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  • How to re-add RAID-10 dropped drive?

    - by thiesdiggity
    I have a problem that I can't seem to solve. We have a Ubuntu server setup with RAID-10 and two of the drives dropped out of the array. When I try to re-add them using the following command: mdadm --manage --re-add /dev/md2 /dev/sdc1 I get the following error message: mdadm: Cannot open /dev/sdc1: Device or resource busy When I do a "cat /proc/mdstat" I get the following: Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [r$ md2 : active raid10 sdb1[0] sdd1[3] 1953519872 blocks 64K chunks 2 near-copies [4/2] [U__U] md1 : active raid1 sda2[0] sdc2[1] 468853696 blocks [2/2] [UU] md0 : active raid1 sda1[0] sdc1[1] 19530688 blocks [2/2] [UU] unused devices: <none> When I run "/sbin/mdadm --detail /dev/md2" I get the following: /dev/md2: Version : 00.90 Creation Time : Mon Sep 5 23:41:13 2011 Raid Level : raid10 Array Size : 1953519872 (1863.02 GiB 2000.40 GB) Used Dev Size : 976759936 (931.51 GiB 1000.20 GB) Raid Devices : 4 Total Devices : 2 Preferred Minor : 2 Persistence : Superblock is persistent Update Time : Thu Oct 25 09:25:08 2012 State : active, degraded Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Layout : near=2, far=1 Chunk Size : 64K UUID : c6d87d27:aeefcb2e:d4453e2e:0b7266cb Events : 0.6688691 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 0 0 1 removed 2 0 0 2 removed 3 8 49 3 active sync /dev/sdd1 Output of df -h is: Filesystem Size Used Avail Use% Mounted on /dev/md1 441G 2.0G 416G 1% / none 32G 236K 32G 1% /dev tmpfs 32G 0 32G 0% /dev/shm none 32G 112K 32G 1% /var/run none 32G 0 32G 0% /var/lock none 32G 0 32G 0% /lib/init/rw tmpfs 64G 215M 63G 1% /mnt/vmware none 441G 2.0G 416G 1% /var/lib/ureadahead/debugfs /dev/mapper/RAID10VG-RAID10LV 1.8T 139G 1.6T 8% /mnt/RAID10 When I do a "fdisk -l" I can see all the drives needed for the RAID-10. The RAID-10 is part of the /dev/mapper, could that be the reason why the device is coming back as busy? Anyone have any suggestions on what I can try to get the drives back into the array? Any help would be greatly appreciated. Thanks!

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  • In MVC , DAO should be called from Controller or Model

    - by tito
    I have seen various arguments against the DAO being called from the Controller class directly and also the DAO from the Model class.Infact I personally feel that if we are following the MVC pattern , the controller should not coupled with the DAO , but the Model class should invoke the DAO from within and controller should invoke the model class.Why because , we can decouple the model class apart from a webapplication and expose the functionalities for various ways like for a REST service to use our model class. If we write the DAO invocation in the controller , it would not be possible for a REST service to reuse the functionality right ? I have summarized both the approaches below. Approach #1 public class CustomerController extends HttpServlet { proctected void doPost(....) { Customer customer = new Customer("xxxxx","23",1); new CustomerDAO().save(customer); } } Approach #2 public class CustomerController extends HttpServlet { proctected void doPost(....) { Customer customer = new Customer("xxxxx","23",1); customer.save(customer); } } public class Customer { ........... private void save(Customer customer){ new CustomerDAO().save(customer); } } Note- Here is what a definition of Model is : Model: The model manages the behavior and data of the application domain, responds to requests for information about its state (usually from the view), and responds to instructions to change state (usually from the controller). In event-driven systems, the model notifies observers (usually views) when the information changes so that they can react. I would need an expert opinion on this because I find many using #1 or #2 , So which one is it ?

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  • Are first-class functions a substitute for the Strategy pattern?

    - by Prog
    The Strategy design pattern is often regarded as a substitute for first-class functions in languages that lack them. So for example say you wanted to pass functionality into an object. In Java you'd have to pass in the object another object which encapsulates the desired behavior. In a language such as Ruby, you'd just pass the functionality itself in the form of an annonymous function. However I was thinking about it and decided that maybe Strategy offers more than a plain annonymous function does. This is because an object can hold state that exists independently of the period when it's method runs. However an annonymous function by itself can only hold state that ceases to exist the moment the function finishes execution. So my question is: when using a language that features first-class functions, would you ever use the Strategy pattern (i.e. encapsulate the functionality you want to pass around in an explicit object), or would you always use an annonymous function? When would you decide to use Strategy when you can use a first-class function?

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  • Unable to install Skype ("Unmet dependencies" error)

    - by Alex Maslakov
    Trying to install skype on Ubuntu 12, I faced and issue. When I type: sudo apt-get update sudo apt-get install skype I get an error Reading package lists... Done Building dependency tree Reading state information... Done skype is already the newest version. You might want to run 'apt-get -f install' to correct these: The following packages have unmet dependencies: skype : Depends: lib32stdc++6 (>= 4.1.1-21) but it is not going to be installed Depends: lib32asound2 (> 1.0.14) but it is not going to be installed Depends: ia32-libs but it is not going to be installed Depends: libc6-i386 (>= 2.7-1) but it is not going to be installed Depends: lib32gcc1 (>= 1:4.1.1-21+ia32.libs.1.19) but it is not going to be installed E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution). How do I solve it? Is the way I'm using the right one to install skype? UPDATE: If I try to do sudo apt-get install lib32stdc++6 lib32asound2 ia32-libs libc6-i386 lib32gcc1 skype then I get Reading package lists... Done Building dependency tree Reading state information... Done skype is already the newest version. You might want to run 'apt-get -f install' to correct these: The following packages have unmet dependencies: ia32-libs : Depends: ia32-libs-multiarch lib32asound2 : Depends: libasound2 (= 1.0.25-1ubuntu10) E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

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  • My Only Gripe With Programming

    - by David Espejo
    Is that im having trouble practicing problems. Even if I decide to practice the problems from my C++ book, they dont give any idea of the way the solution(program) should look like, so that I may compare to see if my program is similar in anyway. My book gives me to many generic "Write a program to do "this" " projects without really showing a concrete example of what "this" really is. In other words How Do I Know That I did "that". One problem in my book said to write a program that calculates the sales tax on a given item????? First of all slase tax differs on state(whats the state,) whats the item(a house, a dog,) How can I check this to see if im right. Programming books dont have answer keys! I know that there is no ABSOLUTE answer, thats just silly, programs can be written in many ways, but a sample of what one would look like based of the difficulty of the problem would really help! Is there a solution to this, maby a book that has worked out examples for the problems they give , or online sources that do something similar.(is there such thing as a programming book with an answer key?)

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  • Uses of persistent data structures in non-functional languages

    - by Ray Toal
    Languages that are purely functional or near-purely functional benefit from persistent data structures because they are immutable and fit well with the stateless style of functional programming. But from time to time we see libraries of persistent data structures for (state-based, OOP) languages like Java. A claim often heard in favor of persistent data structures is that because they are immutable, they are thread-safe. However, the reason that persistent data structures are thread-safe is that if one thread were to "add" an element to a persistent collection, the operation returns a new collection like the original but with the element added. Other threads therefore see the original collection. The two collections share a lot of internal state, of course -- that's why these persistent structures are efficient. But since different threads see different states of data, it would seem that persistent data structures are not in themselves sufficient to handle scenarios where one thread makes a change that is visible to other threads. For this, it seems we must use devices such as atoms, references, software transactional memory, or even classic locks and synchronization mechanisms. Why then, is the immutability of PDSs touted as something beneficial for "thread safety"? Are there any real examples where PDSs help in synchronization, or solving concurrency problems? Or are PDSs simply a way to provide a stateless interface to an object in support of a functional programming style?

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  • SQL Server Database Settings

    - by rbishop
    For those using Data Relationship Management on Oracle DB this does not apply, but for those using Microsoft SQL Server it is highly recommended that you run with Snapshot Isolation Mode. The Data Governance module will not function correctly without this mode enabled. All new Data Relationship Management repositories are created with this mode enabled by default. This mode makes SQL Server (2005+) behave more like Oracle DB where readers simply see older versions of rows while a write is in progress, instead of readers being blocked by locks while a write takes place. Many common sources of deadlocks are eliminated. For example, if one user starts a 5 minute transaction updating half the rows in a table, without snapshot isolation everyone else reading the table will be blocked waiting. With snapshot isolation, they will see the rows as they were before the write transaction started. Conversely, if the readers had started first, the writer won't be stuck waiting for them to finish reading... the writes can begin immediately without affecting the current transactions. To make this change, make sure no one is using the target database (eg: put it into single-user mode), then run these commands: ALTER DATABASE [DB] SET ALLOW_SNAPSHOT_ISOLATION ONALTER DATABASE [DB] SET READ_COMMITTED_SNAPSHOT ON Please make sure you coordinate with your DBA team to ensure tempdb is appropriately setup to support snapshot isolation mode, as the extra row versions are stored in tempdb until the transactions are committed. Let me take this opportunity to extremely strongly highly recommend that you use solid state storage for your databases with appropriate iSCSI, FiberChannel, or SAN bandwidth. The performance gains are significant and there is no excuse for not using 100% solid state storage in 2013. Actually unless you need to store petabytes of archival data, there is no excuse for using hard drives in any systems, whether laptops, desktops, application servers, or database servers. The productivity benefits alone are tremendous, not to mention power consumption, heat, etc.

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  • Problem with APTonCD application

    - by Harikrishnan
    I created a iso image using aptoncd & burned it to a dvd. now when i tried to restore, the program does not detect the dvd in the drive. It shows "Please insert a disc in the drive." and if we click "ok" it shows "E: Failed to mount the cdrom.". The dvd is in the drive itself. I tried "sudo lshw -C disk" and the out put is: *-cdrom description: DVD-RAM writer product: DVDRAM GH22NS50 vendor: HL-DT-ST physical id: 1 bus info: scsi@1:0.0.0 logical name: /dev/cdrom logical name: /dev/cdrw logical name: /dev/dvd logical name: /dev/dvdrw logical name: /dev/scd0 logical name: /dev/sr0 logical name: /media/APTonCD logical name: /media/apt version: TN02 capabilities: removable audio cd-r cd-rw dvd dvd-r dvd-ram configuration: ansiversion=5 mount.fstype=iso9660 mount.options=ro,relatime,uid=1000,gid=1000,iocharset=utf8,mode=0400,dmode=0500 state=mounted status=ready *-medium physical id: 0 logical name: /dev/cdrom logical name: /media/APTonCD logical name: /media/apt configuration: mount.fstype=iso9660 mount.options=ro,relatime,uid=1000,gid=1000,iocharset=utf8,mode=0400,dmode=0500 state=mounted Then i checked in disk utility application. in that dvd rom is shown as "/dvd/sr0". my ubuntu version is 10.10. please help me to solve the problem.

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  • Why do I have an error when adding states in slick?

    - by SystemNetworks
    When I was going to create another state I had an error. This is my code: public static final int play2 = 3; and public Game(String gamename){ this.addState(new mission(play2)); } and public void initStatesList(GameContainer gc) throws SlickException{ this.getState(play2).init(gc, this); } I have an error in the addState. above the above code. I don't know where is the problem. But if you want the whole code it is here: package javagame; import org.newdawn.slick.*; import org.newdawn.slick.state.*; public class Game extends StateBasedGame{ public static final String gamename = "NET FRONT"; public static final int menu = 0; public static final int play = 1; public static final int train = 2; public static final int play2 = 3; public Game(String gamename){ super(gamename); this.addState(new Menu(menu)); this.addState(new Play(play)); this.addState(new train(train)); this.addState(new mission(play2)); } public void initStatesList(GameContainer gc) throws SlickException{ this.getState(menu).init(gc, this); this.getState(play).init(gc, this); this.getState(train).init(gc, this); this.enterState(menu); this.getState(play2).init(gc, this); } public static void main(String[] args) { try{ AppGameContainer app =new AppGameContainer(new Game(gamename)); app.setDisplayMode(1500, 1000, false); app.start(); }catch(SlickException e){ e.printStackTrace(); } } } //SYSTEM NETWORKS(C) 2012 NET FRONT

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  • Prefer class members or passing arguments between internal methods?

    - by geoffjentry
    Suppose within the private portion of a class there is a value which is utilized by multiple private methods. Do people prefer having this defined as a member variable for the class or passing it as an argument to each of the methods - and why? On one hand I could see an argument to be made that reducing state (ie member variables) in a class is generally a good thing, although if the same value is being repeatedly used throughout a class' methods it seems like that would be an ideal candidate for representation as state for the class to make the code visibly cleaner if nothing else. Edit: To clarify some of the comments/questions that were raised, I'm not talking about constants and this isn't relating to any particular case rather just a hypothetical that I was talking to some other people about. Ignoring the OOP angle for a moment, the particular use case that I had in mind was the following (assume pass by reference just to make the pseudocode cleaner) int x doSomething(x) doAnotherThing(x) doYetAnotherThing(x) doSomethingElse(x) So what I mean is that there's some variable that is common between multiple functions - in the case I had in mind it was due to chaining of smaller functions. In an OOP system, if these were all methods of a class (say due to refactoring via extracting methods from a large method), that variable could be passed around them all or it could be a class member.

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  • Cannot install ia32-lib package

    - by A British Person
    I have several programs that reuquire 32 bit packages (pointing to the ia32-lib package). However, when I try to install it, this happens. spirit@ubuntu:~$ sudo apt-get install ia32-libs Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: ia32-libs : Depends: ia32-libs-multiarch but it is not installable E: Unable to correct problems, you have held broken packages. No big whoop, packages die all the time. I tried a month later however and I still got this error, trying to install the specific package produces this error. spirit@ubuntu:~$ sudo apt-get install ia32-libs-multiarch Reading package lists... Done Building dependency tree Reading state information... Done Package ia32-libs-multiarch is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source E: Package 'ia32-libs-multiarch' has no installation candidate I am no Linux whizz-kid, but this seems to be that the package doesn't exist. I searched for Skype in the software centre (I was told this installs the 32-bit packages) and it does not appear in the software centre, and the downloadable from their website produces an error about - funnily enough - no 32-bit packages. Anyone who helps me will get a medal from the gods with the weight of a thousand planets. Just don't wear it for god's sake.

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  • techniques for displaying vehicle damage

    - by norca
    I wonder how I can displaying vehicle damage. I am talking about an good way to show damage on screen. Witch kind of model are common in games and what are the benefits of them. What is state of the art? One way i can imagine is to save a set of textures (normal/color/lightmaps, etc) to a state of the car (normal, damage, burnt out) and switch or blending them. But is this really good without changing the model? Another way i was thinking about is preparing animations for different locations on my car, something like damage on the front, on the leftside/rightside or on the back. And start blending the specific animation. But is this working with good textures? Whats about physik engines? Is it usefull to use it for deforming vertexdata? i think losing parts of my car (doors, sirens, weapons) can looks really nice. my game is a kind of rts in a top down view. vehicles are not the really most importend units (its no racing game), but i have quite a lot in. thx for help

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  • the requested resource is not available [closed]

    - by James Pj
    I have written a Java servlet program and run it through local Tomcat 7, But it was showing following error : HTTP Status 404 - /skypark/registration type Status report message /skypark/registration description The requested resource is not available. Apache Tomcat/7.0.33 I don't know what was the reason for it my Html page is <html> <head> <title> User registration </title> </head> <body> <form action="registration" method="post"> <center> <h2><b>Skypark User Registration</b></h2> <table border="0"> <tr><td> First Name </td><td> <input type="text" name="fname"/></br> </td></tr><tr><td> Last Name </td><td> <input type="text" name="lname"/></br> </td></tr><tr><td> UserName </td><td> <input type="text" name="uname"></br> </td></tr><tr><td> Enter Password </td><td> <input type="password" name="pass"></br> </td></tr><tr><td> Re-Type Password </td><td> <input type="password" name="pass1"></br> </td></tr><tr><td> Enter Email ID </td><td> <input type="email" name="email1"></br> </td></tr><tr><td> Phone Number </td><td> <input type="number" name="phone"> </td></tr><tr><td> Gender<br> </td></tr><tr><td> <input type="radio" name="gender" value="Male">Male</input></br> </td></tr><tr><td> <input type="radio" name="gender" value="Female">Female</input></br> </td></tr><tr><td> Enter Your Date of Birth<br> </td><td> <Table Border=0> <tr> <td> Date </td> <td>Month</td> <td>Year</td> </tr><tr> <td> <select name="date"> <option value="1">1</option> <option value="2">2</option> <option value="3">3</option> <option value="4">4</option> <option value="5">5</option> . . . have some code . . . </table> <input type="submit" value="Submit"></br> </center> </form> </body> </html> My servlet is : package skypark; import skypark.*; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; public class Registration extends HttpServlet { public static Connection prepareConnection()throws ClassNotFoundException,SQLException { String dcn="oracle.jdbc.driver.OracleDriver"; String url="jdbc:oracle:thin:@JamesPJ-PC:1521:skypark"; String usname="system"; String pass="tiger"; Class.forName(dcn); return DriverManager.getConnection(url,usname,pass); } public void doPost(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException { resp.setContentType("text/html"); PrintWriter out=resp.getWriter(); try { String phone1,uname,fname,lname,dob,address,city,state,country,pin,email,password,gender,lang,qual,relegion,privacy,hobbies,fav; uname=req.getParameter("uname"); fname=req.getParameter("fname"); lname=req.getParameter("lname"); dob=req.getParameter("date"); address=req.getParameter("address"); city=req.getParameter("city"); state=req.getParameter("state"); country=req.getParameter("country"); pin=req.getParameter("pin"); email=req.getParameter("email1"); password=req.getParameter("password"); gender=req.getParameter("gender"); phone1=req.getParameter("phone"); lang=""; qual=""; relegion=""; privacy=""; hobbies=""; fav=""; int phone=Integer.parseInt(phone1); Connection con=prepareConnection(); String Query="Insert into regdetails values(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)"; PreparedStatement ps=con.prepareStatement(Query); ps.setString(1,uname); ps.setString(2,fname); ps.setString(3,lname); ps.setString(4,dob); ps.setString(5,address); ps.setString(6,city); ps.setString(7,state); ps.setString(8,country); ps.setString(9,pin); ps.setString(10,lang); ps.setString(11,qual); ps.setString(12,relegion); ps.setString(13,privacy); ps.setString(14,hobbies); ps.setString(15,fav); ps.setString(16,gender); int c=ps.executeUpdate(); String query="insert into passmanager values(?,?,?,?)"; PreparedStatement ps1=con.prepareStatement(query); ps1.setString(1,uname); ps1.setString(2,password); ps1.setString(3,email); ps1.setInt(4,phone); int i=ps1.executeUpdate(); if(c==1||c==Statement.SUCCESS_NO_INFO && i==1||i==Statement.SUCCESS_NO_INFO) { out.println("<html><head><title>Login</title></head><body>"); out.println("<center><h2>Skypark.com</h2>"); out.println("<table border=0><tr>"); out.println("<td>UserName/E-Mail</td>"); out.println("<form action=login method=post"); out.println("<td><input type=text name=uname></td>"); out.println("</tr><tr><td>Password</td>"); out.println("<td><input type=password name=pass></td></tr></table>"); out.println("<input type=submit value=Login>"); out.println("</form></body></html>"); } else { out.println("<html><head><title>Error!</title></head><body>"); out.println("<center><b>Given details are incorrect</b>"); out.println(" Please try again</center></body></html>"); RequestDispatcher rd=req.getRequestDispatcher("registration.html"); rd.include(req,resp); return; } } catch(Exception e) { out.println("<html><head><title>Error!</title><body>"); out.println("<b><i>Unable to process try after some time</i></b>"); out.println("</body></html>"); RequestDispatcher rd=req.getRequestDispatcher("registration.html"); rd.include(req,resp); return; } out.flush(); out.close(); } } And the web.xml file is <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0" metadata-complete="true"> <servlet> <servlet-name>reg</servlet-name> <servlet-class>skypark.Registration</servlet-class> </servlet> <servlet-mapping> <servlet-name>reg</servlet-name> <url-pattern>/registration</url-pattern> </servlet-mapping> This i kept in C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\skypark\WEB_INF\web.xml and servlet class in C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\skypark\WEB_INF\classes\skypark and registration.html in C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\skypark\ if any mistake in this makes above error means please help me.Thanks in advance....

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  • Is there a (family of) monotonically non-decreasing noise function(s)?

    - by Joe Wreschnig
    I'd like a function to animate an object moving from point A to point B over time, such that it reaches B at some fixed time, but its position at any time is randomly perturbed in a continuous fashion, but never goes backwards. The objects move along straight lines, so I only need one dimension. Mathematically, that means I'm looking for some continuous f(x), x ? [0,1], such that: f(0) = 0 f(1) = 1 x < y ? f(x) = f(y) At "most" points f(x + d) - f(x) bears no obvious relation to d. (The function is not uniformly increasing or otherwise predictable; I think that's also equivalent to saying no degree of derivative is a constant.) Ideally, I would actually like some way to have a family of these functions, providing some seed state. I'd need at least 4 bits of seed (16 possible functions), for my current use, but since that's not much feel free to provide even more. To avoid various issues with accumulation errors, I'd prefer the function not require any kind of internal state. That is, I want it to be a real function, not a programming "function".

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  • Browser automatically refreshes and Home folder window opens

    - by Vikash
    I am facing a very strange problem. Out of the blue, my browser starts refreshing itself infinitely. My first guess was firefox is messing up. I installed chrome. But, it happens in chrome as well. Other than that, sometimes my home folder automatically opens and keep opening itself infinitely. My next guess was Mouse is faulty. Replace the mouse - but same things. This happens even if I remove my keyboard. What can be the reason? This started happening after I installed Ubuntu 10.10 few days back. Earlier on windows, everything was working fine. So, I am a bit skeptical to assume that this is a hardware fault. How to fix this problem? UPDATE: xev gives this kind of result: KeyPress event, serial 36, synthetic NO, window 0x4200001, root 0xb8, subw 0x0, time 29897358, (237,791), root:(1252,842), state 0x10, keycode 65 (keysym 0x20, space), same_screen YES, XLookupString gives 1 bytes: (20) " " XmbLookupString gives 1 bytes: (20) " " XFilterEvent returns: False KeyRelease event, serial 36, synthetic NO, window 0x4200001, root 0xb8, subw 0x0, time 29897603, (237,791), root:(1252,842), state 0x10, keycode 65 (keysym 0x20, space), same_screen YES, XLookupString gives 1 bytes: (20) " " XFilterEvent returns: False

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  • How are objects modelled in a functional programming language?

    - by Giorgio
    In an answer to this question (written by Pete) there are some considerations about OOP versus FP. In particular, it is suggested that FP languages are not very suitable for modelling (persistent) objects that have an identity and a mutable state. I was wondering if this is true or, in other words, how one would model objects in a functional programming language. From my basic knowledge of Haskell I thought that one could use monads in some way, but I really do not know enough on this topic to come up with a clear answer. So, how are entities with an identity and a mutable persistent state normally modelled in a functional language? EDIT Here are some further details to clarify what I have in mind. Take a typical Java application in which I can (1) read a record from a database table into a Java object, (2) modify the object in different ways, (3) save the modified object to the database. How would this be implemented e.g. in Haskell? I would initially read the record into a record value (defined by a data definition), perform different transformations by applying functions to this initial value (each intermediate value is a new, modified copy of the original record) and then write the final record value to the database. Is this all there is to it? How can I ensure that at each moment in time only one copy of the record is valid / accessible? One does not want to have different immutable values representing different snapshots of the same object to be accessible at the same time.

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  • Impact of Server Failure on Coherence Request Processing

    - by jpurdy
    Requests against a given cache server may be temporarily blocked for several seconds following the failure of other cluster members. This may cause issues for applications that can not tolerate multi-second response times even during failover processing (ignoring for the moment that in practice there are a variety of issues that make such absolute guarantees challenging even when there are no server failures). In general, Coherence is designed around the principle that failures in one member should not affect the rest of the cluster if at all possible. However, it's obvious that if that failed member was managing a piece of state that another member depends on, the second member will need to wait until a new member assumes responsibility for managing that state. This transfer of responsibility is (as of Coherence 3.7) performed by the primary service thread for each cache service. The finest possible granularity for transferring responsibility is a single partition. So the question becomes how to minimize the time spent processing each partition. Here are some optimizations that may reduce this period: Reduce the size of each partition (by increasing the partition count) Increase the number of JVMs across the cluster (increasing the total number of primary service threads) Increase the number of CPUs across the cluster (making sure that each JVM has a CPU core when needed) Re-evaluate the set of configured indexes (as these will need to be rebuilt when a partition moves) Make sure that the backing map is as fast as possible (in most cases this means running on-heap) Make sure that the cluster is running on hardware with fast CPU cores (since the partition processing is single-threaded) As always, proper testing is required to make sure that configuration changes have the desired effect (and also to quantify that effect).

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  • Command Query Separation

    - by Liam McLennan
    Command query separation is a strategy, proposed by Bertrand Meyer, that each of an object’s methods should be either a command or a query. A command is an operation that changes the state of a system, and a query is an operation that returns a value. This is not the same thing as CQRS, hence why I think that CQRS is poorly named. An Example of Command Query Separation Consider a system that models books and shelves. There is a rule that a shelf may not be removed if it holds any books. One way to implement the removal is to write a method Shelf.Remove() that internally checks to make sure that the shelf is empty before removing it. If the shelf is not empty then it is not removed and an error is returned. To implement this feature following the principle of command query separation would require two methods, one to query the shelf and determine if it is empty and a second method to remove the shelf. Separating the query from the command makes the shelf class simpler to use because the state change is clear and explicit.

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  • How to refactor to cleaner version of maintaing states of the widget

    - by George
    Backstory I inherited a bunch of code that I'd like to refactor. It is a UI application written in javascript. Current state: We have main application which consist of several UI components. And each component has entry fields, textboxes, menus, etc), like "ticket", "customer information", etc. Based on input, where the application was called from, who is the user, we enable/disable, hide, show, change titles. Unfortunately, the app grew to the point where it is really hard to scale, add new features. Main the driver (application code) calls set/unset functions of the respective components. So a lot of the stuff look like this Main app unit function1() { **call_function2()** component1.setX(true); component1.setY(true); component2.setX(false); } call_function2() { // it may repeat some of the code function1 called } and we have a lot of this in the main union. I am cleaning this mess. What is the best way to maintain the state of widgets? Please let me know if you need me to clarify.

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  • Updating entities in response to collisions - should this be in the collision-detection class or in the entity-updater class?

    - by Prog
    In a game I'm working on, there's a class responsible for collision detection. It's method detectCollisions(List<Entity> entities) is called from the main gameloop. The code to update the entities (i.e. where the entities 'act': update their positions, invoke AI, etc) is in a different class, in the method updateEntities(List<Entity> entities). Also called from the gameloop, after the collision detection. When there's a collision between two entities, usually something needs to be done. For example, zero the velocity of both entities in the collision, or kill one of the entities. It would be easy to have this code in the CollisionDetector class. E.g. in psuedocode: for(Entity entityA in entities){ for(Entity entityB in entities){ if(collision(entityA, entityB)){ if(entityA instanceof Robot && entityB instanceof Robot){ entityA.setVelocity(0,0); entityB.setVelocity(0,0); } if(entityA instanceof Missile || entityB instanceof Missile){ entityA.die(); entityB.die(); } } } } However, I'm not sure if updating the state of entities in response to collision should be the job of CollisionDetector. Maybe it should be the job of EntityUpdater, which runs after the collision detection in the gameloop. Is it okay to have the code responding to collisions in the collision detection system? Or should the collision detection class only detect collisions, report them to some other class and have that class affect the state of the entities?

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  • How to read reduce/shift conflicts in LR(1) DFA?

    - by greenoldman
    I am reading an explanation (awesome "Parsing Techniques" by D.Grune and C.J.H.Jacobs; p.293 in the 2nd edition) and I moved forward from my last question: How to get lookahead symbol when constructing LR(1) NFA for parser? Now I have such "problem" (maybe not a problem, but rather need of confirmation from some more knowledgeable people). The authors present state in LR(0) which has reduce/shift conflict. Then they build DFA for LR(1) for the same grammar. And now they say it does not have a conflict (lookaheads at the end): S -> E . eof E -> E . - T eof E -> E . - T - and there is an edge from this state labeled - but no labeled eof. Authors says, that on eof there will be reduce, on - there will be shift. However eof is for shift as well (as lookahead). So my personal understanding of LR(1) DFA is this -- you can drop lookaheads for shifts, because they serve no purpose now -- shifts rely on input, not on lookaheads -- and after that, remove duplicates. S -> E . eof E -> E . - T So the lookahead for reduce serves as input really, because at this stage (all required input is read) it is really incoming symbol right now. For shifts, the input symbols are on the edges. So my question is this -- am I actually right about dropping lookaheads for shifts (after fully constructing DFA)?

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  • Which version management design methodology to be used in a Dependent System nodes?

    - by actiononmail
    This is my first question so please indicate if my question is too vague and not understandable. My question is more related to High Level Design. We have a system (specifically an ATCA Chassis) configured in a Star Topology, having Master Node (MN) and other sub-ordinate nodes(SN). All nodes are connected via Ethernet and shall run on Linux OS with other proprietary applications. I have to build a recovery Framework Design so that any software entity, whether its Linux, Ramdisk or application can be rollback to previous good versions if something bad happens. Thus I think of maintaining a State Version Matrix over MN, where each State(1,2....n) represents Good Kernel, Ramdisk and application versions for each SN. It may happen that one SN version can dependent on other SN's version. Please see following diagram:- So I am in dilemma whether to use Package Management Methodology used by Debian Distributions (Like Ubuntu) or GIT repository methodology; in order to do a Rollback to previous good versions on either one SN or on all the dependent SNs. The method should also be easier for upgrading SNs along with MNs. Some of the features which I am trying to achieve:- 1) Upgrade of even single software entity is achievable without hindering others. 2) Dependency checks must be done before applying rollback or upgrade on each of the SN 3) User Prompt should be given in case dependency fails.If User still go for rollback, all the SNs should get notification to rollback there own releases (if required). 4) The binaries should be distributed on SNs accordingly so that recovery process is faster; rather fetching every time from MN. 5) Release Patches from developer for bug fixes, feature enhancement can be applied on running system. 6) Each version can be easily tracked and distinguishable. Thanks

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  • Handling commands or events that wait for an action to be completed afterwards

    - by virulent
    Say you have two events: Action1 and Action2. When you receive Action1, you want to store some arbitrary data to be used the next time Action2 rolls around. Optimally, Action1 is normally a command however it can also be other events. The idea is still the same. The current way I am implementing this is by storing state and then simply checking when Action2 is called if that specific state is there. This is obviously a bit messy and leads to a lot of redundant code. Here is an example of how I am doing that, in pseudocode form (and broken down quite a bit, obviously): void onAction1(event) { Player = event.getPlayer() Player.addState("my_action_to_do") } void onAction2(event) { Player = event.getPlayer() if not Player.hasState("my_action_to_do") { return } // Do something } When doing this for a lot of other actions it gets somewhat ugly and I wanted to know if there is something I can do to improve upon it. I was thinking of something like this, which wouldn't require passing data around, but is this also not the right direction? void onAction1(event) { Player = event.getPlayer() Player.onAction2(new Runnable() { public void run() { // Do something } }) } If one wanted to take it even further, could you not simply do this? void onPlayerEnter(event) { // When they join the server Player = event.getPlayer() Player.onAction1(new Runnable() { public void run() { // Now wait for action 2 Player.onAction2(new Runnable() { // Do something }) } }, true) // TRUE would be to repeat the event, // not remove it after it is called. } Any input would be wonderful.

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  • what will EcmaScript 6 bring to the table for us

    - by user697296
    Our company ported moderate chunks of business logic to JavaScript. We compile the code with a minifier, which further improves performance. Since the language is dynamically typed, it lends itself well to obfuscation, which occurs as a byproduct of minification. We went to great efforts to ensure it positively screams, performance-wise. We can now do what we did before, faster, better, with less code, on more platforms. In summary, we are very satisfied with the current state of the language. I personally love the language especially for its cross-platform nature. So naturally, I read up a lot about the state of JavaScript compilers, performance and compatibility across as many browsers and platforms as I have time to research. The one theme which has been growing louder and louder these days, is the news about ECMAScript 6. So far, what I have been able to gather is that ES6 promises a better development experience; firstly by enabling new ways to do things, secondly by reporting errors early. This sounds great for those who are still waiting for the language to meet their needs before jumping on board. But we have already jumped on board in a big way. Sure, I expect that we will have to do ongoing maintenance and feature revisions on our code through the years, and that we would obviously make use of best practices at the time. But I don't see us refactoring major portions of it to take advantage of language features that are mostly intended to boost developer productivity. I keep wondering, what impact will the language advances ultimately have on our existing, well-written, well-performing code base? Is there something I am missing? Is there something we ought to look out for? Does anyone have tips or guidance on how we should approach the ecmascript.next finalization? Should we care?

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  • How come there is still so much programming work?

    - by jd_505
    First I'd like to say that I am not pretty sure that this question will meet the guidelines. I think it can goes under the "Freelancing and business concerns" bullet, but I am not sure. Anyway, I will give it a shot. I wonder how the programming jobs hasn't yet "dried" because of the software evolution, for example, I am a developer myself, which means that I do care about software (I mean I am not of the type of guys that needs a computer mainly to just browse the Internet), and still I wouldn't mind if I never receive any more updates on my Ubuntu machine. I find that it provides everything I need, and while the updates provide various bug fixes/improvements, I wouldn't mind using it with it's current state for the rest of my life, for 2 years of Ubuntu usage I have never bumped at a serious bug/problem. Another example is Windows, almost half of it's users still use XP, which is practically ancient, yet they find it satisfying all their needs (and I agreee with them). I could go with many more examples, but by now you are understanding my point and my question. While new "trends" appears all of the time (like a new mobile OS) which runs on new platforms and requires some fresh development work, still the majority of the software effort goes in to what I consider as "completed projects", or at least a state of a project which is enough to be considered as completed. Do you have an explanation ? I can't think of the right tags for this question, please edit it the way you find it to be most appropriate. Thanks.

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