Search Results

Search found 13867 results on 555 pages for 'avoid learning'.

Page 149/555 | < Previous Page | 145 146 147 148 149 150 151 152 153 154 155 156  | Next Page >

• Can my ikmnet test results say something about career choice I should take?

  - by Nicke

  I took 2 tests via ikmnet and scored 70 % on SQL and 65 % on Java. While not bad, it can be improved. The subskills I need to improve according to the test are interfaces and inheritance, compilation and deployment, flow control, The java.lang package and "Java Program Construction" and these topics seems rather broad to me. Rather than just learning by programming, could you advice me to take a certification, follow a course or otherwise improve my skills? By the way, I enjoy python more than Java so should I market myself more of a python programmer or even a role that some companies search for which seems like a system developer with more technical writing where the title is system analysts (evaluating systems in cooperation with management rather than programming.) Thank you for any comment and/or answer.

  Read the article

• Modern programming language with intuitive concurrent programming abstractions

  - by faif

  I am interested in learning concurrent programming, focusing on the application/user level (not system programming). I am looking for a modern high level programming language that provides intuitive abstractions for writing concurrent applications. I want to focus on languages that increase productivity and hide the complexity of concurrent programming. To give some examples, I don't consider a good option writing multithreaded code in C, C++, or Java because IMHO my productivity is reduced and their programming model is not intuitive. On the other hand, languages that increase productivity and offer more intuitive abstractions such as Python and the multiprocessing module, Erlang, Clojure, Scala, etc. would be good options. What would you recommend based on your experience and why?

  Read the article

• What is the most efficient way to convert to binary and back in C#?

  - by Saad Imran.

  I'm trying to write a general purpose socket server for a game I'm working on. I know I could very well use already built servers like SmartFox and Photon, but I wan't to go through the pain of creating one myself for learning purposes. I've come up with a BSON inspired protocol to convert the the basic data types, their arrays, and a special GSObject to binary and arrange them in a way so that it can be put back together into object form on the client end. At the core, the conversion methods utilize the .Net BitConverter class to convert the basic data types to binary. Anyways, the problem is performance, if I loop 50,000 times and convert my GSObject to binary each time it takes about 5500ms (the resulting byte[] is just 192 bytes per conversion). I think think this would be way too slow for an MMO that sends 5-10 position updates per second with a 1000 concurrent users. Yes, I know it's unlikely that a game will have a 1000 users on at the same time, but like I said earlier this is supposed to be a learning process for me, I want to go out of my way and build something that scales well and can handle at least a few thousand users. So yea, if anyone's aware of other conversion techniques or sees where I'm loosing performance I would appreciate the help. GSBitConverter.cs This is the main conversion class, it adds extension methods to main datatypes to convert to the binary format. It uses the BitConverter class to convert the base types. I've shown only the code to convert integer and integer arrays, but the rest of the method are pretty much replicas of those two, they just overload the type. public static class GSBitConverter { public static byte[] ToGSBinary(this short value) { return BitConverter.GetBytes(value); } public static byte[] ToGSBinary(this IEnumerable<short> value) { List<byte> bytes = new List<byte>(); short length = (short)value.Count(); bytes.AddRange(length.ToGSBinary()); for (int i = 0; i < length; i++) bytes.AddRange(value.ElementAt(i).ToGSBinary()); return bytes.ToArray(); } public static byte[] ToGSBinary(this bool value); public static byte[] ToGSBinary(this IEnumerable<bool> value); public static byte[] ToGSBinary(this IEnumerable<byte> value); public static byte[] ToGSBinary(this int value); public static byte[] ToGSBinary(this IEnumerable<int> value); public static byte[] ToGSBinary(this long value); public static byte[] ToGSBinary(this IEnumerable<long> value); public static byte[] ToGSBinary(this float value); public static byte[] ToGSBinary(this IEnumerable<float> value); public static byte[] ToGSBinary(this double value); public static byte[] ToGSBinary(this IEnumerable<double> value); public static byte[] ToGSBinary(this string value); public static byte[] ToGSBinary(this IEnumerable<string> value); public static string GetHexDump(this IEnumerable<byte> value); } Program.cs Here's the the object that I'm converting to binary in a loop. class Program { static void Main(string[] args) { GSObject obj = new GSObject(); obj.AttachShort("smallInt", 15); obj.AttachInt("medInt", 120700); obj.AttachLong("bigInt", 10900800700); obj.AttachDouble("doubleVal", Math.PI); obj.AttachStringArray("muppetNames", new string[] { "Kermit", "Fozzy", "Piggy", "Animal", "Gonzo" }); GSObject apple = new GSObject(); apple.AttachString("name", "Apple"); apple.AttachString("color", "red"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.5); GSObject lemon = new GSObject(); apple.AttachString("name", "Lemon"); apple.AttachString("color", "yellow"); apple.AttachBool("inStock", false); apple.AttachFloat("price", (float)0.8); GSObject apricoat = new GSObject(); apple.AttachString("name", "Apricoat"); apple.AttachString("color", "orange"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)1.9); GSObject kiwi = new GSObject(); apple.AttachString("name", "Kiwi"); apple.AttachString("color", "green"); apple.AttachBool("inStock", true); apple.AttachFloat("price", (float)2.3); GSArray fruits = new GSArray(); fruits.AddGSObject(apple); fruits.AddGSObject(lemon); fruits.AddGSObject(apricoat); fruits.AddGSObject(kiwi); obj.AttachGSArray("fruits", fruits); Stopwatch w1 = Stopwatch.StartNew(); for (int i = 0; i < 50000; i++) { byte[] b = obj.ToGSBinary(); } w1.Stop(); Console.WriteLine(BitConverter.IsLittleEndian ? "Little Endian" : "Big Endian"); Console.WriteLine(w1.ElapsedMilliseconds + "ms"); } Here's the code for some of my other classes that are used in the code above. Most of it is repetitive. GSObject GSArray GSWrappedObject

  Read the article

• How to Configure Ubuntu’s Built-In Firewall

  - by Chris Hoffman

  Ubuntu includes its own firewall, known as ufw – short for “uncomplicated firewall.” Ufw is an easier-to-use frontend for the standard Linux iptables commands. You can even control ufw from a graphical interface. Ubuntu’s firewall is designed as an easy way to perform basic firewall tasks without learning iptables. It doesn’t offer all the power of the standard iptables commands, but it’s less complex. HTG Explains: Why Linux Doesn’t Need Defragmenting How to Convert News Feeds to Ebooks with Calibre How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More

  Read the article

• Introduction to Reading Electronics Schematics [Video]

  - by Jason Fitzpatrick

  If you’re interested in electronics tinkering but a bit overwhelmed by learning electronics schematics, this helpful introductory video will get you started. Courtesy of Make magazine, this video tutorial covers what a schematic is, how schematics are laid out, and the basics of reading a schematic and its component symbols. When you’re done with the video you’ll have a better grasp of electronics circuit schematics than most of the population and, hopefully, and increased comfort reading schematics for all those DIY projects we post here. Collin’s Lab: Schematics [Make via Hacked Gadgets] HTG Explains: When Do You Need to Update Your Drivers? How to Make the Kindle Fire Silk Browser *Actually* Fast! Amazon’s New Kindle Fire Tablet: the How-To Geek Review

  Read the article

• An MCM exam, Rob? Really?

  - by Rob Farley

  I took the SQL 2008 MCM Knowledge exam while in Seattle for the PASS Summit ten days ago. I wasn’t planning to do it, but I got persuaded to try. I was meaning to write this post to explain myself before the result came out, but it seems I didn’t get typing quickly enough. Those of you who know me will know I’m a big fan of certification, to a point. I’ve been involved with Microsoft Learning to help create exams. I’ve kept my certifications current since I first took an exam back in 1998, sitting many in beta, across quite a variety of topics. I’ve probably become quite good at them – I know I’ve definitely passed some that I really should’ve failed. I’ve also written that I don’t think exams are worth studying for. (That’s probably not entirely true, but it depends on your motivation. If you’re doing learning, I would encourage you to focus on what you need to know to do your job better. That will help you pass an exam – but the two skills are very different. I can coach someone on how to pass an exam, but that’s a different kind of teaching when compared to coaching someone about how to do a job. For example, the real world includes a lot of “it depends”, where you develop a feel for what the influencing factors might be. In an exam, its better to be able to know some of the “Don’t use this technology if XYZ is true” concepts better.) As for the Microsoft Certified Master certification… I’m not opposed to the idea of having the MCM (or in the future, MCSM) cert. But the barrier to entry feels quite high for me. When it was first introduced, the nearest testing centres to me were in Kuala Lumpur and Manila. Now there’s one in Perth, but that’s still a big effort. I know there are options in the US – such as one about an hour’s drive away from downtown Seattle, but it all just seems too hard. Plus, these exams are more expensive, and all up – I wasn’t sure I wanted to try them, particularly with the fact that I don’t like to study. I used to study for exams. It would drive my wife crazy. I’d have some exam scheduled for some time in the future (like the time I had two booked for two consecutive days at TechEd Australia 2005), and I’d make sure I was ready. Every waking moment would be spent pouring over exam material, and it wasn’t healthy. I got shaken out of that, though, when I ended up taking four exams in those two days in 2005 and passed them all. I also worked out that if I had a Second Shot available, then failing wasn’t a bad thing at all. Even without Second Shot, I’m much more okay about failing. But even just trying an MCM exam is a big effort. I wouldn’t want to fail one of them. Plus there’s the illusion to maintain. People have told me for a long time that I should just take the MCM exams – that I’d pass no problem. I’ve never been so sure. It was almost becoming a pride-point. Perhaps I should fail just to demonstrate that I can fail these things. Anyway – boB Taylor (@sqlboBT) persuaded me to try the SQL 2008 MCM Knowledge exam at the PASS Summit. They set up a testing centre in one of the room there, so it wasn’t out of my way at all. I had to squeeze it in between other commitments, and I certainly didn’t have time to even see what was on the syllabus, let alone study. In fact, I was so exhausted from the week that I fell asleep at least once (just for a moment though) during the actual exam. Perhaps the questions need more jokes, I’m not sure. I knew if I failed, then I might disappoint some people, but that I wouldn’t’ve spent a great deal of effort in trying to pass. On the other hand, if I did pass I’d then be under pressure to investigate the MCM Lab exam, which can be taken remotely (therefore, a much smaller amount of effort to make happen). In some ways, passing could end up just putting a bunch more pressure on me. Oh, and I did.

  Read the article

• C#/.NET Little Wonders: The EventHandler and EventHandler&lt;TEventArgs&gt; delegates

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the last two weeks, we examined the Action family of delegates (and delegates in general), and the Func family of delegates and how they can be used to support generic, reusable algorithms and classes. So this week, we are going to look at a handy pair of delegates that can be used to eliminate the need for defining custom delegates when creating events: the EventHandler and EventHandler<TEventArgs> delegates. Events and delegates Before we begin, let’s quickly consider events in .NET.  According to the MSDN: An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. So, basically, you can create an event in a type so that users of that type can subscribe to notifications of things of interest.  How is this different than some of the delegate programming that we talked about in the last two weeks?  Well, you can think of an event as a special access modifier on a delegate.  Some differences between the two are: Events are a special access case of delegates They behave much like delegates instances inside the type they are declared in, but outside of that type they can only be (un)subscribed to. Events can specify add/remove behavior explicitly If you want to do additional work when someone subscribes or unsubscribes to an event, you can specify the add and remove actions explicitly. Events have access modifiers, but these only specify the access level of those who can (un)subscribe A public event, for example, means anyone can (un)subscribe, but it does not mean that anyone can raise (invoke) the event directly.  Events can only be raised by the type that contains them In contrast, if a delegate is visible, it can be invoked outside of the object (not even in a sub-class!). Events tend to be for notifications only, and should be treated as optional Semantically speaking, events typically don’t perform work on the the class directly, but tend to just notify subscribers when something of note occurs. My basic rule-of-thumb is that if you are just wanting to notify any listeners (who may or may not care) that something has happened, use an event.  However, if you want the caller to provide some function to perform to direct the class about how it should perform work, make it a delegate. Declaring events using custom delegates To declare an event in a type, we simply use the event keyword and specify its delegate type.  For example, let’s say you wanted to create a new TimeOfDayTimer that triggers at a given time of the day (as opposed to on an interval).  We could write something like this: 1: public delegate void TimeOfDayHandler(object source, ElapsedEventArgs e); 2:  3: // A timer that will fire at time of day each day. 4: public class TimeOfDayTimer : IDisposable 5: { 6: // Event that is triggered at time of day. 7: public event TimeOfDayHandler Elapsed; 8:  9: // ... 10: } The first thing to note is that the event is a delegate type, which tells us what types of methods may subscribe to it.  The second thing to note is the signature of the event handler delegate, according to the MSDN: The standard signature of an event handler delegate defines a method that does not return a value, whose first parameter is of type Object and refers to the instance that raises the event, and whose second parameter is derived from type EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. So, in a nutshell, the event handler delegates should return void and take two parameters: An object reference to the object that raised the event. An EventArgs (or a subclass of EventArgs) reference to event specific information. Even if your event has no additional information to provide, you are still expected to provide an EventArgs instance.  In this case, feel free to pass the EventArgs.Empty singleton instead of creating new instances of EventArgs (to avoid generating unneeded memory garbage). The EventHandler delegate Because many events have no additional information to pass, and thus do not require custom EventArgs, the signature of the delegates for subscribing to these events is typically: 1: // always takes an object and an EventArgs reference 2: public delegate void EventHandler(object sender, EventArgs e) It would be insane to recreate this delegate for every class that had a basic event with no additional event data, so there already exists a delegate for you called EventHandler that has this very definition!  Feel free to use it to define any events which supply no additional event information: 1: public class Cache 2: { 3: // event that is raised whenever the cache performs a cleanup 4: public event EventHandler OnCleanup; 5:  6: // ... 7: } This will handle any event with the standard EventArgs (no additional information).  But what of events that do need to supply additional information?  Does that mean we’re out of luck for subclasses of EventArgs?  That’s where the generic for of EventHandler comes into play… The generic EventHandler<TEventArgs> delegate Starting with the introduction of generics in .NET 2.0, we have a generic delegate called EventHandler<TEventArgs>.  Its signature is as follows: 1: public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e) 2: where TEventArgs : EventArgs This is similar to EventHandler except it has been made generic to support the more general case.  Thus, it will work for any delegate where the first argument is an object (the sender) and the second argument is a class derived from EventArgs (the event data). For example, let’s say we wanted to create a message receiver, and we wanted it to have a few events such as OnConnected that will tell us when a connection is established (probably with no additional information) and OnMessageReceived that will tell us when a new message arrives (probably with a string for the new message text). So for OnMessageReceived, our MessageReceivedEventArgs might look like this: 1: public sealed class MessageReceivedEventArgs : EventArgs 2: { 3: public string Message { get; set; } 4: } And since OnConnected needs no event argument type defined, our class might look something like this: 1: public class MessageReceiver 2: { 3: // event that is called when the receiver connects with sender 4: public event EventHandler OnConnected; 5:  6: // event that is called when a new message is received. 7: public event EventHandler<MessageReceivedEventArgs> OnMessageReceived; 8:  9: // ... 10: } Notice, nowhere did we have to define a delegate to fit our event definition, the EventHandler and generic EventHandler<TEventArgs> delegates fit almost anything we’d need to do with events. Sidebar: Thread-safety and raising an event When the time comes to raise an event, we should always check to make sure there are subscribers, and then only raise the event if anyone is subscribed.  This is important because if no one is subscribed to the event, then the instance will be null and we will get a NullReferenceException if we attempt to raise the event. 1: // This protects against NullReferenceException... or does it? 2: if (OnMessageReceived != null) 3: { 4: OnMessageReceived(this, new MessageReceivedEventArgs(aMessage)); 5: } The above code seems to handle the null reference if no one is subscribed, but there’s a problem if this is being used in multi-threaded environments.  For example, assume we have thread A which is about to raise the event, and it checks and clears the null check and is about to raise the event.  However, before it can do that thread B unsubscribes to the event, which sets the delegate to null.  Now, when thread A attempts to raise the event, this causes the NullReferenceException that we were hoping to avoid! To counter this, the simplest best-practice method is to copy the event (just a multicast delegate) to a temporary local variable just before we raise it.  Since we are inside the class where this event is being raised, we can copy it to a local variable like this, and it will protect us from multi-threading since multicast delegates are immutable and assignments are atomic: 1: // always make copy of the event multi-cast delegate before checking 2: // for null to avoid race-condition between the null-check and raising it. 3: var handler = OnMessageReceived; 4: 5: if (handler != null) 6: { 7: handler(this, new MessageReceivedEventArgs(aMessage)); 8: } The very slight trade-off is that it’s possible a class may get an event after it unsubscribes in a multi-threaded environment, but this is a small risk and classes should be prepared for this possibility anyway.  For a more detailed discussion on this, check out this excellent Eric Lippert blog post on Events and Races. Summary Generic delegates give us a lot of power to make generic algorithms and classes, and the EventHandler delegate family gives us the flexibility to create events easily, without needing to redefine delegates over and over.  Use them whenever you need to define events with or without specialized EventArgs.   Tweet Technorati Tags: .NET, C#, CSharp, Little Wonders, Generics, Delegates, EventHandler

  Read the article

• Is it illegal to rewrite every line of an open source project in a slightly different way, and use it in a closed source project?

  - by optician

  There is some code which is GPL or LGPL that I am considering using for an iPhone project. If I took that code (javascript) and rewrote it in a different language for use on the iPhone would that be a legal issue? In theory the process that has happened is that I have gone through each line of the project, learnt what it is doing, and then re implemented the ideas in a new language. To me it seems this is like learning how to implement something, but then re-implementing it separate from the original licence. Therefore you have only copied the algorithm, which arguably you could have learnt from somewhere else other than the original project. Does the licence cover the specific implementation or the algorithm as well?

  Read the article

• 7 Web Design Tutorials from PSD to HTML/CSS

  - by Sushaantu

  Some time back when I was looking for some tutorials to create a website from scratch i.e. the process from designing the PSD to slice it and CSS/XHTML it, then not many quality results appeared. But that was like almost an year back and a lot of water has flown down the river Thanes since then. In this list I will give you links to some wonderful tutorials teaching you in a step by step way to design a website. These tutorials are ideal for someone who is learning web designing and has grasp of basic CSS, XHTML and little designing on Photoshop. How to Design and Code Web 2.0 Style Web Design Design a website from PSD to HTML Designing and Coding a Grunge Web Design from Scratch Creating a CSS layout from scratch Build a Sleek Portfolio Site from Scratch Designing and Coding a web design from scratch Design and Code a Dark and Sleek Web Design

  Read the article

• Guidance for a C# developer to become better UI developer

  - by Pankaj Upadhyay

  I am a C# developer and had developed simple websites in regular asp.net(with asp.net controls) and a wpf application. Nowadays, I am trying myself in Asp.net MVC3 and been exposed to the HTML with Razor view Engine. To be honest, I am not too good or I should awful at my knowledge of HTML and CSS. Therefore, I keep posting questions now and then on SO for very simple tasks. This has made me very tired of the this Q&A development process. So, now i am thinking of learning the basics of HTML, CSS and maybe some Javascript. Therefore i would request you to guide me to become an efficient enough developer for these technologies. Something that won't take much time and get me up and running fast.

  Read the article

• Is OpenGL after C++ job oriented?

  - by Ani

  First, my regards to all programmers out there who have put their endless efforts in learning and becoming expert, wise, efficient and best. Let me describe my situation. I have just graduated from Electronics and Communication Stream. Though I have more interest in software development and hence I have opted to become a software developer rather than Electronics engg. I have learned C++ and wish to wish to go more deep. I have started to learn OpenGL. Guide me in the following: Is OpenGL good to learn and is it job oriented? Should I learn some other language rather then OpenGL after C++?

  Read the article

• Day 1: iPhone Web Development

  - by BizTalk Visionary

  Preamble: In an attempt to keep an ageing mind alive I have decided to write an iPhone web app. The app will pull together a whole host of disciplines and should be a challenge. The App: Over the last month or so I have been playing around with Google maps and Instead (see InstaMapper.com) so decided the app must build on this learning. Looking to create an Uber-where’s Tigger! Framework: After an exhaustive research period I’m going with JQTouch. tPhone Simulator:   MobiOne More to follow later……

  Read the article

• Clustering Basics and Challenges

  - by Karoly Vegh

  For upcoming posts it seemed to be a good idea to dedicate some time for cluster basic concepts and theory. This post misses a lot of details that would explode the articlesize, should you have questions, do not hesitate to ask them in the comments.  The goal here is to get some concepts straight. I can't promise to give you an overall complete definitions of cluster, cluster agent, quorum, voting, fencing, split brain condition, so the following is more of an explanation. Here we go. -------- Cluster, HA, failover, switchover, scalability -------- An attempted definition of a Cluster: A cluster is a set (2+) server nodes dedicated to keep application services alive, communicating through the cluster software/framework with eachother, test and probe health status of servernodes/services and with quorum based decisions and with switchover/failover techniques keep the application services running on them available. That is, should a node that runs a service unexpectedly lose functionality/connection, the other ones would take over the and run the services, so that availability is guaranteed. To provide availability while strictly sticking to a consistent clusterconfiguration is the main goal of a cluster.  At this point we have to add that this defines a HA-cluster, a High-Availability cluster, where the clusternodes are planned to run the services in an active-standby, or failover fashion. An example could be a single instance database. Some applications can be run in a distributed or scalable fashion. In the latter case instances of the application run actively on separate clusternodes serving servicerequests simultaneously. An example for this version could be a webserver that forwards connection requests to many backend servers in a round-robin way. Or a database running in active-active RAC setup.  -------- Cluster arhitecture, interconnect, topologies -------- Now, what is a cluster made of? Servers, right. These servers (the clusternodes) need to communicate. This of course happens over the network, usually over dedicated network interfaces interconnecting all the clusternodes. These connection are called interconnects.How many clusternodes are in a cluster? There are different cluster topologies. The most simple one is a clustered pair topology, involving only two clusternodes:  There are several more topologies, clicking the image above will take you to the relevant documentation. Also, to answer the question Solaris Cluster allows you to run up to 16 servers in a cluster. Where shall these clusternodes be placed? A very important question. The right answer is: It depends on what you plan to achieve with the cluster. Do you plan to avoid only a server outage? Then you can place them right next to eachother in the datacenter. Do you need to avoid DataCenter outage? In that case of course you should place them at least in different fire zones. Or in two geographically distant DataCenters to avoid disasters like floods, large-scale fires or power outages. We call this a stretched- or campus cluster, the clusternodes being several kilometers away from eachother. To cover really large distances, you probably need to move to a GeoCluster, which is a different kind of animal.  What is a geocluster? A Geographic Cluster in Solaris Cluster terms is actually a metacluster between two, separate (locally-HA) clusters.  -------- Cluster resource types, agents, resources, resource groups -------- So how does the cluster manage my applications? The cluster needs to start, stop and probe your applications. If you application runs, the cluster needs to check regularly if the application state is healthy, does it respond over the network, does it have all the processes running, etc. This is called probing. If the cluster deems the application is in a faulty state, then it can try to restart it locally or decide to switch (stop on node A, start on node B) the service. Starting, stopping and probing are the three actions that a cluster agent does. There are many different kinds of agents included in Solaris Cluster, but you can build your own too. Examples are an agent that manages (mounts, moves) ZFS filesystems, or the Oracle DB HA agent that cares about the database, or an agent that moves a floating IP address between nodes. There are lots of other agents included for Apache, Tomcat, MySQL, Oracle DB, Oracle Weblogic, Zones, LDoms, NFS, DNS, etc.We also need to clarify the difference between a cluster resource and the cluster resource group.A cluster resource is something that is managed by a cluster agent. Cluster resource types are included in Solaris cluster (see above, e.g. HAStoragePlus, HA-Oracle, LogicalHost). You can group cluster resources into cluster resourcegroups, and switch these groups together from one node to another. To stick to the example above, to move an Oracle DB service from one node to another, you have to switch the group between nodes, and the agents of the cluster resources in the group will do the following:  On node A Shut down the DB Unconfigure the LogicalHost IP the DB Listener listens on unmount the filesystem   Then, on node B: mount the FS configure the IP  startup the DB -------- Voting, Quorum, Split Brain Condition, Fencing, Amnesia -------- How do the clusternodes agree upon their action? How do they decide which node runs what services? Another important question. Running a cluster is a strictly democratic thing.Every node has votes, and you need the majority of votes to have the deciding power. Now, this is usually no problem, clusternodes think very much all alike. Still, every action needs to be governed upon in a productive system, and has to be agreed upon. Agreeing is easy as long as the clusternodes all behave and talk to eachother over the interconnect. But if the interconnect is gone/down, this all gets tricky and confusing. Clusternodes think like this: "My job is to run these services. The other node does not answer my interconnect communication, it must be down. I'd better take control and run the services!". The problem is, as I have already mentioned, clusternodes very much think alike. If the interconnect is gone, they all assume the other node is down, and they all want to mount the data backend, enable the IP and run the database. Double IPs, double mounts, double DB instances - now that is trouble. Also, in a 2-node cluster they both have only 50% of the votes, that is, they themselves alone are not allowed to run a cluster.  This is where you need a quorum device. According to Wikipedia, the "requirement for a quorum is protection against totally unrepresentative action in the name of the body by an unduly small number of persons.". They need additional votes to run the cluster. For this requirement a 2-node cluster needs a quorum device or a quorum server. If the interconnect is gone, (this is what we call a split brain condition) both nodes start to race and try to reserve the quorum device to themselves. They do this, because the quorum device bears an additional vote, that could ensure majority (50% +1). The one that manages to lock the quorum device (e.g. if it's an FC LUN, it SCSI reserves it) wins the right to build/run a cluster, the other one - realizing he was late - panics/reboots to ensure the cluster config stays consistent.  Losing the interconnect isn't only endangering the availability of services, but it also endangers the cluster configuration consistence. Just imagine node A being down and during that the cluster configuration changes. Now node B goes down, and node A comes up. It isn't uptodate about the cluster configuration's changes so it will refuse to start a cluster, since that would lead to cluster amnesia, that is the cluster had some changes, but now runs with an older cluster configuration repository state, that is it's like it forgot about the changes.  Also, to ensure application data consistence, the clusternode that wins the race makes sure that a server that isn't part of or can't currently join the cluster can access the devices. This procedure is called fencing. This usually happens to storage LUNs via SCSI reservation.  Now, another important question: Where do I place the quorum disk?  Imagine having two sites, two separate datacenters, one in the north of the city and the other one in the south part of it. You run a stretched cluster in the clustered pair topology. Where do you place the quorum disk/server? If you put it into the north DC, and that gets hit by a meteor, you lose one clusternode, which isn't a problem, but you also lose your quorum, and the south clusternode can't keep the cluster running lacking the votes. This problem can't be solved with two sites and a campus cluster. You will need a third site to either place the quorum server to, or a third clusternode. Otherwise, lacking majority, if you lose the site that had your quorum, you lose the cluster. Okay, we covered the very basics. We haven't talked about virtualization support, CCR, ClusterFilesystems, DID devices, affinities, storage-replication, management tools, upgrade procedures - should those be interesting for you, let me know in the comments, along with any other questions. Given enough demand I'd be glad to write a followup post too. Now I really want to move on to the second part in the series: ClusterInstallation.  Oh, as for additional source of information, I recommend the documentation: http://docs.oracle.com/cd/E23623_01/index.html, and the OTN Oracle Solaris Cluster site: http://www.oracle.com/technetwork/server-storage/solaris-cluster/index.html

  Read the article

• Need help choosing between Grails and Yii Framework

  - by user530207

  I recently started on developing in PHP with the Yii Framework. I recently came across the Grails Framework and I'm pretty impressed by the sites they make, bigger companies seem to use Grails for their web development. When looking at yii, not many big companies are using it. I'm just starting out with the Yii framework and I don't want to turn back halfway when in the middle of learning Yii, so I hope someone can give me some comparison about the 2 in terms of power. Does Grails make things much easier and benefit me in the long run? I only have C++ background for now. It boils down to this. I want a powerful framework which will serve me for a very long time and by looking at the number of big companies using Grails, I feel discouraged to take the Yii path. Thank you! Some sites by Grails: http://video.sky.com/ http://espn.go.com/ http://www.atlassian.com/ http://www.linkedin.com/

  Read the article

• O' Reilly Deal of the Day 26/Jun/2012 - Developer's Guide to Collections in Microsoft® .NET

  - by TATWORTH

  Today's 50% off Deal of the Day at http://shop.oreilly.com/product/0790145317193.do?code=MSDEAL is Developer's Guide to Collections in Microsoft® .NET "Put .NET collections to work—and manage issues with GUI data binding, threading, data querying, and storage. Led by a data collection expert, you'll gain task-oriented guidance, exercises, and extensive code samples to tackle common problems and improve application performance. This one-stop reference is designed for experienced Microsoft Visual Basic® and C# developers—whether you’re already using collections or just starting out." I am reviewing this book. Here are my initial comments:The code is well illustrated by diagrams. The approach is practical. The code is well commented, however the C# code samples would be better had they been fully Style Cop compliant.I recommend this book to all C# and VB.NET Development teams. I concur with the author who states that the book is not for learning C# or VB.NET, however it is an excellent book for C# or VB.NET developers to extend their knowledge of the Dot Net framework.

  Read the article

• Data Mining Resources

  - by Dejan Sarka

  There are many different types of analyses, each one with its own pros and cons. Relational reports have a predefined structure, and end users cannot change it. They are simple to use for end users. Reports can use real-time data and snapshots of data to show the state of a report at specific points in time. One of the drawbacks is that report authoring is limited to IT pros and advanced users. Any kind of dynamic restructuring is very limited. If real-time data is used for a report, the report has a negative impact on the performance of the source system. Processing of the reports might be slow because the data comes from relational database management systems, which are not optimized for reporting only. If you create a semantic model of your data, your end users can create ad-hoc report structures. However, the development is more complex because a developer is needed to create these semantic models. For OLAP, you typically use specialized database management systems. You get lightning speed of analyses. End users can use rich and thin clients to interactively change the structure of the report. Typically, they do it graphically. However, the development of an OLAP system is many times quite complex. It involves the preparation and maintenance of an enterprise data warehouse and OLAP cubes. In order to exploit the possibility of real-time restructuring of reports, the users must be both active and educated. The data is usually stale, as it is loaded into data warehouses and OLAP cubes with a scheduled process. With data mining, a structure is not selected in advance; it searches for the structure. As a result, data mining can give you the most valuable results because you can discover patterns you did not expect. A data mining model structure is limited only by the attributes that you use to train the model. One of the drawbacks is that a lot of knowledge is needed for a successful data mining project. End users have to understand the results. Subject matter experts and IT professionals need to understand business problem thoroughly. The development might be sometimes even more complex than the development of OLAP cubes. Each type of analysis has its own place in an enterprise system. SQL Server has tools for all kinds of analyses. However, data mining is the most advanced way of analyzing the data; this is the “I” in BI. In order to get the most out of it, you need to learn quite a lot. In this blog post, I am gathering together resources for learning, including forthcoming events. Books Multiple authors: SQL Server MVP Deep Dives – I wrote an introductory data mining chapter there. Erik Veerman, Teo Lachev and Dejan Sarka: MCTS Self-Paced Training Kit (Exam 70-448): Microsoft SQL Server 2008 - Business Intelligence Development and Maintenance – you can find a good overview of a complete BI solution, including data mining, in this book. Jamie MacLennan, ZhaoHui Tang, and Bogdan Crivat: Data Mining with Microsoft SQL Server 2008 – can’t miss this book if you want to mine your data with SQL Server tools. Michael Berry, Gordon Linoff: Mastering Data Mining: The Art and Science of Customer Relationship Management – data mining from both, business and technical perspective. Dorian Pyle: Data Preparation for Data Mining – an in-depth book about data preparation. Thomas and Ronald Wonnacott: Introductory Statistics – if you thought that you could get away without statistics, then you are not serious about data mining. Jiawei Han and Micheline Kamber: Data Mining Concepts and Techniques – in-depth explanation of the most popular data mining algorithms. Michael Berry and Gordon Linoff: Data Mining Techniques – another book that explains data mining algorithms, more fro a business perspective. Paolo Guidici: Applied Data Mining – very mathematical book, only if you enjoy statistics and mathematics in general. Forthcoming presentations I am presenting two data mining related sessions during the PASS Summit in Charlotte, NC: Wednesday, October 16th, 2013 - Fraud Detection: Notes from the Field – I am showing how to use data mining for a specific business problem. The presentation is based on real-life projects. Friday, October 18th: Excel 2013 Advanced Analytics – I am focusing on Excel Data Mining Add-ins, and how to use them together with Power Pivot and other add-ins. This is the most you can get out of Excel. Sinergija 2013, Belgrade, Serbia Tuesday, October 22nd: Excel 2013 Analytics to the Max – another presentation focusing on the most advanced analytics you can get in Excel. SQL Rally Amsterdam, Netherlands Thursday, November 7th: Advanced Analytics in Excel 2013 – and again I am presenting about data mining in Excel. Why three different titles for the same presentation? I don’t know, I guess I forgot the name I proposed every time right after I sent the proposal. Courses Data Mining with SQL Server 2012 – I wrote a 3-day course for SolidQ. If you are interested in this course, which I could also deliver in a shorter seminar way, you can contact your closes SolidQ subsidiary, or, of course, me directly on addresses [email protected] or [email protected]. This course could also complement the existing courseware portfolio of training providers, which are welcome to contact me as well. OK, now you know: no more excuses, start learning data mining, get the most out of your data

  Read the article

• Simplifying the process of compiling and running objective-c apps in GNUstep

  - by Matthew

  I just installed GNUstep (following this post: http://www.jaysonjc.com/programming/objective-c-programming-in-windows-gnustep-projectcenter.html) It says to run this code: gcc -o helloworld helloworld.m -I /GNUstep/System/Library/Headers -L /GNUstep/System/Library/Libraries -lobjc -lgnustep-base -fconstant-string-class=NSConstantString every time I want to compile. It works just fine for me. However as I'm learning and will be compiling/running apps way often (making little changes and trying again), I'd like a simpler way to do this. Is there an easier way to compile and then run the app? Or am I just being lazy?

  Read the article

• SLK opens SCORM package as a ZIP file

  - by Cherie Riesberg

  Symptom: After installing SharePoint Learning Kit successfully, (http://www.codeplex.com/SLK), everything works except that the SCORM package (a ZIP extension) is opening as a ZIP file instead of a course. You get the normal ZIP message "Do you want to open or save this file?" Problem: The package is zipped at the upper folder level and does not create a manifest that allows SharePoint to recognize it as a SCORM file instead of a ZIP file. Solution: Add the contents of the course to the ZIP, not the outer (uppermost) folder.  This creates a ZIP file that SharePoint can recognize as a SCORM package.

  Read the article

• What to do if you're burnt out?

  - by rsteckly

  Hi, I'm starting to get really frustrated with ASP.NET. It seems as if much of my time is spent learning abstractions over problems, then having to kick into overdrive when those abstractions (surprise!) have unexpected behavior. It seems as if I spend so much time just fixing those issues because they usually are UI related and therefore require integration testing that I spend very little time programming any kind of meaningful logic. I don't know if it is ASP or if it is programming. I just feel as if I'm getting paid, doing the work but really wasting time. On the other hand, I have fantasies about console programs and actually using algorithms. What is wrong with me? Why can't I force myself to churn through this ASP stuff more?

  Read the article

• Mars Mania and the Google Maps APIs!

  Mars Mania and the Google Maps APIs! Interested in learning how to use the Google Maps API and WebGL to create a dynamic terrain lighting map of the surface of Mars? Or how about using the Street View API and a bit of ImageMagick to view the high resolution panoramic images from the Curiosity Rover? Since Curiosity's touchdown, Brendan Kenny and Paul Saxman have been infected with a bit of Mars Mania. Stop by this week's Google Maps Developers Office Hours to see how they've been seeking therapy through productive programming. From: GoogleDevelopers Views: 1146 28 ratings Time: 34:15 More in Science & Technology

  Read the article

• How can i find touch typing lesson for words with middle row only

  - by user1838032

  I am learning touch typing. i want practice step by step. Is there any site where i can have the options of the keys to select and then have lesson for those slected keys only. I means i select the keys from keyboard and then system prepares the lesson for only those keys with random combination. Current i want to practice keys asdf gh jkl; Now i am not able to find practice for that whole row only. i mena random combinatins

  Read the article

• An MCM exam, Rob? Really?

  - by Rob Farley

  I took the SQL 2008 MCM Knowledge exam while in Seattle for the PASS Summit ten days ago. I wasn’t planning to do it, but I got persuaded to try. I was meaning to write this post to explain myself before the result came out, but it seems I didn’t get typing quickly enough. Those of you who know me will know I’m a big fan of certification, to a point. I’ve been involved with Microsoft Learning to help create exams. I’ve kept my certifications current since I first took an exam back in 1998, sitting many in beta, across quite a variety of topics. I’ve probably become quite good at them – I know I’ve definitely passed some that I really should’ve failed. I’ve also written that I don’t think exams are worth studying for. (That’s probably not entirely true, but it depends on your motivation. If you’re doing learning, I would encourage you to focus on what you need to know to do your job better. That will help you pass an exam – but the two skills are very different. I can coach someone on how to pass an exam, but that’s a different kind of teaching when compared to coaching someone about how to do a job. For example, the real world includes a lot of “it depends”, where you develop a feel for what the influencing factors might be. In an exam, its better to be able to know some of the “Don’t use this technology if XYZ is true” concepts better.) As for the Microsoft Certified Master certification… I’m not opposed to the idea of having the MCM (or in the future, MCSM) cert. But the barrier to entry feels quite high for me. When it was first introduced, the nearest testing centres to me were in Kuala Lumpur and Manila. Now there’s one in Perth, but that’s still a big effort. I know there are options in the US – such as one about an hour’s drive away from downtown Seattle, but it all just seems too hard. Plus, these exams are more expensive, and all up – I wasn’t sure I wanted to try them, particularly with the fact that I don’t like to study. I used to study for exams. It would drive my wife crazy. I’d have some exam scheduled for some time in the future (like the time I had two booked for two consecutive days at TechEd Australia 2005), and I’d make sure I was ready. Every waking moment would be spent pouring over exam material, and it wasn’t healthy. I got shaken out of that, though, when I ended up taking four exams in those two days in 2005 and passed them all. I also worked out that if I had a Second Shot available, then failing wasn’t a bad thing at all. Even without Second Shot, I’m much more okay about failing. But even just trying an MCM exam is a big effort. I wouldn’t want to fail one of them. Plus there’s the illusion to maintain. People have told me for a long time that I should just take the MCM exams – that I’d pass no problem. I’ve never been so sure. It was almost becoming a pride-point. Perhaps I should fail just to demonstrate that I can fail these things. Anyway – boB Taylor (@sqlboBT) persuaded me to try the SQL 2008 MCM Knowledge exam at the PASS Summit. They set up a testing centre in one of the room there, so it wasn’t out of my way at all. I had to squeeze it in between other commitments, and I certainly didn’t have time to even see what was on the syllabus, let alone study. In fact, I was so exhausted from the week that I fell asleep at least once (just for a moment though) during the actual exam. Perhaps the questions need more jokes, I’m not sure. I knew if I failed, then I might disappoint some people, but that I wouldn’t’ve spent a great deal of effort in trying to pass. On the other hand, if I did pass I’d then be under pressure to investigate the MCM Lab exam, which can be taken remotely (therefore, a much smaller amount of effort to make happen). In some ways, passing could end up just putting a bunch more pressure on me. Oh, and I did.

  Read the article

• What are Silverlight, WCF RIA services or applications?

  - by Pankaj Upadhyay

  I asked a question here on programmers yesterday about learning HTML & CSS and the community was pretty generous to provide great answers. One of the answers was given by Emmad Kareem and that was : "if you can't do HTML, don't give up. Consider using Silverlight". This answer made me visit Silverlight.net and I came across the terms WCF RIA Services, Silverlight applications. After going through the website and some articles on website i am unable to draw a conclusive understanding on what this is all about. Is this another way of building websites using .NET, and is just like another framework like ASP.NET MVC3. What scenario's and requirements are basically targeted to silverlight applications or we are free to use either of Asp.net MVC or Silverlight in any web-application requirements.

  Read the article

• Triggering custom events in AJAX callbacks

  - by Sabrina Gelbart

  I'm pretty new to JavaScript, but one of the things that's been frustrating is that our AJAX callbacks have been getting packed with different functionality, making it difficult to keep everything separated and organized. I'm really new to programming, I have a feeling learning MVC a bit more would help me, but for now using custom events seems like it could help me keep my code a lot cleaner and prevent some problems. Here's what I'm talking about: function myAjaxFunction(){ $.post('ajax/test.html', function(data) { $(document).trigger('testDataLoaded',data); }); } function myOtherFunctionThatsDependentUponAjax(){ $(document).one('testDataLoaded', function(data){ alert (data); } } I also don't know if it's ok that I'm triggering document or not... Are there any patterns that look like this that I can read more about? What are the potential problems with this?

  Read the article

• Professional WCF 4.0: Windows Communication Foundation with .NET 4.0

  - by cibrax

  The book in which I been working on since last year finally went to the light this week. It has been the result of hard work between me and three other Connected Systems MVP, my friend Fabio Cozzolino, Kurt Claeys and Johann Grabner. If you are interested in learning the new features in WCF 4.0, but also WCF in general and how to apply in real world scenarios, this book is for you. I dedicated three chapters of this book to one of my favorites topics, Security, from the basics to more complicated scenarios with Claim-Based security and Federated authentication using WCF services with Windows Identity Foundation. You can find more information about the book and the table of contents in the Wrox web site here.

  Read the article

< Previous Page | 145 146 147 148 149 150 151 152 153 154 155 156  | Next Page >