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  • What Counts for a DBA: Skill

    - by drsql
    “Practice makes perfect:” right? Well, not exactly. The reality of it all is that this saying is an untrustworthy aphorism. I discovered this in my “younger” days when I was a passionate tennis player, practicing and playing 20+ hours a week. No matter what my passion level was, without some serious coaching (and perhaps a change in dietary habits), my skill level was never going to rise to a level where I could make any money at the sport that involved something other than selling tennis balls at a sporting goods store. My game may have improved with all that practice but I had too many bad practices to overcome. Practice by itself merely reinforces what we know and what we can figure out naturally. The truth is actually closer to the expression used by Vince Lombardi: “Perfect practice makes perfect.” So how do you get to become skilled as a DBA if practice alone isn’t sufficient? Hit the Internet and start searching for SQL training and you can find 100 different sites. There are also hundreds of blogs, magazines, books, conferences both onsite and virtual. But then how do you know who is good? Unfortunately often the worst guide can be to find out the experience level of the writer. Some of the best DBAs are frighteningly young, and some got their start back when databases were stored on stacks of paper with little holes in it. As a programmer, is it really so hard to understand normalization? Set based theory? Query optimization? Indexing and performance tuning? The biggest barrier often is previous knowledge, particularly programming skills cultivated before you get started with SQL. In the world of technology, it is pretty rare that a fresh programmer will gravitate to database programming. Database programming is very unsexy work, because without a UI all you have are a bunch of text strings that you could never impress anyone with. Newbies spend most of their time building UIs or apps with procedural code in C# or VB scoring obvious interesting wins. Making matters worse is that SQL programming requires mastery of a much different toolset than most any mainstream programming skill. Instead of controlling everything yourself, most of the really difficult work is done by the internals of the engine (written by other non-relational programmers…we just can’t get away from them.) So is there a golden road to achieving a high skill level? Sadly, with tennis, I am pretty sure I’ll never discover it. However, with programming it seems to boil down to practice in applying the appropriate techniques for whatever type of programming you are doing. Can a C# programmer build a great database? As long as they don’t treat SQL like C#, absolutely. Same goes for a DBA writing C# code. None of this stuff is rocket science, as long as you learn to understand that different types of programming require different skill sets and you as a programmer must recognize the difference between one of the procedural languages and SQL and treat them differently. Skill comes from practicing doing things the right way and making “right” a habit.

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  • The long road to bug-free software

    - by Tony Davis
    The past decade has seen a burgeoning interest in functional programming languages such as Haskell or, in the Microsoft world, F#. Though still on the periphery of mainstream programming, functional programming concepts are gradually seeping into the imperative C# language (for example, Lambda expressions have their root in functional programming). One of the more interesting concepts from functional programming languages is the use of formal methods, the lofty ideal behind which is bug-free software. The idea is that we write a specification that describes exactly how our function (say) should behave. We then prove that our function conforms to it, and in doing so have proved beyond any doubt that it is free from bugs. All programmers already use one form of specification, specifically their programming language's type system. If a value has a specific type then, in a type-safe language, the compiler guarantees that value cannot be an instance of a different type. Many extensions to existing type systems, such as generics in Java and .NET, extend the range of programs that can be type-checked. Unfortunately, type systems can only prevent some bugs. To take a classic problem of retrieving an index value from an array, since the type system doesn't specify the length of the array, the compiler has no way of knowing that a request for the "value of index 4" from an array of only two elements is "unsafe". We restore safety via exception handling, but the ideal type system will prevent us from doing anything that is unsafe in the first place and this is where we start to borrow ideas from a language such as Haskell, with its concept of "dependent types". If the type of an array includes its length, we can ensure that any index accesses into the array are valid. The problem is that we now need to carry around the length of arrays and the values of indices throughout our code so that it can be type-checked. In general, writing the specification to prove a positive property, even for a problem very amenable to specification, such as a simple sorting algorithm, turns out to be very hard and the specification will be different for every program. Extend this to writing a specification for, say, Microsoft Word and we can see that the specification would end up being no simpler, and therefore no less buggy, than the implementation. Fortunately, it is easier to write a specification that proves that a program doesn't have certain, specific and undesirable properties, such as infinite loops or accesses to the wrong bit of memory. If we can write the specifications to prove that a program is immune to such problems, we could reuse them in many places. The problem is the lack of specification "provers" that can do this without a lot of manual intervention (i.e. hints from the programmer). All this might feel a very long way off, but computing power and our understanding of the theory of "provers" advances quickly, and Microsoft is doing some of it already. Via their Terminator research project they have started to prove that their device drivers will always terminate, and in so doing have suddenly eliminated a vast range of possible bugs. This is a huge step forward from saying, "we've tested it lots and it seems fine". What do you think? What might be good targets for specification and verification? SQL could be one: the cost of a bug in SQL Server is quite high given how many important systems rely on it, so there's a good incentive to eliminate bugs, even at high initial cost. [Many thanks to Mike Williamson for guidance and useful conversations during the writing of this piece] Cheers, Tony.

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  • WebLogic stuck thread protection

    - by doublep
    By default WebLogic kills stuck threads after 15 min (600 s), this is controlled by StuckThreadMaxTime parameter. However, I cannot find more details on how exactly "stuckness" is defined. Specifically: What is the point at which 15 min countdown begins. Request processing start? Last wait()-like method? Something else? Does this apply only to request-processing threads or to all threads? I.e. can a request-processing thread "escape" this protection by spawning a worker thread for a long task? Especially, can it delegate response writing to such a worker without 15 min countdown? My usecase is download of huge files through a permission system. Since a user needs to be authenticated and have permissions to view a file, I cannot (or at least don't know how) leave this to a simple HTTP server, e.g. Apache. And because files can be huge, download could (at least in theory) take more than 15 minutes.

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  • WCF ChannelFactory caching

    - by Myles J
    I've just read this great article on WCF ChannelFactory caching by Wenlong Dong. My question is simply how can you actually prove that the ChannelFactory is in fact being cached between calls? I've followed the rules regarding the ClientBase’s constructors. We are using the following overloaded constructor on our object that inherits from ClientBase: ClientBase(string endpointConfigurationName, EndpointAddress remoteAddress); In the article mentioned above it is stated that: For these constructors, all arguments (including default ones) are in the following list: · InstanceContext callbackInstance · string endpointConfigurationName · EndpointAddress remoteAddress As long as these three arguments are the same when ClientBase is constructed, we can safely assume that the same ChannelFactory can be used. Fortunately, String and EndpointAddress types are immutable, i.e., we can make simple comparison to determine whether two arguments are the same. For InstanceContext, we can use Object reference comparison. The type EndpointTrait is thus used as the key of the MRU cache. To test the ChannelFactory cache theory we are checking the Hashcode in the ClientBase constructor e.g. var testHash = RuntimeHelpers.GetHashCode(base.ChannelFactory); The hash value is different between calls which makes us think that the ChannelFactory isn't actually cached. Any thoughts? Regards Myles

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  • Gomoku array-based AI-algorithm?

    - by Lasse V. Karlsen
    Way way back (think 20+ years) I encountered a Gomoku game source code in a magazine that I typed in for my computer and had a lot of fun with. The game was difficult to win against, but the core algorithm for the computer AI was really simply and didn't account for a lot of code. I wonder if anyone knows this algorithm and has some links to some source or theory about it. The things I remember was that it basically allocated an array that covered the entire board. Then, whenever I, or it, placed a piece, it would add a number of weights to all locations on the board that the piece would possibly impact. For instance (note that the weights are definitely wrong as I don't remember those): 1 1 1 2 2 2 3 3 3 444 1234X4321 3 3 3 2 2 2 1 1 1 Then it simply scanned the array for an open location with the lowest or highest value. Things I'm fuzzy on: Perhaps it had two arrays, one for me and one for itself and there was a min/max weighting? There might've been more to the algorithm, but at its core it was basically an array and weighted numbers Does this ring a bell with anyone at all? Anyone got anything that would help?

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  • UITabbar without controller

    - by Etienne
    Hello. I have a simple app where the only view controller has an outlet to a UITabBar. It also implements UITabBarDelegate and is set as the delegate for the UITabBar: @interface TheMainViewController : UIViewController <UITabBarDelegate> { IBOutlet UITabBar *theTabBar; } I implemented the following method Which gets called whenever any of my 4 UITabBarItems get tapped. I tried just doing something really simple: - (void)tabBar:(UITabBar *)tabBar didSelectItem:(UITabBarItem *)item { tabBar.selectedItem = [tabBar.items objectAtIndex:0]; return; } In theory, it should always stay selected on my first tab and it works perfectly when I just tap any UITabBarItem (nothing happens, the first one always stays selected). But when I touch a UITabBarItem and hold it (not taking my finger off) the selection changes anyway ! Debugging, everything gets called properly. It's like changing the selectedItem property doesn't have any effect is the user still has the item "down" (with his finger on it). What would be a good workaround? I tried overloading UITabBar and messing with touchesBegan and touchesEnd but they don't even get called. Same with UITabBarItem. Oh and please don't suggest using a UITabBarController as it is not flexible enough for my application. So frustrating....thanks!

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  • Synchronizing Asynchronous request handlers in Silverlight environment

    - by Eric Lifka
    For our senior design project my group is making a Silverlight application that utilizes graph theory concepts and stores the data in a database on the back end. We have a situation where we add a link between two nodes in the graph and upon doing so we run analysis to re-categorize our clusters of nodes. The problem is that this re-categorization is quite complex and involves multiple queries and updates to the database so if multiple instances of it run at once it quickly garbles data and breaks (by trying to re-insert already used primary keys). Essentially it's not thread safe, and we're trying to make it safe, and that's where we're failing and need help :). The create link function looks like this: private Semaphore dblock = new Semaphore(1, 1); // This function is on our service reference and gets called // by the client code. public int addNeed(int nodeOne, int nodeTwo) { dblock.WaitOne(); submitNewNeed(createNewNeed(nodeOne, nodeTwo)); verifyClusters(nodeOne, nodeTwo); dblock.Release(); return 0; } private void verifyClusters(int nodeOne, int nodeTwo) { // Run analysis of nodeOne and nodeTwo in graph } All copies of addNeed should wait for the first one that comes in to finish before another can execute. But instead they all seem to be running and conflicting with each other in the verifyClusters method. One solution would be to force our front end calls to be made synchronously. And in fact, when we do that everything works fine, so the code logic isn't broken. But when it's launched our application will be deployed within a business setting and used by internal IT staff (or at least that's the plan) so we'll have the same problem. We can't force all clients to submit data at different times, so we really need to get it synchronized on the back end. Thanks for any help you can give, I'd be glad to supply any additional information that you could need!

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  • WCF push to client through firewall?

    - by Sire
    See also How does a WCF server inform a WCF client about changes? (Better solution then simple polling, e.g. Coment or long polling) I need to use push-technology with WCF through client firewalls. This must be a common problem, and I know for a fact it works in theory (see links below), but I have failed to get it working, and I haven't been able to find a code sample that demonstrates it. Requirements: WCF Clients connects to server through tcp port 80 (netTcpBinding). Server pushes back information at irregular intervals (1 min to several hours). Users should not have to configure their firewalls, server pushes must pass through firewalls that have all inbound ports closed. TCP duplex on the same connection is needed for this, a dual binding does not work since a port has to be opened on the client firewall. Clients sends heartbeats to server at regular intervals (perhaps every 15 mins) so server knows client is still alive. Server is IIS7 with WAS. The solution seems to be duplex netTcpBinding. Based on this information: WCF through firewalls and NATs Keeping connections open in IIS But I have yet to find a code sample that works.. I've tried combining the "Duplex" and "TcpActivation" samples from Microsoft's WCF Samples without any luck. Please can someone point me to example code that works, or build a small sample app. Thanks a lot!

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  • Ruby - Feedzirra and updates

    - by mplacona
    Hi, trying to get my head around Feedzirra here. I have it all setup and everything, and can even get results and updates, but something odd is going on. I came up with the following code: def initialize(feed_url) @feed_url = feed_url @rssObject = Feedzirra::Feed.fetch_and_parse(@feed_url) end def update_from_feed_continuously() @rssObject = Feedzirra::Feed.update(@rssObject) if @rssObject.updated? puts @rssObject.new_entries.count else puts "nil" end end Right, what I'm doing above, is starting with the big feed, and then only getting updates. I'm sure I must be doing something stupid, as even though I'm able to get the updates, and store them on the same instance variable, after the first time, I'm never able to get those again. Obviously this happens because I'm overwriting my instance variable with only updates, and lose the full feed object. I then thought about changing my code to this: def update_from_feed_continuously() feed = Feedzirra::Feed.update(@rssObject) if feed.updated? puts feed.new_entries.count else puts "nil" end end Well, I'm not overwriting anything and that should be the way to go right? WRONG, this means I'm doomed to always try to get updates to the same static feed object, as although I get the updates on a variable, I'm never actually updating my "static feed object", and newly added items will be appended to my "feed.new_entries" as they in theory are new. I'm sure I;m missing a step here, but I'd really appreciate if someone could shed me a light on it. I've been going through this code for hours, and can't get to grips with it. Obviously it should work fine, if I did something like: if feed.updated? puts feed.new_entries.count @rssObject = initialize(@feed_url) else Because that would reinitialize my instance variable with a brand new feed object, and the updates would come again. But that also means that any new update added on that exact moment would be lost, as well as massive overkill, as I'd have to load the thing again. Thanks in advance!

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  • PHPUnit Selenium captureScreenshotOnFailure does not work?

    - by user342775
    I am using PHPUnit 3.4.12 to drive my selenium tests. I'd like to be able to get a screenshot taken automatically when a test fails. This should be supported as explained at http://www.phpunit.de/manual/current/en/selenium.html#selenium.seleniumtestcase.examples.WebTest2.php class WebTest { protected $captureScreenshotOnFailure = true; protected $screenshotPath = 'C:\selenium'; protected $screnshotUrl = 'http://localhost/screenshots'; public function testLandingPage($selenium) { $selenium->open("http://www.example.com"); $selenium->fail("fail"); ... } } As you can see, I am making the test to fail and in theory when it does it should take a screenshot and put it in C:\selenium, as I am running the selenium RC server on Windows. However, when I run the test it will just give me the following: [root@testbox selenium]$ sh run PHPUnit 3.4.12 by Sebastian Bergmann. F Time: 8 seconds, Memory: 5.50Mb There was 1 failure: 1) WebTest::testLandingPage fail /home/root/selenium/WebTest.php:32 FAILURES! Tests: 1, Assertions: 0, Failures: 1. I do not see any screenshot in C:\selenium. I can however get a screenshot with $selenium-captureScreenshot("C:/selenium/image.png"); Any ideas or suggestions most welcome. Thanks

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  • Implementing a 2 Legged OAuth Provider

    - by Rob Wilkerson
    I'm trying to find my way around the OAuth spec, its requirements and any implementations I can find and, so far, it really seems like more trouble than its worth because I'm having trouble finding a single resource that pulls it all together. Or maybe it's just that I'm looking for something more specialized than most tutorials. I have a set of existing APIs--some in Java, some in PHP--that I now need to secure and, for a number of reasons, OAuth seems like the right way to go. Unfortunately, my inability to track down the right resources to help me get a provider up and running is challenging that theory. Since most of this will be system-to-system API usage, I'll need to implement a 2-legged provider. With that in mind... Does anyone know of any good tutorials for implementing a 2-legged OAuth provider with PHP? Given that I have securable APIs in 2 languages, do I need to implement a provider in both or is there a way to create the provider as a "front controller" that I can funnel all requests through? When securing PHP services, for example, do I have to secure each API individually by including the requisite provider resources on each? Thanks for your help.

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  • Setting httponly in JSESSIONID cookie (Java EE 5)

    - by mythandros
    I'm trying to set the httponly flag on the JSESSIONID cookie. I'm working in Java EE 5, however, and can't use setHttpOnly(). First I tried to create my own JSESSIONID cookie from within the servlet's doPost() by using response.setHeader(). When that didn't work, I tried response.addHeader(). That didn't work either. Then, I learned that the servlet handled converting the session into a JSESSIONID cookie and inserting it into the http header so if I want to play with that cookie, I'll have to write a filter. I wrote a filter and played with setHeader()/addHeader() there, again to no avail. Then, I learned that there's some flush/close action going on in the response object before it gets to the filter so if I want to manipulate the data, I need to extend HttpServletResponseWrapper and pass that to filterChain.doFilter(). This is done but I'm still not getting results. Clearly I'm doing something wrong but I don't know what. I'm not sure if this is at all relevant to the question at hand but no html document is being returned by the servlet to the browser. All that's really happening is that some objects are being populated and returned to a JSP document. I've sort of assumed that The Session object is turned into a JSESSIONID cookie and wrapped -- along with the objects added to the request -- in an http header before being sent to the browser. I'd be happy to post some code but I want to rule out the possibility that my difficulties stem from a misunderstanding of the theory first.

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  • Facebooker Causing Problems with Rails Integration Testing

    - by Eric Lubow
    I am (finally) attempting to write some integration tests for my application (because every deploy is getting scarier). Since testing is a horribly documented feature of Rails, this was the best I could get going with shoulda. class DeleteBusinessTest < ActionController::IntegrationTest context "log skydiver in and" do setup do @skydiver = Factory( :skydiver ) @skydiver_session = SkydiverSession.create(@skydiver) @biz = Factory( :business, :ownership = Factory(:ownership, :skydiver = @skydiver )) end context "delete business" do setup do @skydiver_session = SkydiverSession.find post '/businesses/destroy', :id = @biz.id end should_redirect_to('businesses_path()'){businesses_path()} end end end In theory, this test seems like it should pass. My factories seem like they are pushing the right data in: Factory.define :skydiver do |s| s.sequence(:login) { |n| "test#{n}" } s.sequence(:email) { |n| "test#{n}@example.com" } s.crypted_password '1805986f044ced38691118acfb26a6d6d49be0d0' s.password 'secret' s.password_confirmation { |u| u.password } s.salt 'aowgeUne1R4-F6FFC1ad' s.firstname 'Test' s.lastname 'Salt' s.nickname 'Mr. Password Testy' s.facebook_user_id '507743444' end The problem I am getting seems to be from Facebooker only seems to happen on login attempts. When the test runs, I am getting the error: The error occurred while evaluating nil.set_facebook_session. I believe that error is to be expected in a certain sense since I am not using Facebook here for this session. Can anyone provide any insight as to how to either get around this or at least help me out with what is going wrong?

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  • Excel export displaying '#####...'

    - by Cypher
    I'm trying to export an Excel database into .txt (Tab Delimited), but some of my cells are quite large. When I export into a txt some of the cells are exported as '#######....' which is surprisingly useless. Has this happened to anyone else? Do you know an easy fix? Data from one cell of my column: Accounting, African Studies, Agricultural/Bioresource Engineering, Agricultural Economics, Agricultural Science, Anatomy/Cell Biology, Animal Biology, Animal Science, Anthropology, Applied Zoology, Architecture, Art History, Atmospheric/Oceanic Science, Biochemistry, Biology, Botanical Sciences, Canadian Studies, Chemical Engineering, Chemistry/Bio-Organic/Environmental/Materials,ChurchMusicPerformance, Civil Engineering/Applied Mechanics, Classics, Composition, Computer Engineering,ComputerScience, ContemporaryGerman Studies, Dietetics, Early Music Performance, Earth/Planetary Sciences, East Asian Studies, Economics, Electrical Engineering, English Literature/ Drama/Theatre/Cultural Studies, Entrepreneurship, Environment, Environmental Biology, Finance, Food Science, Foundations of Computing, French Language/Linguistics/Literature/Translation, Geography, Geography/ Urban Systems, German, German Language/Literature/Culture, Hispanic Languages/Literature/Culture,History,Humanistic Studies, Industrial Relations, Information Systems, International Business, International Development Studies, Italian Studies/Medieval/Renaissance, Jazz Performance, Jewish Studies, Keyboard Studies, Kindergarten/Elementary Education, Kindergarten/Elementary Education/Jewish Studies,Kinesiology, Labor/Management Relations, Latin American/Caribbean Studies, Linguistics, Literature/Translation, Management Science, Marketing, Materials Engineering,Mathematics,Mathematics/Statistics,Mechanical Engineering, Microbiology, Microbiology/Immunology, Middle Eastern Studies, Mining Engineering, Music, Music Education, MusicHistory,Music Technology,Music Theory,North American Studies, Nutrition,OperationsManagement,OrganizationalBehavior/Human Resources Management, Performing Arts, Philosophy, Physical Education, Physics, Physiology, Plant Sciences, Political Science, Psychology, Quebec Studies, Religious Studies/Scriptures/Interpretations/World Religions,ResourceConservation,Russian, Science for Teachers,Secondary Education, Secondary Education/Music, Secondary Education/Science, SocialWork, Sociology, Software Engineering, Soil Science, Strategic Management, Teaching of French/English as a Second Language, Theology, Wildlife Biology, Wildlife Resources, Women’s Studies.

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  • Nested Routes and Parameters for Rails URLs (Best Practice)

    - by viatropos
    Hey there, I have a decent understanding of RESTful urls and all the theory behind not nesting urls, but I'm still not quite sure how this looks in an enterprise application, like something like Amazon, StackOverflow, or Google... Google has urls like this: http://code.google.com/apis/ajax/ http://code.google.com/apis/maps/documentation/staticmaps/ https://www.google.com/calendar/render?tab=mc Amazon like this: http://www.amazon.com/books-used-books-textbooks/b/ref=sa_menu_bo0?ie=UTF8&node=283155&pf_rd_p=328655101&pf_rd_s=left-nav-1&pf_rd_t=101&pf_rd_i=507846&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1PK4ZKN4YWJJ9B86ANC9 http://www.amazon.com/Ruby-Programming-Language-David-Flanagan/dp/0596516177/ref=sr_1_1?ie=UTF8&s=books&qid=1258755625&sr=1-1 And StackOverflow like this: http://stackoverflow.com/users/169992/viatropos http://stackoverflow.com/questions/tagged/html http://stackoverflow.com/questions/tagged?tagnames=html&sort=newest&pagesize=15 So my question is, what is best practice in terms of creating urls for systems like these? When do you start storing parameters in the url, when don't you? These big companies don't seem to be following the rules so hotly debated in the ruby community (that you should almost never nest URLs for example), so I'm wondering how you go about implementing your own urls in larger scale projects because it seems like the idea of not nesting urls breaks down at anything larger than a blog. Any tips?

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  • Why does the the Java VM not recover after "Too many open files" errors?

    - by Michael
    In certain well-understood circumstances, our application will open too many sockets (database connections) and reach the maximum open files that the OS allows. We understand this; we are fixing the issue and also bumping up the limit. What we can't explain is why parts of our application don't recover even after the number of connections abates and we're well within the limit. In this case, it's an application running under Tomcat. When this happens, we first start seeing "Too many open files" errors: SEVERE: Socket accept failed java.net.SocketException: Too many open files at java.net.PlainSocketImpl.socketAccept(Native Method) at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:390) at java.net.ServerSocket.implAccept(ServerSocket.java:453) at java.net.ServerSocket.accept(ServerSocket.java:421) at org.apache.tomcat.util.net.DefaultServerSocketFactory.acceptSocket(DefaultServerSocketFactory.java:61) at org.apache.tomcat.util.net.JIoEndpoint$Acceptor.run(JIoEndpoint.java:310) at java.lang.Thread.run(Thread.java:619) Eventually, we start seeing NoClassDefFoundErrors inside an application thread that's trying to open HTTP connections: java.lang.NoClassDefFoundError: org/apache/commons/httpclient/protocol/ControllerThreadSocketFactory at org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:128) at org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:707) at org.apache.commons.httpclient.MultiThreadedHttpConnectionManager$HttpConnectionAdapter.open(MultiThreadedHttpConnectionManager.java:1349) [...] Caused by: java.lang.ClassNotFoundException: org.apache.commons.httpclient.protocol.ControllerThreadSocketFactory at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1387) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1233) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) ... 8 more When the errant connections go away, the server starts accepting connections again, and everything seems ok, but we're left with the latter error constantly being spewed to stderr. Although the application typically logs unloaded classes to stdout, I don't see any such logs just before, during or after the "Too many open files" errors. My initial theory was that the Hotspot JVM would unload seemingly unused classes when it encounters "Too many open files," but if so, it doesn't log the fact. I'd also expect it to recover if that were the case. Platform details: Java(TM) SE Runtime Environment (build 1.6.0_14-b08) Java HotSpot(TM) 64-Bit Server VM (build 14.0-b16, mixed mode) Apache Tomcat Version 6.0.18

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  • What's all this fuss about?

    - by atch
    Hi guys, At the beginning I want to state that it is not my intention to upset anyone who uses/like language other than C++. I'm saying that due to the fact that on one forum everytime when I've tried to ask questions of similiar nature I was almost always accused of trying to create a raw. Ok that's having done this is my question: I don't understand why java/c# creators thought/think that having something like vm and having source code compiled to bytecode instead of native code is in a long run any advantage. And why having function compiled for a first time when they are invoked is any advantege? And what's the story about write once run everywhere? When I think about the business of having something written once and it can run everywhere - well in theory this is all well. But I know for a fact that in practice it doesn't look that well at all. It is rather like write once test everywhere. And why would I preffer something to be compiled on runtime instead of compiletime. If I would have to wait even one hour longer for program to be installed once and for all and all the compilation would be done and nothing would be compiled after that I would preffer that. And I don't really know how it works in the real world (I'm a student never worked in IT business) but for example if I have working program written in C++ for Windows and I have wish to move it to another platform wouldn't I have to take my source code and compile it on desired machine? So in other words isn't that rather problem of having compiler which will compile source code on different machines (as far as I'm concerned there is just one C++ and source code will look identical in every machine). And last but not least if you think about it how many programs they are which are really word porting? I personnally can think of 3 maybe four.

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  • Computer science textbooks

    - by Barrett Conrad
    I would like to try the book question a little bit differently. My goal is to know what the community thinks are the quintessential computer science textbooks. <beginsadstory>I lost all of my computer science and math books from college in Hurricane Katrina in 2005. I greatly miss having my familiar tomes to refer to when topics and problems come up, so I am looking to rebuild my library.<endsadstory> What are your recommendations for the best examples of academic caliber books for the field of computer science and its associated mathematics? I am looking for books on subjects like computational theory, programming languages, compilers, operating systems, algorithms and so on. Don't limit your suggestions to your textbooks only. If there is a book you have read that covers computer science or a related math in a formal way, but is not strictly a textbook, I would be love to hear about them as well. Finally, for the sake of creating a good reference for all of us, may I suggest posting one book per answer so they can be rated individually.

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  • Choosing random numbers efficiently

    - by Frederik Wordenskjold
    I have a method, which uses random samples to approximate a calculation. This method is called millions of times, so its very important that the process of choosing the random numbers is efficient. I'm not sure how fast javas Random().nextInt really are, but my program does not seem to benefit as much as I would like it too. When choosing the random numbers, I do the following (in semi pseudo-code): // Repeat this 300000 times Set set = new Set(); while(set.length != 5) set.add(randomNumber(MIN,MAX)); Now, this obviously has a bad worst-case running time, as the random-function in theory can add duplicated numbers for an eternity, thus staying in the while-loop forever. However, the numbers are chosen from {0..45}, so a duplicated value is for the most part unlikely. When I use the above method, its only 40% faster than my other method, which does not approximate, but yields the correct result. This is ran ~ 1 million times, so I was expecting this new method to be at least 50% faster. Do you have any suggestions for a faster method? Or maybe you know of a more efficient way of generation a set of random numbers.

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  • WCF- "The underlying connection was closed: The connection was closed unexpectedly"

    - by SumGuy
    Hi there. I'm recieving that wonderfuly ambiguous error message when using one of my webmethods on my WCF webservice. As that error message doesn't provide any explanation whatsoever allow me to post my theory. I believe it may have something to do with the return type I'm using I have a Types DLL which is refrenced in both the webservice and the client. In this DLL is the base class ExceptionMessages. There is a child of this class called DrawingExcepions. Here is some code: public class ExceptionMessages { public object[] ReturnValue { get; set; } } public class DrawingExceptions : ExceptionMessages { private List<DrawingException> des = new List<DrawingException>(); } public class DrawingException { public Exception ExceptionMsg { get; set; } public List<object> Errors { get; set; } } The using code: [OperationContract] ExceptionMessages createNewBom(Bom bom, DrawingFiles dfs); public ExceptionMessages createNewBOM(Bom bom, DrawingFiles dfs) { return insertAssembly(bom, dfs); } public DrawingExceptions insertAssembly(Bom bom, DrawingFiles dfs) { DrawingExceptions des = new DrawingExceptions(); foreach (DrawingFile d in dfs.drawingFiles) { DrawingException temp = insertNewDrawing(bom, d); if (temp != null) des.addDrawingException(temp); if (d.Child != null) des.addDrawingException(insertAssembly(bom, d.Child)); } return des; } Returns to: ExceptionMessages ems = client.createNewBom(bom, currentDFS); if (ems is DrawingExceptions) { } Basically the return type from the webmethod is ExceptionMessages however I would usually be sending the child class back instead. My only idea is that it's the child that's causing the error but as far as I've read, this should have no effect. Has anyone got any ideas what could be going wrong here? If any more info is required, just ask :) Thanks.

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  • CS Master's Degree Project vs. Thesis options

    - by Nwosh
    I'm doing a master's degree in computer science, and I'm currently at the point where I have to decide between the thesis and non-thesis options offered by my university. The thesis option was my first choice, it entails taking less courses but tends to take more time doing your thesis. The non-thesis option involves taking more coursework, taking a comprehensive exam, and doing a project in one semester with a faculty member. I'd like to pursue a PhD degree eventually (although not right away, I want to get some years of professional experience first), and I heard that having demonstrated the ability to work on a thesis helps a lot with admission (like: not doing thesis raises questions and suggests not being interested in research) and that the experience itself is very good. At the same time, almost everyone I know who did a thesis at my university took a long time (2-3 years), in theory it could be done in 1.5 years. I'm a part time student and I don't really want to spend so much time just getting a master's degree, I could still publish a few papers while working on the project option and I'd be done in a year or so, additionally, I heard having a master's degree with a project and more coursework is more desirable for the industry. So, when applying for a PhD degree in CS at some of the better universities, would the time spent working on the master's thesis help in getting me accepted? Or should I opt for the non-thesis option and hope that the extra coursework and publishing some papers would make up for not working on a thesis?

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  • Getting browser to make an AJAX call ASAP, while page is still loading

    - by Chris
    I'm looking for tips on how to get the browser to kick off an AJAX call as soon as possible into processing a web page, ideally before the page is fully downloaded. Here's my approximate motivation: I have a web page that takes, say, 5 seconds to load. It calls a web service that takes, say, 10 seconds to load. If loading the page and calling the web service happened sequentially, the user would have to wait 15 seconds to see all the information. However, if I can get the web service call started before the 5 second page load is complete, then at least some of the work can happened in parallel. Ideally I'd like as much of the work to happen in parallel as possible. My initial theory was that I should place the AJAX-calling javascript as high up as possible in the web page HTML source (being mindful of putting it after the jquery.js include, because I'm making the call using jquery ajax). I'm also being mindful not to wrap the AJAX call in a jquery ready event handler. (I mention this because ready events are popular in a lot of jquery example code.) However, the AJAX call still doesn't seem to get kicked off as early as I'm hoping (at least as judged by the Google Chrome "Timeline" feature), so I'm wondering what other considerations apply. One thing that might potentially be detrimental is that the AJAX call is back to the same web server that's serving the original web page, so I might be in danger of hitting a browser limit on the # of HTTP connections back to that one machine? (The HTML page loads a number of images, css files, etc..)

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  • Flash movies in inactive browser tabs pause or don't execute in real time

    - by ZenBlender
    I'm noticing some unexpected behavior. Some time in the last few months, a change in either Firefox, the Flash player, or both, has made it so that Flash movies that are in inactive browser tabs no longer execute in real time. They appear to still execute, but only in bursts, and not in a predictable way. This is a problem because I develop a Flash-based (Actionscript 2.0, Flash CS3) multiplayer game that maintains a network connection and allows players to chat, etc. Many of our players complain about Firefox crashing while playing the game. I have noticed it too, not too frequently, but it crashes several times a week. (Firefox crashes, I do not get a message from Flash player that indicates an infinite loop or problem in my code) My theory is that this new behavior is causing crashes when there is a lot of activity in my game, leading to lots of unhandled network traffic for my game getting buffered before Firefox/Flash will give it a chance to execute. Maybe this leads to a buffer overflow or missing packets, and as a result, something crashes. At times I will switch back to the tab that is running my game and discover a display bug, which looks as though Flash has simply failed to execute something that it was supposed to. I would assume this new behavior is on purpose, for example to prevent all the Flash-based advertisements in inactive tabs from executing and therefore killing performance. In a quick test on Chrome (5.0.342.9 beta), this "pausing" of Flash seems to be there as well, but somehow it seems much less of a problem. My users have only complained about Firefox crashing, not other browsers. My machine: Windows 7 x64 Firefox 3.6.3 Flash Player 10.1.50.426 My game: triplejack.com Any ideas? Ideally I'd like to disable this behavior for my Flash game so it can execute in real time even when in an inactive tab. Thanks for any help!

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  • F# and .Net versions

    - by rwallace
    I'm writing a program in F# at the moment, which I specified in the Visual Studio project setup to target .Net 3.5, this being the highest offered, on the theory that I might as well get the best available. Then I tried just now running the compiled program on an XP box, not expecting it to work, but just to see what would happen. Unsurprisingly I just got an error message demanding an appropriate version of the framework, but surprisingly it wasn't 3.5 it demanded, but 2.0.50727. An additional puzzle is the version of MSBuild I'm using to compile the release version of the program, which I found in the framework 3.5 directory but claims to be framework 2.0 and build engine 3.5. I just guessed it was the right version of MSBuild to use because it seemed to correspond with the highest framework version F# seems to be able to target, but should I be using a different version? Anyone have any idea what's going on? C:\Windows>dir/s msbuild.exe Volume in drive C is OS Volume Serial Number is 0422-C2D0 Directory of C:\Windows\Microsoft.NET\Framework\v2.0.50727 27/07/2008 19:03 69,632 MSBuild.exe 1 File(s) 69,632 bytes Directory of C:\Windows\Microsoft.NET\Framework\v3.5 29/07/2008 23:40 91,136 MSBuild.exe 1 File(s) 91,136 bytes Directory of C:\Windows\Microsoft.NET\Framework\v4.0.30319 18/03/2010 16:47 132,944 MSBuild.exe 1 File(s) 132,944 bytes Directory of C:\Windows\winsxs\x86_msbuild_b03f5f7f11d50a3a_6.0.6000.16386_none_815e96e1b0e084be 20/10/2006 02:14 69,632 MSBuild.exe 1 File(s) 69,632 bytes Directory of C:\Windows\winsxs\x86_msbuild_b03f5f7f11d50a3a_6.0.6000.16720_none_81591d45b0e55432 27/07/2008 19:00 69,632 MSBuild.exe 1 File(s) 69,632 bytes Directory of C:\Windows\winsxs\x86_msbuild_b03f5f7f11d50a3a_6.0.6000.20883_none_6a9133e9ca879925 27/07/2008 18:55 69,632 MSBuild.exe 1 File(s) 69,632 bytes C:\Windows>cd Microsoft.NET\Framework\v3.5 C:\Windows\Microsoft.NET\Framework\v3.5>msbuild /ver Microsoft (R) Build Engine Version 3.5.30729.1 [Microsoft .NET Framework, Version 2.0.50727.3053] Copyright (C) Microsoft Corporation 2007. All rights reserved. 3.5.30729.1

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  • Subdomain on different host

    - by mattsmith321
    Hi everyone! I'm trying to host a subdomain for my site with a different hosting company and I'm running into issues on how to set it up. Here are the specifics: - Domain is registered with GoDaddy. - Nameservers are pointing to DiscountASP.net where ASP.NET app has been happily running for couple of years. - Would like blog.mydomain.com to point to my account with DreamHost.com to take advantage of their LAMP stack. I have added blog.mydomain.com to DreamHost (after adding mydomain.com) via their control panel. I thought I would be able to add a subdomain entry on GoDaddy to point to DreamHost, but all they allow is blog.mydomain.com = new url. In theory I could just take our .biz or .net domain and host it on DreamHost but was hoping I could do it all with a subdomain. So, to summarize I'd like to know if what I want to do is feasible and if so, how do I go about it (given the constraints of GoDaddy, DiscountASP, & DreamHost). Thanks, Matt

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