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• Very poor read performance compared to write performance on md(raid1) / crypt(luks) / lvm

  - by Android5360

  I'm experiencing very poor read performance over raid1/crypt/lvm. In the same time, write speeds are about 2x+ faster on the same setup. On another raid1 setup on the same machine I get normal read speeds (maybe because I'm not using cryptsetup). OS related disks: sda + sdb. I have raid1 configuration with two disks, both are in place. I'm using LVM over the RAID. No encryption. Both disks are WD Green, 5400 rpm. IO test results on this raid1: dd if=/dev/zero of=/tmp/output.img3 bs=8k count=256k conv=fsync - 2147483648 bytes (2.1 GB) copied, 22.3392 s, 96.1 MB/s sync echo 3 > /proc/sys/vm/drop_caches dd if=/tmp/output.img3 of=/dev/null bs=8k - 2147483648 bytes (2.1 GB) copied, 15.9 s, 135 MB/s And here is the problematic setup (on the same machine). Currently I have only one sdc (WD Green, 5400rpm) configured in software raid1 + crypt (luks, serpent-xts-plain) + lvm. Tomorrow I will attach another disk (sdd) to complete this two-disk raid1 setup. IO tests results on this raid1: dd if=/dev/zero of=output.img3 bs=8k count=256k conv=fsync 2147483648 bytes (2.1 GB) copied, 17.7235 s, 121 MB/s sync echo 3 > /proc/sys/vm/drop_caches dd if=output.img3 of=/dev/null bs=8k 2147483648 bytes (2.1 GB) copied, 36.2454 s, 59.2 MB/s We can see that the read performance is very very bad (59MB/s compared to 135MB/s when using no encryption). Nothing is using the disks during benchmark. I can confirm this because I checked with iostat and dstat. Details on the hardware: disks: all are WD green, 5400rpm, 64mb cache. cpu: FX-8350 at stock speed ram: 4x4GB at 1066Mhz. Details on the software: OS: Debian Wheezy 7, amd64 mdadm: v3.2.5 - 18th May 2012 LVM version: 2.02.95(2) (2012-03-06) LVM Library version: 1.02.74 (2012-03-06) LVM Driver version: 4.22.0 cryptsetup: 1.4.3 Here is how I configured the slow raid1+crypt+lvm setup: parted /dev/sdc mklabel gpt type: ext4 start: 2048s end: -1 Now the raid, crypt and the lvm configuration: mdadm --create /dev/md1 --level=1 --raid-disks=2 missing /dev/sdc cryptsetup --cipher serpent-xts-plain luksFormat /dev/md1 cryptsetup luksOpen /dev/md1 md1_crypt vgcreate vg_sql /dev/mapper/md1_crypt lvcreate -l 100%VG vg_sql -n lv_sql mkfs.ext4 /dev/mapper/vg_sql-lv-sql mount /dev/mapper/vg_sql-lv_sql /sql So guys, can you help me identify the reason and fix it? It has to be something with the cryptsetup as there is no such read slowdown on the other setup (sda+sdb) where no encryption is present. But I have no idea what to do. Thanks!

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• System Requirements of a write-heavy applications serving hundreds of requests per second

  - by Rolando Cruz

  NOTE: I am a self-taught PHP developer who has little to none experience managing web and database servers. I am about to write a web-based attendance system for a very large userbase. I expect around 1000 to 1500 users logged-in at the same time making at least 1 request every 10 seconds or so for a span of 30 minutes a day, 3 times a week. So it's more or less 100 requests per second, or at the very worst 1000 requests in a second (average of 16 concurrent requests? But it could be higher given the short timeframe that users will make these requests. crosses fingers to avoid 100 concurrent requests). I expect two types of transactions, a local (not referring to a local network) and a foreign transaction. local transactions basically download userdata in their locality and cache it for 1 - 2 weeks. Attendance equests will probably be two numeric strings only: userid and eventid. foreign transactions are for attendance of those do not belong in the current locality. This will pass in the following data instead: (numeric) locality_id, (string) full_name. Both requests are done in Ajax so no HTML data included, only JSON. Both type of requests expect at the very least a single numeric response from the server. I think there will be a 50-50 split on the frequency of local and foreign transactions, but there's only a few bytes of difference anyways in the sizes of these transactions. As of this moment the userid may only reach 6 digits and eventid are 4 to 5-digit integers too. I expect my users table to have at least 400k rows, and the event table to have as many as 10k rows, a locality table with at least 1500 rows, and my main attendance table to increase by 400k rows (based on the number of users in the users table) a day for 3 days a week (1.2M rows a week). For me, this sounds big. But is this really that big? Or can this be handled by a single server (not sure about the server specs yet since I'll probably avail of a VPS from ServInt or others)? I tried to read on multiple server setups Heatbeat, DRBD, master-slave setups. But I wonder if they're really necessary. the users table will add around 500 1k rows a week. If this can't be handled by a single server, then if I am to choose a MySQL replication topology, what would be the best setup for this case? Sorry, if I sound vague or the question is too wide. I just don't know what to ask or what do you want to know at this point.

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• Avoid read-write access to bad sectors on HDD to continue working on the HDD

  - by goldenmean

  I have a HP Pavilion dv6446 notebook. It had Windows Vista Home premium. After 4.5+ years of usage, just recently it started malfunctioning. While working fine, its screen goes white or sometimes some thin black lines horizontally. Laptop freezes. Hard reboot works. Again it works for some 2 hrs or so, same error. To diagnose I did run the Memory and Hard disk check which is present in the Bios Setup. Memory test passed. Hard disk test returned an error saying something like - "Replace the hard disk". Bad.. Some sectors or platters have gone bad on the disk. (I confirmed this later by further tests mentioned below) Then I tried installing a Ubuntu 11.10. It listed 3 partitions /dev/sda1, sda2, sda2. It again gave error and could not install grub loader on /dev/sda1. Bad sectors. Then redid the Ubuntu installation, this time asked to to install the Ubuntu on /dev/sda3. and kept /dev/sda1 for /home. Installed fine, and works fine as well. Due to unavailability of WiFi/ Ethernet driver for that adapters under Ubuntu( at least I could not configure them and get the networking working at all), I decided to go back to reinstall windows Vista. It did install fine. I did not have to format one data partition which has my data. I just formatted one partition which installed Windows So in effect HDD has not undergone a full format here. Worked ok for 1 day. But same white screen and freeze happened. Looks like while it is in use, it accesses the bad sectors for storing some data and that's when it bombs. I am inclined to think HDD has not failed fully or crashed but has developed bad sectors. Else if it was a HDD crash, it would have refused to boot at all let alone install on it. Questions: Is there any HDD test check under windows or any such tools windows/linux based ewhere which can identify the bad sectors of the HDD and 'lock/isolate' them from further read-write access of any kind. If not what are my options, if any to salvage this laptop HDD without replacing it. EDIT: Would the Disk Error checking tool under windows help in any way?

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• PPTP VPN Not Working - Peer failed CHAP authentication, PTY read or GRE write failed

  - by armani

  Brand-new install of CentOS 6.3. Followed this guide: http://www.members.optushome.com.au/~wskwok/poptop_ads_howto_1.htm And I got PPTPd running [v1.3.4]. I got the VPN to authenticate users against our Active Directory using winbind, smb, etc. All my tests to see if I'm still authenticated to the AD server pass ["kinit -V [email protected]", "smbclient", "wbinfo -t"]. VPN users were able to connect for like . . . an hour. I tried connecting from my Android phone using domain credentials and saw that I got an IP allocated for internal VPN users [which I've since changed the range, but even setting it back to the initial doesn't work]. Ever since then, no matter what settings I try, I pretty much consistently get this in my /var/log/messages [and the VPN client fails]: [root@vpn2 ~]# tail /var/log/messages Aug 31 15:57:22 vpn2 pppd[18386]: pppd 2.4.5 started by root, uid 0 Aug 31 15:57:22 vpn2 pppd[18386]: Using interface ppp0 Aug 31 15:57:22 vpn2 pppd[18386]: Connect: ppp0 <--> /dev/pts/1 Aug 31 15:57:22 vpn2 pptpd[18385]: GRE: Bad checksum from pppd. Aug 31 15:57:24 vpn2 pppd[18386]: Peer armaniadm failed CHAP authentication Aug 31 15:57:24 vpn2 pppd[18386]: Connection terminated. Aug 31 15:57:24 vpn2 pppd[18386]: Exit. Aug 31 15:57:24 vpn2 pptpd[18385]: GRE: read(fd=6,buffer=8059660,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs Aug 31 15:57:24 vpn2 pptpd[18385]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7) Aug 31 15:57:24 vpn2 pptpd[18385]: CTRL: Client 208.54.86.242 control connection finished Now before you go blaming the firewall [all other forum posts I find seem to go there], this VPN server is on our DMZ network. We're using a Juniper SSG-5 Gateway, and I've assigned a WAN IP to the VPN box itself, zoned into the DMZ zone. Then, I have full "Any IP / Any Protocol" open traffic rules between DMZ<--Untrust Zone, and DMZ<--Trust Zone. I'll limit this later to just the authenticating traffic it needs, but for now I think we can rule out the firewall blocking anything. Here's my /etc/pptpd.conf [omitting comments]: option /etc/ppp/options.pptpd logwtmp localip [EXTERNAL_IP_ADDRESS] remoteip [ANOTHER_EXTERNAL_IP_ADDRESS, AND HAVE TRIED AN ARBITRARY GROUP LIKE 5.5.0.0-100] Here's my /etc/ppp/options.pptpd.conf [omitting comments]: name pptpd refuse-pap refuse-chap refuse-mschap require-mschap-v2 require-mppe-128 ms-dns 192.168.200.42 # This is our internal domain controller ms-wins 192.168.200.42 proxyarp lock nobsdcomp novj novjccomp nologfd auth nodefaultroute plugin winbind.so ntlm_auth-helper "/usr/bin/ntlm_auth --helper-protocol=ntlm-server-1" Any help is GREATLY appreciated. I can give you any more info you need to know, and it's a new test server, so I can perform any tests/reboots required to get it up and going. Thanks a ton.

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• Bulk Copy from one server to another

  - by Joseph

  Hi All, I've one situation where I need to copy part of the data from one server to another. The table schema are exactly same. I need to move partial data from the source, which may or may not be available in the destination table. The solution I'm thinking is, use bcp to export data to a text(or .dat) file and then take that file to the destination as both are not accessible at the same time (Different network), then import the data to the destination. There are some conditions I need to satisfy. 1. I need to export only a list of data from the table, not whole. My client is going to give me IDs which needs to be moved from source to destination. I've around 3000 records in the master table, and same in the child tables too. What I expect is, only 300 records to be moved. 2. If the record exists in the destination, the client is going to instruct as whether to ignore or overwrite case to case. 90% of the time, we need to ignore the records without overwriting, but log the records in a log file. Please help me with the best approach. I thought of using BCP with query option to filter the data, but while importing, how do I bypass inserting the existing records? If I need to overwrite, how to do it? Thanks a lot in advance. ~Joseph

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• openCV Won't copy to image after changed color ( opencv and c++ )

  - by user1656647

  I am a beginner at opencv. I have this task: Make a new image Put a certain image in it at 0,0 Convert the certain image to gray scale put the grayscaled image next to it ( at 300, 0 ) This is what I did. I have a class imagehandler that has constructor and all the functions. cv::Mat m_image is the member field. Constructor to make new image: imagehandler::imagehandler(int width, int height) : m_image(width, height, CV_8UC3){ } Constructor to read image from file: imagehandler::imagehandler(const std::string& fileName) : m_image(imread(fileName, CV_LOAD_IMAGE_COLOR)) { if(!m_image.data) { cout << "Failed loading " << fileName << endl; } } This is the function to convert to grayscale: void imagehandler::rgb_to_greyscale(){ cv::cvtColor(m_image, m_image, CV_RGB2GRAY); } This is the function to copy paste image: //paste image to dst image at xloc,yloc void imagehandler::copy_paste_image(imagehandler& dst, int xLoc, int yLoc){ cv::Rect roi(xLoc, yLoc, m_image.size().width, m_image.size().height); cv::Mat imageROI (dst.m_image, roi); m_image.copyTo(imageROI); } Now, in the main, this is what I did : imagehandler CSImg(600, 320); //declare the new image imagehandler myimg(filepath); myimg.copy_paste_image(CSImg, 0, 0); CSImg.displayImage(); //this one showed the full colour image correctly myimg.rgb_to_greyscale(); myimg.displayImage(); //this shows the colour image in GRAY scale, works correctly myimg.copy_paste_image(CSImg, 300, 0); CSImg.displayImage(); // this one shows only the full colour image at 0,0 and does NOT show the greyscaled one at ALL! What seems to be the problem? I've been scratching my head for hours on this one!!!

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• Doubts About Core Data NSManagedObject Deep Copy

  - by Jigzat

  Hello everyone, I have a situation where I must copy one NSManagedObject from the main context into an editing context. It sounds unnecessary to most people as I have seen in similar situations described in Stackoverflow but I looks like I need it. In my app there are many views in a tab bar and every view handles different information that is related to the other views. I think I need multiple MOCs since the user may jump from tab to tab and leave unsaved changes in some tab but maybe it saves data in some other tab/view so if that happens the changes in the rest of the views are saved without user consent and in the worst case scenario makes the app crash. For adding new information I got away by using an adding MOC and then merging changes in both MOCs but for editing is not that easy. I saw a similar situation here in Stackoverflow but the app crashes since my data model doesn't seem to use NSMutableSet for the relationships (I don't think I have a many-to-many relationship, just one-to-many) I think it can be modified so I can retrieve the relationships as if they were attributes for (NSString *attr in relationships) { [cloned setValue:[source valueForKey:attr] forKey:attr]; } but I don't know how to merge the changes of the cloned and original objects. I think I could just delete the object from the main context, then merge both contexts and save changes in the main context but I don't know if is the right way to do it. I'm also concerned about database integrity since I'm not sure that the inverse relationships will keep the same reference to the cloned object as if it were the original one. Can some one please enlighten me about this?

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• Fork or copy a users browser session in IE

  - by jmoeller

  Is it possible to fork a users session (or do something similar) in a Internet Explorer plugin? I want to process the page the user is on when they click a button in the toolbar. To avoid interrupting the users browsing, I'd like to "copy" everything so I can parse and process the page in the background. The processing can involve things such as loading the content of the result links on a Google search, if that's where the button was clicked. So - what I basically want is to imitate "Ctrl+N" but hide the window from the user, so they won't be interrupted. As you can see, if you fill out and submit the form on http://www.snee.com/xml/crud/posttest.html and press "Ctrl+N", everything posted will still appear in the new window, but it won't post the data twice. I was thinking of somehow copying the IWebBrowser2, but: I'm not sure if that's possible (I haven't been able to find any information on MSDN) I don't know if it copies the sessions as well. Creating a new instance of the IWebBrowser2 and simply navigating to the current URL isn't a valid solution as POST-variables of course doesn't get carried over.

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• XML generation with java, trying to copy the whole node

  - by Pawel Mysior

  I've got an xml document that filled with people (parent node is "students", and there are 25+ "student" nodes). Each student looks like this: <student> <name></name> <surname></surname> <grades> <subject name=""> <small_grades></small_grades> <final_grade></final_grade> </subject> <subject name=""> <small_grades></small_grades> <final_grade></final_grade> </subject> </grades> <average></average> </student> Basically, what I want to do ('ve been asked to do) is to make a program that would get 3 students with the best average. While parsing the document and getting three best students isn't too difficult, the XML generation is a pain in the ass. Right now, what I'm doing is getting every single node from student and recreating it to a new file. Is there a way to copy the whole student node with everything that's in it? Regards, Paul

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• A copy of ApplicationController has been removed from the module tree but is still active

  - by Matchu

  Whenever two concurrent HTTP requests go to my Rails app, the second always returns the following error: A copy of ApplicationController has been removed from the module tree but is still active! From there it gives an unhelpful stack trace to the effect of "we went through the standard server stuff, ran your first before_filter on ApplicationController (and I checked; it's just whichever filter runs first)", then offers the following: /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:414:in `load_missing_constant' /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:96:in `const_missing' which I'm assuming is a generic response and doesn't really say much. Google seems to tell me that people developing Rails Engines will encounter this, but I don't do that. All I've done is upgrade my Rails app from 2.2 (2.1?) to 2.3. What are some possible causes for this error, and how can I go about tracking down what's really going on? I know this question is vague, so would any other information be helpful? More importantly: I tried doing a test run in a "production" environment just now, and the error doesn't seem to persist. Does this only affect development, then, and need I not worry too much?

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• copy a text file in C#

  - by melt

  I am trying to copy a text file in an other text file line by line. It seems that there is a buffer of 1024 character. If there is less than 1024 character in my file, my function will not copie in the other file. Also if there is more than 1024 character but less a factor of 1024, these exceeding characters will not be copied. Ex: 2048 character in initial file - 2048 copied 988 character in initial file - 0 copied 1256 character in initial file - 1024 copied Thks! private void button3_Click(object sender, EventArgs e) { // écrire code pour reprendre le nom du fichier sélectionné et //ajouter un suffix "_poly.txt" string ma_ligne; const int RMV_CARCT = 9; //délcaration des fichier FileStream apt_file = new FileStream(textBox1.Text, FileMode.Open, FileAccess.Read); textBox1.Text = textBox1.Text.Replace(".txt", "_mod.txt"); FileStream mdi_file = new FileStream(textBox1.Text, FileMode.OpenOrCreate,FileAccess.ReadWrite); //lecture/ecriture des fichiers en question StreamReader apt = new StreamReader(apt_file); StreamWriter mdi_line = new StreamWriter(mdi_file, System.Text.Encoding.UTF8, 16); while (apt.Peek() >= 0) { ma_ligne = apt.ReadLine(); //if (ma_ligne.StartsWith("GOTO")) //{ // ma_ligne = ma_ligne.Remove(0, RMV_CARCT); // ma_ligne = ma_ligne.Replace(" ",""); // ma_ligne = ma_ligne.Replace(",", " "); mdi_line.WriteLine(ma_ligne); //} } apt_file.Close(); mdi_file.Close(); }

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• Copy a directory from a jar file

  - by Macarse

  Hi. I recently finished and application and created a jar file. One of my classes creates an output directory populating it with files from it's resource. The code is something like this: // Copy files from dir "template" in this class resource to output. private void createOutput(File output) throws IOException { File template = new File(FileHelper.URL2Path(getClass().getResource("template"))); FileHelper.copyDirectory(template, output); } The problem is that now that I am running for a jar, this doesn't work. I tried without luck: Using Streams to solve similar stuff on other classes but it doesn't work with dirs. Code was similar to http://www.exampledepot.com/egs/java.io/CopyFile.html Creating the File template with new File(getClass().getResource("template").toUri()) While writting this I was thinking about instead of having a template dir in the resource path having a zip file of it. Doing it this way I could get the file as an inputStream and unzip it where I need to. But I am not sure if it's the correct way. Thanks for reading!

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• Deep copy objects from different namespaces

  - by Wasim

  Hi all, I have the following situation: I have class User with the follwing properies : public class User { string user name ; List <Contact> contacts ; List <BookMark> book marks; . . . } I have the same class in a different namespace , with some different properties . BWT , it's the same situation of it's classes (Contact) and (BookMark). I need to make a deep copy of the same properties from the two classes . Actually , I arrive to this situation by having an Entity Framework edmx file . I created the first database (SQL server 2008) from this model . And copied he same edmx file to another project and created the database with SQL CE db. Now I get the first data model objects by WCF service and need to persist them in the local database in my application . The objects are the same but there are some changs because of the modeling issue with a different databse. Do you have any workarround about this assue. Thanks in advance ...

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• Enum "copy" problem

  - by f0b0s

  Hi all! I have a class, let's call it A. It has a enum (E) and a method Foo(E e), with gets E in the arguments. I want to write a wrapper (decorator) W for A. So it'll have its own method Foo(A::E). But I want to have some kind of encapsulation, so this method should defined as Foo(F f), where F is another enum defined in W, that can be converted to A::E. For example: class A { public: enum E { ONE, TWO, THREE }; void Foo(E e); }; class B { //enum F; // ??? void Foo(F f) { a_.Foo(f); } private: A a_; }; How F should be defined? I don't want to copy value like this: enum F { ONE = A::ONE, TWO = A::TWO, THREE = A::THREE }; because its a potential error in the near feature. Is the typedef definition: typedef A::E F; is the best decision? Is it legal?

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• Drag Drop copy file

  - by Graham Warrender

  I've perhaps done something marginally stupid, but can't see what it is!! string pegasusKey = @"HKEY_LOCAL_MACHINE\SOFTWARE\Pegasus\"; string opera2ServerPath = @"Server VFP\"; string opera3ServerPath = @"O3 Client VFP\"; string opera2InstallationPath = null; string opera3InstallationPath = null; //Gets the opera Installtion paths and reads to the string opera*InstallationPath opera2InstallationPath = (string)Registry.GetValue(pegasusKey + opera2ServerPath + "System", "PathToServerDynamic", null); opera3InstallationPath = (string)Registry.GetValue(pegasusKey + opera3ServerPath + "System", "PathToServerDynamic", null); string Filesource = null; string[] FileList = (string[])e.Data.GetData(DataFormats.FileDrop, false); foreach (string File in FileList) Filesource = File; label.Text = Filesource; if (System.IO.Directory.Exists(opera3InstallationPath)) { System.IO.File.Copy(Filesource, opera3InstallationPath); MessageBox.Show("File Copied from" + Filesource + "\n to" + opera3InstallationPath); } else { MessageBox.Show("Directory Doesn't Exist"); } The user drags the file onto the window, I then get the installation path of an application which is then used as the destination for the source file.. When the application is runs, it throws the error directory not found. But surely if the directory doesn't exists is should step into the else statement? a simple application that is becoming a headache!!

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• How to copy a variable in JavaScript?

  - by Michael Stum

  I have this JavaScript code: for (var idx in data) { var row = $("<tr></tr>"); row.click(function() { alert(idx); }); table.append(row); } So I'm looking through an array, dynamically creating rows (the part where I create the cells is omitted as it's not important). Important is that I create a new function which encloses the idx variable. However, idx is only a reference, so at the end of the loop, all rows have the same function and all alert the same value. One way I solve this at the moment is by doing this: function GetRowClickFunction(idx){ return function() { alert(idx); } } and in the calling code I call row.click(GetRowClickFunction(idx)); This works, but is somewhat ugly. I wonder if there is a better way to just copy the current value of idx inside the loop? While the problem itself is not jQuery specific (it's related to JavaScript closures/scope), I use jQuery and hence a jQuery-only solution is okay if it works.

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• Copy a LinkedList that has a Random Pointer in it

  - by Bragaadeesh

  Hi, First of all this is not a homework, this is an interview question that I got from a company I attended today. You have a singly linked list with the Node structure as the following class Node{ int data; Node next; Node random; } You have a typical singly linked list of length n. The random pointer in each node in the linkedlist randomly points to some Node within the linked list. The Question is to create a copy of the linked list efficiently into a different LinkedList. I said that I will first calculate the Random pointer's position in the linked list and store it in an array. Then create a new linked list normally. Then iterate through the linked list by setting the random pointer where they belong by reading the values stored from the array. I know its a very brute force technique and the interviewer asked me to come up with a better solution but I couldnt. Please can someone answer this? I can explain if the question is not clear.

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• copy rows with special condition

  - by pooria_googooli

  I have a table with a lot of columns. For example I have a table with these columns : ID,Fname,Lname,Tel,Mob,Email,Job,Code,Company,...... ID column is auto number column. I want to copy all rows in this table to this table and change the company column value to 12 in this copied row. I don't want to write name all of the columns because I have a lot of table with a lot of columns. I tried this code but I had this error : declare @c int; declare @i int; select * into CmDet from CmDet; select @C= count(id) from CmDet; while @i < @C begin UPDATE CmDet SET company =12 WHERE company=11 set @i += 1 end error : Msg 2714, Level 16, State 6, Line 3 There is already an object named 'CmDet' in the database. I changed the code to this declare @c int declare @i int insert into CmDet select * from CmDet; select @C= count(id) from CmDet; while @i < @C begin UPDATE CmDet SET company =12 WHERE company=11 set @i += 1 end and I had this error : Msg 8101, Level 16, State 1, Line 3 An explicit value for the identity column in table 'CmDet' can only be specified when a column list is used and IDENTITY_INSERT is ON. What should I do ?

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• C++ Template Classes and Copy Construction

  - by themoondothshine

  Is there any way I can construct an new object from the given object if the template parameters of both objects are identical at run-time? For example: I have a template class with the declaration: template<typename _Type1, typename _Type2> class Object; Next, I have two instantiations of the template: template class Object<char, int>; template class Object<wchar_t, wint_t>; Now, I want to write a member function such as: template<typename _Type1, typename _Type2> Object<char, int> Object<_Type1, _Type2>::toCharObject() { if(__gnu_cxx::__are_same<_Type1, char>::__value) return *this; else { //Perform some kind of conversion and return an Object<char, int> } } I have tried a couple of techniques, such as using __gnu_cxx::__enable_if<__gnu_cxx::__are_same<_Type1, char>::__value, _Type1>::__type in a copy constructor for the Oject class, but I keep running into the error: error: conversion from ‘Object<wchar_t, wint_t>’ to non-scalar type ‘Object<char, int>’ requested Is there no way I can do this? Any help will be greatly appreciated!

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• Powershell wait for file to delete, then copy a folder

  - by user3317623

  Morning guys, I have a couple of scripts that have to sync a folder from the network server, to the local terminal server, and lastly into the %LOCALAPPDATA%. I need to first check if a folder is being synced (this is done by creating a temporary COPYING.TXT on the server), and wait until that is removed, THEN copy to %LOCALAPPDATA%. Something like this: Server-side script executes, which syncs my folder to all of my terminal servers. It creates a COPYING.TXT temporary file, which indicates the sync is in progress. Once the sync is finished, the script removes the COPYING.TXT If someone logs on during the sync, I need a script to wait until the COPYING.TXT is deleted I.E the sync is finished, then resume the local sync into their %LOCALAPPDATA%. do{cp c:\folder\program $env:LOCALAPPDATA} while(!(test-path c:\folder\COPYING.txt)) (So that copies the folder while the file DOESN'T exist, but I don't think that exits cleanly) I cannot format the above as code for some reason I'm sorry? Or: while(!(test-path c:\folder\COPYING.txt)){ cp c:\folder\program $env:LOCALAPPDATA\ -recurse -force if (!(test-path c:\folder\program)){return} } But that script quits if the COPYING.TXT exists. I think I need to create a function and insert that function within itself, or a nested while loop, but that is starting to make my head hurt. Any help would be greatly appreciated. Thanks guys.

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• Javascript floodlight tracking iframe leaves browser window blank, please help!

  - by Ben Paton

  Hello, I have been asked to implement a javascript floodlight tag onto my site which is to be called everytime a customer downloads a pdf file. I have tried to implement this as follows: <script type="text/javascript"> function appForm() { var axel = Math.random() + ""; var a = axel * 10000000000000; document.write('<IFRAME SRC="http://fls.doubleclick.net/activityi;src=1234567;type=count123;cat=123do456;ord=1;num='+ a + '?" WIDTH=1 HEIGHT=1 FRAMEBORDER=0></IFRAME>'); return false; } <a href="appForm.pdf" target="_blank" onClick="appForm();">Download PDF</a> This seems to almost work. The pdf file opens in a new window. But the window where you clicked the download link turns blank. Is there a way of opening this tracking iframe and then having the pdf opening without the parent window going blank? Your help will be very much appreciated on this.

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• Robotium - Write to file in eclipse workspace or computer file system

  - by Flavio Capaccio

  I'm running some tests using Robotium on an Android application that interacts with a web-portal. I'd like to save some information to file; for example I need to save the id of the username I created from the app and I want to make it read from Selenium to run tests on web-portal to verify a webpage for that user has been created. Is it possible? Could someone suggest me a solution or a work-around? This is an example of code, but it doesn't work (I want to write to a file for example on c:\myworkspace\filename.txt a string): public void test_write_file(){ if(!solo.searchText("HOME")){ signIn("39777555333", VALID_PASSWORD); } try { String content = "This is the content to write into file"; File file = new File("filename.txt"); // if file doesnt exists, then create it if (!file.exists()) { file.createNewFile(); } FileWriter fw = new FileWriter(file.getAbsoluteFile()); BufferedWriter bw = new BufferedWriter(fw); bw.write(content); bw.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } assertTrue(solo.searchText("HOME")); }

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• How can I write good "research code"?

  - by John

  "Research code" is often held up as a paragon of what not to do when writing software. Certainly, the kind of code that often results from trying to solve a research problem can end up being poorly-designed, difficult to debug, etc. But my question is this: does research code have to be this way? Is it possible to write good research code? Is the only approach to consider the first version a poorly-written prototype to be discarded in favour of the better-designed second version? Software engineering has all sorts of best practices about how to design and write good code, but I don't usually find this relevant when you don't have a good idea ahead of time what the final system will look like. The final system is likely to be a result of what did or didn't work along the way, and the only way to determine what does or doesn't work is to write the code first. As you find things that don't work, you change what the final system looks like, moving further away from your original design (assuming you had one). I'd be interested in any personal experience with these issues, as well as any books or other resources anyone can point me to.

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• Write asynchronously to file in perl

  - by Stefhen

  Basically I would like to: Read a large amount of data from the network into an array into memory. Asynchronously write this array data, running it thru bzip2 before it hits the disk. repeat.. Is this possible? If this is possible, I know that I will have to somehow read the next pass of data into a different array as the AIO docs say that this array must not be altered before the async write is complete. I would like to background all of my writes to disk in order as the bzip2 pass is going to take much longer than the network read. Is this doable? Below is a simple example of what I think is needed, but this just reads a file into array @a for testing. use warnings; use strict; use EV; use IO::AIO; use Compress::Bzip2; use FileHandle; use Fcntl; my @a; print "loading to array...\n"; while(<>) { $a[$. - 1] = $_; } print "array loaded...\n"; my $aio_w = EV::io IO::AIO::poll_fileno, EV::WRITE, \&IO::AIO::poll_cb; aio_open "./out", O_WRONLY || O_NONBLOCK, 0, sub { my $fh = shift or die "error while opening: $!\n"; aio_write $fh, undef, undef, $a, -1, sub { $_[0] > 0 or die "error: $!\n"; EV::unloop; }; }; EV::loop EV::LOOP_NONBLOCK;

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• lseek/write suddenly returns -1 with errno = 9 (Bad file descriptor)

  - by Ger Teunis

  My application uses lseek to seek the desired position to write data. The file is opened using open() command successfully and my application was able to use lseek and wite lots of times. At a given time, for some users and not easily reproducible the lseek returns -1 with an errno of 9. File is not closed before this and the filehandle (int) isn't reset. After this an other file is created open is okay again and lseek and write works again. To make it even worse, this user tried the complete sequence again and all was well. So my question is, can the OS close the file handle for me for some reason? What could cause this? A file indexer or file scanner of some sort? What is the best way to solve this; is this pseudo code the best solution? (never mind the code layout, will create functions for it) int fd=open(...); if (fd>-1) { long result = lseek(fd,....); if (result == -1 && errno==9) { close(fd..); //make sure we try to close nicely fd=open(...); result = lseek(fd,....); } } Anybody experience with something similar? Summary: file seek and write works okay for a given fd and suddenly gives back errno=9 without a reason.

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