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• Robotic Arm &ndash; Hardware

  - by Szymon Kobalczyk

  This is first in series of articles about project I've been building  in my spare time since last Summer. Actually it all began when I was researching a topic of modeling human motion kinematics in order to create gesture recognition library for Kinect. This ties heavily into motion theory of robotic manipulators so I also glanced at some designs of robotic arms. Somehow I stumbled upon this cool looking open source robotic arm: It was featured on Thingiverse and published by user jjshortcut (Jan-Jaap). Since for some time I got hooked on toying with microcontrollers, robots and other electronics, I decided to give it a try and build it myself. In this post I will describe the hardware build of the arm and in later posts I will be writing about the software to control it. Another reason to build the arm myself was the cost factor. Even small commercial robotic arms are quite expensive – products from Lynxmotion and Dagu look great but both cost around USD $300 (actually there is one cheap arm available but it looks more like a toy to me). In comparison this design is quite cheap. It uses seven hobby grade servos and even the cheapest ones should work fine. The structure is build from a set of laser cut parts connected with few metal spacers (15mm and 47mm) and lots of M3 screws. Other than that you’d only need a microcontroller board to drive the servos. So in total it comes a lot cheaper to build it yourself than buy an of the shelf robotic arm. Oh, and if you don’t like this one there are few more robotic arm projects at Thingiverse (including one by oomlout). Laser cut parts Some time ago I’ve build another robot using laser cut parts so I knew the process already. You can grab the design files in both DXF and EPS format from Thingiverse, and there are also 3D models of each part in STL. Actually the design is split into a second project for the mini servo gripper (there is also a standard servo version available but it won’t fit this arm).  I wanted to make some small adjustments, layout, and add measurements to the parts before sending it for cutting. I’ve looked at some free 2D CAD programs, and finally did all this work using QCad 3 Beta with worked great for me (I also tried LibreCAD but it didn’t work that well). All parts are cut from 4 mm thick material. Because I was worried that acrylic is too fragile and might break, I also ordered another set cut from plywood. In the end I build it from plywood because it was easier to glue (I was told acrylic requires a special glue). Btw. I found a great laser cutter service in Kraków and highly recommend it (www.ebbox.com.pl). It cost me only USD $26 for both sets ($16 acrylic + $10 plywood). Metal parts I bought all the M3 screws and nuts at local hardware store. Make sure to look for nylon lock (nyloc) nuts for the gripper because otherwise it unscrews and comes apart quickly. I couldn’t find local store with metal spacers and had to order them online (you’d need 11 x 47mm and 3 x 15mm). I think I paid less than USD $10 for all metal parts. Servos This arm uses five standards size servos to drive the arm itself, and two micro servos are used on the gripper. Author of the project used Modelcraft RS-2 Servo and Modelcraft ES-05 HT Servo. I had two Futaba S3001 servos laying around, and ordered additional TowerPro SG-5010 standard size servos and TowerPro SG90 micro servos. However it turned out that the SG90 won’t fit in the gripper so I had to replace it with a slightly smaller E-Sky EK2-0508 micro servo. Later it also turned out that Futaba servos make some strange noise while working so I swapped one with TowerPro SG-5010 which has higher torque (8kg / cm). I’ve also bought three servo extension cables. All servos cost me USD $45. Assembly The build process is not difficult but you need to think carefully about order of assembling it. You can do the base and upper arm first. Because two servos in the base are close together you need to put first with one piece of lower arm already connected before you put the second servo. Then you connect the upper arm and finally put the second piece of lower arm to hold it together. Gripper and base require some gluing so think it through too. Make sure to look closely at all the photos on Thingiverse (also other people copies) and read additional posts on jjshortcust’s blog: My mini servo grippers and completed robotic arm  Multiply the robotic arm and electronics Here is also Rob’s copy cut from aluminum My assembled arm looks like this – I think it turned out really nice: Servo controller board The last piece of hardware I needed was an electronic board that would take command from PC and drive all seven servos. I could probably use Arduino for this task, and in fact there are several Arduino servo shields available (for example from Adafruit or Renbotics).  However one problem is that most support only up to six servos, and second that their accuracy is limited by Arduino’s timer frequency. So instead I looked for dedicated servo controller and found a series of Maestro boards from Pololu. I picked the Pololu Mini Maestro 12-Channel USB Servo Controller. It has many nice features including native USB connection, high resolution pulses (0.25µs) with no jitter, built-in speed and acceleration control, and even scripting capability. Another cool feature is that besides servo control, each channel can be configured as either general input or output. So far I’m using seven channels so I still have five available to connect some sensors (for example distance sensor mounted on gripper might be useful). And last but important factor was that they have SDK in .NET – what more I could wish for! The board itself is very small – half of the size of Tic-Tac box. I picked one for about USD $35 in this store. Perhaps another good alternative would be the Phidgets Advanced Servo 8-Motor – but it is significantly more expensive at USD $87.30. The Maestro Controller Driver and Software package includes Maestro Control Center program with lets you immediately configure the board. For each servo I first figured out their move range and set the min/max limits. I played with setting the speed an acceleration values as well. Big issue for me was that there are two servos that control position of lower arm (shoulder joint), and both have to be moved at the same time. This is where the scripting feature of Pololu board turned out very helpful. I wrote a script that synchronizes position of second servo with first one – so now I only need to move one servo and other will follow automatically. This turned out tricky because I couldn’t find simple offset mapping of the move range for each servo – I had to divide it into several sub-ranges and map each individually. The scripting language is bit assembler-like but gets the job done. And there is even a runtime debugging and stack view available. Altogether I’m very happy with the Pololu Mini Maestro Servo Controller, and with this final piece I completed the build and was able to move my arm from the Meastro Control program.   The total cost of my robotic arm was: $10 laser cut parts $10 metal parts $45 servos $35 servo controller ----------------------- $100 total So here you have all the information about the hardware. In next post I’ll start talking about the software that I wrote in Microsoft Robotics Developer Studio 4. Stay tuned!

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• User Guide to Dropbox Shared Folders

  - by Matthew Guay

  Dropbox is an incredibly useful tool for keeping all your files synced between your computers and the cloud.  Here we’re going to look at how you can keep all of your team on the same page with Dropbox shared folders. Creating a Shared Folder Setting up a shared folder in Dropbox is easy.  Add the files you want to share to a folder in Dropbox on your computer, then right-click in the folder, select Dropbox, and then choose Share This Folder.   Alternately, log into your Dropbox account online, click the drop-down menu beside the folder you want to share, and click Share this folder. Now, enter the email addresses of the people you want to share the folder with, and optionally enter a message explaining why you’re sharing the folder. The people you invite will receive an email inviting them to view and join the shared folder.  If they haven’t signed up for Dropbox, they can directly signup; otherwise, they can simply log into their Dropbox account and start adding or editing files. Shared folders have a slightly different icon in your Dropbox.  Notice the shared folder on the left has an icon with 2 people, while the folder on the right that is not shared, shows previews of its contents. See Your Shared Folder’s History Whenever your collaborators with your shared folders add or change files, you will see a tooltip notification telling you what changed. You can also view the changes online.  Log into your Dropbox account in your browser and select the Events tab.  This shows all changes to your Dropbox, but you can view only the changes in your shared folder by selecting its name on the left sidebar. Now you can see all recent changes to your folder, and can also see who added or removed each file.   On the bottom of the page, you can even add a comment that all the collaborators will see. If someone deleted a file you still need, you can restore it by clicking its link in this online history.  Or, you can view any deleted files by right-clicking in your Dropbox folder in Explorer.  Select Dropbox, and then click Show Deleted Files.   Get Notified When a Change is Made You’re not always in front of your computer; you’ve got a life beyond your projects, after all (at least hopefully).  If you really want to stay connected to what’s happening with your project, though, you can easily do that no matter where you are. Your shared Dropbox folder’s history page offers an RSS feed of all changes to the folder.  Click  the Subscribe to this feed hyperlink. Now, in the popup that opens, click “Copy to clipboard” so you can use this RSS feed. You can subscribe to RSS feeds through many web browsers, email clients, dedicated feed readers, and more.  In Firefox, Internet Explorer 7/8, or Opera, you can paste the feed address into your address bar and subscribe to the feed directly in your browser.   However, subscribing to the feed in a desktop application won’t help you much when you’re away from your computer.  One great option is to subscribe in the popular Google Reader.  Then you can check your feed from any browser, on any computer or mobile device. To add your Dropbox feed to Google Reader, log into Google Reader (link below), click Add a subscription on the top left, paste your RSS feed from Dropbox, and click Add.   Now you can see any changes to files or folders in Google Reader. You can even add your feed to your iGoogle homepage.  Click the Add it Now button on the right in the front page of Google Reader to add your feeds to iGoogle.   Now you can see updates on your files from your homepage.  If you’re using a different computer, just login to your Google account to see what’s happening. You can also access your Google Reader feeds from many programs and apps for most major Smartphones including iPhone, Windows Phone, and Blackberry. Receive a Tweet or Text When Changes are Made If you’re a hyper-connected individual, chances are you send and receive tweets on the go.  If so, this might be the best way for you to get notified when changes are made to your Dropbox shared folder.  To do this, first create a new Twitter account to publish your changes through.  If you don’t want the whole world to see your updates, click Settings and set your new Twitter account to Private. Once the new account is created, follow it with your normal Twitter account so you’ll see updates. Now, let’s publish our Dropbox RSS feed to Twitter.  Create an account with Twitterfeed (link below). Once your account is setup, add your feed to it.  Name your feed, and enter your Feed address from Dropbox.  Click Advanced Settings to make your feed work just like you want. In Advanced Settings, change the frequency to “Every 30 mins” to make sure you’re updated on changes as quick as possible.  You can also change other settings if you like. Click “Continue to Step 2”, and then click Twitter under the available services to add your account. Make sure your signed into your new Twitter account, and then click Authenticate Twitter. Allow the application. Now, finally, click Create Service. Whenever a change is made, you will receive a tweet via your new Twitter account.  And since you can receive tweets via text message or many mobile applications, you’ll never be very far away from your Dropbox changes!   Conclusion Dropbox shared folders are a great way to keep your whole team working together on the same files in a project.  And with these handy tricks, you can keep up with your shared files wherever you are! There are a lot of cool things you can do with Dropbox make sure to check out our posts on adding Dropbox to the Windows 7 Start menu, Accessing Dropbox files from Chrome, and Syncing your Pidgin Profile Across Multiple PCs. Links Signup or access your Dropbox account Google Reader Tweet your feed with Twitterfeed Similar Articles Productive Geek Tips How to Add and Manage Shared Folders on Windows Home ServerManage User Accounts in Windows Home ServerAdd "My Dropbox" to Your Windows 7 Start MenuComplete Guide to Networking Windows 7 with XP and VistaMoving Your Personal Data Folders in Windows Vista the Easy Way 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 DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Office 2010 reviewed in depth by Ed Bott FoxClocks adds World Times in your Statusbar (Firefox) Have Fun Editing Photo Editing with Citrify Outlook Connector Upgrade Error Gadfly is a cool Twitter/Silverlight app Enable DreamScene in Windows 7

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• Integrating Coherence & Java EE 6 Applications using ActiveCache

  - by Ricardo Ferreira

  OK, so you are a developer and are starting a new Java EE 6 application using the most wonderful features of the Java EE platform like Enterprise JavaBeans, JavaServer Faces, CDI, JPA e another cool stuff technologies. And your architecture need to hold piece of data into distributed caches to improve application's performance, scalability and reliability? If this is your current facing scenario, maybe you should look closely in the solutions provided by Oracle WebLogic Server. Oracle had integrated WebLogic Server and its champion data caching technology called Oracle Coherence. This seamless integration between this two products provides a comprehensive environment to develop applications without the complexity of extra Java code to manage cache as a dependency, since Oracle provides an DI ("Dependency Injection") mechanism for Coherence, the same DI mechanism available in standard Java EE applications. This feature is called ActiveCache. In this article, I will show you how to configure ActiveCache in WebLogic and at your Java EE application. Configuring WebLogic to manage Coherence Before you start changing your application to use Coherence, you need to configure your Coherence distributed cache. The good news is, you can manage all this stuff without writing a single line of code of XML or even Java. This configuration can be done entirely in the WebLogic administration console. The first thing to do is the setup of a Coherence cluster. A Coherence cluster is a set of Coherence JVMs configured to form one single view of the cache. This means that you can insert or remove members of the cluster without the client application (the application that generates or consume data from the cache) knows about the changes. This concept allows your solution to scale-out without changing the application server JVMs. You can growth your application only in the data grid layer. To start the configuration, you need to configure an machine that points to the server in which you want to execute the Coherence JVMs. WebLogic Server allows you to do this very easily using the Administration Console. In this example, I will call the machine as "coherence-server". Remember that in order to the machine concept works, you need to ensure that the NodeManager are being executed in the target server that the machine points to. The NodeManager executable can be found in <WLS_HOME>/server/bin/startNodeManager.sh. The next thing to do is to configure a Coherence cluster. In the WebLogic administration console, go to Environment > Coherence Clusters and click in "New". Call this Coherence cluster of "my-coherence-cluster". Click in next. Specify a valid cluster address and port. The Coherence members will communicate with each other through this address and port. Our Coherence cluster are now configured. Now it is time to configure the Coherence members and add them to this cluster. In the WebLogic administration console, go to Environment > Coherence Servers and click in "New". In the field "Name" set to "coh-server-1". In the field "Machine", associate this Coherence server to the machine "coherence-server". In the field "Cluster", associate this Coherence server to the cluster named "my-coherence-cluster". Click in "Finish". Start the Coherence server using the "Control" tab of WebLogic administration console. This will instruct WebLogic to start a new JVM of Coherence in the target machine that should join the pre-defined Coherence cluster. Configuring your Java EE Application to Access Coherence Now lets pass to the funny part of the configuration. The first thing to do is to inform your Java EE application which Coherence cluster to join. Oracle had updated WebLogic server deployment descriptors so you will not have to change your code or the containers deployment descriptors like application.xml, ejb-jar.xml or web.xml. In this example, I will show you how to enable DI ("Dependency Injection") to a Coherence cache from a Servlet 3.0 component. In the WEB-INF/weblogic.xml deployment descriptor, put the following metadata information: <?xml version="1.0" encoding="UTF-8"?> <wls:weblogic-web-app xmlns:wls="http://xmlns.oracle.com/weblogic/weblogic-web-app" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd http://xmlns.oracle.com/weblogic/weblogic-web-app http://xmlns.oracle.com/weblogic/weblogic-web-app/1.4/weblogic-web-app.xsd"> <wls:context-root>myWebApp</wls:context-root> <wls:coherence-cluster-ref> <wls:coherence-cluster-name>my-coherence-cluster</wls:coherence-cluster-name> </wls:coherence-cluster-ref> </wls:weblogic-web-app> As you can see, using the "coherence-cluster-name" tag, we are informing our Java EE application that it should join the "my-coherence-cluster" when it loads in the web container. Without this information, the application will not be able to access the predefined Coherence cluster. It will form its own Coherence cluster without any members. So never forget to put this information. Now put the coherence.jar and active-cache-1.0.jar dependencies at your WEB-INF/lib application classpath. You need to deploy this dependencies so ActiveCache can automatically take care of the Coherence cluster join phase. This dependencies can be found in the following locations: - <WLS_HOME>/common/deployable-libraries/active-cache-1.0.jar - <COHERENCE_HOME>/lib/coherence.jar Finally, you need to write down the access code to the Coherence cache at your Servlet. In the following example, we have a Servlet 3.0 component that access a Coherence cache named "transactions" and prints into the browser output the content (the ammount property) of one specific transaction. package com.oracle.coherence.demo.activecache; import java.io.IOException; import javax.annotation.Resource; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.tangosol.net.NamedCache; @WebServlet("/demo/specificTransaction") public class TransactionServletExample extends HttpServlet { @Resource(mappedName = "transactions") NamedCache transactions; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { int transId = Integer.parseInt(request.getParameter("transId")); Transaction transaction = (Transaction) transactions.get(transId); response.getWriter().println("<center>" + transaction.getAmmount() + "</center>"); } } Thats it! No more configuration is necessary and you have all set to start producing and getting data to/from Coherence. As you can see in the example code, the Coherence cache are treated as a normal dependency in the Java EE container. The magic happens behind the scenes when the ActiveCache allows your application to join the defined Coherence cluster. The most interesting thing about this approach is, no matter which type of Coherence cache your are using (Distributed, Partitioned, Replicated, WAN-Remote) for the client application, it is just a simple attribute member of com.tangosol.net.NamedCache type. And its all managed by the Java EE container as an dependency. This means that if you inject the same dependency (the Coherence cache named "transactions") in another Java EE component (JSF managed-bean, Stateless EJB) the cache will be the same. Cool isn't it? Thanks to the CDI technology, we can extend the same support for non-Java EE standards components like simple POJOs. This means that you are not forced to only use Servlets, EJBs or JSF in order to inject Coherence caches. You can do the same approach for regular POJOs created for you and managed by lightweight containers like Spring or Seam.

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• C# Extension Methods - To Extend or Not To Extend...

  - by James Michael Hare

  I've been thinking a lot about extension methods lately, and I must admit I both love them and hate them. They are a lot like sugar, they taste so nice and sweet, but they'll rot your teeth if you eat them too much.   I can't deny that they aren't useful and very handy. One of the major components of the Shared Component library where I work is a set of useful extension methods. But, I also can't deny that they tend to be overused and abused to willy-nilly extend every living type.   So what constitutes a good extension method? Obviously, you can write an extension method for nearly anything whether it is a good idea or not. Many times, in fact, an idea seems like a good extension method but in retrospect really doesn't fit.   So what's the litmus test? To me, an extension method should be like in the movies when a person runs into their twin, separated at birth. You just know you're related. Obviously, that's hard to quantify, so let's try to put a few rules-of-thumb around them.   A good extension method should:     Apply to any possible instance of the type it extends.     Simplify logic and improve readability/maintainability.     Apply to the most specific type or interface applicable.     Be isolated in a namespace so that it does not pollute IntelliSense.     So let's look at a few examples in relation to these rules.   The first rule, to me, is the most important of all. Once again, it bears repeating, a good extension method should apply to all possible instances of the type it extends. It should feel like the long lost relative that should have been included in the original class but somehow was missing from the family tree.    Take this nifty little int extension, I saw this once in a blog and at first I really thought it was pretty cool, but then I started noticing a code smell I couldn't quite put my finger on. So let's look:       public static class IntExtensinos     {         public static int Seconds(int num)         {             return num * 1000;         }           public static int Minutes(int num)         {             return num * 60000;         }     }     This is so you could do things like:       ...     Thread.Sleep(5.Seconds());     ...     proxy.Timeout = 1.Minutes();     ...     Awww, you say, that's cute! Well, that's the problem, it's kitschy and it doesn't always apply (and incidentally you could achieve the same thing with TimeStamp.FromSeconds(5)). It's syntactical candy that looks cool, but tends to rot and pollute the code. It would allow things like:       total += numberOfTodaysOrders.Seconds();     which makes no sense and should never be allowed. The problem is you're applying an extension method to a logical domain, not a type domain. That is, the extension method Seconds() doesn't really apply to ALL ints, it applies to ints that are representative of time that you want to convert to milliseconds.    Do you see what I mean? The two problems, in a nutshell, are that a) Seconds() called off a non-time value makes no sense and b) calling Seconds() off something to pass to something that does not take milliseconds will be off by a factor of 1000 or worse.   Thus, in my mind, you should only ever have an extension method that applies to the whole domain of that type.   For example, this is one of my personal favorites:       public static bool IsBetween<T>(this T value, T low, T high)         where T : IComparable<T>     {         return value.CompareTo(low) >= 0 && value.CompareTo(high) <= 0;     }   This allows you to check if any IComparable<T> is within an upper and lower bound. Think of how many times you type something like:       if (response.Employee.Address.YearsAt >= 2         && response.Employee.Address.YearsAt <= 10)     {     ...     }     Now, you can instead type:       if(response.Employee.Address.YearsAt.IsBetween(2, 10))     {     ...     }     Note that this applies to all IComparable<T> -- that's ints, chars, strings, DateTime, etc -- and does not depend on any logical domain. In addition, it satisfies the second point and actually makes the code more readable and maintainable.   Let's look at the third point. In it we said that an extension method should fit the most specific interface or type possible. Now, I'm not saying if you have something that applies to enumerables, you create an extension for List, Array, Dictionary, etc (though you may have reasons for doing so), but that you should beware of making things TOO general.   For example, let's say we had an extension method like this:       public static T ConvertTo<T>(this object value)     {         return (T)Convert.ChangeType(value, typeof(T));     }         This lets you do more fluent conversions like:       double d = "5.0".ConvertTo<double>();     However, if you dig into Reflector (LOVE that tool) you will see that if the type you are calling on does not implement IConvertible, what you convert to MUST be the exact type or it will throw an InvalidCastException. Now this may or may not be what you want in this situation, and I leave that up to you. Things like this would fail:       object value = new Employee();     ...     // class cast exception because typeof(IEmployee) != typeof(Employee)     IEmployee emp = value.ConvertTo<IEmployee>();       Yes, that's a downfall of working with Convertible in general, but if you wanted your fluent interface to be more type-safe so that ConvertTo were only callable on IConvertibles (and let casting be a manual task), you could easily make it:         public static T ConvertTo<T>(this IConvertible value)     {         return (T)Convert.ChangeType(value, typeof(T));     }         This is what I mean by choosing the best type to extend. Consider that if we used the previous (object) version, every time we typed a dot ('.') on an instance we'd pull up ConvertTo() whether it was applicable or not. By filtering our extension method down to only valid types (those that implement IConvertible) we greatly reduce our IntelliSense pollution and apply a good level of compile-time correctness.   Now my fourth rule is just my general rule-of-thumb. Obviously, you can make extension methods as in-your-face as you want. I included all mine in my work libraries in its own sub-namespace, something akin to:       namespace Shared.Core.Extensions { ... }     This is in a library called Shared.Core, so just referencing the Core library doesn't pollute your IntelliSense, you have to actually do a using on Shared.Core.Extensions to bring the methods in. This is very similar to the way Microsoft puts its extension methods in System.Linq. This way, if you want 'em, you use the appropriate namespace. If you don't want 'em, they won't pollute your namespace.   To really make this work, however, that namespace should only include extension methods and subordinate types those extensions themselves may use. If you plant other useful classes in those namespaces, once a user includes it, they get all the extensions too.   Also, just as a personal preference, extension methods that aren't simply syntactical shortcuts, I like to put in a static utility class and then have extension methods for syntactical candy. For instance, I think it imaginable that any object could be converted to XML:       namespace Shared.Core     {         // A collection of XML Utility classes         public static class XmlUtility         {             ...             // Serialize an object into an xml string             public static string ToXml(object input)             {                 var xs = new XmlSerializer(input.GetType());                   // use new UTF8Encoding here, not Encoding.UTF8. The later includes                 // the BOM which screws up subsequent reads, the former does not.                 using (var memoryStream = new MemoryStream())                 using (var xmlTextWriter = new XmlTextWriter(memoryStream, new UTF8Encoding()))                 {                     xs.Serialize(xmlTextWriter, input);                     return Encoding.UTF8.GetString(memoryStream.ToArray());                 }             }             ...         }     }   I also wanted to be able to call this from an object like:       value.ToXml();     But here's the problem, if i made this an extension method from the start with that one little keyword "this", it would pop into IntelliSense for all objects which could be very polluting. Instead, I put the logic into a utility class so that users have the choice of whether or not they want to use it as just a class and not pollute IntelliSense, then in my extensions namespace, I add the syntactical candy:       namespace Shared.Core.Extensions     {         public static class XmlExtensions         {             public static string ToXml(this object value)             {                 return XmlUtility.ToXml(value);             }         }     }   So now it's the best of both worlds. On one hand, they can use the utility class if they don't want to pollute IntelliSense, and on the other hand they can include the Extensions namespace and use as an extension if they want. The neat thing is it also adheres to the Single Responsibility Principle. The XmlUtility is responsible for converting objects to XML, and the XmlExtensions is responsible for extending object's interface for ToXml().

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• Sliding collision response

  - by dbostream

  I have been reading plenty of tutorials about sliding collision responses yet I am not able to implement it properly in my project. What I want to do is make a puck slide along the rounded corner boards of a hockey rink. In my latest attempt the puck does slide along the boards but there are some strange velocity behaviors. First of all the puck slows down a lot pretty much right away and then it slides for awhile and stops before exiting the corner. Even if I double the speed I get a similar behavior and the puck does not make it out of the corner. I used some ideas from this document http://www.peroxide.dk/papers/collision/collision.pdf. This is what I have: Update method called from the game loop when it is time to update the puck (I removed some irrelevant parts). I use two states (current, previous) which are used to interpolate the position during rendering. public override void Update(double fixedTimeStep) { /* Acceleration is set to 0 for now. */ Acceleration.Zero(); PreviousState = CurrentState; _collisionRecursionDepth = 0; CurrentState.Position = SlidingCollision(CurrentState.Position, CurrentState.Velocity * fixedTimeStep + 0.5 * Acceleration * fixedTimeStep * fixedTimeStep); /* Should not this be affected by a sliding collision? and not only the position. */ CurrentState.Velocity = CurrentState.Velocity + Acceleration * fixedTimeStep; Heading = Vector2.NormalizeRet(CurrentState.Velocity); } private Vector2 SlidingCollision(Vector2 position, Vector2 velocity) { if(_collisionRecursionDepth > 5) return position; bool collisionFound = false; Vector2 futurePosition = position + velocity; Vector2 intersectionPoint = new Vector2(); Vector2 intersectionPointNormal = new Vector2(); /* I did not include the collision detection code, if a collision is detected the intersection point and normal in that point is returned. */ if(!collisionFound) return futurePosition; /* If no collision was detected it is safe to move to the future position. */ /* It is not exactly the intersection point, but slightly before. */ Vector2 newPosition = intersectionPoint; /* oldVelocity is set to the distance from the newPosition(intersection point) to the position it had moved to had it not collided. */ Vector2 oldVelocity = futurePosition - newPosition; /* Project the distance left to move along the intersection normal. */ Vector2 newVelocity = oldVelocity - intersectionPointNormal * oldVelocity.DotProduct(intersectionPointNormal); if(newVelocity.LengthSq() < 0.001) return newPosition; /* If almost no speed, no need to continue. */ _collisionRecursionDepth++; return SlidingCollision(newPosition, newVelocity); } What am I doing wrong with the velocity? I have been staring at this for very long so I have gone blind. I have tried different values of recursion depth but it does not seem to make it better. Let me know if you need more information. I appreciate any help. EDIT: A combination of Patrick Hughes' and teodron's answers solved the velocity problem (I think), thanks a lot! This is the new code: I decided to use a separate recursion method now too since I don't want to recalculate the acceleration in each recursion. public override void Update(double fixedTimeStep) { Acceleration.Zero();// = CalculateAcceleration(fixedTimeStep); PreviousState = new MovingEntityState(CurrentState.Position, CurrentState.Velocity); CurrentState = SlidingCollision(CurrentState, fixedTimeStep); Heading = Vector2.NormalizeRet(CurrentState.Velocity); } private MovingEntityState SlidingCollision(MovingEntityState state, double timeStep) { bool collisionFound = false; /* Calculate the next position given no detected collision. */ Vector2 futurePosition = state.Position + state.Velocity * timeStep; Vector2 intersectionPoint = new Vector2(); Vector2 intersectionPointNormal = new Vector2(); /* I did not include the collision detection code, if a collision is detected the intersection point and normal in that point is returned. */ /* If no collision was detected it is safe to move to the future position. */ if (!collisionFound) return new MovingEntityState(futurePosition, state.Velocity); /* Set new position to the intersection point (slightly before). */ Vector2 newPosition = intersectionPoint; /* Project the new velocity along the intersection normal. */ Vector2 newVelocity = state.Velocity - 1.90 * intersectionPointNormal * state.Velocity.DotProduct(intersectionPointNormal); /* Calculate the time of collision. */ double timeOfCollision = Math.Sqrt((newPosition - state.Position).LengthSq() / (futurePosition - state.Position).LengthSq()); /* Calculate new time step, remaining time of full step after the collision * current time step. */ double newTimeStep = timeStep * (1 - timeOfCollision); return SlidingCollision(new MovingEntityState(newPosition, newVelocity), newTimeStep); } Even though the code above seems to slide the puck correctly please have a look at it. I have a few questions, if I don't multiply by 1.90 in the newVelocity calculation it doesn't work (I get a stack overflow when the puck enters the corner because the timeStep decreases very slowly - a collision is found early in every recursion), why is that? what does 1.90 really do and why 1.90? Also I have a new problem, the puck does not move parallell to the short side after exiting the curve; to be more exact it moves outside the rink (I am not checking for any collisions with the short side at the moment). When I perform the collision detection I first check that the puck is in the correct quadrant. For example bottom-right corner is quadrant four i.e. circleCenter.X < puck.X && circleCenter.Y puck.Y is this a problem? or should the short side of the rink be the one to make the puck go parallell to it and not the last collision in the corner? EDIT2: This is the code I use for collision detection, maybe it has something to do with the fact that I can't make the puck slide (-1.0) but only reflect (-2.0): /* Point is the current position (not the predicted one) and quadrant is 4 for the bottom-right corner for example. */ if (GeometryHelper.PointInCircleQuadrant(circleCenter, circleRadius, state.Position, quadrant)) { /* The line is: from = state.Position, to = futurePosition. So a collision is detected when from is inside the circle and to is outside. */ if (GeometryHelper.LineCircleIntersection2d(state.Position, futurePosition, circleCenter, circleRadius, intersectionPoint, quadrant)) { collisionFound = true; /* Set the intersection point to slightly before the real intersection point (I read somewhere this was good to do because of floting point precision, not sure exactly how much though). */ intersectionPoint = intersectionPoint - Vector2.NormalizeRet(state.Velocity) * 0.001; /* Normal at the intersection point. */ intersectionPointNormal = Vector2.NormalizeRet(circleCenter - intersectionPoint) } } When I set the intersection point, if I for example use 0.1 instead of 0.001 the puck travels further before it gets stuck, but for all values I have tried (including 0 - the real intersection point) it gets stuck somewhere (but I necessarily not get a stack overflow). Can something in this part be the cause of my problem? I can see why I get the stack overflow when using -1.0 when calculating the new velocity vector; but not how to solve it. I traced the time steps used in the recursion (initial time step is always 1/60 ~ 0.01666): Recursion depth Time step next recursive call [Start recursion, time step ~ 0.016666] 0 0,000985806527246773 [No collision, stop recursion] [Start recursion, time step ~ 0.016666] 0 0,0149596704364629 1 0,0144883449376379 2 0,0143155612984837 3 0,014224925727213 4 0,0141673917461608 5 0,0141265435314026 6 0,0140953966184117 7 0,0140704653746625 ...and so on. As you can see the collision is detected early in every recursive call which means the next time step decreases very slowly thus the recursion depth gets very big - stack overflow.

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• SQL SERVER – Weekly Series – Memory Lane – #034

  - by Pinal Dave

  Here is the list of selected articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2007 UDF – User Defined Function to Strip HTML – Parse HTML – No Regular Expression The UDF used in the blog does fantastic task – it scans entire HTML text and removes all the HTML tags. It keeps only valid text data without HTML task. This is one of the quite commonly requested tasks many developers have to face everyday. De-fragmentation of Database at Operating System to Improve Performance Operating system skips MDF file while defragging the entire filesystem of the operating system. It is absolutely fine and there is no impact of the same on performance. Read the entire blog post for my conversation with our network engineers. Delay Function – WAITFOR clause – Delay Execution of Commands How do you delay execution of the commands in SQL Server – ofcourse by using WAITFOR keyword. In this blog post, I explain the same with the help of T-SQL script. Find Length of Text Field To measure the length of TEXT fields the function is DATALENGTH(textfield). Len will not work for text field. As of SQL Server 2005, developers should migrate all the text fields to VARCHAR(MAX) as that is the way forward. Retrieve Current Date Time in SQL Server CURRENT_TIMESTAMP, GETDATE(), {fn NOW()} There are three ways to retrieve the current datetime in SQL SERVER. CURRENT_TIMESTAMP, GETDATE(), {fn NOW()} Explanation and Comparison of NULLIF and ISNULL An interesting observation is NULLIF returns null if it comparison is successful, whereas ISNULL returns not null if its comparison is successful. In one way they are opposite to each other. Here is my question to you - How to create infinite loop using NULLIF and ISNULL? If this is even possible? 2008 Introduction to SERVERPROPERTY and example SERVERPROPERTY is a very interesting system function. It returns many of the system values. I use it very frequently to get different server values like Server Collation, Server Name etc. SQL Server Start Time We can use DMV to find out what is the start time of SQL Server in 2008 and later version. In this blog you can see how you can do the same. Find Current Identity of Table Many times we need to know what is the current identity of the column. I have found one of my developers using aggregated function MAX () to find the current identity. However, I prefer following DBCC command to figure out current identity. Create Check Constraint on Column Some time we just need to create a simple constraint over the table but I have noticed that developers do many different things to make table column follow rules than just creating constraint. I suggest constraint is a very useful concept and every SQL Developer should pay good attention to this subject. 2009 List Schema Name and Table Name for Database This is one of the blog post where I straight forward display script. One of the kind of blog posts, which I still love to read and write. Clustered Index on Separate Drive From Table Location A table devoid of primary key index is called heap, and here data is not arranged in a particular order, which gives rise to issues that adversely affect performance. Data must be stored in some kind of order. If we put clustered index on it then the order will be forced by that index and the data will be stored in that particular order. Understanding Table Hints with Examples Hints are options and strong suggestions specified for enforcement by the SQL Server query processor on DML statements. The hints override any execution plan the query optimizer might select for a query. 2010 Data Pages in Buffer Pool – Data Stored in Memory Cache One of my earlier year article, which I still read it many times and point developers to read it again. It is clear from the Resultset that when more than one index is used, datapages related to both or all of the indexes are stored in Memory Cache separately. TRANSACTION, DML and Schema Locks Can you create a situation where you can see Schema Lock? Well, this is a very simple question, however during the interview I notice over 50 candidates failed to come up with the scenario. In this blog post, I have demonstrated the situation where we can see the schema lock in database. 2011 Solution – Puzzle – Statistics are not updated but are Created Once In this example I have created following situation: Create Table Insert 1000 Records Check the Statistics Now insert 10 times more 10,000 indexes Check the Statistics – it will be NOT updated Auto Update Statistics and Auto Create Statistics for database is TRUE Now I have requested two things in the example 1) Why this is happening? 2) How to fix this issue? Selecting Domain from Email Address This is a straight to script blog post where I explain how to select only domain name from entire email address. Solution – Generating Zero Without using Any Numbers in T-SQL How to get zero digit without using any digit? This is indeed a very interesting question and the answer is even interesting. Try to come up with answer in next 10 minutes and if you can’t come up with the answer the blog post read this post for solution. 2012 Simple Explanation and Puzzle with SOUNDEX Function and DIFFERENCE Function In simple words - SOUNDEX converts an alphanumeric string to a four-character code to find similar-sounding words or names. DIFFERENCE function returns an integer value. The  integer returned is the number of characters in the SOUNDEX values that are the same. Read Only Files and SQL Server Management Studio (SSMS) I have come across a very interesting feature in SSMS related to “Read Only” files. I believe it is a little unknown feature as well so decided to write a blog about the same. Identifying Column Data Type of uniqueidentifier without Querying System Tables How do I know if any table has a uniqueidentifier column and what is its value without using any DMV or System Catalogues? Only information you know is the table name and you are allowed to return any kind of error if the table does not have uniqueidentifier column. Read the blog post to find the answer. Solution – User Not Able to See Any User Created Object in Tables – Security and Permissions Issue Interesting question – “When I try to connect to SQL Server, it lets me connect just fine as well let me open and explore the database. I noticed that I do not see any user created instances but when my colleague attempts to connect to the server, he is able to explore the database as well see all the user created tables and other objects. Can you help me fix it?” Importing CSV File Into Database – SQL in Sixty Seconds #018 – Video Here is interesting small 60 second video on how to import CSV file into Database. ColumnStore Index – Batch Mode vs Row Mode Here is the logic behind when Columnstore Index uses Batch Mode and when it uses Row Mode. A batch typically represents about 1000 rows of data. Batch mode processing also uses algorithms that are optimized for the multicore CPUs and increased memory throughput. Follow up – Usage of $rowguid and $IDENTITY This is an excellent follow up blog post of my earlier blog post where I explain where to use $rowguid and $identity.  If you do not know the difference between them, this is a blog with a script example. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Superclass Sensitive Actions

  - by Geertjan

  I've created a small piece of functionality that enables you to create actions for Java classes in the IDE. When the user right-clicks on a Java class, they will see one or more actions depending on the superclass of the selected class. To explain this visually, here I have "BlaTopComponent.java". I right-click on its node in the Projects window and I see "This is a TopComponent": Indeed, when you look at the source code of "BlaTopComponent.java", you'll see that it implements the TopComponent class. Next, in the screenshot below, you see that I have right-click a different class. In this case, there's an action available because the selected class implements the ActionListener class. Then, take a look at this one. Here both TopComponent and ActionListener are superclasses of the current class, hence both the actions are available to be invoked: Finally, here's a class that subclasses neither TopComponent nor ActionListener, hence neither of the actions that I created for doing something that relates to TopComponents or ActionListeners is available, since those actions are irrelevant in this context: How does this work? Well, it's a combination of my blog entries "Generic Node Popup Registration Solution" and "Showing an Action on a TopComponent Node". The cool part is that the definition of the two actions that you see above is remarkably trivial: import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JOptionPane; import org.openide.loaders.DataObject; import org.openide.util.Utilities; public class TopComponentSensitiveAction implements ActionListener { private final DataObject context; public TopComponentSensitiveAction() { context = Utilities.actionsGlobalContext().lookup(DataObject.class); } @Override public void actionPerformed(ActionEvent ev) { //Do something with the context: JOptionPane.showMessageDialog(null, "TopComponent: " + context.getNodeDelegate().getDisplayName()); } } The above is the action that will be available if you right-click a Java class that extends TopComponent. This, in turn, is the action that will be available if you right-click a Java class that implements ActionListener: import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JOptionPane; import org.openide.loaders.DataObject; import org.openide.util.Utilities; public class ActionListenerSensitiveAction implements ActionListener { private final DataObject context; public ActionListenerSensitiveAction() { context = Utilities.actionsGlobalContext().lookup(DataObject.class); } @Override public void actionPerformed(ActionEvent ev) { //Do something with the context: JOptionPane.showMessageDialog(null, "ActionListener: " + context.getNodeDelegate().getDisplayName()); } } Indeed, the classes, at this stage are the same. But, depending on what I want to do with TopComponents or ActionListeners, I now have a starting point, which includes access to the DataObject, from where I can get down into the source code, as shown here. This is how the two ActionListeners that you see defined above are registered in the layer, which could ultimately be done via annotations on the ActionListeners, of course: <folder name="Actions"> <folder name="Tools"> <file name="org-netbeans-sbas-impl-TopComponentSensitiveAction.instance"> <attr stringvalue="This is a TopComponent" name="displayName"/> <attr name="instanceCreate" methodvalue="org.netbeans.sbas.SuperclassSensitiveAction.create"/> <attr name="type" stringvalue="org.openide.windows.TopComponent"/> <attr name="delegate" newvalue="org.netbeans.sbas.impl.TopComponentSensitiveAction"/> </file> <file name="org-netbeans-sbas-impl-ActionListenerSensitiveAction.instance"> <attr stringvalue="This is an ActionListener" name="displayName"/> <attr name="instanceCreate" methodvalue="org.netbeans.sbas.SuperclassSensitiveAction.create"/> <attr name="type" stringvalue="java.awt.event.ActionListener"/> <attr name="delegate" newvalue="org.netbeans.sbas.impl.ActionListenerSensitiveAction"/> </file> </folder> </folder> <folder name="Loaders"> <folder name="text"> <folder name="x-java"> <folder name="Actions"> <file name="org-netbeans-sbas-impl-TopComponentSensitiveAction.shadow"> <attr name="originalFile" stringvalue="Actions/Tools/org-netbeans-sbas-impl-TopComponentSensitiveAction.instance"/> <attr intvalue="150" name="position"/> </file> <file name="org-netbeans-sbas-impl-ActionListenerSensitiveAction.shadow"> <attr name="originalFile" stringvalue="Actions/Tools/org-netbeans-sbas-impl-ActionListenerSensitiveAction.instance"/> <attr intvalue="160" name="position"/> </file> </folder> </folder> </folder> </folder> The most important parts of the layer registration are the lines that are highlighted above. Those lines connect the layer to the generic action that delegates back to the action listeners defined above, as follows: public final class SuperclassSensitiveAction extends AbstractAction implements ContextAwareAction { private final Map map; //This method is called from the layer, via "instanceCreate", //magically receiving a map, which contains all the attributes //that are defined in the layer for the file: static SuperclassSensitiveAction create(Map map) { return new SuperclassSensitiveAction(Utilities.actionsGlobalContext(), map); } public SuperclassSensitiveAction(Lookup context, Map m) { super(m.get("displayName").toString()); this.map = m; String superclass = m.get("type").toString(); //Enable the menu item only if //we're dealing with a class of type superclass: JavaSource javaSource = JavaSource.forFileObject( context.lookup(DataObject.class).getPrimaryFile()); try { javaSource.runUserActionTask(new ScanTask(this, superclass), true); } catch (IOException ex) { Exceptions.printStackTrace(ex); } //Hide the menu item if it isn't enabled: putValue(DynamicMenuContent.HIDE_WHEN_DISABLED, true); } @Override public void actionPerformed(ActionEvent ev) { ActionListener delegatedAction = (ActionListener)map.get("delegate"); delegatedAction.actionPerformed(ev); } @Override public Action createContextAwareInstance(Lookup actionContext) { return new SuperclassSensitiveAction(actionContext, map); } private class ScanTask implements Task<CompilationController> { private SuperclassSensitiveAction action = null; private String superclass; private ScanTask(SuperclassSensitiveAction action, String superclass) { this.action = action; this.superclass = superclass; } @Override public void run(final CompilationController info) throws Exception { info.toPhase(Phase.ELEMENTS_RESOLVED); new EnableIfGivenSuperclassMatches(info, action, superclass).scan( info.getCompilationUnit(), null); } } private static class EnableIfGivenSuperclassMatches extends TreePathScanner<Void, Void> { private CompilationInfo info; private final AbstractAction action; private final String superclassName; public EnableIfGivenSuperclassMatches(CompilationInfo info, AbstractAction action, String superclassName) { this.info = info; this.action = action; this.superclassName = superclassName; } @Override public Void visitClass(ClassTree t, Void v) { Element el = info.getTrees().getElement(getCurrentPath()); if (el != null) { TypeElement te = (TypeElement) el; List<? extends TypeMirror> interfaces = te.getInterfaces(); if (te.getSuperclass().toString().equals(superclassName)) { action.setEnabled(true); } else { action.setEnabled(false); } for (TypeMirror typeMirror : interfaces) { if (typeMirror.toString().equals(superclassName)){ action.setEnabled(true); } } } return null; } } } This is a pretty cool solution and, as you can see, very generic. Create a new ActionListener, register it in the layer so that it maps to the generic class above, and make sure to set the type attribute, which defines the superclass to which the action should be sensitive.

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• Visiting the Fire Station in Coromandel

  Hm, I just tried to remember how we actually came up with this cool idea... but it's already too blurred and it doesn't really matter after all. Anyway, if I remember correctly (IIRC), it happened during one of the Linux meetups at Mugg & Bean, Bagatelle where Ajay and I brought our children along and we had a brief conversation about how cool it would be to check out one of the fire stations here in Mauritius. We both thought that it would be a great experience and adventure for the little ones. An idea takes shape And there we go, down the usual routine these... having an idea, checking out the options and discussing who's doing what. Except this time, it was all up to Ajay, and he did a fantastic job. End of August, he told me that he got in touch with one of his friends which actually works as a fire fighter at the station in Coromandel and that there could be an option to come and visit them (soon). A couple of days later - Confirmed! Be there, and in time... What time? Anyway, doesn't really matter... Everything was settled and arranged. I asked the kids on Friday afternoon if they might be interested to see the fire engines and what a fire fighter is doing. Of course, they were all in! Getting up early on Sunday morning isn't really a regular exercise for all of us but everything went smooth and after a short breakfast it was time to leave. Where are we going? Are we there yet? Now, we are in Bambous. Why do you go this way? The kids were so much into it. Absolutely amazing to see their excitement. Are we there yet? Well, we went through the sugar cane fields towards Chebel and then down into the industrial zone at Coromandel. Honestly, I had a clue where the fire station is located but having Google Maps in reach that shouldn't be a problem in case that we might get lost. But my worries were washed away when our children guided us... "There! Over there are the fire engines! We have to turn left, dad." - No comment, the kids were right! As we were there a little bit too early, we parked the car and the kids started to explore the area and outskirts of the fire station. Some minutes later, as if we had placed an order a unit of two cars had to go out for an alarm and the kids could witness them leaving as closely as possible. Sirens on and wow!!! Ladder truck L32 - MAN truck with Rosenbauer built-up and equipment by Metz Taking the tour Ajay arrived shortly after that and guided us finally inside the station to meet with his pal. The three guys were absolutely well-prepared and showed us around in the hall, explaining that there two units out at the moment. But the ladder truck (with max. 32m expandable height) was still around we all got a great insight into the technique and equipment on the vehicle. It was amazing to see all three kids listening to Mambo as give some figures about the truck and how the fire fighters are actually it. The children and 'our' fire fighters of the day had great fun with the various fire engines Absolutely fantastic that the children were allowed to experience this - we had so much fun! Ajay's son brought two of his toy fire engines along, shared them with ours, and they all played very well together. As a parent it was really amazing to see them at such an ease. Enough theory Shortly afterwards the ladder truck was moved outside, got stabilised and ready to go for 'real-life' exercising. With the additional equipment of safety helmets, security belts and so on, we all got a first-hand impression about how it could be as a fire-fighter. Actually, I was totally amazed by the curiousity and excitement of my BWE. She was really into it and asked lots of interesting questions - in general but also technical. And while our fighters were busy with Ajay and family, I gave her some more details and explanations about the truck, the expandable ladder, the safety cage at the top and other equipment available. Safety first! No exceptions and always be prepared for the worst case... Also, the equipped has been checked prior to excuse - This is your life saver... Hooked up and ready to go... ...of course not too high. This is just a demonstration - and 32 meters above ground isn't for everyone. Well, after that it was me that had the asking looks on me, and I finally revealed to the local fire fighters that I was in the auxiliary fire brigade, more precisely in the hazard department, for more than 10 years. So not a professional fire fighter but at least a passionate and educated one as them. Inside the station Our fire fighters really took their time to explain their daily job to kids, provided them access to operation seat on the ladder truck and how the truck cabin is actually equipped with the different radios and so on. It was really a great time. Later on we had a brief tour through the building itself, and again all of our questions were answered. We had great fun and started to joke about bits and pieces. For me it was also very interesting to see the comparison between the fire station here in Mauritius and the ones I have been to back in Germany. Amazing to see them completely captivated in the play - the children had lots of fun! Also, that there are currently ten fire stations all over the island, plus two additional but private ones at the airport and at the harbour. The newest one is actually down in Black River on the west coast because the time from Quatre Bornes takes too long to have any chance of an effective alarm at all. IMHO, a very good decision as time is the most important factor in getting fire incidents under control. After all it was great experience for all of us, especially for the children to see and understand that their toy trucks are only copies of the real thing and that the job of a (professional) fire fighter is very important in our society. Don't forget that those guys run into the danger zone while you're trying to get away from it as much as possible. Another unit just came back from a grass fire - and shortly after they went out again. No time to rest, too much to do! Mauritian Fire Fighters now and (maybe) in the future... Thank you! It was an honour to be around! Thank you to Ajay for organising and arranging this Sunday morning event, and of course of Big Thank You to the three guys that took some time off to have us at the Fire Station in Coromandel and guide us through their daily job! And remember to call 115 in case of emergencies!

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• Benchmarking MySQL Replication with Multi-Threaded Slaves

  - by Mat Keep

  0 0 1 1145 6530 Homework 54 15 7660 14.0 Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-ansi-language:EN-US;} The objective of this benchmark is to measure the performance improvement achieved when enabling the Multi-Threaded Slave enhancement delivered as a part MySQL 5.6. As the results demonstrate, Multi-Threaded Slaves delivers 5x higher replication performance based on a configuration with 10 databases/schemas. For real-world deployments, higher replication performance directly translates to: · Improved consistency of reads from slaves (i.e. reduced risk of reading "stale" data) · Reduced risk of data loss should the master fail before replicating all events in its binary log (binlog) The multi-threaded slave splits processing between worker threads based on schema, allowing updates to be applied in parallel, rather than sequentially. This delivers benefits to those workloads that isolate application data using databases - e.g. multi-tenant systems deployed in cloud environments. Multi-Threaded Slaves are just one of many enhancements to replication previewed as part of the MySQL 5.6 Development Release, which include: · Global Transaction Identifiers coupled with MySQL utilities for automatic failover / switchover and slave promotion · Crash Safe Slaves and Binlog · Optimized Row Based Replication · Replication Event Checksums · Time Delayed Replication These and many more are discussed in the “MySQL 5.6 Replication: Enabling the Next Generation of Web & Cloud Services” Developer Zone article  Back to the benchmark - details are as follows. Environment The test environment consisted of two Linux servers: · one running the replication master · one running the replication slave. Only the slave was involved in the actual measurements, and was based on the following configuration: - Hardware: Oracle Sun Fire X4170 M2 Server - CPU: 2 sockets, 6 cores with hyper-threading, 2930 MHz. - OS: 64-bit Oracle Enterprise Linux 6.1 - Memory: 48 GB Test Procedure Initial Setup: Two MySQL servers were started on two different hosts, configured as replication master and slave. 10 sysbench schemas were created, each with a single table: CREATE TABLE `sbtest` (    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,    `k` int(10) unsigned NOT NULL DEFAULT '0',    `c` char(120) NOT NULL DEFAULT '',    `pad` char(60) NOT NULL DEFAULT '',    PRIMARY KEY (`id`),    KEY `k` (`k`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 10,000 rows were inserted in each of the 10 tables, for a total of 100,000 rows. When the inserts had replicated to the slave, the slave threads were stopped. The slave data directory was copied to a backup location and the slave threads position in the master binlog noted. 10 sysbench clients, each configured with 10 threads, were spawned at the same time to generate a random schema load against each of the 10 schemas on the master. Each sysbench client executed 10,000 "update key" statements: UPDATE sbtest set k=k+1 WHERE id = <random row> In total, this generated 100,000 update statements to later replicate during the test itself. Test Methodology: The number of slave workers to test with was configured using: SET GLOBAL slave_parallel_workers=<workers> Then the slave IO thread was started and the test waited for all the update queries to be copied over to the relay log on the slave. The benchmark clock was started and then the slave SQL thread was started. The test waited for the slave SQL thread to finish executing the 100k update queries, doing "select master_pos_wait()". When master_pos_wait() returned, the benchmark clock was stopped and the duration calculated. The calculated duration from the benchmark clock should be close to the time it took for the SQL thread to execute the 100,000 update queries. The 100k queries divided by this duration gave the benchmark metric, reported as Queries Per Second (QPS). Test Reset: The test-reset cycle was implemented as follows: · the slave was stopped · the slave data directory replaced with the previous backup · the slave restarted with the slave threads replication pointer repositioned to the point before the update queries in the binlog. The test could then be repeated with identical set of queries but a different number of slave worker threads, enabling a fair comparison. The Test-Reset cycle was repeated 3 times for 0-24 number of workers and the QPS metric calculated and averaged for each worker count. MySQL Configuration The relevant configuration settings used for MySQL are as follows: binlog-format=STATEMENT relay-log-info-repository=TABLE master-info-repository=TABLE As described in the test procedure, the slave_parallel_workers setting was modified as part of the test logic. The consequence of changing this setting is: 0 worker threads:    - current (i.e. single threaded) sequential mode    - 1 x IO thread and 1 x SQL thread    - SQL thread both reads and executes the events 1 worker thread:    - sequential mode    - 1 x IO thread, 1 x Coordinator SQL thread and 1 x Worker thread    - coordinator reads the event and hands it to the worker who executes 2+ worker threads:    - parallel execution    - 1 x IO thread, 1 x Coordinator SQL thread and 2+ Worker threads    - coordinator reads events and hands them to the workers who execute them Results Figure 1 below shows that Multi-Threaded Slaves deliver ~5x higher replication performance when configured with 10 worker threads, with the load evenly distributed across our 10 x schemas. This result is compared to the current replication implementation which is based on a single SQL thread only (i.e. zero worker threads). Figure 1: 5x Higher Performance with Multi-Threaded Slaves The following figure shows more detailed results, with QPS sampled and reported as the worker threads are incremented. The raw numbers behind this graph are reported in the Appendix section of this post. Figure 2: Detailed Results As the results above show, the configuration does not scale noticably from 5 to 9 worker threads. When configured with 10 worker threads however, scalability increases significantly. The conclusion therefore is that it is desirable to configure the same number of worker threads as schemas. Other conclusions from the results: · Running with 1 worker compared to zero workers just introduces overhead without the benefit of parallel execution. · As expected, having more workers than schemas adds no visible benefit. Aside from what is shown in the results above, testing also demonstrated that the following settings had a very positive effect on slave performance: relay-log-info-repository=TABLE master-info-repository=TABLE For 5+ workers, it was up to 2.3 times as fast to run with TABLE compared to FILE. Conclusion As the results demonstrate, Multi-Threaded Slaves deliver significant performance increases to MySQL replication when handling multiple schemas. This, and the other replication enhancements introduced in MySQL 5.6 are fully available for you to download and evaluate now from the MySQL Developer site (select Development Release tab). You can learn more about MySQL 5.6 from the documentation  Please don’t hesitate to comment on this or other replication blogs with feedback and questions. Appendix – Detailed Results

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• ApiChange Is Released!

  - by Alois Kraus

  I have been working on little tool to simplify my life and perhaps yours as developer as well. It is basically a command line tool that allows you to execute queries on your compiled .NET code base. The main purpose is to find out how big the impact of an api change would be if you changed this or that.  Now you can do high level operations like Diff public types for breaking changes. Who uses a method? Who uses a type? Who uses implements an interface? Who references me? What format has the binary  (32/64, Managed C++, Pure IL, Unmanaged)? Search for all event subscribers and unsubscribers. A unique feature is to check for event subscription imbalances. Forgotten event subscriptions are the 90% cause of managed memory leaks. It is done at a per class level. If one class does subscribe to one event more often than it does unsubscribe it is treated as possible event subscription imbalance. Another unique ability is to search for users of string literals which allows you to track users of a string constant which is not possible otherwise. For incremental builds the ShowRebuildTargets command can be used to identify the dependant targets that need a rebuild after you did compile one assembly. It has some heuristics in place to determine the impact of breaking changes and finds out which targets need to be recompiled as well. It has a ton of other features and a an API to access these things programmatically so you can build upon these simple queries create even better tools. Perhaps we get a Visual Studio plug in? You can download it from CodePlex here. It works via XCopy deployment. Simply let it run and check the command line help out. The best feature in my opinion is that the output of nearly all commands can be piped to Excel for further analysis. Since it does read also the pdbs it can show you the source file name and line number as well for all matches. The following picture shows the output of a –WhousesType query. The following command checks where type from BaseLibraryV1.dll are used inside DependantLibV1.dll. All matches are printed out with the reason and matching item along with file and line number. There is even a hyper link to the match which will open Visual Studio. ApiChange -whousestype "*" BaseLibraryV1.dll -in DependantLibV1.dll –excel The "*” is the actual query which means all types. The syntax is the same like in C# just that placeholders are allowed ;-). More info's can be found at the Codeplex Documentation.     The tool was developed in a TDD style manner which means that it is heavily tested and already used by a quite large user base inside the company I do work for. Luckily for you I got the permission to make it public so you take advantage of it. It is fully instrumented with tracing. If you find bugs simply add the –trace command line switch to find out what is failing and send me the output. How is it done? Your first guess might be that it uses reflection. Wrong. It is based on Mono Cecil a free IL parser with a fantastic API to access all internals of a managed assembly. The speed is awesome and to make it even faster I did make the tool heavily multi threaded. The query above did execute in 1.8s with the Excel output. On a rather slow machine I can analyze over 1500 assemblies in less than 40s with a very low memory consumption. The true power of Mono Cecil is that I can load an assembly like any other data file. I have no problems unloading a file but if I would have used reflection I would need to unload a whole AppDomain just to get rid of one assembly in my memory. Just to give you a glimpse how ApiChange.Api.dll can be used I show you one of the unit tests:           public void Can_Find_GenericMethodInvocations_With_Type_Parameters()         { // 1. Create an aggregator to collect our matches             UsageQueryAggregator agg = new UsageQueryAggregator();   // 2. This is the type we want to search for. Load it via the type query             var decimalType = TypeQuery.GetTypeByName(TestConstants.MscorlibAssembly, "System.Decimal");   // 3. register the type query which searches for uses of the Decimal type             new WhoUsesType(agg, decimalType);   // 4. Search for all users of the Decimal type in the DependandLibV1Assembly             agg.Analyze(TestConstants.DependandLibV1Assembly);   // Extract matches and assert             Assert.AreEqual(2, agg.MethodMatches.Count, "Method match count");             Assert.AreEqual("UseGenericMethod", agg.MethodMatches[0].Match.Name);             Assert.AreEqual("UseGenericMethod", agg.MethodMatches[1].Match.Name);         } Many thanks go from here to Jb Evian for the creation of Mono.Cecil. Without this fantastic piece of code it would have been much much harder. There are other options around like the Common Compiler Infrastructure  Metadata Api which should do the same thing but it was not a real option since the Microsoft reader did fail on even simple assemblies (at least in September 2009 this was the case). Besides this I found the CCI Apis much harder to use. The only real competitor was Reflector which does support many things but does not let me access his cool high level analyze commands. So I decided to dig into the IL specs and as a result you can query your compiled binaries from the command line or programmatically. The best thing is you try it out for yourself and give me some feedback what you miss. If you want to contribute or have a cool idea what should be added drop me a mail at A Kraus1@___No [email protected]. There is much more inside the tool I did not talk about it (yet).

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• DBA Best Practices - A Blog Series: Episode 1 - Backups

  - by Argenis

    This blog post is part of the DBA Best Practices series, on which various topics of concern for daily database operations are discussed. Your feedback and comments are very much welcome, so please drop by the comments section and be sure to leave your thoughts on the subject. Morning Coffee When I was a DBA, the first thing I did when I sat down at my desk at work was checking that all backups had completed successfully. It really was more of a ritual, since I had a dual system in place to check for backup completion: 1) the scheduled agent jobs to back up the databases were set to alert the NOC in failure, and 2) I had a script run from a central server every so often to check for any backup failures. Why the redundancy, you might ask. Well, for one I was once bitten by the fact that database mail doesn't work 100% of the time. Potential causes for failure include issues on the SMTP box that relays your server email, firewall problems, DNS issues, etc. And so to be sure that my backups completed fine, I needed to rely on a mechanism other than having the servers do the taking - I needed to interrogate the servers and ask each one if an issue had occurred. This is why I had a script run every so often. Some of you might have monitoring tools in place like Microsoft System Center Operations Manager (SCOM) or similar 3rd party products that would track all these things for you. But at that moment, we had no resort but to write our own Powershell scripts to do it. Now it goes without saying that if you don't have backups in place, you might as well find another career. Your most sacred job as a DBA is to protect the data from a disaster, and only properly safeguarded backups can offer you peace of mind here. "But, we have a cluster...we don't need backups" Sadly I've heard this line more than I would have liked to. You need to understand that a cluster is comprised of shared storage, and that is precisely your single point of failure. A cluster will protect you from an issue at the Operating System level, and also under an outage of any SQL-related service or dependent devices. But it will most definitely NOT protect you against corruption, nor will it protect you against somebody deleting data from a table - accidentally or otherwise. Backup, fine. How often do I take a backup? The answer to this is something you will hear frequently when working with databases: it depends. What does it depend on? For one, you need to understand how much data your business is willing to lose. This is what's called Recovery Point Objective, or RPO. If you don't know how much data your business is willing to lose, you need to have an honest and realistic conversation about data loss expectations with your customers, internal or external. From my experience, their first answer to the question "how much data loss can you withstand?" will be "zero". In that case, you will need to explain how zero data loss is very difficult and very costly to achieve, even in today's computing environments. Do you want to go ahead and take full backups of all your databases every hour, or even every day? Probably not, because of the impact that taking a full backup can have on a system. That's what differential and transaction log backups are for. Have I answered the question of how often to take a backup? No, and I did that on purpose. You need to think about how much time you have to recover from any event that requires you to restore your databases. This is what's called Recovery Time Objective. Again, if you go ask your customer how long of an outage they can withstand, at first you will get a completely unrealistic number - and that will be your starting point for discussing a solution that is cost effective. The point that I'm trying to get across is that you need to have a plan. This plan needs to be practiced, and tested. Like a football playbook, you need to rehearse the moves you'll perform when the time comes. How often is up to you, and the objective is that you feel better about yourself and the steps you need to follow when emergency strikes. A backup is nothing more than an untested restore Backups are files. Files are prone to corruption. Put those two together and realize how you feel about those backups sitting on that network drive. When was the last time you restored any of those? Restoring your backups on another box - that, by the way, doesn't have to match the specs of your production server - will give you two things: 1) peace of mind, because now you know that your backups are good and 2) a place to offload your consistency checks with DBCC CHECKDB or any of the other DBCC commands like CHECKTABLE or CHECKCATALOG. This is a great strategy for VLDBs that cannot withstand the additional load created by the consistency checks. If you choose to offload your consistency checks to another server though, be sure to run DBCC CHECKDB WITH PHYSICALONLY on the production server, and if you're using SQL Server 2008 R2 SP1 CU4 and above, be sure to enable traceflags 2562 and/or 2549, which will speed up the PHYSICALONLY checks further - you can read more about this enhancement here. Back to the "How Often" question for a second. If you have the disk, and the network latency, and the system resources to do so, why not backup the transaction log often? As in, every 5 minutes, or even less than that? There's not much downside to doing it, as you will have to clear the log with a backup sooner than later, lest you risk running out space on your tlog, or even your drive. The one drawback to this approach is that you will have more files to deal with at restore time, and processing each file will add a bit of extra time to the entire process. But it might be worth that time knowing that you minimized the amount of data lost. Again, test your plan to make sure that it matches your particular needs. Where to back up to? Network share? Locally? SAN volume? This is another topic where everybody has a favorite choice. So, I'll stick to mentioning what I like to do and what I consider to be the best practice in this regard. I like to backup to a SAN volume, i.e., a drive that actually lives in the SAN, and can be easily attached to another server in a pinch, saving you valuable time - you wouldn't need to restore files on the network (slow) or pull out drives out a dead server (been there, done that, it’s also slow!). The key is to have a copy of those backup files made quickly, and, if at all possible, to a remote target on a different datacenter - or even the cloud. There are plenty of solutions out there that can help you put such a solution together. That right there is the first step towards a practical Disaster Recovery plan. But there's much more to DR, and that's material for a different blog post in this series.

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• DBA Best Practices - A Blog Series: Episode 1 - Backups

  - by Argenis

    This blog post is part of the DBA Best Practices series, on which various topics of concern for daily database operations are discussed. Your feedback and comments are very much welcome, so please drop by the comments section and be sure to leave your thoughts on the subject. Morning Coffee When I was a DBA, the first thing I did when I sat down at my desk at work was checking that all backups have completed successfully. It really was more of a ritual, since I had a dual system in place to check for backup completion: 1) the scheduled agent jobs to back up the databases were set to alert the NOC in failure, and 2) I had a script run from a central server every so often to check for any backup failures. Why the redundancy, you might ask. Well, for one I was once bitten by the fact that database mail doesn't work 100% of the time. Potential causes for failure include issues on the SMTP box that relays your server email, firewall problems, DNS issues, etc. And so to be sure that my backups completed fine, I needed to rely on a mechanism other than having the servers do the taking - I needed to interrogate the servers and ask each one if an issue had occurred. This is why I had a script run every so often. Some of you might have monitoring tools in place like Microsoft System Center Operations Manager (SCOM) or similar 3rd party products that would track all these things for you. But at that moment, we had no resort but to write our own Powershell scripts to do it. Now it goes without saying that if you don't have backups in place, you might as well find another career. Your most sacred job as a DBA is to protect the data from a disaster, and only properly safeguarded backups can offer you peace of mind here. "But, we have a cluster...we don't need backups" Sadly I've heard this line more than I would have liked to. You need to understand that a cluster is comprised of shared storage, and that is precisely your single point of failure. A cluster will protect you from an issue at the Operating System level, and also under an outage of any SQL-related service or dependent devices. But it will most definitely NOT protect you against corruption, nor will it protect you against somebody deleting data from a table - accidentally or otherwise. Backup, fine. How often do I take a backup? The answer to this is something you will hear frequently when working with databases: it depends. What does it depend on? For one, you need to understand how much data your business is willing to lose. This is what's called Recovery Point Objective, or RPO. If you don't know how much data your business is willing to lose, you need to have an honest and realistic conversation about data loss expectations with your customers, internal or external. From my experience, their first answer to the question "how much data loss can you withstand?" will be "zero". In that case, you will need to explain how zero data loss is very difficult and very costly to achieve, even in today's computing environments. Do you want to go ahead and take full backups of all your databases every hour, or even every day? Probably not, because of the impact that taking a full backup can have on a system. That's what differential and transaction log backups are for. Have I answered the question of how often to take a backup? No, and I did that on purpose. You need to think about how much time you have to recover from any event that requires you to restore your databases. This is what's called Recovery Time Objective. Again, if you go ask your customer how long of an outage they can withstand, at first you will get a completely unrealistic number - and that will be your starting point for discussing a solution that is cost effective. The point that I'm trying to get across is that you need to have a plan. This plan needs to be practiced, and tested. Like a football playbook, you need to rehearse the moves you'll perform when the time comes. How often is up to you, and the objective is that you feel better about yourself and the steps you need to follow when emergency strikes. A backup is nothing more than an untested restore Backups are files. Files are prone to corruption. Put those two together and realize how you feel about those backups sitting on that network drive. When was the last time you restored any of those? Restoring your backups on another box - that, by the way, doesn't have to match the specs of your production server - will give you two things: 1) peace of mind, because now you know that your backups are good and 2) a place to offload your consistency checks with DBCC CHECKDB or any of the other DBCC commands like CHECKTABLE or CHECKCATALOG. This is a great strategy for VLDBs that cannot withstand the additional load created by the consistency checks. If you choose to offload your consistency checks to another server though, be sure to run DBCC CHECKDB WITH PHYSICALONLY on the production server, and if you're using SQL Server 2008 R2 SP1 CU4 and above, be sure to enable traceflags 2562 and/or 2549, which will speed up the PHYSICALONLY checks further - you can read more about this enhancement here. Back to the "How Often" question for a second. If you have the disk, and the network latency, and the system resources to do so, why not backup the transaction log often? As in, every 5 minutes, or even less than that? There's not much downside to doing it, as you will have to clear the log with a backup sooner than later, lest you risk running out space on your tlog, or even your drive. The one drawback to this approach is that you will have more files to deal with at restore time, and processing each file will add a bit of extra time to the entire process. But it might be worth that time knowing that you minimized the amount of data lost. Again, test your plan to make sure that it matches your particular needs. Where to back up to? Network share? Locally? SAN volume? This is another topic where everybody has a favorite choice. So, I'll stick to mentioning what I like to do and what I consider to be the best practice in this regard. I like to backup to a SAN volume, i.e., a drive that actually lives in the SAN, and can be easily attached to another server in a pinch, saving you valuable time - you wouldn't need to restore files on the network (slow) or pull out drives out a dead server (been there, done that, it’s also slow!). The key is to have a copy of those backup files made quickly, and, if at all possible, to a remote target on a different datacenter - or even the cloud. There are plenty of solutions out there that can help you put such a solution together. That right there is the first step towards a practical Disaster Recovery plan. But there's much more to DR, and that's material for a different blog post in this series.

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• Feedback on meeting of the Linux User Group of Mauritius

  Once upon a time in a country far far away... Okay, actually it's not that bad but it has been a while since the last meeting of the Linux User Group of Mauritius (LUGM). There have been plans in the past but it never really happened. Finally, Selven took the opportunity and organised a new meetup with low administrative overhead, proper scheduling on alternative dates and a small attendee's survey on the preferred option. All the pre-work was nicely executed. First, I wasn't sure whether it would be possible to attend. Luckily I got some additional information, like children should come, too, and I was sold to this community gathering. According to other long-term members of the LUGM it was the first time 'ever' that a gathering was organised outside of Quatre Bornes, and I have to admit it was great! LUGM - user group meeting on the 15.06.2013 in L'Escalier Quick overview of Linux & the LUGM With a little bit of delay the LUGM meeting officially started with a quick overview and introduction to Linux presented by Avinash. During the session he told the audience that there had been quite some activity over the island some years ago but unfortunately it had been quiet during recent times. Of course, we also spoke about the acknowledged world dominance of Linux - thanks to Android - and the interesting possibilities for countries like Mauritius. It is known that a couple of public institutions have there back-end infrastructure running on Red Hat Linux systems but the presence on the desktop is still very low. Users are simply hanging on to Windows XP and older versions of Microsoft Office. Following the introduction of the LUGM Ajay joined into the session and it quickly changed into a panel discussion with lots of interesting questions and answers, sharing of first-hand experience either on the job or in private use of Linux, and a couple of ideas about how the LUGM could promote Linux a bit more in Mauritius. It was great to get an insight into other attendee's opinion and activities. Especially taking into consideration that I'm already using Linux since around 1996/97. Frankly speaking, I bought a SuSE 4.x distribution back in those days because I couldn't achieve certain tasks on Windows NT 4.0 without spending a fortune. OpenELEC Mediacenter Next, Selven gave us decent introduction on OpenELEC: Open Embedded Linux Entertainment Center (OpenELEC) is a small Linux distribution built from scratch as a platform to turn your computer into an XBMC media center. OpenELEC is designed to make your system boot fast, and the install is so easy that anyone can turn a blank PC into a media machine in less than 15 minutes. I didn't know about it until this presentation. In the past, I was mainly attached to Video Disk Recorder (VDR) as it allows the use of satellite receiver cards very easily. Hm, somehow I'm still missing my precious HTPC that I had to leave back in Germany years ago. It was great piece of hardware and software; self-built PC in a standard HiFi-sized (43cm) black desktop casing with 2 full-featured Hauppauge DVB-s cards, an old-fashioned Voodoo graphics card, WiFi card, Pioneer slot-in DVD drive, and fully remote controlled via infra-red thanks to Debian, VDR and LIRC. With EP Guide, scheduled recordings and general multimedia centre it offered all the necessary comfort in the living room, besides a Nintendo game console; actually a GameCube at that time... But I have to admit that putting OpenELEC on a Raspberry Pi would be a cool DIY project in the near future. LUGM - our next generation of linux users (15.06.2013) Project Evil Genius (PEG) Don't be scared of the paragraph header. Ish gave us a cool explanation why he named it PEG - Project Evil Genius; it's because of the time of the day when he was scripting down his ideas to be able to build, package and provide software applications to various Linux distributions. The main influence came from openSuSE but the platform didn't cater for his needs and ideas, so he started to work out something on his own. During his passionate session he also talked about the amazing experience he had due to other Linux users from all over the world. During the next couple of days Ish promised to put his script to GitHub... Looking forward to that. Check out Ish's personal blog over at hacklog.in. Highly recommended to read. Why India? Simply because the registration fees per year for an Indian domain are approximately 20 times less than for a Mauritian domain (.mu). Exploring the beach of L'Escalier af the meeting 'After-party' at the beach of L'Escalier Puh, after such interesting sessions, ideas around Linux and good conversation during the breaks and over lunch it was time for a little break-out. Selven suggested that we all should head down to the beach of L'Escalier and get some impressions of nature down here in the south of the island. Talking about 'beach' ;-) - absolutely not comparable to the white-sanded ones here in Flic en Flac... There are no lagoons down at the south coast of Mauriitus, and watching the breaking waves is a different experience and joy after all. Unfortunately, I was a little bit worried about the thoughtless littering at such a remote location. You have to drive on natural paths through the sugar cane fields and I was really shocked by the amount of rubbish lying around almost everywhere. Sad, really sad and it concurs with Yasir's recent article on the same topic. Resumé & outlook It was a great event. I met with new people, had some good conversations, and even my children enjoyed themselves the whole day. The location was well-chosen, enough space for each and everyone, parking spaces and even a playground for the children. Also, a big "Thank You" to Selven and his helpers for the organisation and preparation of lunch. I'm kind of sure that this was an exceptional meeting of LUGM and I'm really looking forward to the next gathering of Linux geeks. Hopefully, soon. All images are courtesy of Avinash Meetoo. More pictures are available on Flickr.

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• Blogging locally and globally–my experience

  - by DigiMortal

  In Baltic MVP Summit 2011 there was discussion about having two blogs - one for local and another for global audience – and how to publish once written information in these blogs. There are many ways how to optimize your blogging activities if you have more than one audience and here you can find my experiences, best practices and advices about this topic. My two blogs I have to working blogs: this one here technology and programming blog for local market My local blog is almost five years old and it makes it one of the oldest company blogs in Estonia. It is still active and I write there as much as I have time for it. This blog here is active since September 2007, so it is about 3.5 years old right now. Both of these blogs are  my major hits in my MVP carrier and they have very good web statistics too. My local blog My local blog is about programming, web and technology. It has way wider target audience then this blog here has. By example, in my local blog I blog also about local events, cool new concept phones, different webs providing some interesting services etc. But local guys can find there also my postings about how to solve one or another programming problem and postings about Microsoft technologies I am playing with. This far my local blog has a lot of readers for such a small country that Estonia is. This blog has made me a lot of cool contacts and I have had there a lot of interesting discussions about different technical topics. Why I started this blog? Living in small country is different than living in big country. In small country you have less people and therefore smaller audience so you have to target more than one technical topic to find enough readers. In a same time you are still interested in your main topics and you want to reach to more people who are sharing same interests with you. Practically one day y will grow out from local market and you go global. This is how this blog was born. Was it worth to create, promote and mess with it? Every second I have put on my time to this blog has been worth of it. Thanks to this blog I have found new good friends and without them I think it is more boring to work on different problems and solutions. Defining target audiences One thing you should always do when having more than one blog is defining target audiences. If you are just technomaniac interested in sharing your stuff and make some new friends and have something to write to your MVP nomination form then you don’t have to go through complex targeting process. You can do it simple way and same effectively. Here is how I defined target audiences to my blogs: local blog – reader of my local blog is IT professional, software developer, technology innovator or just some guy who is interested in technology,   this blog – reader of this blog is experienced professional software developer who works on Microsoft technologies or software developer who is open minded and open to new technologies and interesting solutions to development problems. You can see how local blog – due to small market with less people – has wider definition for audience while this blog is heavily targeted to Microsoft technologies and specially to software development. On practical side these decisions are also made well I think because it is very hard to build up popular common IT blog. On global level it is better to target some specific niche and find readers who are professionals on your favorite topics. Thanks to this blog I have found new friends who are professional developers and I am very happy about all the discussions I have had with them. Publishing content to different blogs My local blog and this blog have some overlapping topics like .NET, databases and SEO. Due to this overlapping there is question: when I write posting to my local blog then should I have to publish same thing in my global blog? And if I write something to my global blog then should I publish same thing also in my local blog? Well, it really depends on the definition of your target audiences. If they match then of course it is good idea to translate you post and publish it also to another blog. But if you have different audiences then you may need to modify your posting before publishing it. The questions you have to answer are: is target audience interested in this topic? is target audience expecting more specific and deeper handling of this topic or are they expecting more general handling of topic? is the problem you are discussing actual for target audience or not? You have to answer these questions and after that make your decision. If you need to modify your original posting then take some time and do it. Provide quality to all your readers because they will respect you if you respect them. Cross-posting and referencing It is tempting to save time that preparing some blog post takes and if you have are done with posting in one blog it may seem like good idea to make short posting to another blog and add reference to first one where topic is discussed longer. Well, don’t do it – all your readers expect good quality content from you and jumping from one blog post to another is disturbing for them. Of course, there is problem with differences between target audiences. You may have wider target audience and some people may be interested in more specific handling of topic. In this case feel free to refer your blog you are writing in english. This is not working very well in opposite direction because almost all my global blog readers understand english but not estonian. By example, estonian language is complex one and online translating tools make very poor translations from estonian language. This is why I don’t even plan to publish postings here that refer to my local blog for more information. I am keeping these two blogs as two different worlds and if there is posting that fits well to both blogs I will write my posting to one blog and then answer previous three questions before posting same thing to another blog. Conclusion Growing out of your local market is not anything mysterious if you are living in small country. As it is harder to find people there who are interested in same topics with you then sooner or later you will start finding these new contacts from global audience. Global audience is bigger and to be visible there you must provide high quality content to your audience. It is something you will learn over time and you will learn every day something new when you are posting to your global blog. You may ask: if global blog is much more complex thing to do then is it worth to do at all? My answer is: yes, do it for sure. It is not easy thing to do when you start but if you work on your global blog and improve it over time you will get over all obstacles pretty soon. Just don’t forget one thing – content is king and your readers expect high quality from you.

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• C# 2D Camera Max Zoom

  - by Craig

  I have a simple ship sprite moving around the screen along with a 2D Camera. I have zooming in and out working, however when I zoom out it goes past the world bounds and has the cornflower blue background showing. How do I sort it that I can only zoom out as far as showing the entire world (which is a picture of OZ) and thats it? I dont want any of the cornflower blue showing. Cheers! namespace GamesCoursework_1 { /// <summary> /// This is the main type for your game /// </summary> public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; SpriteBatch spriteBatch; // player variables Texture2D Ship; Vector2 Ship_Position; float Ship_Rotation = 0.0f; Vector2 Ship_Origin; Vector2 Ship_Velocity; const float tangentialVelocity = 4f; float friction = 0.05f; static Point CameraViewport = new Point(800, 800); Camera2d cam = new Camera2d((int)CameraViewport.X, (int)CameraViewport.Y); //Size of world static Point worldSize = new Point(1600, 1600); // Screen variables static Point worldCenter = new Point(worldSize.X / 2, worldSize.Y / 2); Rectangle playerBounds = new Rectangle(CameraViewport.X / 2, CameraViewport.Y / 2, worldSize.X - CameraViewport.X, worldSize.Y - CameraViewport.Y); Rectangle worldBounds = new Rectangle(0, 0, worldSize.X, worldSize.Y); Texture2D background; public Game1() { graphics = new GraphicsDeviceManager(this); graphics.PreferredBackBufferWidth = CameraViewport.X; graphics.PreferredBackBufferHeight = CameraViewport.Y; Content.RootDirectory = "Content"; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { // TODO: Add your initialization logic here base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { // Create a new SpriteBatch, which can be used to draw textures. spriteBatch = new SpriteBatch(GraphicsDevice); // TODO: use this.Content to load your game content here Ship = Content.Load<Texture2D>("Ship"); Ship_Origin.X = Ship.Width / 2; Ship_Origin.Y = Ship.Height / 2; background = Content.Load<Texture2D>("aus"); Ship_Position = new Vector2(worldCenter.X, worldCenter.Y); cam.Pos = Ship_Position; cam.Zoom = 1f; } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { // TODO: Unload any non ContentManager content here } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { // Allows the game to exit if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) this.Exit(); // TODO: Add your update logic here Ship_Position = Ship_Velocity + Ship_Position; keyPressed(); base.Update(gameTime); } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); // TODO: Add your drawing code here spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, null, null, null,null, cam.get_transformation(GraphicsDevice)); spriteBatch.Draw(background, Vector2.Zero, Color.White); spriteBatch.Draw(Ship, Ship_Position, Ship.Bounds, Color.White, Ship_Rotation, Ship_Origin, 1.0f, SpriteEffects.None, 0f); spriteBatch.End(); base.Draw(gameTime); } private void Ship_Move(Vector2 move) { Ship_Position += move; } private void keyPressed() { KeyboardState keyState; // Move right keyState = Keyboard.GetState(); if (keyState.IsKeyDown(Keys.Right)) { Ship_Rotation = Ship_Rotation + 0.1f; } if (keyState.IsKeyDown(Keys.Left)) { Ship_Rotation = Ship_Rotation - 0.1f; } if (keyState.IsKeyDown(Keys.Up)) { Ship_Velocity.X = (float)Math.Cos(Ship_Rotation) * tangentialVelocity; Ship_Velocity.Y = (float)Math.Sin(Ship_Rotation) * tangentialVelocity; if ((int)Ship_Position.Y < playerBounds.Bottom && (int)Ship_Position.Y > playerBounds.Top) cam._pos.Y = Ship_Position.Y; if ((int)Ship_Position.X > playerBounds.Left && (int)Ship_Position.X < playerBounds.Right) cam._pos.X = Ship_Position.X; Ship_Position += new Vector2(tangentialVelocity, 0); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(tangentialVelocity * 2, 0.0f); Ship_Position += new Vector2(-tangentialVelocity, 0.0f); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(-tangentialVelocity * 2, 0.0f); Ship_Position += new Vector2(0.0f, -tangentialVelocity); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(0.0f, -tangentialVelocity * 2); Ship_Position += new Vector2(0.0f, tangentialVelocity); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(0.0f, 2 * tangentialVelocity); } else if(Ship_Velocity != Vector2.Zero) { float i = Ship_Velocity.X; float j = Ship_Velocity.Y; Ship_Velocity.X = i -= friction * i; Ship_Velocity.Y = j -= friction * j; if ((int)Ship_Position.Y < playerBounds.Bottom && (int)Ship_Position.Y > playerBounds.Top) cam._pos.Y = Ship_Position.Y; if ((int)Ship_Position.X > playerBounds.Left && (int)Ship_Position.X < playerBounds.Right) cam._pos.X = Ship_Position.X; Ship_Position += new Vector2(tangentialVelocity, 0); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(tangentialVelocity * 2, 0.0f); Ship_Position += new Vector2(-tangentialVelocity, 0.0f); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(-tangentialVelocity * 2, 0.0f); Ship_Position += new Vector2(0.0f, -tangentialVelocity); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(0.0f, -tangentialVelocity * 2); Ship_Position += new Vector2(0.0f, tangentialVelocity); if (!worldBounds.Contains(new Point((int)Ship_Position.X, (int)Ship_Position.Y))) Ship_Position -= new Vector2(0.0f, 2 * tangentialVelocity); } if (keyState.IsKeyDown(Keys.Q)) { if (cam.Zoom < 2f) cam.Zoom += 0.05f; } if (keyState.IsKeyDown(Keys.A)) { if (cam.Zoom > 0.3f) cam.Zoom -= 0.05f; } } } }

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• FreeBSD performance tuning. Sysctls, loader.conf, kernel

  - by SaveTheRbtz

  I wanted to share knowledge of tuning FreeBSD via sysctl.conf/loader.conf/KENCONF. It was initially based on Igor Sysoev's (author of nginx) presentation about FreeBSD tuning up to 100,000-200,000 active connections. Tunings are for FreeBSD-CURRENT. Since 7.2 amd64 some of them are tuned well by default. Prior 7.0 some of them are boot only (set via /boot/loader.conf) or does not exist at all. sysctl.conf: # No zero mapping feature # May break wine # (There are also reports about broken samba3) #security.bsd.map_at_zero=0 # If you have really busy webserver with apache13 you may run out of processes #kern.maxproc=10000 # Same for servers with apache2 / Pound #kern.threads.max_threads_per_proc=4096 # Max. backlog size kern.ipc.somaxconn=4096 # Shared memory // 7.2+ can use shared memory > 2Gb kern.ipc.shmmax=2147483648 # Sockets kern.ipc.maxsockets=204800 # Can cause this on older kernels: # http://old.nabble.com/Significant-performance-regression-for-increased-maxsockbuf-on-8.0-RELEASE-tt26745981.html#a26745981 ) kern.ipc.maxsockbuf=10485760 # Mbuf 2k clusters (on amd64 7.2+ 25600 is default) # For such high value vm.kmem_size must be increased to 3G kern.ipc.nmbclusters=262144 # Jumbo pagesize(_SC_PAGESIZE) clusters # Used as general packet storage for jumbo frames # can be monitored via `netstat -m` #kern.ipc.nmbjumbop=262144 # Jumbo 9k/16k clusters # If you are using them #kern.ipc.nmbjumbo9=65536 #kern.ipc.nmbjumbo16=32768 # For lower latency you can decrease scheduler's maximum time slice # default: stathz/10 (~ 13) #kern.sched.slice=1 # Increase max command-line length showed in `ps` (e.g for Tomcat/Java) # Default is PAGE_SIZE / 16 or 256 on x86 # This avoids commands to be presented as [executable] in `ps` # For more info see: http://www.freebsd.org/cgi/query-pr.cgi?pr=120749 kern.ps_arg_cache_limit=4096 # Every socket is a file, so increase them kern.maxfiles=204800 kern.maxfilesperproc=200000 kern.maxvnodes=200000 # On some systems HPET is almost 2 times faster than default ACPI-fast # Useful on systems with lots of clock_gettime / gettimeofday calls # See http://old.nabble.com/ACPI-fast-default-timecounter,-but-HPET-83--faster-td23248172.html # After revision 222222 HPET became default: http://svnweb.freebsd.org/base?view=revision&revision=222222 kern.timecounter.hardware=HPET # Small receive space, only usable on http-server, on file server this # should be increased to 65535 or even more #net.inet.tcp.recvspace=8192 # This is useful on Fat-Long-Pipes #net.inet.tcp.recvbuf_max=10485760 #net.inet.tcp.recvbuf_inc=65535 # Small send space is useful for http servers that serve small files # Autotuned since 7.x net.inet.tcp.sendspace=16384 # This is useful on Fat-Long-Pipes #net.inet.tcp.sendbuf_max=10485760 #net.inet.tcp.sendbuf_inc=65535 # Turn off receive autotuning # You can play with it. #net.inet.tcp.recvbuf_auto=0 #net.inet.tcp.sendbuf_auto=0 # This should be enabled if you going to use big spaces (>64k) # Also timestamp field is useful when using syncookies net.inet.tcp.rfc1323=1 # Turn this off on high-speed, lossless connections (LAN 1Gbit+) # If you set it there is no need in TCP_NODELAY sockopt (see man tcp) net.inet.tcp.delayed_ack=0 # This feature is useful if you are serving data over modems, Gigabit Ethernet, # or even high speed WAN links (or any other link with a high bandwidth delay product), # especially if you are also using window scaling or have configured a large send window. # Automatically disables on small RTT ( http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_subr.c?#rev1.237 ) # This sysctl was removed in 10-CURRENT: # See: http://www.mail-archive.com/[email protected]/msg06178.html #net.inet.tcp.inflight.enable=0 # TCP slowstart algorithm tunings # We assuming we have very fast clients #net.inet.tcp.slowstart_flightsize=100 #net.inet.tcp.local_slowstart_flightsize=100 # Disable randomizing of ports to avoid false RST # Before usage check SA here www.bsdcan.org/2006/papers/ImprovingTCPIP.pdf # (it's also says that port randomization auto-disables at some conn.rates, but I didn't checked it thou) #net.inet.ip.portrange.randomized=0 # Increase portrange # For outgoing connections only. Good for seed-boxes and ftp servers. net.inet.ip.portrange.first=1024 net.inet.ip.portrange.last=65535 # # stops route cache degregation during a high-bandwidth flood # http://www.freebsd.org/doc/en/books/handbook/securing-freebsd.html #net.inet.ip.rtexpire=2 net.inet.ip.rtminexpire=2 net.inet.ip.rtmaxcache=1024 # Security net.inet.ip.redirect=0 net.inet.ip.sourceroute=0 net.inet.ip.accept_sourceroute=0 net.inet.icmp.maskrepl=0 net.inet.icmp.log_redirect=0 net.inet.icmp.drop_redirect=1 net.inet.tcp.drop_synfin=1 # # There is also good example of sysctl.conf with comments: # http://www.thern.org/projects/sysctl.conf # # icmp may NOT rst, helpful for those pesky spoofed # icmp/udp floods that end up taking up your outgoing # bandwidth/ifqueue due to all that outgoing RST traffic. # #net.inet.tcp.icmp_may_rst=0 # Security net.inet.udp.blackhole=1 net.inet.tcp.blackhole=2 # IPv6 Security # For more info see http://www.fosslc.org/drupal/content/security-implications-ipv6 # Disable Node info replies # To see this vulnerability in action run `ping6 -a sglAac ::1` or `ping6 -w ::1` on unprotected node net.inet6.icmp6.nodeinfo=0 # Turn on IPv6 privacy extensions # For more info see proposal http://unix.derkeiler.com/Mailing-Lists/FreeBSD/net/2008-06/msg00103.html net.inet6.ip6.use_tempaddr=1 net.inet6.ip6.prefer_tempaddr=1 # Disable ICMP redirect net.inet6.icmp6.rediraccept=0 # Disable acceptation of RA and auto linklocal generation if you don't use them #net.inet6.ip6.accept_rtadv=0 #net.inet6.ip6.auto_linklocal=0 # Increases default TTL, sometimes useful # Default is 64 net.inet.ip.ttl=128 # Lessen max segment life to conserve resources # ACK waiting time in miliseconds # (default: 30000. RFC from 1979 recommends 120000) net.inet.tcp.msl=5000 # Max bumber of timewait sockets net.inet.tcp.maxtcptw=200000 # Don't use tw on local connections # As of 15 Apr 2009. Igor Sysoev says that nolocaltimewait has some buggy realization. # So disable it or now till get fixed #net.inet.tcp.nolocaltimewait=1 # FIN_WAIT_2 state fast recycle net.inet.tcp.fast_finwait2_recycle=1 # Time before tcp keepalive probe is sent # default is 2 hours (7200000) #net.inet.tcp.keepidle=60000 # Should be increased until net.inet.ip.intr_queue_drops is zero net.inet.ip.intr_queue_maxlen=4096 # Interrupt handling via multiple CPU, but with context switch. # You can play with it. Default is 1; #net.isr.direct=0 # This is for routers only #net.inet.ip.forwarding=1 #net.inet.ip.fastforwarding=1 # This speed ups dummynet when channel isn't saturated net.inet.ip.dummynet.io_fast=1 # Increase dummynet(4) hash #net.inet.ip.dummynet.hash_size=2048 #net.inet.ip.dummynet.max_chain_len # Should be increased when you have A LOT of files on server # (Increase until vfs.ufs.dirhash_mem becomes lower) vfs.ufs.dirhash_maxmem=67108864 # Note from commit http://svn.freebsd.org/base/head@211031 : # For systems with RAID volumes and/or virtualization envirnments, where # read performance is very important, increasing this sysctl tunable to 32 # or even more will demonstratively yield additional performance benefits. vfs.read_max=32 # Explicit Congestion Notification (see http://en.wikipedia.org/wiki/Explicit_Congestion_Notification) net.inet.tcp.ecn.enable=1 # Flowtable - flow caching mechanism # Useful for routers #net.inet.flowtable.enable=1 #net.inet.flowtable.nmbflows=65535 # Extreme polling tuning #kern.polling.burst_max=1000 #kern.polling.each_burst=1000 #kern.polling.reg_frac=100 #kern.polling.user_frac=1 #kern.polling.idle_poll=0 # IPFW dynamic rules and timeouts tuning # Increase dyn_buckets till net.inet.ip.fw.curr_dyn_buckets is lower net.inet.ip.fw.dyn_buckets=65536 net.inet.ip.fw.dyn_max=65536 net.inet.ip.fw.dyn_ack_lifetime=120 net.inet.ip.fw.dyn_syn_lifetime=10 net.inet.ip.fw.dyn_fin_lifetime=2 net.inet.ip.fw.dyn_short_lifetime=10 # Make packets pass firewall only once when using dummynet # i.e. packets going thru pipe are passing out from firewall with accept #net.inet.ip.fw.one_pass=1 # shm_use_phys Wires all shared pages, making them unswappable # Use this to lessen Virtual Memory Manager's work when using Shared Mem. # Useful for databases #kern.ipc.shm_use_phys=1 # ZFS # Enable prefetch. Useful for sequential load type i.e fileserver. # FreeBSD sets vfs.zfs.prefetch_disable to 1 on any i386 systems and # on any amd64 systems with less than 4GB of avaiable memory # For additional info check this nabble thread http://old.nabble.com/Samba-read-speed-performance-tuning-td27964534.html #vfs.zfs.prefetch_disable=0 # On highload servers you may notice following message in dmesg: # "Approaching the limit on PV entries, consider increasing either the # vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable" vm.pmap.shpgperproc=2048 loader.conf: # Accept filters for data, http and DNS requests # Useful when your software uses select() instead of kevent/kqueue or when you under DDoS # DNS accf available on 8.0+ accf_data_load="YES" accf_http_load="YES" accf_dns_load="YES" # Async IO system calls aio_load="YES" # Linux specific devices in /dev # As for 8.1 it only /dev/full #lindev_load="YES" # Adds NCQ support in FreeBSD # WARNING! all ad[0-9]+ devices will be renamed to ada[0-9]+ # 8.0+ only #ahci_load="YES" #siis_load="YES" # FreeBSD 8.2+ # New Congestion Control for FreeBSD # http://caia.swin.edu.au/urp/newtcp/tools/cc_chd-readme-0.1.txt # http://www.ietf.org/proceedings/78/slides/iccrg-5.pdf # Initial merge commit message http://www.mail-archive.com/[email protected]/msg31410.html #cc_chd_load="YES" # Increase kernel memory size to 3G. # # Use ONLY if you have KVA_PAGES in kernel configuration, and you have more than 3G RAM # Otherwise panic will happen on next reboot! # # It's required for high buffer sizes: kern.ipc.nmbjumbop, kern.ipc.nmbclusters, etc # Useful on highload stateful firewalls, proxies or ZFS fileservers # (FreeBSD 7.2+ amd64 users: Check that current value is lower!) #vm.kmem_size="3G" # If your server has lots of swap (>4Gb) you should increase following value # according to http://lists.freebsd.org/pipermail/freebsd-hackers/2009-October/029616.html # Otherwise you'll be getting errors # "kernel: swap zone exhausted, increase kern.maxswzone" # kern.maxswzone="256M" # Older versions of FreeBSD can't tune maxfiles on the fly #kern.maxfiles="200000" # Useful for databases # Sets maximum data size to 1G # (FreeBSD 7.2+ amd64 users: Check that current value is lower!) #kern.maxdsiz="1G" # Maximum buffer size(vfs.maxbufspace) # You can check current one via vfs.bufspace # Should be lowered/upped depending on server's load-type # Usually decreased to preserve kmem # (default is 10% of mem) #kern.maxbcache="512M" # Sendfile buffers # For i386 only #kern.ipc.nsfbufs=10240 # FreeBSD 9+ # HPET "legacy route" support. It should allow HPET to work per-CPU # See http://www.mail-archive.com/[email protected]/msg03603.html #hint.atrtc.0.clock=0 #hint.attimer.0.clock=0 #hint.hpet.0.legacy_route=1 # syncache Hash table tuning net.inet.tcp.syncache.hashsize=1024 net.inet.tcp.syncache.bucketlimit=512 net.inet.tcp.syncache.cachelimit=65536 # Increased hostcache # Later host cache can be viewed via net.inet.tcp.hostcache.list hidden sysctl # Very useful for it's RTT RTTVAR # Must be power of two net.inet.tcp.hostcache.hashsize=65536 # hashsize * bucketlimit (which is 30 by default) # It allocates 255Mb (1966080*136) of RAM net.inet.tcp.hostcache.cachelimit=1966080 # TCP control-block Hash table tuning net.inet.tcp.tcbhashsize=4096 # Disable ipfw deny all # Should be uncommented when there is a chance that # kernel and ipfw binary may be out-of sync on next reboot #net.inet.ip.fw.default_to_accept=1 # # SIFTR (Statistical Information For TCP Research) is a kernel module that # logs a range of statistics on active TCP connections to a log file. # See prerelease notes http://groups.google.com/group/mailing.freebsd.current/browse_thread/thread/b4c18be6cdce76e4 # and man 4 sitfr #siftr_load="YES" # Enable superpages, for 7.2+ only # Also read http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030094.html vm.pmap.pg_ps_enabled=1 # Usefull if you are using Intel-Gigabit NIC #hw.em.rxd=4096 #hw.em.txd=4096 #hw.em.rx_process_limit="-1" # Also if you have ALOT interrupts on NIC - play with following parameters # NOTE: You should set them for every NIC #dev.em.0.rx_int_delay: 250 #dev.em.0.tx_int_delay: 250 #dev.em.0.rx_abs_int_delay: 250 #dev.em.0.tx_abs_int_delay: 250 # There is also multithreaded version of em/igb drivers can be found here: # http://people.yandex-team.ru/~wawa/ # # for additional em monitoring and statistics use # sysctl dev.em.0.stats=1 ; dmesg # sysctl dev.em.0.debug=1 ; dmesg # Also after r209242 (-CURRENT) there is a separate sysctl for each stat variable; # Same tunings for igb #hw.igb.rxd=4096 #hw.igb.txd=4096 #hw.igb.rx_process_limit=100 # Some useful netisr tunables. See sysctl net.isr #net.isr.maxthreads=4 #net.isr.defaultqlimit=4096 #net.isr.maxqlimit: 10240 # Bind netisr threads to CPUs #net.isr.bindthreads=1 # # FreeBSD 9.x+ # Increase interface send queue length # See commit message http://svn.freebsd.org/viewvc/base?view=revision&revision=207554 #net.link.ifqmaxlen=1024 # Nicer boot logo =) loader_logo="beastie" And finally here is KERNCONF: # Just some of them, see also # cat /sys/{i386,amd64,}/conf/NOTES # This one useful only on i386 #options KVA_PAGES=512 # You can play with HZ in environments with high interrupt rate (default is 1000) # 100 is for my notebook to prolong it's battery life #options HZ=100 # Polling is goot on network loads with high packet rates and low-end NICs # NB! Do not enable it if you want more than one netisr thread #options DEVICE_POLLING # Eliminate datacopy on socket read-write # To take advantage with zero copy sockets you should have an MTU >= 4k # This req. is only for receiving data. # Read more in man zero_copy_sockets # Also this epic thread on kernel trap: # http://kerneltrap.org/node/6506 # Here Linus says that "anybody that does it that way (FreeBSD) is totally incompetent" #options ZERO_COPY_SOCKETS # Support TCP sign. Used for IPSec options TCP_SIGNATURE # There was stackoverflow found in KAME IPSec stack: # See http://secunia.com/advisories/43995/ # For quick workaround you can use `ipfw add deny proto ipcomp` options IPSEC # This ones can be loaded as modules. They described in loader.conf section #options ACCEPT_FILTER_DATA #options ACCEPT_FILTER_HTTP # Adding ipfw, also can be loaded as modules options IPFIREWALL # On 8.1+ you can disable verbose to see blocked packets on ipfw0 interface. # Also there is no point in compiling verbose into the kernel, because # now there is net.inet.ip.fw.verbose tunable. #options IPFIREWALL_VERBOSE #options IPFIREWALL_VERBOSE_LIMIT=10 options IPFIREWALL_FORWARD # Adding kernel NAT options IPFIREWALL_NAT options LIBALIAS # Traffic shaping options DUMMYNET # Divert, i.e. for userspace NAT options IPDIVERT # This is for OpenBSD's pf firewall device pf device pflog # pf's QoS - ALTQ options ALTQ options ALTQ_CBQ # Class Bases Queuing (CBQ) options ALTQ_RED # Random Early Detection (RED) options ALTQ_RIO # RED In/Out options ALTQ_HFSC # Hierarchical Packet Scheduler (HFSC) options ALTQ_PRIQ # Priority Queuing (PRIQ) options ALTQ_NOPCC # Required for SMP build # Pretty console # Manual can be found here http://forums.freebsd.org/showthread.php?t=6134 #options VESA #options SC_PIXEL_MODE # Disable reboot on Ctrl Alt Del #options SC_DISABLE_REBOOT # Change normal|kernel messages color options SC_NORM_ATTR=(FG_GREEN|BG_BLACK) options SC_KERNEL_CONS_ATTR=(FG_YELLOW|BG_BLACK) # More scroll space options SC_HISTORY_SIZE=8192 # Adding hardware crypto device device crypto device cryptodev # Useful network interfaces device vlan device tap #Virtual Ethernet driver device gre #IP over IP tunneling device if_bridge #Bridge interface device pfsync #synchronization interface for PF device carp #Common Address Redundancy Protocol device enc #IPsec interface device lagg #Link aggregation interface device stf #IPv4-IPv6 port # Also for my notebook, but may be used with Opteron device amdtemp # Same for Intel processors device coretemp # man 4 cpuctl device cpuctl # CPU control pseudo-device # Support for ECMP. More than one route for destination # Works even with default route so one can use it as LB for two ISP # For now code is unstable and panics (panic: rtfree 2) on route deletions. #options RADIX_MPATH # Multicast routing #options MROUTING #options PIM # Debug & DTrace options KDB # Kernel debugger related code options KDB_TRACE # Print a stack trace for a panic options KDTRACE_FRAME # amd64-only(?) options KDTRACE_HOOKS # all architectures - enable general DTrace hooks #options DDB #options DDB_CTF # all architectures - kernel ELF linker loads CTF data # Adaptive spining in lockmgr (8.x+) # See http://www.mail-archive.com/[email protected]/msg10782.html options ADAPTIVE_LOCKMGRS # UTF-8 in console (8.x+) #options TEKEN_UTF8 # FreeBSD 8.1+ # Deadlock resolver thread # For additional information see http://www.mail-archive.com/[email protected]/msg18124.html # (FYI: "resolution" is panic so use with caution) #options DEADLKRES # Increase maximum size of Raw I/O and sendfile(2) readahead #options MAXPHYS=(1024*1024) #options MAXBSIZE=(1024*1024) # For scheduler debug enable following option. # Debug will be available via `kern.sched.stats` sysctl # For more information see http://svnweb.freebsd.org/base/head/sys/conf/NOTES?view=markup #options SCHED_STATS If you are tuning network for maximum performance you may wish to play with ifconfig options like: # You can list all capabilities via `ifconfig -m` ifconfig [-]rxcsum [-]txcsum [-]tso [-]lro mtu In case you've enabled DDB in kernel config, you should edit your /etc/ddb.conf and add something like this to enable automatic reboot (and textdump as bonus): script kdb.enter.panic=textdump set; capture on; show pcpu; bt; ps; alltrace; capture off; call doadump; reset script kdb.enter.default=textdump set; capture on; bt; ps; capture off; call doadump; reset And do not forget to add ddb_enable="YES" to /etc/rc.conf Since FreeBSD 9 you can select to enable/disable flowcontrol on your NIC: # See http://en.wikipedia.org/wiki/Ethernet_flow_control and # http://www.mail-archive.com/[email protected]/msg07927.html for additional info ifconfig bge0 media auto mediaopt flowcontrol PS. Also most of FreeBSD's limits can be monitored by # vmstat -z and # limits PPS. variety of network counters can be monitored via # netstat -s In FreeBSD-9 netstat's -Q option appeared, try following command to display netisr stats # netstat -Q PPPS. also see # man 7 tuning PPPPS. I wanted to thank FreeBSD community, especially author of nginx - Igor Sysoev, nginx-ru@ and FreeBSD-performance@ mailing lists for providing useful information about FreeBSD tuning. FreeBSD WIP * Whats cooking for FreeBSD 7? * Whats cooking for FreeBSD 8? * Whats cooking for FreeBSD 9? So here is the question: What tunings are you using on yours FreeBSD servers? You can also post your /etc/sysctl.conf, /boot/loader.conf, kernel options, etc with description of its' meaning (do not copy-paste from sysctl -d). Don't forget to specify server type (web, smb, gateway, etc) Let's share experience!

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• Why do I get Detached Entity exception when upgrading Spring Boot 1.1.4 to 1.1.5

  - by mmeany

  On updating Spring Boot from 1.1.4 to 1.1.5 a simple web application started generating detached entity exceptions. Specifically, a post authentication inteceptor that bumped number of visits was causing the problem. A quick check of loaded dependencies showed that Spring Data has been updated from 1.6.1 to 1.6.2 and a further check of the change log shows a couple of issues relating to optimistic locking, version fields and JPA issues that have been fixed. Well I am using a version field and it starts out as Null following recommendation to not set in the specification. I have produced a very simple test scenario where I get detached entity exceptions if the version field starts as null or zero. If I create an entity with version 1 however then I do not get these exceptions. Is this expected behaviour or is there still something amiss? Below is the test scenario I have for this condition. In the scenario the service layer that has been annotated @Transactional. Each test case makes multiple calls to the service layer - the tests are working with detached entities as this is the scenario I am working with in the full blown application. The test case comprises four tests: Test 1 - versionNullCausesAnExceptionOnUpdate() In this test the version field in the detached object is Null. This is how I would usually create the object prior to passing to the service. This test fails with a Detached Entity exception. I would have expected this test to pass. If there is a flaw in the test then the rest of the scenario is probably moot. Test 2 - versionZeroCausesExceptionOnUpdate() In this test I have set the version to value Long(0L). This is an edge case test and included because I found reference to Zero values being used for version field in the Spring Data change log. This test fails with a Detached Entity exception. Of interest simply because the following two tests pass leaving this as an anomaly. Test 3 - versionOneDoesNotCausesExceptionOnUpdate() In this test the version field is set to value Long(1L). Not something I would usually do, but considering the notes in the Spring Data change log I decided to give it a go. This test passes. Would not usually set the version field, but this looks like a work-around until I figure out why the first test is failing. Test 4 - versionOneDoesNotCausesExceptionWithMultipleUpdates() Encouraged by the result of test 3 I pushed the scenario a step further and perform multiple updates on the entity that started life with a version of Long(1L). This test passes. Reinforcement that this may be a useable work-around. The entity: package com.mvmlabs.domain; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; import javax.persistence.Version; @Entity @Table(name="user_details") public class User { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; @Version private Long version; @Column(nullable = false, unique = true) private String username; @Column(nullable = false) private Integer numberOfVisits; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public Long getVersion() { return version; } public void setVersion(Long version) { this.version = version; } public Integer getNumberOfVisits() { return numberOfVisits == null ? 0 : numberOfVisits; } public void setNumberOfVisits(Integer numberOfVisits) { this.numberOfVisits = numberOfVisits; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } } The repository: package com.mvmlabs.dao; import org.springframework.data.repository.CrudRepository; import com.mvmlabs.domain.User; public interface UserDao extends CrudRepository<User, Long>{ } The service interface: package com.mvmlabs.service; import com.mvmlabs.domain.User; public interface UserService { User save(User user); User loadUser(Long id); User registerVisit(User user); } The service implementation: package com.mvmlabs.service; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import org.springframework.transaction.annotation.Propagation; import org.springframework.transaction.annotation.Transactional; import org.springframework.transaction.support.TransactionSynchronizationManager; import com.mvmlabs.dao.UserDao; import com.mvmlabs.domain.User; @Service @Transactional(propagation=Propagation.REQUIRED, readOnly=false) public class UserServiceJpaImpl implements UserService { @Autowired private UserDao userDao; @Transactional(readOnly=true) @Override public User loadUser(Long id) { return userDao.findOne(id); } @Override public User registerVisit(User user) { user.setNumberOfVisits(user.getNumberOfVisits() + 1); return userDao.save(user); } @Override public User save(User user) { return userDao.save(user); } } The application class: package com.mvmlabs; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.EnableAutoConfiguration; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; @Configuration @ComponentScan @EnableAutoConfiguration public class Application { public static void main(String[] args) { SpringApplication.run(Application.class, args); } } The POM: <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.mvmlabs</groupId> <artifactId>jpa-issue</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>spring-boot-jpa-issue</name> <description>JPA Issue between spring boot 1.1.4 and 1.1.5</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.1.5.RELEASE</version> <relativePath /> <!-- lookup parent from repository --> </parent> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>org.hsqldb</groupId> <artifactId>hsqldb</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> </dependencies> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <start-class>com.mvmlabs.Application</start-class> <java.version>1.7</java.version> </properties> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> The application properties: spring.jpa.hibernate.ddl-auto: create spring.jpa.hibernate.naming_strategy: org.hibernate.cfg.ImprovedNamingStrategy spring.jpa.database: HSQL spring.jpa.show-sql: true spring.datasource.url=jdbc:hsqldb:file:./target/testdb spring.datasource.username=sa spring.datasource.password= spring.datasource.driverClassName=org.hsqldb.jdbcDriver The test case: package com.mvmlabs; import org.junit.Assert; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.SpringApplicationConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import com.mvmlabs.domain.User; import com.mvmlabs.service.UserService; @RunWith(SpringJUnit4ClassRunner.class) @SpringApplicationConfiguration(classes = Application.class) public class ApplicationTests { @Autowired UserService userService; @Test public void versionNullCausesAnExceptionOnUpdate() throws Exception { User user = new User(); user.setUsername("Version Null"); user.setNumberOfVisits(0); user.setVersion(null); user = userService.save(user); user = userService.registerVisit(user); Assert.assertEquals(new Integer(1), user.getNumberOfVisits()); Assert.assertEquals(new Long(1L), user.getVersion()); } @Test public void versionZeroCausesExceptionOnUpdate() throws Exception { User user = new User(); user.setUsername("Version Zero"); user.setNumberOfVisits(0); user.setVersion(0L); user = userService.save(user); user = userService.registerVisit(user); Assert.assertEquals(new Integer(1), user.getNumberOfVisits()); Assert.assertEquals(new Long(1L), user.getVersion()); } @Test public void versionOneDoesNotCausesExceptionOnUpdate() throws Exception { User user = new User(); user.setUsername("Version One"); user.setNumberOfVisits(0); user.setVersion(1L); user = userService.save(user); user = userService.registerVisit(user); Assert.assertEquals(new Integer(1), user.getNumberOfVisits()); Assert.assertEquals(new Long(2L), user.getVersion()); } @Test public void versionOneDoesNotCausesExceptionWithMultipleUpdates() throws Exception { User user = new User(); user.setUsername("Version One Multiple"); user.setNumberOfVisits(0); user.setVersion(1L); user = userService.save(user); user = userService.registerVisit(user); user = userService.registerVisit(user); user = userService.registerVisit(user); Assert.assertEquals(new Integer(3), user.getNumberOfVisits()); Assert.assertEquals(new Long(4L), user.getVersion()); } } The first two tests fail with detached entity exception. The last two tests pass as expected. Now change Spring Boot version to 1.1.4 and rerun, all tests pass. Are my expectations wrong? Edit: This code saved to GitHub at https://github.com/mmeany/spring-boot-detached-entity-issue

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• DB2 insert performance - How to measure

  - by svrist

  [From stackoverflow] Im trying to find a way to speedup my inserts to a DB2 9.7.1 (ubuntu linux) Im watching vmstat and trying to gather some statistics via the db2 get snapshot commands but im not able to figure out which numbers im looking for to be able to see where the trouble is. I've read lits of stuff like http://www.eggheadcafe.com/software/aspnet/35692526/question-multiple-row-in.aspx, and http://www.ibm.com/developerworks/data/library/tips/dm-0403wilkins/ and tricks like ALTER TABLE lalala APPEND ON works somewhat (the difference between a dd if=/dev/zero and insert is still a factor 10) but I would like to be able to find the counters or other performance indicators that actually show why it makes sense to use those tricks. For example: What is the metric called that shows me that it is buffer pages allocation (FSCR stuff) that is the problem Where do I see that the insert time is hampered by clustered indexes? I find db2top very useful but im still searching for more direct view of "this is your bottleneck" methods

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• How to use BCDEdit to dual boot Windows installations?

  - by Ian Boyd

  What are the bcdedit commands necessary to setup dual boot between different installations of Windows?5 Background i recently installed Windows 8 onto a separate hard drive1. Now that Windows 8 in installed i want to dual-boot back to Windows 7. i have my two2 hard drives: So you can see that i have my two disks, with the partitions containing Windows: Windows 7: \\PhysicalDisk0 (partition 03) Windows 8: \\PhysicalDisk2 (partition 1) What i'm trying to figure out how is how to use bcdedit to instruct the thing that boots Windows that there is another Windows installation out there. Running bcdedit now, it shows current configuration: C:\WINDOWS\system32>bcdedit Windows Boot Manager -------------------- identifier {bootmgr} device partition=\Device\HarddiskVolume2 description Windows Boot Manager locale en-US inherit {globalsettings} integrityservices Enable default {current} resumeobject {ce153eb7-3786-11e2-87c0-e740e123299f} displayorder {current} toolsdisplayorder {memdiag} timeout 30 Windows Boot Loader ------------------- identifier {current} device partition=C: path \WINDOWS\system32\winload.exe description Windows 8 locale en-US inherit {bootloadersettings} recoverysequence {ce153eb9-3786-11e2-87c0-e740e123299f} integrityservices Enable recoveryenabled Yes allowedinmemorysettings 0x15000075 osdevice partition=C: systemroot \WINDOWS resumeobject {ce153eb7-3786-11e2-87c0-e740e123299f} nx OptIn bootmenupolicy Standard hypervisorlaunchtype Auto i cannot find any documentation on the difference between Windows Boot Manager and Windows Boot Loader. Documentation There is some documentation on Bcdedit: Technet: Command Line Reference - Bcdedit Technet: Windows Automated Installation Kit - BCDEdit Command Line Options Whitepaper - BCDEdit Commands for Boot Environment (Word Document) But they don't explain how edit the binary boot configuration data If i had to guess, i would think that a Windows Boot Manager instructs the BIOS what program it should run. That program would give the user a set of boot choices. That leaves Windows Boot Loader do be a particular boot choice, that represents a particular installation of Windows. If that is the case i would need to create a new Windows Boot Loader entry. This means i might want to use the /create parameter: /create Creates a new boot entry: bcdedit [/store filename] /create [id] /d description [/application apptype | /inherit [apptype] | /inherit DEVICE | /device] So i assume a syntax of: >bcdedit /create /d "The old Windows 7" /application osloader Where application can be one of the following types: Apptype Description BOOTSECTOR The boot sector application OSLOADER The Windows boot loader RESUME A resume application Unfortunately, the only documentation about osloader is "The Windows boot loader". i don't see how that can differentiate between Windows 8 on one hard drive, and Windows 7 on another. The other possible parameter when /create a boot loader is >bcdedit /create /D "Windows Vista" /device "The Quick Brown Fox" Unfortunately the documentation is missing for /device: /device Optional. If id is not set to a well-known identifier, the option that is used to specify the new boot entry as an additional device options entry. Since i did not set id to a well-known identifier, i must set /device to "the option that is used to specify the new boot entry as an additional device options entry". i know all those words; they're all English. But i have on idea what it is saying; those words in that order seem nonsensical. So i'm somewhat stymied. i don't want to be like Dan Stolts from Microsoft: I found no content that was particularly helpful when I hosed my machine by playing with BCDEdit. This post would have been ok if there was much more detail especially on the /set command OSDevice, etc. So once I got my machine fixed, I documented the solution and the information is here.... i mean, if a Microsoft guy can't even figure out how to use BCDEdit to edit his BCD, then what chance to i have? Bonus Reading BCDEdit Command-Line Options Bcdedit Server 2008 R2 or Windows 7 System Will NOT Boot After Making Changes To Boot Manager Using BCDEdit Visual BCD Editor4 Windows 7 and Windows 8 RTM Dual Boot Setup Footnotes 1 Since the Windows 8 installer would have damaged my Windows 7 install, i decided to unplug my "main" hard drive during the install. Which is a long-winded explanation of why the Windows 8 installer didn't detect the existing Windows 7 install. Normally the installer would have automatically created the required entries for dual-boot. Not that the reason i'm asking the question is important. 2 Really there's three drives, but the third is just bulk storage. The existence of a 3rd hard drive is irrelevant to the question. i only mention it in case someone wants to know why the screenshot has 3 hard drives when i only mention two. 3 i arbitrarily started numbering partitions at "zero"; not to imply that partitions are numbered starting at zero. i only mention partitions because i don't see how any boot-loader could do its job without knowing which partition, and which folder, an installation of Windows is located in. 4 i'm asking about BCDEdit. i tried Visual BCD Editor. It seems to be a visual BCD editor. That is to say that it's a GUI, but still uses the same terminology as BCDEdit, and requires the same knowledge that BCD doesn't document. 5 For simplicity sake we'll assume that all installation of Windows i want to dual-boot between are Windows Vista or later, making them all compatible with the BCDEdit and the binary boot loader. The alternative would require delving into the intricacies of the old ntloader. Nor am i asking about dual booting to Linux; or how to boot to a Virtual Hard Drive (vhd) image. Just modern versions of Windows on existing hard drives in the same machine. Note: You can ignore everything after the word Background. It's all pointless exposition to satisfy some people's need for "research effort" before they'll consider being helpful. Some people have even been known to summarily close questions unless there is research effort. Some people have been know to close questions if there is too much research effort. Some people close questions when i put the note saying that they can ignore everything after the Background out of spite. Some people are just grumpy.

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• ESXi and Windows Server CPU parking

  - by Chris J

  For those that don't know, CPU parking is a feature in recent Windows Server releases that allows Windows to pretty much drop a CPU core to zero use, and having nothing use it. It's been introduced as a power-saving measure. There's more detail about it here, amongst other places. However what I'm curious about is whether this matter on a virtualised guest - or is CPU parking more of a hindrance than a help, given that the physical CPUs are managed by ESXi, not Windows, and that a parked CPU is less likely to deal with traffic unless the scheduler deems there's enough work to unpark the CPU? I've not found anything about this - I do suspect it will be very much based on a given workload, but I've not seen any discussion (unlike, say, whether hyper-threading has any effect, which seems to be discussed regularly). Whilst I do understand the "test with your workload" I was wondering if there was any advice/guidelines out there that I've missed.

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• Removing duplicate images (deduplication) - calculating "overlap" of images

  - by jotango

  Hello, I have a ton of product images on our file system. Our code removes 100% identical images (or does not allow them to be uploaded). However our sellers often upload items pictures which are very similar, but not exactly. They could have more whitespace, a worse quality (compression), a different size etc. Is there any way I can calculate the degree of overlap between two images, to flag ones for deletion? Kind of like a Levenshtein distance between two images... Any pointers would be very cool. Thanks!

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• What's the most efficient way to reclaim disk space after deleting lots of data from a database on Sybase ASE 15?

  - by Ernie Longmire

  As I understand it, based on some research but zero real-world experience with Sybase ASE, the only way to reclaim disk space once it's been allocated to a database is to export that database, create a new DB with the same schema, and reload all the exported data to the new database. Is this correct, or is there some other method? Then: assuming the above is correct and a full export-recreate-reload is required, what's the most efficient way to do that? Are there tools that will automate all or part of that process? I'm being told we would have to write separate bcp export and import commands for each and every object in the database, which if true sounds easily scriptable by someone who knows Sybase ASE well enough. (I don't.) This seems to me like a really basic housekeeping task, and it feels like I'm missing something obvious.

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• How to connect two monitors to a macbook pro?

  - by CIRK

  I have a 13" macbook pro, and I need much more space right now, so I decided to buy two smaller monitors. (these from LG). But I don't really know how will I connect them. I've seen some products like this Diamond BVU195, but it's not currently in stores in my country. I've found these Equip 128450 USB 2.0 Display Adapter DELOCK USB 2.0 to DVI/VGA/HDMI Adapter The second one looks pretty cool, but it says that Windows is a system requirement or what, so I'm not sure if it will work with mac os x? So how did you connected multiple monitors to you mac, and are these adapters the best choices, if yes then is there an OS independent one?

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• How does DNS "get stuck"?

  - by Muhammad Mussnoon

  I recently registered a domain and got hosting from Dreamhost. But when even after three days, the website was not accessible, I contacted support about it. This is the response the support person gave me: "My apologies! The DNS had gotten stuck, so I went ahead and pushed that through for you. Please allow 2-3 hours for the DNS to propagate." Now I have to say that my knowledge regarding these things is virtually zero, and I couldn't understand what the support person meant, so I ran a search and it seemed that Mr. Google knew just as much as I did regarding this. Can someone tell me what "dns getting stuck" means?

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• KVM slow guest i/o

  - by Akarot

  Host: Debian 6.0 (squeeze) with qemu-kvm and libvirt from squeeze-backports ii qemu-kvm 1.0+dfsg-8~bpo60+1 ii libvirt-bin 0.9.8-2~bpo60+2 Has 3TB sata drives with software raid and lvm. It has a sequential write speed of ~140MB/s measured with dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync Elevator set to cfq Guest Debian 6.0 (squeeze) Uses LVM as storage. Drivers are virtio and cache='none' Sequential write speed is considerably slower with only 25-50MB/s Elevator set to noop I'm kind of running out of ideas for further tweaks but I'm sure that I/O speed should be much faster because many people are reporting almost native performance with lvm.

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