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  • HBase as web app backend

    - by NathanD
    Can anyone advise if it is a good idea to have HBase as primary data source for web-based application? My primary concern is HBase's response time to queries. Is it possible to have sub-second response? edit: more details about the app itself. Amount of data: ~500GB of text data, expect to reach 1TB soon Number of concurrent users using the app: up to 50 The app will be used to present reports about data stored in HBase, like how many times keyword "X" occured in last 24h. For ~80% of requests from that app I will know the exact key, 20% will be scans (I'm looking into HBase schema design related topics to make it run fast)

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  • What is my problem with ASP.NET pubslishing?

    - by Shankarooni
    I am done testing my site and I want to upload it to a site like this http://www.university.edu/mydepartment/myname the admin told me the server runs on .NET 3.5. So i used Linq ... now i tried to upload the site by two ways: when i just copy everything (with modification of web.config database settings) i get an error: CS0246: The type or namespace name 'DataClassesDataContext' could not be found (are you missing a using directive or an assembly reference?) Version Information: Microsoft .NET Framework Version:2.0.50727.3082; ASP.NET Version:2.0.50727.3082 Note here it says version 2.0 did he just lie to me? or its my configuration mistake? anyway, i added the reference, nothing changes. I tried also publishing (Build, publish) with option to keep the pre-comiled site updatable, and I get one line saying: this is a makefile and should be deleted! what is going on?

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  • Uniquely identify two instances of one browser that share Session state?

    - by jdk
    I want to make sure that a user isn't editing the same form data in two different browser tabs or windows (of the same web browser instance). It's to stop the user from stupidly overwriting their own data as they continue through a very long form process. On the server ongoing data input through the screens is collected into the Session. Assume for any browser, all tabs and windows run in the same instance of it (i.e. not each in a separate process). Obviously the browser tabs and windows share the same cookies in this scenario so cookie modification seems out of the question for viable solutions. This is also the reason they shared the same session. Considering that the form is already created and this is one of the final touches, how can I use ASP.NET, hopefully easily, to oversee this "feature"?

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  • How to manage db connections on server?

    - by simpatico
    I have a severe problem with my database connection in my web application. Since I use a single database connection for the whole application from singleton Database class, if i try concurrent db operations (two users) the database rollsback the transactions. This is my static method used: All threads/servlets call static Database.doSomething(...) methods, which in turn call the the below method. private static /* synchronized*/ Connection getConnection(final boolean autoCommit) throws SQLException { if (con == null) { con = new MyRegistrationBean().getConnection(); } con.setAutoCommit(true); //TODO return con; } What's the recommended way to manage this db connection/s I have, so that I don't incurr in the same problem.

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  • More elegant way to make a C++ member function change different member variables based on template p

    - by Eric Moyer
    Today, I wrote some code that needed to add elements to different container variables depending on the type of a template parameter. I solved it by writing a friend helper class specialized on its own template parameter which had a member variable of the original class. It saved me a few hundred lines of repeating myself without adding much complexity. However, it seemed kludgey. I would like to know if there is a better, more elegant way. The code below is a greatly simplified example illustrating the problem and my solution. It compiles in g++. #include <vector> #include <algorithm> #include <iostream> namespace myNS{ template<class Elt> struct Container{ std::vector<Elt> contents; template<class Iter> void set(Iter begin, Iter end){ contents.erase(contents.begin(), contents.end()); std::copy(begin, end, back_inserter(contents)); } }; struct User; namespace WkNS{ template<class Elt> struct Worker{ User& u; Worker(User& u):u(u){} template<class Iter> void set(Iter begin, Iter end); }; }; struct F{ int x; explicit F(int x):x(x){} }; struct G{ double x; explicit G(double x):x(x){} }; struct User{ Container<F> a; Container<G> b; template<class Elt> void doIt(Elt x, Elt y){ std::vector<Elt> v; v.push_back(x); v.push_back(y); Worker<Elt>(*this).set(v.begin(), v.end()); } }; namespace WkNS{ template<class Elt> template<class Iter> void Worker<Elt>::set(Iter begin, Iter end){ std::cout << "Set a." << std::endl; u.a.set(begin, end); } template<> template<class Iter> void Worker<G>::set(Iter begin, Iter end){ std::cout << "Set b." << std::endl; u.b.set(begin, end); } }; }; int main(){ using myNS::F; using myNS::G; myNS::User u; u.doIt(F(1),F(2)); u.doIt(G(3),G(4)); } User is the class I was writing. Worker is my helper class. I have it in its own namespace because I don't want it causing trouble outside myNS. Container is a container class whose definition I don't want to modify, but is used by User in its instance variables. doIt<F> should modify a. doIt<G> should modify b. F and G are open to limited modification if that would produce a more elegant solution. (As an example of one such modification, in the real application F's constructor takes a dummy parameter to make it look like G's constructor and save me from repeating myself.) In the real code, Worker is a friend of User and member variables are private. To make the example simpler to write, I made everything public. However, a solution that requires things to be public really doesn't answer my question. Given all these caveats, is there a better way to write User::doIt?

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  • Why doesn't ConcurrentQueue<T>.Count return 0 when IsEmpty == true?

    - by DanTup - Danny Tuppeny
    I was reading about the new concurrent collection classes in .NET 4 on James Michael Hare's blog, and the page talking about ConcurrentQueue<T> says: It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. I'm curious - if there is a reason to use IsEmpty instead of comparing Count to 0, why does the class not internally check IsEmpty and return 0 before doing any of the expensive work to count? E.g.: public int Count { get { // Check IsEmpty so we can bail out quicker if (this.IsEmpty) return 0; // Rest of "expensive" counting code } } It seems strange to suggest this if it could be "fixed" so easily with no side-effects?

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  • How bad is opening and closing a SQL connection for several times? What is the exact effect?

    - by Eren
    For example, I need to fill lots of DataTables with SQLDataAdapter's Fill() method: DataAdapter1.Fill(DataTable1); DataAdapter2.Fill(DataTable2); DataAdapter3.Fill(DataTable3); DataAdapter4.Fill(DataTable4); DataAdapter5.Fill(DataTable5); .... .... Even all the dataadapter objects use the same SQLConnection, each Fill method will open and close the connection unless the connection state is already open before the method call. What I want to know is how does unnecessarily opening and closing SQLConnections affect the performance of the application. How much does it need to scale to see the bad effects of this problem (100,000s of concurrent users?). In a mid-size website (daily 50000 users) does it worth bothering and searching for all the Fill() calls, keeping them together in the code and opening the connection before any Fill() call and closing afterwards?

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  • Setting creation or change timestamps

    - by Thanatos
    Using utimes, futimes, futimens, etc., it is possible to set the access and modification timestamps on a file. Is there a function to set change timestamps? (I understand the cyclic nature of wanting to change the change timestamp, but think archiving software - it would be nice to restore a file exactly as it was.) Are there any functions at all for creation timestamps? (I realize that ext2 does not support this, but I was wondering if Linux did, for those filesystems that do support it.) If it's not possible, what is the reasoning behind it not being so?

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  • How do I modify gitstats to only utilize a specified file extension for it's statistics?

    - by Fake Code Monkey Rashid
    Hello good people! The website of the statistics generator in question is: http://gitstats.sourceforge.net/ It's git repo can be cloned from: git clone git://repo.or.cz/gitstats.git What I want to do is something like: ./gitstatus --ext=".py" /input/foo /output/bar Failing being able to easily pass the above option without heavy modification, I'd just hardcore the file extentsion I want to be included. However, I'm unsure of the relevant section of code to modify and even if I did no, I'm unsure of how to start such modifications. It's seems like it'd be rather simple but alas...

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  • While using ConcurrentQueue, trying to dequeue while looping through in parallel

    - by James Black
    I am using the parallel data structures in my .NET 4 application and I have a ConcurrentQueue that gets added to while I am processing through it. I want to do something like: personqueue.AsParallel().WithDegreeOfParallelism(20).ForAll(i => ... ); as I make database calls to save the data, so I am limiting the number of concurrent threads. But, I expect that the ForAll isn't going to dequeue, and I am concerned about just doing ForAll(i => { personqueue.personqueue.TryDequeue(...); ... }); as there is no guarantee that I am popping off the correct one. So, how can I iterate through the collection and dequeue, in a parallel fashion. Or, would it be better to use PLINQ to do this processing, in parallel?

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  • iPhone: One Object, One Thread

    - by GingerBreadMane
    On the iPhone, I would like to do some operations on an image in a separate thread. Rather than dealing with semiphores, locking, etc., I'd like to use the 'One Object, One Thread' method of safely writing this concurrent operation. I'm not sure what is the correct way to copy my object into a new thread so that the object is not accessed in the main thread. Do I use the 'copy' method? If so, do I do this before the thread or inside the thread? ... -(void)someMethod{ UIImage *myImage; [NSThread detachNewThreadSelector:@selector(getRotatedImage:) toTarget:self withObject:myImage]; } -(void)getRotatedImage:(UIImage *)image{ ... ... UIImage *copiedImage = [image copy]; ... ... }

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • Script Speed vs Memory Usage

    - by Doug Neiner
    I am working on an image generation script in PHP and have gotten it working two ways. One way is slow but uses a limited amount of memory, the second is much faster, but uses 6x the memory . There is no leakage in either script (as far as I can tell). In a limited benchmark, here is how they performed: -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 65.626 | 540,036 | 200 Two | 20.207 | 3,269,600 | 200 -------------------------------------------- And here is the average of the previous numbers (if you don't want to do your own math): -------------------------------------------- METHOD | TOTAL TIME | PEAK MEMORY | IMAGES -------------------------------------------- One | 0.328 | 540,036 | 1 Two | 0.101 | 3,269,600 | 1 -------------------------------------------- Which method should I use and why? I anticipate this being used by a high volume of users, with each user making 10-20 requests to this script during a normal visit. I am leaning toward the faster method because though it uses more memory, it is for a 1/3 of the time and would reduce the number of concurrent requests.

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  • ASP.NET Thread Safety in aspx.cs code behind file

    - by Tim Michalski
    I am thinking of adding a DataContext as a member variable to my aspx.cs code-behind class for executing LinqToSql queries. Is this thread safe? I am not sure if a new instance of this code-behind class is created for each HTTP request, or if the instance is shared amongst all request threads? My fear is that I will get 10 simultaneous concurrent http requests that will be using the same database session. public partial class MyPage : System.Web.UI.Page { private DataContext myDB = new DataContext(); protected void MyAction_Click(object sender, EventArgs e) { myDB.DoWork(); } }

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  • CURL alternative - Design ideas

    - by Vincent
    All, I am looking for some web application design ideas here. I have a server X that hosts an SDK, which has the capacity to talk a piece of hardware. When I make an HTTPS request from an external PHP web application (hosted on Server Y) to Server X through curl, Server X gives JSON data as a response. I use this data to render my UI for the web app on Server Y. The above method seems to be slow and has a tendency to fail in production if there are too many concurrent requests. Can anybody let me know if there is an alternative to CURL or any other design people are using to pull data like this from servers? Thanks

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  • Good code visualization / refactoring tools for C++?

    - by Paul D.
    I've found myself coming across a lot of reasonably large, complicated codebases at work recently which I've been asked to either review or refactor or both. This can be extremely time consuming when the code is highly concurrent, makes heavy use of templates (particularly static polymorphism) and has logic that depends on callbacks/signals/condition variables/etc. Are there any good visualization tools for C++ period, and of those are there any that actually play well with "advanced" C++ features? Anything would probably be better than my approach now, which is basically pen+paper or stepping through the debugger. The debugger method can be good for following a particular code path, but isn't great for seeing the big picture you really need when doing serious refactoring. EDIT: I should mention that Visual Studio plugins aren't going to be a lot of help to me, since our stuff is mostly Linux-only.

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  • Python: Taking an array and break it into subarrays based on some criteria

    - by randombits
    I have an array of files. I'd like to be able to break that array down into one array with multiple subarrays, each subarray contains files that were created on the same day. So right now if the array contains files from March 1 - March 31, I'd like to have an array with 31 subarrays (assuming there is at least 1 file for each day). In the long run, I'm trying to find the file from each day with the latest creation/modification time. If there is a way to bundle that into the iterations that are required above to save some CPU cycles, that would be even more ideal. Then I'd have one flat array with 31 files, one for each day, for the latest file created on each individual day.

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  • Replacing objects, handling clones, dealing with write logs

    - by Alix
    Hi everyone, I'm dealing with a problem I can't figure out how to solve, and I'd love to hear some suggestions. [NOTE: I realise I'm asking several questions; however, answers need to take into account all of the issues, so I cannot split this into several questions] Here's the deal: I'm implementing a system that underlies user applications and that protect shared objects from concurrent accesses. The application programmer (whose application will run on top of my system) defines such shared objects like this: public class MyAtomicObject { // These are just examples of fields you may want to have in your class. public virtual int x { get; set; } public virtual List<int> list { get; set; } public virtual MyClassA objA { get; set; } public virtual MyClassB objB { get; set; } } As you can see they declare the fields of their class as auto-generated properties (auto-generated means they don't need to implement get and set). This is so that I can go in and extend their class and implement each get and set myself in order to handle possible concurrent accesses, etc. This is all well and good, but now it starts to get ugly: the application threads run transactions, like this: The thread signals it's starting a transaction. This means we now need to monitor its accesses to the fields of the atomic objects. The thread runs its code, possibly accessing fields for reading or writing. If there are accesses for writing, we'll hide them from the other transactions (other threads), and only make them visible in step 3. This is because the transaction may fail and have to roll back (undo) its updates, and in that case we don't want other threads to see its "dirty" data. The thread signals it wants to commit the transaction. If the commit is successful, the updates it made will now become visible to everyone else. Otherwise, the transaction will abort, the updates will remain invisible, and no one will ever know the transaction was there. So basically the concept of transaction is a series of accesses that appear to have happened atomically, that is, all at the same time, in the same instant, which would be the moment of successful commit. (This is as opposed to its updates becoming visible as it makes them) In order to hide the write accesses in step 2, I clone the accessed field (let's say it's the field list) and put it in the transaction's write log. After that, any time the transaction accesses list, it will actually be accessing the clone in its write log, and not the global copy everyone else sees. Like this, any changes it makes will be done to the (invisible) clone, not to the global copy. If in step 3 the commit is successful, the transaction should replace the global copy with the updated list it has in its write log, and then the changes become visible for everyone else at once. It would be something like this: myAtomicObject.list = updatedCloneOfListInTheWriteLog; Problem #1: possible references to the list. Let's say someone puts a reference to the global list in a dictionary. When I do... myAtomicObject.list = updatedCloneOfListInTheWriteLog; ...I'm just replacing the reference in the field list, but not the real object (I'm not overwriting the data), so in the dictionary we'll still have a reference to the old version of the list. A possible solution would be to overwrite the data (in the case of a list, empty the global list and add all the elements of the clone). More generically, I would need to copy the fields of one list to the other. I can do this with reflection, but that's not very pretty. Is there any other way to do it? Problem #2: even if problem #1 is solved, I still have a similar problem with the clone: the application programmer doesn't know I'm giving him a clone and not the global copy. What if he puts the clone in a dictionary? Then at commit there will be some references to the global copy and some to the clone, when in truth they should all point to the same object. I thought about providing a wrapper object that contains both the cloned list and a pointer to the global copy, but the programmer doesn't know about this wrapper, so they're not going to use the pointer at all. The wrapper would be like this: public class Wrapper<T> : T { // This would be the pointer to the global copy. The local data is contained in whatever fields the wrapper inherits from T. private T thisPtr; } I do need this wrapper for comparisons: if I have a dictionary that has an entry with the global copy as key, if I look it up with the clone, like this: dictionary[updatedCloneOfListInTheWriteLog] I need it to return the entry, that is, to think that updatedCloneOfListInTheWriteLog and the global copy are the same thing. For this, I can just override Equals, GetHashCode, operator== and operator!=, no problem. However I still don't know how to solve the case in which the programmer unknowingly inserts a reference to the clone in a dictionary. Problem #3: the wrapper must extend the class of the object it wraps (if it's wrapping MyClassA, it must extend MyClassA) so that it's accepted wherever an object of that class (MyClass) would be accepted. However, that class (MyClassA) may be final. This is pretty horrible :$. Any suggestions? I don't need to use a wrapper, anything you can think of is fine. What I cannot change is the write log (I need to have a write log) and the fact that the programmer doesn't know about the clone. I hope I've made some sense. Feel free to ask for more info if something needs some clearing up. Thanks so much!

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  • (win32) What to do when a file remains left open when a remote application crashes or forgets to clo

    - by Stephane R.
    Hi I have not worked so much with files: I am wondering about possible issues with accessing remote files on another computer. What if the distant application crashes and doesn't close the file ? My aim is to use this win32 function: HFILE WINAPI OpenFile(LPCSTR lpFileName, LPOFSTRUCT lpReOpenBuff, UINT uStyle); Using the flag OF_SHARE_EXCLUSIVE assures me that any concurrent access will be denied (because several machines are writing to this file from time to time). But what if the file is left open ? (application crash for example ?) How to put the file back to normal ?

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  • Sort/Enumerate an NSArray from somewhere in the middle?

    - by Kenny Winker
    I have an NSArray, with objects ordered like so: a b c d e f I would like to enumerate through this array in this order: c d e f a b i.e. starting at some point that is not the beginning, but hitting all the items. I imagine this is a matter of sorting first and then enumerating the array, but I'm not sure if that's the best technique... or, frankly, how to sort the array like this. Edit Adding details: These will be relatively small arrays, varying from 3 to 10 objects. No concurrent access. I'd like to permanently alter the sort order of the array each time I do this operation.

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  • I work on local copies of files and upload them to a remote server on save. What version control sys

    - by 10goto10
    Here's my situation: My files are on a remote server (Linux). When I want to edit a file at home on my Windows machine, my editor (PSPad) downloads a copy. When I save the document, my editor uploads it to the server, overwriting the previous version. Is there a version control system, preferably GUI driven, that can handle this situation? Additional info: I probably can't install elaborate software on the remote server, but can on my own computer. Concurrent Versions System (CVS) is installed on the remote server. Uploading/downloading goes through an FTP-to-SFTP bridge set up with Bitvise Tunnelier.

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  • How does browser work with expiration headers, cache-control headers, last-modified-header ?

    - by Umair
    I am a web developer, have worked with PHP and .NET both. having over a year of experience working on web I haven't been able to understand the browser caching features thoroughly, I hope Web Gurus here can help me with it. Questions I have in my mind are : How does browser actually caches stuff, does it request for to see if the cached file has changed on the server or not, What is the Ideal way for a developer to make use of browser chaching to its full, but also to be able to push new changes on the site with no hassle at all. I think if browser somehow chaches my CSS and JS and Images, and then just makes a checks for their modification to the server everytime, this can sort the issue. but I am not sure how to do it, waiting for interesting answers :)

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  • Suggest a open source project which heavily uses java concurrency utilities?

    - by user49767
    I have done good amount of Java programming, but yet to master Threading & Concurrency. I would like to become an expert programmer in threading & concurrency. I have also took a short at Tomcat code, I was able to understand, but looking even more complex project. Could you suggest any open source project which heavily uses java threading & concurrency utilities? Note : I have also reading java.util.concurrent package source code, but eager to learn from Application perspective, than creating my own threading utilities.

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  • Flymake quits right ahead after loading with js2-mode

    - by artistoex
    When opening .js files, js2-mode and, subsequently, flymake-js is automatically loaded. But flymake unloads right ahead with the message Toggling flymake-mode off; better pass an explicit argument. However, when enabling it manually, using M-x flymake-mode, it keeps activated. Has anybody encountered similar behavior and has fixed it? My setup: I followed the instructions on emacswiki to set up Flymake to work with the most recent js2-mode with a little modification: (add-hook 'js2-mode-hook '(lambda () (flymake-js-load))) instead of (add-hook 'javascript-mode-hook '(lambda () (flymake-js-load)))

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  • how to add language support to android

    - by avar
    hello i hope someone put me on the right direction with my problem i want to work on supporting my language, specially the writing on android we use Arabic characters with little modification ( like parsi, urdu etc).. i was hoping android has fully supported Arabic , then i would make changes to work with my language. but even 2.2 dosn't support Arabic . it just show Arabic characters and it is not connected. that is "????? " is displayed "? ? ? ? ?". some individuals have made Arabic support on CyanogenMod ROM's for some HTC phones, but they would not tell how they made it. I'v got the android source code, i want to know where to start, where to make changes , what is the library that handle fonts , shaping engine etc .. ps : android.com and other android related google groups are blocked in my country.

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