory that is created beneath the Binaries folder during a team build. The error description really says it all (although slightly cryptic), when using test containers, MSTest needs to load all assemblies and see if they contain any unit tests. During this serach, it finds the ‘myassembly.dll’ in two different locations. First it is found directly beneth the Binaries folder, and then it is alos found beneath the _PublishedWebsites\Project\bin folder. The reason is that the default setting for test containers in a TFS 2010 build definition is **\*test*.dll:   This pattern means that MSTest will search recursively for all assemblies beneath the Binaries folder, and during the search it will find the MyAssembly.dll twice. The solution is simple, set the Test assembly file specification property to *test*.dll instead, this will disable the recursive search:

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• Free Certification Exams for Visual Studio 2010

  - by budugu

  Get promotional codes from herehttp://blogs.msdn.com/gerryo/archive/2010/03/17/register-for-visual-studio-2010-beta-exams.aspx You don’t have to pay anything to take these exams.  These are 100% free. If you pass the exam, you earn the certification just the same as if you took it in a non-beta environment. From Gerry O'Brien’s blog...  2) Is this a real exam? – Yes it is.  Even though the questions are not scored at the time you take the exam, they are real questions and the exam is real.  If you pass the exam, you earn the certification just the same as if you took it in a non-beta environment.  This means you don’t get a pass/fail or score immediately following the exam, but you do get notified 8 to 10 weeks later because we move slow in getting the final scoring in place.  4) What is the main difference between a beta and non-beta exam, besides cost? – The beta exam will show you questions that have not been through a final QA check.  You are that final QA check.  Non-beta exams expose you to 40 or 45 questions and you have a total of two hours to complete it.  The beta exam could expose you to as many as 125 to 150 questions and take up to four hours.   Following exams are for Asp.Net developers Exam 71-515, TS: Web Applications Development with Microsoft .NET Framework 4Exam 71-519: Pro: Designing and Developing Web Applications Using Microsoft .NET Framework 4

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• Inside Red Gate - Introduction

  - by Simon Cooper

  I work for Red Gate Software, a software company based in Cambridge, UK. In this series of posts, I'll be discussing how we develop software at Red Gate, and what we get up to, all from a dev's perspective. Before I start the series proper, in this post I'll give you a brief background to what I have done and continue to do as part of my job. The initial few posts will be giving an overview of how the development sections of the company work. There is much more to a software company than writing the products, but as I'm a developer my experience is biased towards that, and so that is what this series will concentrate on. My background Red Gate was founded in 1999 by Neil Davidson & Simon Galbraith, who continue to be joint CEOs. I joined in September 2007, and immediately set to work writing a new Check for Updates client and server (CfU), as part of a team of 2. That was finished at the end of 2007. I then joined the SQL Compare team. The first large project I worked on was updating SQL Compare for SQL Server 2008, resulting in SQL Compare 7, followed by a UI redesign in SQL Compare 8. By the end of this project in early 2009 I had become the 'go-to' guy for the SQL Compare Engine (I'll explain what that means in a later post), which is used by most of the other tools in the SQL Tools division in one way or another. After that, we decided to expand into Oracle, and I wrote the prototype for what became the engine of Schema Compare for Oracle (SCO). In the latter half of 2009 a full project was started, resulting in the release of SCO v1 in early 2010. Near the end of 2010 I moved to the .NET division, where I joined the team working on SmartAssembly. That's what I continue to work on today. The posts in this series will cover my experience in software development at Red Gate, within the SQL Tools and .NET divisions. Hopefully, you'll find this series an interesting look at what exactly goes into producing the software at Red Gate.

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• Load and Web Performance Testing using Visual Studio Ultimate 2010-Part 2

  - by Tarun Arora

  Welcome back, in part 1 of Load and Web Performance Testing using Visual Studio 2010 I talked about why Performance Testing the application is important, the test tools available in Visual Studio Ultimate 2010 and various test rig topologies. In this blog post I’ll get into the details of web performance & load tests as well as why it’s important to follow a goal based pattern while performance testing your application. Tools => Options => Test Tools Have you visited the treasures of Visual Studio Menu bar tools => Options => Test Tools lately? The options to enable disable prompts on creating, editing, deleting or running manual/automated tests can be controller from here. The default test project language and default test types created on a new test project creation could be selected/unselected from here. Ever wondered how you can change the default limit of 25 test results, this can again be changed from here. If you record a lot of Web Tests and wish for the web test recorder to start with “that” URL populated, well this again can be specified from here. If you haven’t so far, I would urge you to spend 2 minutes in the test tools options.   Test Menu => Ready Steady Test Action! The Test tools are under the Test Menu in Visual Studio, apart from being able to create a new Test and Test List you can also load an existing vsmdi file. You can also manage your test controllers from here. A solution can have one or more test setting files, but there can only be one active test settings file at any time. Again, this selection can be done from here.  You can open the various test windows from under the windows option from the test menu. If you open the Test view window you will see that you have the option to group the tests by work items, project, test type, etc. You can set these properties by right clicking a test in the test list and choosing properties from the context menu.    So, what is a vsmdi file? vsmdi stands for Visual Studio Test Metadata File. Placed under the Solution Items this file keeps track of the list of unit tests in your solution. If you open the vsmdi file as an xml file you will see a series of Test Links nested with in the list Test List tags along with the Run Configuration tag. When in visual studio you run tests, the IDE looks at the vsmdi file to see what tests need to be run. You also have the option of using the vsmdi file in your team builds to specify which tests need to run as part of the build. Refer here for a walkthrough from a fellow blogger on how to use the vsmdi file in the team builds. Web Performance Test – The Truth! In Visual Studio 2010 “Web Tests” have been renamed to “Web Performance Tests”. Apart from renaming this test type there have been several improvements to this test type in visual studio 2010. I am very active on the MSDN Visual Studio And Load Testing forum and a frequent question from many users is “Do Web Tests support Pages that run JavaScript?” I will start with a little bit of background before answering this question. Web Performance Tests operate at the HTTP Layer, but why? To enable you to generate high loads with a relatively low amount of hardware, Web performance tests are driven at the protocol layer rather than instantiating a browser.The most common source of confusion is that users do not realize Web Performance Tests work at the HTTP layer. The tool adds to that misconception. After all, you record in IE, and when running a Web test you can select which browser to use, and then the result viewer shows the results in a browser window. So that means the tests run through the browser, right? NO! The Web test engine works at the HTTP layer, and does not instantiate a browser. What does that mean? In the diagram below, you can see there are no browsers running when the engine is sending and receiving requests. Does that mean I can’t test pages that use Java script? The best example for java script generating HTTP traffic is AJAX calls. The most common example of browser plugins are Silverlight or Flash. The Web test recorder will record HTTP traffic from AJAX calls and from most (but not all) browser plugins. This means you will still be able to web performance test pages that use java script or plugin and play back the results but the playback engine will not show the java script or plug in results in the ‘browser control’. If you want to test the page behaviour as a result of the java script or plug in consider using Coded UI Tests. This page looks like it failed, when in fact it succeeded! Looking closely at the response, and subsequent requests, it is clear the operation succeeded. As stated above, the reason why the browser control is pasting this message is because java script has been disabled in this control. So, to reiterate, the web performance test recorder: - Sends and receives data at the HTTP layer. - Does NOT run a browser. - Does NOT run java script. - Does NOT host ActiveX controls or plugins. There is a great series of blog posts from Ed Glas, i would highly recommend his blog to any one performing Load/Performance testing through Visual Studio. Demo – Web Performance Test [Demo] - Visual Studio Ultimate 2010: Test Settings and Configuration   [Demo]–Visual Studio Ultimate 2010: Web Performance Test   In this short video I try and answer the following questions, Why is performance Testing important? How does Visual Studio Help you performance Test your applications? How do i record a web performance test? How do make a web performance test data driven, transaction driven, loop driven, convert to code, add validations? Best practices for recording Web Performance Tests. I have a web performance test, what next? Creating the Web Performance Test was the first step towards load testing your application. Now that we have the base test we can test the page behaviour when N-users access the page. Have you ever had the head of business call you and mention that the marketing team has done a fantastic job and are expecting increased traffic on the web site, can the website survive the weekend with that additional load? This is the perfect opportunity to capacity test your application to see how your website holds up under various levels of load, you can work the results backwards to see how much hardware you may need to scale up your application to survive the weekend. Apart from that it is always a good idea to have some benchmarks around how the application performs under light loads for short duration, under heavy load for long duration and soak test the application run a constant load for a very week or two to record the effects of constant load for really long durations, this is a great way of identifying how your application handles the default IIS application pool reset which by default is configured to once every 25 hours. These bench marks will act as the perfect yard stick to measure performance gains when you start making improvements. BUT there are some best practices! => Goal Based Load Testing Approach Since the subject is vast and there are a lot of things to measure and analyse, … it is very easy to get distracted from the real goal!  You can optimize your application once you know where the pain points are. There is no point performing a load test of 5000 users if your intranet application will only have a 100 simultaneous users, it is important to keep focussed on the real goals of the project. So the idea is to have a user story around your load testing scenarios and test realistically. So it is recommended that you follow the below outline, It is an Iterative process, refine your objectives, identify the key scenarios, what is the expected workload, key metrics you want to report, record the web performance tests, simulate load and analyse results. Is your application already deployed in Production? This is great! You can analyse the IIS Logs to understand the user behaviour… But what are IIS LOGS? The IIS logs allow you to record events for each application and Web site on the Web server. You can create separate logs for each of your applications and Web sites. Logging information in IIS goes beyond the scope of the event logging or performance monitoring features provided by Windows. The IIS logs can include information, such as who has visited your site, what the visitor viewed, and when the information was last viewed. You can use the IIS logs to identify any attempts to gain unauthorized access to your Web server. How to configure IIS LOGS? For those Ninjas who already have IIS Logs configured (by the way its on by default) and need a way to analyse the IIS Logs, can use the Windows IIS Utility – Log Parser. Log Parser is a very powerful tool that provides a generic SQL-like language on top of many types of data like IIS Logs, Event Viewer entries, XML files, CSV files, File System and others; and it allows you to export the result of the queries to many output formats such as CSV, XML, SQL Server, Charts and others; and it works well with IIS 5, 6, 7 and 7.5. Frequently used Log Parser queries. Demo – Load Test [Demo]–Visual Studio Ultimate 2010: Load Testing   In this short video I try and answer the following questions, - Types of Performance Testing? - Perform Goal driven Load Testing, analyse Test Run Result and Generate a report? Recap A quick recap of what we have covered so far,     Thank you for taking the time out and reading this blog post, in part III of this blog series I’ll be getting into the details of Test Result Analysis, Test Result Drill through, Test Report Generation, Test Run Comparison, and the Asp.net Profiler. If you enjoyed the post, remember to subscribe to http://feeds.feedburner.com/TarunArora. Questions/Feedback/Suggestions, etc please leave a comment. See you on in Part III   Share this post : CodeProject

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• On contract work, obligations to said contract, and looking out for yourself…

  - by jlnorsworthy

  Without boring you all with details, my last two contract assignments were cut short; I was given 3 days notice on one, and 4 weeks notice on the other. Neither of these were due to performance – they both basically came down budget issues. On my second contract, I got the feeling that I may not have been a great place to stay for the duration of my contract. Because of money/time spent getting me in the door, and the possible negative effect of my employer/recruiter, I decided to stay at least for a few months (and start looking several weeks before the end of my supposedly “extendable” contract). These experiences have left me a little wary of contract work. It seems that if I land a bad contract, that my recruiter would take a hit (reputation or otherwise) if I quickly found another job. But on the other hand, the client company won’t think twice of ending the contract early for any reason. I know that the counter argument to this is “maybe your recruiter shouldn’t have put you into a crappy assignment”… either way, it seems that since I am relying on him to provide me with work, that I should try to not damage his reputation with client companies. I’m basically brand new to contracting (these were my first two contracts) so these concerns are new to me. TLDR: Is contract work, by its very nature, largely unstable? Am I worried too much about my recruiter? Should I be quicker to start looking for a new job even after just weeks at a new company (when the environment seems unstable)? If so, do I look through my recruiter or just find another position by any means necessary?

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• Scheduling of jobs in the presence of constraints in Java

  - by Asgard

  I want to know how to implement a solution to this problem: A task is performed by running, by more people, some basic jobs with known duration in time units (days, months, etc..). The execution of the jobs could lead to the existence of time constraints: a job, for example, can not start if it is not over another (or others) and so on. I want to design and build an application to check the correctness of jobs activities and to propose a schedule of jobs, if any, which is respectful of the constraints. Input must provide the jobs and associated constraints. The expected output is the scheduling of jobs. The specification of an elementary job consists of the pair <jobs-id, duration> A constraint is expressed by means of a quintuple of the type <S/E, id-job1, B/A, S/E, id-job2> the beginning (S) or the end (E) of a jobs Id-job1, must take place before (B) / after (A) of the beginning (S) / end (E) of the Id-job2. If there are no dependencies between some jobs, then jobs can be done before, in parallel. As a simple example, consider the input: jobs jobs(0, 3) jobs(1, 4) jobs(2, 5) jobs(3, 3) jobs(4, 3) constraints constraints(S, 1, A, E, 0) constraints(S, 4, A, E, 2) Possible output: t 0 1 2 3 4 0 * - * * - 1 * - * * - 2 * - * * - 3 * - * * - 4 - * * - - 5 - * * - - 6 - * - - * 7 - * - - * 8 - * - - * 9 - - - - * How to code an efficient java scheduler(avoiding the intense backtracking if is possible) to manage the jobs with these constraints, as described??? I have seen a discussion on a thread in a forum where an user seems has solved the problem easily, but He haven't given enough details to the users to compile a working project(I'm noob), and I'm interested to know an effective implementation of the solution (without using external libraries). If someone help me, I'll give to him a very good feedback ;)

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• SQL Authority News – Download SQL Server Data Type Conversion Chart

  - by pinaldave

  Datatypes are very important concepts of SQL Server and there are quite often need to convert them from one datatypes to another datatype. I have seen that deveoper often get confused when they have to convert the datatype. There are two important concept when it is about datatype conversion. Implicit Conversion: Implicit conversions are those conversions that occur without specifying either the CAST or CONVERT function. Explicit Conversions: Explicit conversions are those conversions that require the CAST or CONVERT function to be specified. What it means is that if you are trying to convert value from datetime2 to time or from tinyint to int, SQL Server will automatically convert (implicit conversation) for you. However, if you are attempting to convert timestamp to smalldatetime or datetime to int you will need to explicitely convert them using either CAST or CONVERT function as well appropriate parameters. Let us see a quick example of Implict Conversion and Explict Conversion. Implicit Conversion: Explicit Conversion: You can see from above example that how we need both of the types of conversion in different situation. There are so many different datatypes and it is humanly impossible to know which datatype require implicit and which require explicit conversion. Additionally there are cases when the conversion is not possible as well. Microsoft have published a chart where the grid displays various conversion possibilities as well a quick guide. Download SQL Server Data Type Conversion Chart Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Download, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Investigation: Can different combinations of components effect Dataflow performance?

  - by jamiet

  Introduction The Dataflow task is one of the core components (if not the core component) of SQL Server Integration Services (SSIS) and often the most misunderstood. This is not surprising, its an incredibly complicated beast and we’re abstracted away from that complexity via some boxes that go yellow red or green and that have some lines drawn between them. Example dataflow In this blog post I intend to look under that facade and get into some of the nuts and bolts of the Dataflow Task by investigating how the decisions we make when building our packages can affect performance. I will do this by comparing the performance of three dataflows that all have the same input, all produce the same output, but which all operate slightly differently by way of having different transformation components. I also want to use this blog post to challenge a common held opinion that I see perpetuated over and over again on the SSIS forum. That is, that people assume adding components to a dataflow will be detrimental to overall performance. Its not surprising that people think this –it is intuitive to think that more components means more work- however this is not a view that I share. I have always been of the opinion that there are many factors affecting dataflow duration and the number of components is actually one of the less important ones; having said that I have never proven that assertion and that is one reason for this investigation. I have actually seen evidence that some people think dataflow duration is simply a function of number of rows and number of components. I’ll happily call that one out as a myth even without any investigation!  The Setup I have a 2GB datafile which is a list of 4731904 (~4.7million) customer records with various attributes against them and it contains 2 columns that I am going to use for categorisation: [YearlyIncome] [BirthDate] The data file is a SSIS raw format file which I chose to use because it is the quickest way of getting data into a dataflow and given that I am testing the transformations, not the source or destination adapters, I want to minimise external influences as much as possible. In the test I will split the customers according to month of birth (12 of those) and whether or not their yearly income is above or below 50000 (2 of those); in other words I will be splitting them into 24 discrete categories and in order to do it I shall be using different combinations of SSIS’ Conditional Split and Derived Column transformation components. The 24 datapaths that occur will each input to a rowcount component, again because this is the least resource intensive means of terminating a datapath. The test is being carried out on a Dell XPS Studio laptop with a quad core (8 logical Procs) Intel Core i7 at 1.73GHz and Samsung SSD hard drive. Its running SQL Server 2008 R2 on Windows 7. The Variables Here are the three combinations of components that I am going to test:     One Conditional Split - A single Conditional Split component CSPL Split by Month of Birth and income category that will use expressions on [YearlyIncome] & [BirthDate] to send each row to one of 24 outputs. This next screenshot displays the expression logic in use: Derived Column & Conditional Split - A Derived Column component DER Income Category that adds a new column [IncomeCategory] which will contain one of two possible text values {“LessThan50000”,”GreaterThan50000”} and uses [YearlyIncome] to determine which value each row should get. A Conditional Split component CSPL Split by Month of Birth and Income Category then uses that new column in conjunction with [BirthDate] to determine which of the same 24 outputs to send each row to. Put more simply, I am separating the Conditional Split of #1 into a Derived Column and a Conditional Split. The next screenshots display the expression logic in use: DER Income Category         CSPL Split by Month of Birth and Income Category       Three Conditional Splits - A Conditional Split component that produces two outputs based on [YearlyIncome], one for each Income Category. Each of those outputs will go to a further Conditional Split that splits the input into 12 outputs, one for each month of birth (identical logic in each). In this case then I am separating the single Conditional Split of #1 into three Conditional Split components. The next screenshots display the expression logic in use: CSPL Split by Income Category         CSPL Split by Month of Birth 1& 2       Each of these combinations will provide an input to one of the 24 rowcount components, just the same as before. For illustration here is a screenshot of the dataflow containing three Conditional Split components: As you can these dataflows have a fair bit of work to do and remember that they’re doing that work for 4.7million rows. I will execute each dataflow 10 times and use the average for comparison. I foresee three possible outcomes: The dataflow containing just one Conditional Split (i.e. #1) will be quicker There is no significant difference between any of them One of the two dataflows containing multiple transformation components will be quicker Regardless of which of those outcomes come to pass we will have learnt something and that makes this an interesting test to carry out. Note that I will be executing the dataflows using dtexec.exe rather than hitting F5 within BIDS. The Results and Analysis The table below shows all of the executions, 10 for each dataflow. It also shows the average for each along with a standard deviation. All durations are in seconds. I’m pasting a screenshot because I frankly can’t be bothered with the faffing about needed to make a presentable HTML table. It is plain to see from the average that the dataflow containing three conditional splits is significantly faster, the other two taking 43% and 52% longer respectively. This seems strange though, right? Why does the dataflow containing the most components outperform the other two by such a big margin? The answer is actually quite logical when you put some thought into it and I’ll explain that below. Before progressing, a side note. The standard deviation for the “Three Conditional Splits” dataflow is orders of magnitude smaller – indicating that performance for this dataflow can be predicted with much greater confidence too. The Explanation I refer you to the screenshot above that shows how CSPL Split by Month of Birth and salary category in the first dataflow is setup. Observe that there is a case for each combination of Month Of Date and Income Category – 24 in total. These expressions get evaluated in the order that they appear and hence if we assume that Month of Date and Income Category are uniformly distributed in the dataset we can deduce that the expected number of expression evaluations for each row is 12.5 i.e. 1 (the minimum) + 24 (the maximum) divided by 2 = 12.5. Now take a look at the screenshots for the second dataflow. We are doing one expression evaluation in DER Income Category and we have the same 24 cases in CSPL Split by Month of Birth and Income Category as we had before, only the expression differs slightly. In this case then we have 1 + 12.5 = 13.5 expected evaluations for each row – that would account for the slightly longer average execution time for this dataflow. Now onto the third dataflow, the quick one. CSPL Split by Income Category does a maximum of 2 expression evaluations thus the expected number of evaluations per row is 1.5. CSPL Split by Month of Birth 1 & CSPL Split by Month of Birth 2 both have less work to do than the previous Conditional Split components because they only have 12 cases to test for thus the expected number of expression evaluations is 6.5 There are two of them so total expected number of expression evaluations for this dataflow is 6.5 + 6.5 + 1.5 = 14.5. 14.5 is still more than 12.5 & 13.5 though so why is the third dataflow so much quicker? Simple, the conditional expressions in the first two dataflows have two boolean predicates to evaluate – one for Income Category and one for Month of Birth; the expressions in the Conditional Split in the third dataflow however only have one predicate thus they are doing a lot less work. To sum up, the difference in execution times can be attributed to the difference between: MONTH(BirthDate) == 1 && YearlyIncome <= 50000 and MONTH(BirthDate) == 1 In the first two dataflows YearlyIncome <= 50000 gets evaluated an average of 12.5 times for every row whereas in the third dataflow it is evaluated once and once only. Multiply those 11.5 extra operations by 4.7million rows and you get a significant amount of extra CPU cycles – that’s where our duration difference comes from. The Wrap-up The obvious point here is that adding new components to a dataflow isn’t necessarily going to make it go any slower, moreover you may be able to achieve significant improvements by splitting logic over multiple components rather than one. Performance tuning is all about reducing the amount of work that needs to be done and that doesn’t necessarily mean use less components, indeed sometimes you may be able to reduce workload in ways that aren’t immediately obvious as I think I have proven here. Of course there are many variables in play here and your mileage will most definitely vary. I encourage you to download the package and see if you get similar results – let me know in the comments. The package contains all three dataflows plus a fourth dataflow that will create the 2GB raw file for you (you will also need the [AdventureWorksDW2008] sample database from which to source the data); simply disable all dataflows except the one you want to test before executing the package and remember, execute using dtexec, not within BIDS. If you want to explore dataflow performance tuning in more detail then here are some links you might want to check out: Inequality joins, Asynchronous transformations and Lookups Destination Adapter Comparison Don’t turn the dataflow into a cursor SSIS Dataflow – Designing for performance (webinar) Any comments? Let me know! @Jamiet

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• Microsoft Kinect Sales Are 2X Faster Than iPad

  - by Gopinath

  Apple iPad broke many records and it was crowned as the fastest adopted digital device in the history. 2 million iPads were sold in two months and Apple fan boys are all happy with the news. Here comes some good news for Microsoft lovers – Microsoft’s Kinect is selling twice as fast as Apple iPads. In just 25 days after the launch, 2 million Kinects are sold across the globe – that means 100K Kinect sales per day. Very impressive! Kinect was originally released for XBox 360 gaming console but hackers and geeks are able to connect Kinect to Windows 7 PC to control computers using gestures. The possibilities Kinect usage in building natural user interfaces looks very promising. If this growth sustains after the festive season, Microsoft Kinect will displace iPad from the crown of fastest adopted digital device. More details at Xbox 360 Surpasses 2.5 Million Kinect Sensors Sold This article titled,Microsoft Kinect Sales Are 2X Faster Than iPad, was originally published at Tech Dreams. Grab our rss feed or fan us on Facebook to get updates from us.

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• LINQ: Enhancing Distinct With The PredicateEqualityComparer

  - by Paulo Morgado

  Today I was writing a LINQ query and I needed to select distinct values based on a comparison criteria. Fortunately, LINQ’s Distinct method allows an equality comparer to be supplied, but, unfortunately, sometimes, this means having to write custom equality comparer. Because I was going to need more than one equality comparer for this set of tools I was building, I decided to build a generic equality comparer that would just take a custom predicate. Something like this: public class PredicateEqualityComparer<T> : EqualityComparer<T> { private Func<T, T, bool> predicate; public PredicateEqualityComparer(Func<T, T, bool> predicate) : base() { this.predicate = predicate; } public override bool Equals(T x, T y) { if (x != null) { return ((y != null) && this.predicate(x, y)); } if (y != null) { return false; } return true; } public override int GetHashCode(T obj) { if (obj == null) { return 0; } return obj.GetHashCode(); } } Now I can write code like this: .Distinct(new PredicateEqualityComparer<Item>((x, y) => x.Field == y.Field)) But I felt that I’d lost all conciseness and expressiveness of LINQ and it doesn’t support anonymous types. So I came up with another Distinct extension method: public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source, Func<TSource, TSource, bool> predicate) { return source.Distinct(new PredicateEqualityComparer<TSource>(predicate)); } And the query is now written like this: .Distinct((x, y) => x.Field == y.Field) Looks a lot better, doesn’t it?

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• Don&rsquo;t use MySQL .net connector, here is why ?

  - by Anirudha

  Originally posted on: http://geekswithblogs.net/anirugu/archive/2013/11/04/donrsquot-use-mysql-.net-connector-here-is-why.aspxIf you use .net mysql connector and all project new or old use different different version of Mysql .net connector then you need to upgrade it to latest (if you don’t use copy local=true for bin assembly). This is not the single problem happen to me.   In my case I use .net connector 6.7.4.0 and let’s see what happen to me after I start using it. 6.7.4.0 install register the mysql module in machine.config and it’s broke every software you haven’t deployed with Mysql.   Suppose for example I just create a website ( in webmatrix 3) put my index.cshtml and now see what it preview for me. This means I need to add the mysql.Web even I don’t use any kind of database. I need to do every asp.net mvc project no matter they use mysql. it’s problematic when we use older .net  mysql connector in some of my project.   If you have trouble like this simply use nuget and say Bye bye to this trouble.

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• View Word Definitions in IE 8 with the Define with Bing Accelerator

  - by Asian Angel

  Do you need an easy way to view word definitions while browsing with Internet Explorer? The Define with Bing Accelerator will display definitions in the same (or a new) tab and save you time while browsing. Using Define with Bing The installation consists of two steps. First, click on Add to Internet Explorer to start the process. Next you will be asked to confirm the installation. Once you have clicked Add your new accelerator is ready to use (no browser restart required). Whenever you encounter a word that needs defining highlight it, click on the small blue square, go to All Accelerators, and then Define with Bing. There are two ways to access the definition: Hover your mouse over the Define with Bing text to open a small popup window Click on Define with Bing to open a definition search in a new tab Being able to access a definition or explanation in the same tab will definitely save you time while browsing. In the example shown here you can get an idea of what SCORM means but clicking on the links inside the popup window is not recommended (webpage opens in popup and is not resizable). In the situation shown above it is better to click on Define with Bing and see more information in a new tab. Conclusion The Define with Bing Accelerator can be a very useful time saver while browsing with Internet Explorer. Finding those word definitions will be a much more pleasant experience now. Add the Define with Bing Accelerator to Internet Explorer Similar Articles Productive Geek Tips Add Google Dictionary Power to ChromeChoose Custom New Tab Pages in ChromeSearch Alternative Search Engines from within Bing’s Search PageView Word Definitions in Google Chrome with DictionaryTipThe New Bing Bar Provides Easy Access to Searches and Microsoft Live Services TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips CloudBerry Online Backup 1.5 for Windows Home Server Snagit 10 VMware Workstation 7 Acronis Online Backup Sculptris 1.0, 3D Drawing app AceStock, a Tiny Desktop Quote Monitor Gmail Button Addon (Firefox) Hyperwords addon (Firefox) Backup Outlook 2010 Daily Motivator (Firefox)

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• Restrict SSL access for some paths on a apache2 server

  - by valmar

  I wanted to allow access to www.mydomain.com/login through ssl only. E.g.: Whenever someone accessed http://www.mydomain.com/login, I wanted him to be redirect to https://www.mydomain.com/login so it's impossible for him/her to access that site without SSL. I accomplished this by adding the following lines to the virtual host for www.mydomain.com on port 80 in /etc/apache2/sites-available/default: RewriteEngine on RewriteCond %{SERVER_PORT} ^80$ RewriteRule ^/login(.*)$ https://%{SERVER_NAME}/login$1 [L,R] RewriteLog "/var/log/apache2/rewrite.log" Now, I want to restrict using SSL for www.mydomain.com. That means, whenever someone accessed https://www.mydomain.com, I want him to be redirected to http://www.mydomain.com (for performance reasons). I tried this by adding the following lines to the virtual host of www.mydomain.com on port 443 in /etc/apache2/sites-available/default-ssl: RewriteEngine on RewriteCond %{SERVER_PORT} ^443$ RewriteRule ^/(.*)$ http://%{SERVER_NAME}/$1 [L,R] RewriteLog "/var/log/apache2/rewrite.log" But when I now try to access www.mydomain.com/login, I get an error message that the server has caused to many redirects. That does make sense. Obviously, the two RewriteRules are playing ping-pong against each other. How could I work around this?

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• Ranking hit after site migration

  - by Ben

  I migrated my site from its old domain over a month ago. I followed Google Webmaster Tools completely, including 301 redirects from every existing URL to the new domain, and then submitting a change of address. Traffic continued as normal, but then a few days after submitting the change of address traffic plummeted to about 20-30% of what it was previously. Most of my traffic comes from organic search, and I can see that for the keywords I had targeted before and performed well with and am now ranking much much lower for. In some cases for low competition keywords I've only lost a few places, for higher competition terms I have really suffered. This has started to pick up a bit (one of my keywords I have risen from 195 to 100 in the last week), but it seems to be a very slow process. How seamless is this process normally? I was under the impression that this would not affect my rankings too severely, but it has now been a month since the move and recovery seems to be very slow, if at all. Is it likely that I've missed something? The only change is that I have moved what was the home page to be more of a sub-page, and now in its place is a magazine-style home page. I understand that links to the old site will now be pointing to the latter which means that rankings for some keywords attributed to the old home page will take a hit, but even on other pages that seem to fit in exactly the same page structure as the previous site I have seen a drop in rankings.

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• Daylight Saving Time Visualized

  - by Jason Fitzpatrick

  When you map out the Daylight Saving Time adjusted sunrise and sunset times over the course of the year, an interesting pattern emerges. Chart designer Germanium writes: I tried to come up with the reason for the daylight saving time change by just looking at the data for sunset and sunrise times. The figure represents sunset and sunrise times thought the year. It shows that the daylight saving time change marked by the lines (DLS) is keeping the sunrise time pretty much constant throughout the whole year, while making the sunset time change a lot. The spread of sunrise times as measured by the standard deviation is 42 minutes, which means that the sunrise time changes within that range the whole year, while the standard deviation for the sunset times is 1:30 hours. Whatever the argument for doing this is, it’s pretty clear that reason is to keep the sunrise time constant. You can read more about the controversial history of Daylight Saving Time here. Daylight Saving Time Explained [via Cool Infographics] 6 Ways Windows 8 Is More Secure Than Windows 7 HTG Explains: Why It’s Good That Your Computer’s RAM Is Full 10 Awesome Improvements For Desktop Users in Windows 8

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• SOA Governance Starts with People and Processes

  - by Jyothi Swaroop

  While we all agree that SOA Governance is about People, Processes and Technology. Some experts are of the opinion that SOA Governance begins with People and Processes but needs to be empowered with technology to achieve the best results. Here's an interesting piece from David Linthicum on eBizq: In the world of SOA, the concept of SOA governance is getting a lot of attention. However, how SOA governance is defined and implemented really depends on the SOA governance vendor who just left the building within most enterprises. Indeed, confusion is a huge issue when considering SOA governance, and the core issues are more about the fundamentals of people and processes, and not about the technology. SOA governance is a concept used for activities related to exercising control over services in an SOA, including tracking the services, monitoring the service, and controlling changes made to the services, simple put. The trouble comes in when SOA governance vendors attempt to define SOA governance around their technology, all with different approaches to SOA governance. Thus, it's important that those building SOAs within the enterprise take a step back and understand what really need to support the concept of SOA governance. The value of SOA governance is pretty simple. Since services make up the foundation of an SOA, and are at their essence the behavior and information from existing systems externalized, it's critical to make sure that those accessing, creating, and changing services do so using a well controlled and orderly mechanism. Those of you, who already have governance in place, typically around enterprise architecture efforts, will be happy to know that SOA governance does not replace those processes, but becomes a mechanism within the larger enterprise governance concept. People and processes are first thing on the list to get under control before you begin to toss technology at this problem. This means establishing an understanding of SOA governance within the team members, including why it's important, who's involved, and the core processes that are to be follow to make SOA governance work. Indeed, when creating the core SOA governance strategy should really be independent of the technology. The technology will change over the years, but the core processes and discipline should be relatively durable over time.

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• Autoscaling in a modern world&hellip;. Part 1

  - by Steve Loethen

  It has been a while since I have had time to sit down and blog.  I need to make sure I take the time.  It helps me to focus on technology and not let the administrivia keep me from doing the things I love. I have been focusing on the cloud for the last couple of years.  Specifically the  PaaS platform from Microsoft called Azure.  Time to dig in.. I wanted to explore Autoscaling.  Autoscaling is not native part of Azure.  The platform has the needed connection points.  You can write code that looks at the health and performance of your application components and react to needed scaling changes.  But that means you have to write all the code.  Luckily, an add on to the Enterprise Library provides a lot of code that gets you a long way to being able to autoscale without having to start from scratch. The tool set is primarily composed of a Autoscaler object that you need to host.  This object, when hosted and configured, looks at the performance criteria you specify and adjusts your application based on your needs.  Sounds perfect. I started with the a set of HOL’s that gave me a good basis to understand the mechanics.  I worked through labs 1 and 2 just to get the feel, but let’s start our saga at the end of lab3.  Lab3 end results in a web application, hosted in Azure and a console app running on premise.  The web app has a few buttons on it.  One set adds messages to a queue, another removes them.  A second set of buttons drives processor utilization to 100%.  If you want to guess, a safe bet is that the Autoscaler is configured to react to a queue that has filled up or high cpu usage.  We will continue our saga in the next post…

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• Two Copies of Pete Brown's "Silverlight 5 In Action" to Give Away

  - by Dave Campbell

  Yes... you read that correctly... I have two copies of Pete Brown's excellent book "Silverlight 5 In Action" to give away... if you're not familiar with Pete's book, here is a short synopsis for a large book: Silverlight 5 in Action teaches you how to build desktop-quality applications you can deploy on the web. Beginners will appreciate the progression from simple examples to full applications that employ good design and coding practices. Seasoned . NET developers will love how the sample code embraces and extends what they already know. As with other give-aways I've done on my blog, rather than me trying to pick the most worthy 2 people of all submittals, what I'm going to do is randomly select 2 entries from those that are submitted. Email address for Submittals I have a special email address for submittals: mailto:[email protected]?Subject=Giveaway. Deadline for Submittals I will take submittals dated from the time this post hits until midnight Sunday night, June 17, 2012 - Arizona time. That means sometime Monday morning June 18th, I will announce the winners. Send in an email and good luck... it's a great book! But wait, there's more! If you don't want to wait until next Tuesday to get into Pete's book, or you don't figure you're that lucky to get one of the two I'm giving away, I also have a 39% off discount code for "Silverlight 5 In Action" if used at Manning.com!! Just order your book online, and use the discount code 12s5sc and you'll get the book on it's way immediately. Either way you go... you won't be disappointed. I've been reading this as it goes and it is a treasure-trove of information. Grab your copy, and Stay in the 'Light!

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• Depth interpolation for z-buffer, with scanline

  - by Twodordan

  I have to write my own software 3d rasterizer, and so far I am able to project my 3d model made of triangles into 2d space: I rotate, translate and project my points to get a 2d space representation of each triangle. Then, I take the 3 triangle points and I implement the scanline algorithm (using linear interpolation) to find all points[x][y] along the edges(left and right) of the triangles, so that I can scan the triangle horizontally, row by row, and fill it with pixels. This works. Except I have to also implement z-buffering. This means that knowing the rotated&translated z coordinates of the 3 vertices of the triangle, I must interpolate the z coordinate for all other points I find with my scanline algorithm. The concept seems clear enough, I first find Za and Zb with these calculations: var Z_Slope = (bottom_point_z - top_point_z) / (bottom_point_y - top_point_y); var Za = top_point_z + ((current_point_y - top_point_y) * Z_Slope); Then for each Zp I do the same interpolation horizontally: var Z_Slope = (right_z - left_z) / (right_x - left_x); var Zp = left_z + ((current_point_x - left_x) * Z_Slope); And of course I add to the zBuffer, if current z is closer to the viewer than the previous value at that index. (my coordinate system is x: left - right; y: top - bottom; z: your face - computer screen;) The problem is, it goes haywire. The project is here and if you select the "Z-Buffered" radio button, you'll see the results... (note that the rest of the options before "Z-Buffered" use the Painter's algorithm to correctly order the triangles. I also use the painter's algorithm -only- to draw the wireframe in "Z-Buffered" mode for debugging purposes) PS: I've read here that you must turn the z's into their reciprocals (meaning z = 1/z) before you interpolate. I tried that, and it appears that there's no change. What am I missing? (could anyone clarify, precisely where you must turn z into 1/z and where to turn it back?)

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