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  • How to make active services highly available?

    - by Jader Dias
    I know that with Network Load Balancing and Failover Clusteringwe can make passive services highly available. But what about active apps? Example: One of my apps retrieves some content from a external resource in a fixed interval. I have imagined the following scenarios: Run it in a single machine. Problem: if this instance falls, the content won't be retrieved Run it in each machine of the cluster. Problem: the content will be retrieved multiple times Have it in each machine of the cluster, but run it only in one of them. Each instance will have to check some sort of common resource to decide whether it its turn to do the task or not. When I was thinking about the solution #3 I have wondered what should be the common resource. I have thought of creating a table in the database, where we could use it to get a global lock. Is this the best solution? How does people usually do this? By the way it's a C# .NET WCF app running on Windows Server 2008

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  • help optimize sql query

    - by msony
    I have tracking table tbl_track with id, session_id, created_date fields I need count unique session_id for one day here what i got: select count(0) from ( select distinct session_id from tbl_track where created_date between getdate()-1 and getdate() group by session_id )tbl im feeling that it could be better solution for it

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  • Caching Authentication Data

    - by PartlyCloudy
    Hi, I'm currently implementing a REST web service using CouchDB and RESTlet. The RESTlet layer is mainly for authentication and some minor filtering of the JSON data served by CouchDB: Clients <= HTTP = [ RESTlet <= HTTP = CouchDB ] I'm using CouchDB also to store user login data, because I don't want to add an additional database server for that purpose. Thus, each request to my service causes two CouchDB requests conducted by RESTlet (auth data + "real" request). In order to keep the service as efficent as possible, I want to reduce the number of requests, in this case redundant requests for login data. My idea now is to provide a cache (i.e.LRU-Cache via LinkedHashMap) within my RESTlet application that caches login data, because HTTP caching will probabily not be enough. But how do I invalidate the cache data, once a user changes the password, for instance. Thanks to REST, the application might run on several servers in parallel, and I don't want to create a central instance just to cache login data. Currently, I save requested auth data in the cache and try to auth new requests by using them. If a authentication fails or there is now entry available, I'll dispatch a GET request to my CouchDB storage in order to obtain the actual auth data. So in a worst case, users that have changed their data will perhaps still be able to login with their old credentials. How can I deal with that? Or what is a good strategy to keep the cache(s) up-to-date in general? Thanks in advance.

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  • Is there a generic class to write structured Text Files?

    - by Burnsys
    I have several projects that need to write structured Textfiles, some with fixed size fields, other delimited by characters. Is there a .net class that could be used for that? I know there is a "Microsoft.VisualBasic.FileIO.TextFieldParser" that is useful for reading textfiles, i am actually searching for a ""Microsoft.VisualBasic.FileIO.TextFieldWriter" Related: http://stackoverflow.com/questions/34182/reading-text-files-using-net

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  • What is the recommended approach towards multi-tenant databases in MongoDB?

    - by Braintapper
    I'm thinking of creating a multi-tenant app using MongoDB. I don't have any guesses in terms of how many tenants I'd have yet, but I would like to be able to scale into the thousands. I can think of three strategies: All tenants in the same collection, using tenant-specific fields for security 1 Collection per tenant in a single shared DB 1 Database per tenant The voice in my head is suggesting that I go with option 2. Thoughts and implications, anyone?

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  • Get list of duplicate rows in MySql

    - by user347033
    Hi, i have a table like this ID nachname vorname 1 john doe 2 john doe 3 jim doe 4 Michael Knight I need a query that will return all the fields (select *) from the records that have the same nachname and vorname (in this case, records 1 and 2). Can anyone help me with this? Thanks

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  • Fastest way to convert a list of doubles to a unique list of integers?

    - by javanix
    I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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  • Javascript onclick stops working, multiple dynamically created divs.

    - by Patrick
    I have run into a strange problem, i am creating a lot of dynamically divs. And i recently found out that some of my divs doesn't fire the onclick event? All the divs are created using the same template, so why are some not working? Most of the time, its the 4-5 from the bottom. If you click on one of the others and then try again, you might get one of those to trigger. But only sporadically. Code to create the divs: GameField.prototype.InitField = function(fieldNumber) { var newField = document.createElement("div"); if (fieldNumber == 0 || fieldNumber == 6 || fieldNumber == 8 || fieldNumber == 17) newField.className = 'gameCellSmall borderFull gameText gameTextAlign'; else newField.className = 'gameCellSmall borderWithoutTop gameText gameTextAlign'; var instance = this; if (fieldNumber == 6 || fieldNumber == 7 || fieldNumber == 17) { } else newField.onclick = function() { instance.DivClick(fieldNumber); return false; } this.fields[fieldNumber] = newField; this.score[fieldNumber] = 0; return newField; } I added the return false to the click function, but it still behaves strangely. Why are some not triggering? I create around 18 divs / player. But it happens even if i just create one player. Do i perhaps need to cancel the event once i am done with it? (Like the return false; is trying to do)

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  • Error querying database.

    - by user296516
    Hi, Once I have successfully connected to the database, i have a line that must insert values. mysqli_query($edb, "INSERT INTO elvis_table (name,email) VALUES ('$name','$email')" ) or die('Error querying database.'); It works fine on my computer ( xampp ), but once I upload it onto a server, it starts giving an error. Yes, I have a database with a corresponding table and fields on a server, it connects to the database fine, but gives an error on this line... Thanks!

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  • Spring Transactional Parameterized Test and Autowiring

    - by James Kingsbery
    Is there a way to get a class that extends AbstractTransactionalJUnit4SpringContexts to play nicely with JUnit's own @RunWith(Parameterized), so that fields marked as Autowired get wired in properly? @RunWith(Parameterized) public class Foo extends AbstractTransactionalJUnit4SpringContexts { @Autowired private Bar bar @Parameters public static Collection data() { // return parameters, following pattern in // http://junit.org/apidocs/org/junit/runners/Parameterized.html } @Test public void someTest(){ bar.baz() //NullPointerException } }

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  • Should I define a single "DataContext" and pass references to it around or define muliple "DataConte

    - by Nate Bross
    I have a Silverlight application that consists of a MainWindow and several classes which update and draw images on the MainWindow. I'm now expanding this to keep track of everything in a database. Without going into specifics, lets say I have a structure like this: MainWindow Drawing-Surface Class1 -- Supports Drawing DataContext + DataServiceCollection<T> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) Class3 Each "Class" is passed a reference to the Drawing Surface so they can interact with it independently. I'm starting to use WCF Data Services in Class1 and its working well; however, the other classes are also going to need access to the WCF Data Services. (Should I define my "DataContext" in MainWindow and pass a reference to each child class?) Class1 will need READ access to the "transactions" data, and Class2 will need READ access to some of the drawing data. So my question is, where does it make the most sense to define my DataContext? Does it make sense to: Define a "global" WCF Data Service "Context" object and pass references to that in all of my subsequent classes? Define an instance of the "Context" for each Class1, Class2, etc Have each method that requires access to data define its own instance of the "Context" and use closures handle the async load/complete events? Would a structure like this make more sense? Is there any danger in keeping an active "DataContext" open for an extended period of time? Typical usecase of this application could range from 1 minute to 40+ minutes. MainWindow Drawing-Surface DataContext Class1 -- Supports Drawing DataServiceCollection<DrawingType> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) DataServiceCollection<TransactionType> w/events Class3 DataServiceCollection<T> w/events

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  • XmlSerialize a custom collection with an Attribute

    - by roomaroo
    I've got a simple class that inherits from Collection and adds a couple of properties. I need to serialize this class to XML, but the XMLSerializer ignores my additional properties. I assume this is because of the special treatment that XMLSerializer gives ICollection and IEnumerable objects. What's the best way around this? Here's some sample code: using System.Collections.ObjectModel; using System.IO; using System.Xml.Serialization; namespace SerialiseCollection { class Program { static void Main(string[] args) { var c = new MyCollection(); c.Add("Hello"); c.Add("Goodbye"); var serializer = new XmlSerializer(typeof(MyCollection)); using (var writer = new StreamWriter("test.xml")) serializer.Serialize(writer, c); } } [XmlRoot("MyCollection")] public class MyCollection : Collection<string> { [XmlAttribute()] public string MyAttribute { get; set; } public MyCollection() { this.MyAttribute = "SerializeThis"; } } } This outputs the following XML (note MyAttribute is missing in the MyCollection element): <?xml version="1.0" encoding="utf-8"?> <MyCollection xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <string>Hello</string> <string>Goodbye</string> </MyCollection> What I want is <MyCollection MyAttribute="SerializeThis" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <string>Hello</string> <string>Goodbye</string> </MyCollection> Any ideas? The simpler the better. Thanks.

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  • how to get access to private members of nested class?

    - by macias
    Background: I have enclosed (parent) class E with nested class N with several instances of N in E. In the enclosed (parent) class I am doing some calculations and I am setting the values for each instance of nested class. Something like this: n1.field1 = ...; n1.field2 = ...; n1.field3 = ...; n2.field1 = ...; ... It is one big eval method (in parent class). My intention is -- since all calculations are in parent class (they cannot be done per nested instance because it would make code more complicated) -- make the setters only available to parent class and getters public. And now there is a problem: when I make the setters private, parent class cannot acces them when I make them public, everybody can change the values and C# does not have friend concept I cannot pass values in constructor because lazy evaluation mechanism is used (so the instances have to be created when referencing them -- I create all objects and the calculation is triggered on demand) I am stuck -- how to do this (limit access up to parent class, no more, no less)? I suspect I'll get answer-question first -- "but why you don't split the evaluation per each field" -- so I answer this by example: how do you calculate min and max value of a collection? In a fast way? The answer is -- in one pass. This is why I have one eval function which does calculations and sets all fields at once.

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  • Does pressing Back always cause Activity to finish()?

    - by stormin986
    I've heard that pressing the back button will essentially cause the current Activity to finish(). Is this always the case? Seems like it would be with the way it pops the Activity off the stack. The one situation I'm not so sure about is when the root Activity in a Task has back pressed. I'm currently experiencing a very weird effect, described as follows: On loading my application, the first Activity is for initialization, and once it finishes, it calls my main Activity (a TabActivity). This first init activity has android:noHistory="true" set in the Manifest so pressing Back from my main Activity won't go back to that. It goes to the Launcher. When I click on my App in the Launcher a second time, the initialization activity loads again, and loads the main Activity when done. Almost immediately after, it loads a second instance of my main Activity. But ONLY after the Application has already been run once, and was exited by pressing BACK from the main Activity. It does it every subsequent time until I force quit the app or load a new version from the IDE. Based on this, I am suspecting some kind of Activity instance is lying around and being reused, since it only happens on the second+ time I run the application (and exit with BACK -- using HOME just returns to the last state of the app, no big deal). Anyone have any thoughts??

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  • Common lisp, CFFI, and instantiating c structs

    - by andrew
    Hi, I've been on google for about, oh, 3 hours looking for a solution to this "problem." I'm trying to figure out how to instantiate a C structure in lisp using CFFI. I have a struct in c: struct cpVect{cpFloat x,y;} Simple right? I have auto-generated CFFI bindings (swig, I think) to this struct: (cffi:defcstruct #.(chipmunk-lispify "cpVect" 'classname) (#.(chipmunk-lispify "x" 'slotname) :double) (#.(chipmunk-lispify "y" 'slotname) :double)) This generates a struct "VECT" with slots :X and :Y, which foreign-slot-names confirms (please note that I neither generated the bindings or programmed the C library (chipmunk physics), but the actual functions are being called from lisp just fine). I've searched far and wide, and maybe I've seen it 100 times and glossed over it, but I cannot figure out how to create a instance of cpVect in lisp to use in other functions. Note the function: cpShape *cpPolyShapeNew(cpBody *body, int numVerts, cpVect *verts, cpVect offset) Takes not only a cpVect, but also a pointer to a set of cpVects, which brings me to my second question: how do I create a pointer to a set of structs? I've been to http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html and tried the code, but get "Error: Unbound variable: PTR" (I'm in Clozure CL), not to mention that looks to only return a pointer, not an instance. I'm new to lisp, been going pretty strong so far, but this is the first real problem I've hit that I can't figure out. Thanks!

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  • PDF to PNG Processor - Paperclip

    - by Josh Crowder
    I am trying to develop a system in which a user can upload a slideshow (pdf) and it'll export each slide as a png. After some digging around I came across a post on here that suggested using a processor. I've had a go, but I cant get the command to run, if it is running then I don't know what is happening because no errors are being shown. Any help would be appreciated! module Paperclip class Slides < Processor def initialize(file, options = {}, attachment = nill) super @file = file @instance = options[:instance] @current_format = File.extname(@file.path) @basename = File.basename(@file.path, @current_format) end def make dst = Tempfile.new( [ @basename, @format].compact.join(".")) dst.binmode command = <<-end_command -size 640x300 #{ File.expand_path(dst.path) } tester.png end_command begin success = Paperclip.run("convert", command.gsub(/\s+/, " "))) rescue PaperclipCommandLineError raise PaperclipError, "There was an error processing the thumbnail for #{@basename}" end end end end I think my problem is with the convert command... When I run that command by hand, it works but it doesn't give the details of each slide it just executes it. What I need to happen is once its made all the slides, pass back the data to a new model... or I know where all the slides are, but once I get to that point I'm not sure what todo.

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  • XSLT - How to select top a to top b

    - by user812241
    how can I extract the first 2 C-Values ('Baby' and 'Cola') where B is 'RED'. Input instance is: <Root> <A> <B>BLACK</B> <C>Apple</C> </A> <A> <B>RED</B> <C>Baby</C> </A> <A> <B>GREEN</B> <C>Sun</C> </A> <A> <B>RED</B> <C>Cola</C> </A> <A> <B>RED</B> <C>Mobile</C> </A> </Root> Output instance must be: <Root> <D>Baby</D> <D>Cola</D> </Root> I thought about the combination of for-each and global variables. But in XSLT it is not possible to change the value for a global variable to break the for-each. I have no idea anymore.

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  • Using XPath on String in Android (JAVA)

    - by Rav
    I am looking for some examples of using xpath in Android? Or if anyone can share their experiences. I have been struggeling to make tail or head of this problem :-( I have a string that contains a standard xml file. I believe I need to convert that into an xml document. I have found this code which I think will do the trick: public static Document stringToDom(String xmlSource) throws SAXException, ParserConfigurationException, IOException { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); return builder.parse(new InputSource(new StringReader(xmlSource))); } Next steps Assuming the code above is OK, I need to apply xpath to get values from cat: "/animal/mammal/feline/cat" I look at the dev doc here: http://developer.android.com/reference/javax/xml/xpath/XPath.html and also look online, but I am not sure where to start! I have tried to use the following code: XPathFactory xPathFactory = XPathFactory.newInstance(); // To get an instance of the XPathFactory object itself. XPath xPath = xPathFactory.newXPath(); // Create an instance of XPath from the factory class. String expression = "SomeXPathExpression"; XPathExpression xPathExpression = xPath.compile(expression); // Compile the expression to get a XPathExpression object. Object result = xPathExpression.evaluate(xmlDocument); // Evaluate the expression against the XML Document to get the result. But I get "Cannot be resolved". Eclipse doesn't seem to be able to fix this import. I tried manually entering: javax.xml.xpath.XPath But this did not work. Does anyone know any good source code that I can utilise, for Android platform? 1.5

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  • How do I populate a MEF plugin with data that is not hard coded into the assembly?

    - by hjoelr
    I am working on a program that will communicate with various pieces of hardware. Because of the varied nature of the items it communicates and controls, I need to have a different "driver" for each different piece of hardware. This made me think that MEF would be a great way to make those drivers as plugins that can be added even after the product has been released. I've looked at a lot of examples of how to use MEF, but the question that I haven't been able to find an answer to is how to populate a MEF plugin with external data (eg. from a database). All the examples I can find have the "data" hard-coded into the assembly, like the following example: [Export( typeof( IRule ) )] public class RuleInstance : IRule { public void DoIt() {} public string Name { get { return "Rule Instance 3"; } } public string Version { get { return "1.1.0.0"; } } public string Description { get { return "Some Rule Instance"; } } } What if I want Name, Version and Description to come from a database? How would I tell MEF where to get that information? I may be missing something very obvious, but I don't know what it is. Thanks! Joel

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