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• What are the problems with a relatively large common library?

  - by Sam Pearson

  As long as the code in the base library is as loosely coupled as splitting it up into separate libraries, what's the problem? In general, having a lot of assemblies composing a .NET solution is painful. Plus, when code in one solution needs to be shared, it can just be added to the common library, rather than deciding which common library it should be added to or creating yet another library. edit: the question comes to me after using Smalltalk for a bit, where all the code is available to use, all the time.

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• Are XML Comments Necessary Documentation?

  - by Bob Horn

  I used to be a fan of requiring XML comments for documentation. I've since changed my mind for two main reasons: Like good code, methods should be self-explanatory. In practice, most XML comments are useless noise that provide no additional value. Many times we simply use GhostDoc to generate generic comments, and this is what I mean by useless noise: /// <summary> /// Gets or sets the unit of measure. /// </summary> /// <value> /// The unit of measure. /// </value> public string UnitOfMeasure { get; set; } To me, that's obvious. Having said that, if there were special instructions to include, then we should absolutely use XML comments. I like this excerpt from this article: Sometimes, you will need to write comments. But, it should be the exception not the rule. Comments should only be used when they are expressing something that cannot be expressed in code. If you want to write elegant code, strive to eliminate comments and instead write self-documenting code. Am I wrong to think we should only be using XML comments when the code isn't enough to explain itself on its own? I believe this is a good example where XML comments make pretty code look ugly. It takes a class like this... public class RawMaterialLabel : EntityBase { public long Id { get; set; } public string ManufacturerId { get; set; } public string PartNumber { get; set; } public string Quantity { get; set; } public string UnitOfMeasure { get; set; } public string LotNumber { get; set; } public string SublotNumber { get; set; } public int LabelSerialNumber { get; set; } public string PurchaseOrderNumber { get; set; } public string PurchaseOrderLineNumber { get; set; } public DateTime ManufacturingDate { get; set; } public string LastModifiedUser { get; set; } public DateTime LastModifiedTime { get; set; } public Binary VersionNumber { get; set; } public ICollection<LotEquipmentScan> LotEquipmentScans { get; private set; } } ... And turns it into this: /// <summary> /// Container for properties of a raw material label /// </summary> public class RawMaterialLabel : EntityBase { /// <summary> /// Gets or sets the id. /// </summary> /// <value> /// The id. /// </value> public long Id { get; set; } /// <summary> /// Gets or sets the manufacturer id. /// </summary> /// <value> /// The manufacturer id. /// </value> public string ManufacturerId { get; set; } /// <summary> /// Gets or sets the part number. /// </summary> /// <value> /// The part number. /// </value> public string PartNumber { get; set; } /// <summary> /// Gets or sets the quantity. /// </summary> /// <value> /// The quantity. /// </value> public string Quantity { get; set; } /// <summary> /// Gets or sets the unit of measure. /// </summary> /// <value> /// The unit of measure. /// </value> public string UnitOfMeasure { get; set; } /// <summary> /// Gets or sets the lot number. /// </summary> /// <value> /// The lot number. /// </value> public string LotNumber { get; set; } /// <summary> /// Gets or sets the sublot number. /// </summary> /// <value> /// The sublot number. /// </value> public string SublotNumber { get; set; } /// <summary> /// Gets or sets the label serial number. /// </summary> /// <value> /// The label serial number. /// </value> public int LabelSerialNumber { get; set; } /// <summary> /// Gets or sets the purchase order number. /// </summary> /// <value> /// The purchase order number. /// </value> public string PurchaseOrderNumber { get; set; } /// <summary> /// Gets or sets the purchase order line number. /// </summary> /// <value> /// The purchase order line number. /// </value> public string PurchaseOrderLineNumber { get; set; } /// <summary> /// Gets or sets the manufacturing date. /// </summary> /// <value> /// The manufacturing date. /// </value> public DateTime ManufacturingDate { get; set; } /// <summary> /// Gets or sets the last modified user. /// </summary> /// <value> /// The last modified user. /// </value> public string LastModifiedUser { get; set; } /// <summary> /// Gets or sets the last modified time. /// </summary> /// <value> /// The last modified time. /// </value> public DateTime LastModifiedTime { get; set; } /// <summary> /// Gets or sets the version number. /// </summary> /// <value> /// The version number. /// </value> public Binary VersionNumber { get; set; } /// <summary> /// Gets the lot equipment scans. /// </summary> /// <value> /// The lot equipment scans. /// </value> public ICollection<LotEquipmentScan> LotEquipmentScans { get; private set; } }

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• Is committing/checking code everyday a good practice?

  - by ArtB

  I've been reading Martin Fowler's note on Continuous Integration and he lists as a must "Everyone Commits To the Mainline Every Day". I do not like to commit code unless the section I'm working on is complete and that in practice I commit my code every three days: one day to investigate/reproduce the task and make some preliminary changes, a second day to complete the changes, and a third day to write the tests and clean it up^ for submission. I would not feel comfortable submitting the code sooner. Now, I pull changes from the repository and integrate them locally usually twice a day, but I do not commit that often unless I can carve out a smaller piece of work. Question: is committing everyday such a good practice that I should change my workflow to accomodate it, or it is not that advisable? ^ The order is more arbitrary and depends on the task, my point was to illustrate the time span and activities, not the exact sequence.

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• Could someone break this nasty habit of mine please?

  - by MimiEAM

  I recently graduated in cs and was mostly unsatisfied since I realized that I received only a basic theoretical approach in a wide range of subjects (which is what college is supposed to do but still...) . Anyway I took the habit of spending a lot of time looking for implementations of concepts and upon finding those I will used them as guides to writing my own implementation of those concepts just for fun. But now I feel like the only way I can fully understand a new concept is by trying to implement from scratch no matter how unoptimized the result may be. Anyway this behavior lead me to choose by default the hard way, that is time consuming instead of using a nicely written library until I hit my head again a huge wall and then try to find a library that works for my purpose.... Does anyone else do that and why? It seems so weird why would anyone (including me) do that ? Is it a bad practice ? and if so how can i stop doing that ?

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• Is it a bad idea to list every function/method argument on a new line and why?

  - by dgnball

  I work with someone who, every time they call a function they put the arguments on a new line e.g. aFunction( byte1, short1, int1, int2, int3, int4, int5 ) ; I find this very annoying as it means the code isn't very compact, so I have to scan up and down more to actually make any sense of the logic. I'm interested to know whether this is actually bad practice and if so, how can I persuade them not to do it?

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• Programming Interview Question [duplicate]

  - by user136494

  This question already has an answer here: How to prepare yourself for programming interview questions? [duplicate] 6 answers I have an upcoming interview in a couple of days and had a question for you guys. I've heard that programming interviews have whiteboard problems where you solve a simple problem on a whiteboard. My question to you is? How many whiteboard problems do you have to solve? Is there more than 1? What are examples of whiteboard problems? Is FizzBuzz one of them? Where can I find practice problems for them? Anyone know of any good web sites?

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• What are some reasonable stylistic limits on type inference?

  - by Jon Purdy

  C++0x adds pretty darn comprehensive type inference support. I'm sorely tempted to use it everywhere possible to avoid undue repetition, but I'm wondering if removing explicit type information all over the place is such a good idea. Consider this rather contrived example: Foo.h: #include <set> class Foo { private: static std::set<Foo*> instances; public: Foo(); ~Foo(); // What does it return? Who cares! Just forward it! static decltype(instances.begin()) begin() { return instances.begin(); } static decltype(instances.end()) end() { return instances.end(); } }; Foo.cpp: #include <Foo.h> #include <Bar.h> // The type need only be specified in one location! // But I do have to open the header to find out what it actually is. decltype(Foo::instances) Foo::instances; Foo() { // What is the type of x? auto x = Bar::get_something(); // What does do_something() return? auto y = x.do_something(*this); // Well, it's convertible to bool somehow... if (!y) throw "a constant, old school"; instances.insert(this); } ~Foo() { instances.erase(this); } Would you say this is reasonable, or is it completely ridiculous? After all, especially if you're used to developing in a dynamic language, you don't really need to care all that much about the types of things, and can trust that the compiler will catch any egregious abuses of the type system. But for those of you that rely on editor support for method signatures, you're out of luck, so using this style in a library interface is probably really bad practice. I find that writing things with all possible types implicit actually makes my code a lot easier for me to follow, because it removes nearly all of the usual clutter of C++. Your mileage may, of course, vary, and that's what I'm interested in hearing about. What are the specific advantages and disadvantages to radical use of type inference?

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• How to tell your boss that his programming style is really bad?

  - by Roflcoptr

  I'm a student and in my spare time I'm working for a big enterprise as Java developer. The job is good, but the problem is, my boss is writing very strange code. I don't want to complain, but some issues are in my opinion really strange. For example: he doesn't know any booleans. All boolean conditions are Strings called "YesOrNo" and then in the condition he uses if (YesOrNo == "Yes") there are a lot of very strange characters in method names and variables like é õ ô or è all loops are infinite loops in the style of for(;;). Then at the end of the loop the condition is tested and if the conditions is fulfilled break; is called. I don't now if I should tell him that I think this isn't a good practice, since he is my boss and decides how and what to do. On the other hand some of this examples are really very weird. Any hints how to cope with? And is this only me who thinks that's bad style?

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• How do you track bugs in your personal projects?

  - by bedwyr

  I'm trying to decide if I need to reassess my defect-tracking process for my home-grown projects. For the last several years, I really just track defects using TODO tags in the code, and keeping track of them in a specific view (I use Eclipse, which has a decent tagging system). Unfortunately, I'm starting to wonder if this system is unsustainable. The defects I find are typically associated with a snippet of code I'm working on; bugs which are not immediately understood tend to be forgotten, or ignored. I wrote an application for my wife which has had a severe defect for almost 9 months, and I keep forgetting to fix it. What mechanism do you use to track defects in your personal projects? Do you have a specific system, or a process for prioritizing and managing them?

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• Which is more important in a web application code promotion hierarchy? production environment to repo equivalence or unidirectional propagation?

  - by ghbarratt

  Lets say you have a code promotion hierarchy consisting of several environments, (the polar end) two of which are development (dev) and production (prod). Lets say you also have a web application where important (but not developer controlled) files are created (and perhaps altered) in the production environment. Lets say that you (or someone above you) decided that the files which are controlled/created/altered/deleted in the production environment needed to go into the repository. Which of the following two sets of practice / approaches do you find best: Committing these non-developed file modifications made in the production environment so that the repository reflects the production environment as closely and as often as possible. Generally ignoring the non-developed production environment alterations, placing confidence in backups to restore the production environment should it be harmed, and keeping a resolution to avoid pushing developments through the promotion hierarchy in the reverse direction (avoiding pushing from prod to dev), only committing the files found in the production environment if they were absolutely necessary in other environments for development. So, 1 or 2, and why? PS - I am currently slightly biased toward maintaining production environment to repository equivalence (option 1), but I keep an open mind and would accept an answer supporting either.

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• Database Maintenance Scripting Done Right

  - by KKline

  I first wrote about useful database maintenance scripts on my SQLBlog account way back in 2008. Hmmm - now that I think about it, I first wrote about my own useful database maintenance scripts in a journal called SQL Server Professional back in the mid-1990's on SQL Server v6.5 or some such. But I digress... Anyway, I pointed out a couple useful sites where you could get some good scripts that would take care of preventative maintenance on your SQL Server, such as index defragmentation, updating...(read more)

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• How to estimate freight / shipping costs ??

  - by Vani

  Hi, I am working on a PHP web application and want to know the best way to estimate freight costs in USA. The site deals with construction materials that uses LTL or Truck loads. I found a few sites like www.freightCenter.com that provide quotes using webservice. Two drawbacks, its paid service and the other, my site response time is slow if I use the webservice. Is there a open source tool/logic avaliable for estimating shipping / freight costs?? Or a way to determine the rate per mile per pound for different freight classes? Thank you, Vani

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• Maintainability of Boolean logic - Is nesting if statements needed?

  - by Vaccano

  Which of these is better for maintainability? if (byteArrayVariable != null) if (byteArrayVariable .Length != 0) //Do something with byteArrayVariable OR if ((byteArrayVariable != null) && (byteArrayVariable.Length != 0)) //Do something with byteArrayVariable I prefer reading and writing the second, but I recall reading in code complete that doing things like that is bad for maintainability. This is because you are relying on the language to not evaluate the second part of the if if the first part is false and not all languages do that. (The second part will throw an exception if evaluated with a null byteArrayVariable.) I don't know if that is really something to worry about or not, and I would like general feedback on the question. Thanks.

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• I'm trying to understand hash tables - can someone explain it to me - clearly?

  - by Stevo

  I want to understand the correct use and implementation of hash tables in php (sorry). I read somewhere that an in-experienced programmer created a hash table and then iterated through it. Now, I understand why that is wrong but I haven't quite got the full knowledge to know if my understanding is correct (if you know what I mean). So could someone explain to me how to implement a hash table in php (presumably an associative array) and perhaps more importantly, how to access the values 'with a hash' and what that actually means?

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• Studying computer science - what am I getting myself into?

  - by clankercrusher

  I'm a student considering the possibility of studying computer science. I've picked up programming indie games and websites as a hobby and I really enjoy it. Despite my fairly positive experience, I somehow get the feeling that computer science in the business world will be completely different than do-it-for-fun game making. Since I'm interested in the field and I'd like to study well, I want to prepare myself for the onslaught. (If that’s even possible) What are some of the most important principals I need to know if I decide to study computer science? What will I need to know about computer science that a University probably won't teach me? Is there any way I can get hands on experience before or while I'm at a University? What am I getting myself into? P.S. Is this the right stack exchange site for this type of question?

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• Refactor or Concentrate on Completing App

  - by Jiew Meng

  Would you refactor your app as you go or focus on completing app first? Refactoring will mean progress of app app will slow down. Completing app will mean you get a possibly very hard to maintain app later on? The app is a personal project. I don't really know how to answer "What drives the functionality and design", but I guess it's to solve inefficiencies in current software out there. I like minimal easy to use software too. So I am removing some features and add some that I feel will help.

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• Is it a good pattern that no objects should know more than what it needs to know?

  - by Jim Thio

  I am implementing a viewController class. The view controller class got NSNotification when the Grabbing class start or finish updating. I have 2 choices. I can make the grabbing class to provide a public read only property so all other classes can know whether it is still uploading. Or I can let view Controller to listen to 2 different events. Start updating and finish updating events. The truth is the viewController do need to know whether the grabbing class is still updating or not at any other time. So I am thinking of creating 2 events would be a better way to go. Actually, what do you think?

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• How often is your "Go-To" language the same as your favorite??

  - by K-RAN

  I know that there's already a question asking for your favorite programming language here. I'm curious though, what's your go-to language? The two can be very different. For example, I love Haskell. I learned it this past semester and I fell in love with it's very concise solutions and awesome syntax (I love theoretical math so something like fib = 1 : 1 : [ f | f <- zipWith (+) fibSeq (tail fibSeq)] makes my inner mathematician and computer scientist jump with joy!). However, the majority of my projects for classes and jobs have been in C/C++ & Java. As a result, most of the time when I'm testing something like an algorithm or Data Structure I go straight to C++. What about you guys? What languages do you love and why? What about your go-to language? What language do you use most often to get things done for work or personal projects and why? How often does a language fall into both categories??

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• How to export 3D models that consist of several parts (eg. turret on a tank)?

  - by Will

  What are the standard alternatives for the mechanics of attaching turrets and such to 3D models for use in-game? I don't mean the logic, but rather the graphics aspects. My naive approach is to extend the MD2-like format that I'm using (blender-exported using a script) to include a new set of properties for a mesh that: is anchored in another 'parent' mesh. The anchor is a point and normal in the parent mesh and a point and normal in the child mesh; these will always be colinear, giving the child rotation but not translation relative to the parent point. has a normal that is aligned with a 'target'. Classically this target is the enemy that is being engaged, but it might be some other vector e.g. 'the wind' (for sails and flags (and smoke, which is a particle system but the same principle applies)) or 'upwards' (e.g. so bodies of riders bend properly when riding a horse up an incline etc). that the anchor and target alignments have maximum and minimum and a speed coeff. there is game logic for multiple turrets and on a model and deciding which engages which enemy. 'primary' and 'secondary' or 'target0' ... 'targetN' or some such annotation will be there. So to illustrate, a classic tank would be made from three meshes; a main body mesh, a turret mesh that is anchored to the top of the main body so it can spin only horizontally and a barrel mesh that is anchored to the front of the turret and can only move vertically within some bounds. And there might be a forth flag mesh on top of the turret that is aligned with 'wind' where wind is a function the engine solves that merges environment's wind angle with angle the vehicle is travelling in an velocity, or something fancy. This gives each mesh one degree of freedom relative to its parent. Things with multiple degrees of freedom can be modelled by zero-vertex connecting meshes perhaps? This is where I think the approach I outlined begins to feel inelegant, yet perhaps its still a workable system? This is why I want to know how it is done in professional games ;) Are there better approaches? Are there formats that already include this information? Is this routine?

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• How to write efficient code in spite of heavy deadlines

  - by gladysbixly

  Hi all, I am working in an environment wherein we have many projects with strict deadlines on deliverables. We even talk directly to the clients so getting the jobs done and fast is a must. My issue is that i'd always write code for the first solution that comes to my mind, which of course I thought as best at that moment. It always ends up ugly though and i'd later realize that there are better ways to do it but can't afford to change due to time restrictions. Are there any tips by which I could make my code efficient yet deliver on time?

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• Hard Copies VS Soft Copies

  - by Garet Claborn

  Where do you draw the line and say, "OK, I'm actually going to print out this piece of code, spec, formula, or other info and carry it around but these pieces can stay on disk." Well, more importantly why do you draw the line there? I've encountered this a number of times and have some sort of vague conceptions beyond "oh now I'm REALLY stuck, better print this out." I've also found some quicksheets of basic specs to be handy. Really though, I have no particular logic behind what is useful to physically have available in the design and development process. I have a great pile of 'stuff' papers that seemed at least partially relevant at the time, but I only really use about a third of them ever and often end up wishing I had different info on hand. Edit: So this is what I'm hearing in a nutshell: Major parts of the design pattern Common, fairly static and prominently useful code (reference or specs) Some representation of data useful in collaborating or sharing with team Extreme cases of tough problem solving Overwhelmingly,almost never print anything.

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• Started wrong with a project. Should I start over?

  - by solidsnake

  I'm a beginner web developer (one year of experience). A couple of weeks after graduating, I got offered a job to build a web application for a company whose owner is not much of a tech guy. He recruited me to avoid theft of his idea, the high cost of development charged by a service company, and to have someone young he can trust onboard to maintain the project for the long run (I came to these conclusions by myself long after being hired). Cocky as I was back then, with a diploma in computer science, I accepted the offer thinking I can build anything. I was calling the shots. After some research I settled on PHP, and started with plain PHP, no objects, just ugly procedural code. Two months later, everything was getting messy, and it was hard to make any progress. The web application is huge. So I decided to check out an MVC framework that would make my life easier. That's where I stumbled upon the cool kid in the PHP community: Laravel. I loved it, it was easy to learn, and I started coding right away. My code looked cleaner, more organized. It looked very good. But again the web application was huge. The company was pressuring me to deliver the first version, which they wanted to deploy, obviously, and start seeking customers. Because Laravel was fun to work with, it made me remember why I chose this industry in the first place - something I forgot while stuck in the shitty education system. So I started working on small projects at night, reading about methodologies and best practice. I revisited OOP, moved on to object-oriented design and analysis, and read Uncle Bob's book Clean Code. This helped me realize that I really knew nothing. I did not know how to build software THE RIGHT WAY. But at this point it was too late, and now I'm almost done. My code is not clean at all, just spaghetti code, a real pain to fix a bug, all the logic is in the controllers, and there is little object oriented design. I'm having this persistent thought that I have to rewrite the whole project. However, I can't do it... They keep asking when is it going to be all done. I can not imagine this code deployed on a server. Plus I still know nothing about code efficiency and the web application's performance. On one hand, the company is waiting for the product and can not wait anymore. On the other hand I can't see myself going any further with the actual code. I could finish up, wrap it up and deploy, but god only knows what might happen when people start using it. What do you think I should do?

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• More than one way to skin an Audit

  - by BuckWoody

  I get asked quite a bit about auditing in SQL Server. By "audit", people mean everything from tracking logins to finding out exactly who ran a particular SELECT statement. In the really early versions of SQL Server, we didn't have a great story for very granular audits, so lots of workarounds were suggested. As time progressed, more and more audit capabilities were added to the product, and in typical database platform fashion, as we added a feature we didn't often take the others away. So now, instead of not having an option to audit actions by users, you might face the opposite problem - too many ways to audit! You can read more about the options you have for tracking users here: http://msdn.microsoft.com/en-us/library/cc280526(v=SQL.100).aspx  In SQL Server 2008, we introduced SQL Server Audit, which uses Extended Events to really get a simple way to implement high-level or granular auditing. You can read more about that here: http://msdn.microsoft.com/en-us/library/dd392015.aspx  As with any feature, you should understand what your needs are first. Auditing isn't "free" in the performance sense, so you need to make sure you're only auditing what you need to. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Pay in the future should make you think in the present

  - by BuckWoody

  Distributed Computing - and more importantly “-as-a-Service” models of computing have a different cost model. This is something that sounds obvious on the surface but it’s often forgotten during the design and coding phase of a project. In on-premises computing, we’re used to purchasing a server and all of the hardware infrastructure and software licenses needed not only for one project, but several. This is an up-front or “sunk” cost that we consume by running code the organization needs to perform its function. Using a direct connection over wires you’ve already paid for, we don’t often have to think about bandwidth, hits on the data store or the amount of compute we use - we just know more is better. In a pay-as-you-go model, however, each of these architecture decisions has a potential cost impact. The amount of data you store, the number of times you access it, and the amount you send back all come with a charge. The offset is that you don’t buy anything at all up-front, so that sunk cost is freed up. And financial professionals know that money now is worth more than money later. Saving that up-front cost allows you to invest it in other things. It’s not just that you’re using things that now cost money - it’s that the design itself in distributed computing has a cost impact. That can be a really good thing, such as when you dynamically add capacity for paying customers. If you can tie back the cost of a series of clicks to what a user will pay to do so, you can set a profit margin that is easy to track. Here’s a case in point: Assume you are using a large instance in Windows Azure to compute some data that you retrieve from a SQL Azure database. If you don’t monitor the path of the application, you may not know what you are really using. Since you’re paying by the size of the instance, it’s best to maximize it all the time. Recently I evaluated just this situation, and found that downsizing the instance and adding another one where needed, adding a caching function to the application, moving part of the data into Windows Azure tables not only increased the speed of the application, but reduced the cost and more closely tied the cost to the profit. The key is this: from the very outset - the design - make sure you include metrics to measure for the cost/performance (sometimes these are the same) for your application. Windows Azure opens up awesome new ways of doing things, so make sure you study distributed systems architecture before you try and force in the application design you have on premises into your new application structure.

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• Why do I need two Instances in Windows Azure?

  - by BuckWoody

  Windows Azure as a Platform as a Service (PaaS) means that there are various components you can use in it to solve a problem: Compute “Roles” - Computers running an OS and optionally IIS - you can have more than one "Instance" of a given Role Storage - Blobs, Tables and Queues for Storage Other Services - Things like the Service Bus, Azure Connection Services, SQL Azure and Caching It’s important to understand that some of these services are Stateless and others maintain State. Stateless means (at least in this case) that a system might disappear from one physical location and appear elsewhere. You can think of this as a cashier at the front of a store. If you’re in line, a cashier might take his break, and another person might replace him. As long as the order proceeds, you as the customer aren’t really affected except for the few seconds it takes to change them out. The cashier function in this example is stateless. The Compute Role Instances in Windows Azure are Stateless. To upgrade hardware, because of a fault or many other reasons, a Compute Role's Instance might stop on one physical server, and another will pick it up. This is done through the controlling fabric that Windows Azure uses to manage the systems. It’s important to note that storage in Azure does maintain State. Your data will not simply disappear - it is maintained - in fact, it’s maintained three times in a single datacenter and all those copies are replicated to another for safety. Going back to our example, storage is similar to the cash register itself. Even though a cashier leaves, the record of your payment is maintained. So if a Compute Role Instance can disappear and re-appear, the things running on that first Instance would stop working. If you wrote your code in a Stateless way, then another Role Instance simply re-starts that transaction and keeps working, just like the other cashier in the example. But if you only have one Instance of a Role, then when the Role Instance is re-started, or when you need to upgrade your own code, you can face downtime, since there’s only one. That means you should deploy at least two of each Role Instance not only for scale to handle load, but so that the first “cashier” has someone to replace them when they disappear. It’s not just a good idea - to gain the Service Level Agreement (SLA) for our uptime in Azure it’s a requirement. We point this out right in the Management Portal when you deploy the application: (Click to enlarge) When you deploy a Role Instance you can also set the “Upgrade Domain”. Placing Roles on separate Upgrade Domains means that you have a continuous service whenever you upgrade (more on upgrades in another post) - the process looks like this for two Roles. This example covers the scenario for upgrade, so you have four roles total - One Web and one Worker running the "older" code, and one of each running the new code. In all those Roles you want at least two instances, and this example shows that you're covered for High Availability and upgrade paths: The take-away is this - always plan for forward-facing Roles to have at least two copies. For Worker Roles that do background processing, there are ways to architect around this number, but it does affect the SLA if you have only one.

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