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  • Are the atomic builtins provided by gcc actually translated into the example code, or is that just f

    - by Jared P
    So I was reading http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html, and came across this: type __sync_and_and_fetch (type *ptr, type value, ...) type __sync_xor_and_fetch (type *ptr, type value, ...) type __sync_nand_and_fetch (type *ptr, type value, ...) These builtins perform the operation suggested by the name, and return the new value. That is, { *ptr op= value; return *ptr; } { *ptr = ~*ptr & value; return *ptr; } // nand Is this code literal? or is it just to explain what gcc is doing atomically using c-like syntax? And if this is the direct translation, can someone explain how it is atomic?

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  • SIM card number swap

    - by DaGhostman Dimitrov
    Is it possible to swap two numbers between two sim cards (I am just got an new phone and it is using a micro sim) And I have a old number that I want to use but it is on standart sim card. Is it possible to swap the numbers between the cards using a SIM Card reader. What software and hardware should I use? Note: I have talked with my provider but I have to cancel my old numbers contract but I like it and do not want to pay the remaining period of the contract to turn it in to PayAsYouGo and then swap ..

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  • Processing a list of atomic operations, allowing for interruptions

    - by JDB
    I'm looking for a design pattern that addresses the following situation: There exists a list of tasks that must be processed. Tasks may be added at any time. Each task is wholly independent from all other tasks. The order in which tasks are processed has no effect on the overall system or on the tasks themselves. Every task must be processed once and only once. The "main" process which launches the task processors may start and stop without warning. When stopped, the "main" process loses all in-memory data. Obviously this is going to involve some state, but are there any design patterns which discuss where and how to maintain that state? Are there any relevant anti-patterns? Named patterns are especially helpful so that we can discuss this topic with other organizations without having to describe the entire problem domain.

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  • Windows 7 - swap file on a USB disk? [closed]

    - by Sara Cohen
    Possible Duplicate: How to move the page file to another physical disk location Windows 7 I was given temporarily a PC, running Windows 7 Ultimate. The problem is it's hard drive is full, there are like 250 MB free. The swap file is set to none. It has 4 GB RAM. When I load a few tabs in Chrome or IE and start a game it runs out of memory. I already emptied Recycle Bin, %temp%, etc. Deleting/moving user files or adding RAM is not an option. Now I have a USB 3 7200 RPM drive, it's connected to a USB 3 port and is really fast. Is there a way to create a swap file on that drive?

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  • Ubuntu 12.04 Faster boot, Hibernate & other questions

    - by Samarth Shukla
    I've recently started exploring Ubuntu (my 1st distro). I fresh installed precise without a swap (4GB ram). The only issues are, slow boot (regardless of the swap) and instability after a few days of installation. The runtime performance is immaculate otherwise. Even though not needed, I still set swappiness = 10. I've tried the quiet splash profile to GRUB; already have preload installed. But it still is pretty slow. I am not too confident on recompiling the kernel yet. But you could please advice me on that too. I've also added the following to fstab: #Move /tmp to RAM: tmpfs /tmp tmpfs defaults,noexec,nosuid 0 0 (Also if you could please tell me the exact implication/scope of this tweak on physical ram & the swap.) But nothing has happened really. So what alternatives are there to make it boot faster? Also, right after fresh install, though no swap partition, the system still showed /dev/zram0 of arond 2GB which was never used (probably because of the above fstab edit). Finally, I experimented with Hibernate a little, but many claim that it doesn't work on 12.04. (Not to mention, I made a swap file of 4GB for it). What I did was: sudo gedit /var/lib/polkit-1/localauthority/50-local.d/hibernate.pkla Then I added the following lines, saved the file, and closed the text editor: [Re-enable Hibernate] Identity=unix-user:* Action=org.freedesktop.upower.hibernate ResultActive=yes I also edited the upower policy for hibernate: gksudo gedit /usr/share/polkit-1/actions/org.freedesktop.upower.policy I added these lines: < allow_inactive >no< /allow_inactive > < allow_active >yes< /allow_active > But it did not work. So is there an alternate method perhaps that can make it work on 12.04?

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  • "Not enough free swap" error when trying to hibernate

    - by Spirit Zhang
    I recently upgraded from 11.04 to 11.10, but I get "Not enough free swap" error when trying to put my laptop to hibernation. I have 2G of physical memory and 3G for swap. Besides, the hibernate works fine in 11.04. So what might be the problem ? Thanks in advance. UPDATE: The error happens when I try to hibernate. And the memoinfo is here: SwapCached: 0 kB SwapTotal: 4028604 kB SwapFree: 4028604 kB

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  • Lightweight spinlocks built from GCC atomic operations?

    - by Thomas
    I'd like to minimize synchronization and write lock-free code when possible in a project of mine. When absolutely necessary I'd love to substitute light-weight spinlocks built from atomic operations for pthread and win32 mutex locks. My understanding is that these are system calls underneath and could cause a context switch (which may be unnecessary for very quick critical sections where simply spinning a few times would be preferable). The atomic operations I'm referring to are well documented here: http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Atomic-Builtins.html Here is an example to illustrate what I'm talking about. Imagine a RB-tree with multiple readers and writers possible. RBTree::exists() is read-only and thread safe, RBTree::insert() would require exclusive access by a single writer (and no readers) to be safe. Some code: class IntSetTest { private: unsigned short lock; RBTree<int>* myset; public: // ... void add_number(int n) { // Aquire once locked==false (atomic) while (__sync_bool_compare_and_swap(&lock, 0, 0xffff) == false); // Perform a thread-unsafe operation on the set myset->insert(n); // Unlock (atomic) __sync_bool_compare_and_swap(&lock, 0xffff, 0); } bool check_number(int n) { // Increment once the lock is below 0xffff u16 savedlock = lock; while (savedlock == 0xffff || __sync_bool_compare_and_swap(&lock, savedlock, savedlock+1) == false) savedlock = lock; // Perform read-only operation bool exists = tree->exists(n); // Decrement savedlock = lock; while (__sync_bool_compare_and_swap(&lock, savedlock, savedlock-1) == false) savedlock = lock; return exists; } }; (lets assume it need not be exception-safe) Is this code indeed thread-safe? Are there any pros/cons to this idea? Any advice? Is the use of spinlocks like this a bad idea if the threads are not truly concurrent? Thanks in advance. ;)

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  • Swap files in Cloud Infrastructures

    - by ffeldhaus
    At our company we set up an OpenStack Cloud and are currently creating internal guidelines for creation of OS templates / images. One controversial topic was if we should provide swap inside the VM templates. Therefore I'd like to ask the following questions From an elastic Cloud provider point of view, does it make sense to offer swap partitions / files in the VM templates or is swap not needed when a VM can be resized? Which scenarios necessarily demand a swap file to be present? What kind of Storage should be used for swap files (e.g. local / central, FC / iSCSI / NFS)? Are there any best practices for offering swap files in a performant way in Cloud Infrastructures?

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  • Where's the Swap File/Partition?

    - by chrisbunney
    I'm investigating the virtual memory configuration of a Debian based Amazon EC2 instance, and as my background isn't in system admin, I'm slightly confused by what I'm seeing. We're using MongoDB, and the monitoring server we have indicates that the Mongo process is using about 20GB of swap space, however I can't figure out where this is located on the server. As far as I can tell from using the various suggested methods from Google, there is either a much smaller amount, or none at all. top indicates that there is 1.8GB of swap memory: top - 15:35:21 up 6 days, 3:23, 1 user, load average: 1.60, 1.43, 1.37 Tasks: 47 total, 2 running, 45 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0%us, 1.3%sy, 0.0%ni, 14.7%id, 83.8%wa, 0.0%hi, 0.0%si, 0.1%st Mem: 3928924k total, 2855572k used, 1073352k free, 640564k buffers Swap: 0k total, 0k used, 0k free, 1887788k cached swapon -s doesn't seem to think there's any swap space: Filename Type Size Used Priority free -m doesn't think there's any swap either: total used free shared buffers cached Mem: 3836 3663 172 0 626 2701 -/+ buffers/cache: 336 3500 Swap: 0 0 0 And neither does vmstat: procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 3 0 66224 641372 2874744 0 0 21 5012 21 33 2 2 76 19 But cat /etc/fstab thinks there is a swap partition: /dev/xvda1 / ext3 defaults 1 1 /dev/xvda2 /mnt ext3 defaults 0 0 /dev/xvda3 swap swap defaults 0 0 none /proc proc defaults 0 0 none /sys sysfs defaults 0 0 However df -k gives no indication of the xvda3 partition: Filesystem 1K-blocks Used Available Use% Mounted on /dev/xvda1 16513960 15675324 0 100% / tmpfs 1964460 8 1964452 1% /lib/init/rw udev 1914148 28 1914120 1% /dev tmpfs 1964460 4 1964456 1% /dev/shm So I really don't know what to make of this, because I appear to have a process using about 10 times more virtual memory than what might be available, and I have no idea where this virtual memory is on the system. I'm probably misinterpreting the output of the tools, so I'd be grateful if someone would be able to set me straight: What have I got wrong, what's the right interpretation, and how do you reach that interpretation? EDIT0: We use 10gen's MMS for monitoring the database, the relevant section for memory from the last data point is: "mem": { "virtual": 20749, "bits": 64, "supported": true, "mappedWithJournal": 20376, "mapped": 10188, "resident": 1219 }, This JSON is specific to the database process (I believe) rather than the system as a whole. fdisk -l /dev/xvda outputs... nothing? I tried each of the 3 xvda entries in /etc/fstab as well: root@ip:~# fdisk -l /dev/xvda1 Disk /dev/xvda1: 34.4 GB, 34359738368 bytes 255 heads, 63 sectors/track, 4177 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/xvda1 doesn't contain a valid partition table root@ip:~# fdisk -l /dev/xvda2 root@ip:~# fdisk -l /dev/xvda3 root@ip:~# Edit1: Output of cat /proc/meminfo for the sake of completeness: MemTotal: 3928924 kB MemFree: 726600 kB Buffers: 648368 kB Cached: 2216556 kB SwapCached: 0 kB Active: 1945100 kB Inactive: 994016 kB Active(anon): 60476 kB Inactive(anon): 12952 kB Active(file): 1884624 kB Inactive(file): 981064 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 387180 kB Writeback: 0 kB AnonPages: 73380 kB Mapped: 1188260 kB Shmem: 48 kB Slab: 149768 kB SReclaimable: 146076 kB SUnreclaim: 3692 kB KernelStack: 1104 kB PageTables: 16096 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 1964460 kB Committed_AS: 305572 kB VmallocTotal: 34359738367 kB VmallocUsed: 16760 kB VmallocChunk: 34359721448 kB HardwareCorrupted: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB DirectMap4k: 3932160 kB DirectMap2M: 0 kB

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  • Are memory barriers necessary for atomic reference counting shared immutable data?

    - by Dietrich Epp
    I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

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  • Moving the swapfiles to a dedicated partition in Snow Leopard

    - by e.James
    I have been able to move Apple's virtual memory swapfiles to a dedicated partition on my hard drive up until now. The technique I have been using is described in a thread on forums.macosxhints.com. However, with the developer preview of Snow Leopard, this method no longer works. Does anyone know how it could be done with the new OS? Update: I have marked dblu's answer as accepted even though it didn't quite work because he gave excellent, detailed instructions and because his suggestion to use plutil ultimately pointed me in the right direction. The complete, working solution is posted here in the question because I don't have enough reputation to edit the accepted answer. Complete solution: 1. Open Terminal and make a backup copy of Apple's default dynamic_pager.plist: $ cd /System/Library/LaunchDaemons $ sudo cp com.apple.dynamic_pager.plist{,_bak} 2. Convert the plist from binary to plain XML: $ sudo plutil -convert xml1 com.apple.dynamic_pager.plist 3. Open the converted plist with your text editor of choice. (I use pico, see dblu's answer for an example using vim): $ sudo pico -w com.apple.dynamic_pager.plist It should look as follows: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs$ <plist version="1.0"> <dict> <key>EnableTransactions</key> <true/> <key>HopefullyExitsLast</key> <true/> <key>Label</key> <string>com.apple.dynamic_pager</string> <key>OnDemand</key> <false/> <key>ProgramArguments</key> <array> <string>/sbin/dynamic_pager</string> <string>-F</string> <string>/private/var/vm/swapfile</string> </array> </dict> </plist> 4. Change the ProgramArguments array (lines 13 through 18) so that it launches an intermediate shell script instead of launching dynamic_pager directly. See note #1 for details on why this is necessary. <key>ProgramArguments</key> <array> <string>/sbin/dynamic_pager_init</string> </array> 5. Save the plist, and return to the terminal prompt. Using pico, the commands would be: <ctrl+o> to save the file <enter> to accept the same filename (com.apple.dynamic_pager.plist) <ctrl+x> to exit 6. Convert the modified plist back to binary: $ sudo plutil -convert binary1 com.apple.dynamic_pager.plist 7. Create the intermediate shell script: $ cd /sbin $ sudo pico -w dynamic_pager_init The script should look as follows (my partition is called 'Swap', and I chose to put the swapfiles in a hidden directory on that partition, called '.vm' be sure that the directory you specify actually exists): Update: This version of the script makes use of wait4path as suggested by ZILjr: #!/bin/bash #launch Apple's dynamic_pager only when the swap volume is mounted echo "Waiting for Swap volume to mount"; wait4path /Volumes/Swap; echo "Launching dynamic pager on volume Swap"; /sbin/dynamic_pager -F /Volumes/Swap/.vm/swapfile; 8. Save and close dynamic_pager_init (same commands as step 5) 9. Modify permissions and ownership for dynamic_pager_init: $ sudo chmod a+x-w /sbin/dynamic_pager_init $ sudo chown root:wheel /sbin/dynamic_pager_init 10. Verify the permissions on dynamic_pager_init: $ ls -l dynamic_pager_init -r-xr-xr-x 1 root wheel 6 18 Sep 15:11 dynamic_pager_init 11. Restart your Mac. If you run into trouble, switch to verbose startup mode by holding down Command-v immediately after the startup chime. This will let you see all of the startup messages that appear during startup. If you run into even worse trouble (i.e. you never see the login screen), hold down Command-s instead. This will boot the computer in single-user mode (no graphical UI, just a command prompt) and allow you to restore the backup copy of com.apple.dynamic_pager.plist that you made in step 1. 12. Once the computer boots, fire up Terminal and verify that the swap files have actually been moved: $ cd /Volumes/Swap/.vm $ ls -l You should see something like this: -rw------- 1 someUser staff 67108864 18 Sep 12:02 swapfile0 13. Delete the old swapfiles: $ cd /private/var/vm $ sudo rm swapfile* 14. Profit! Note 1 Simply modifying the arguments to dynamic_pager in the plist does not always work, and when it fails, it does so in a spectacularly silent way. The problem stems from the fact that dynamic_pager is launched very early in the startup process. If your swap partition has not yet been mounted when dynamic_pager is first loaded (in my experience, this happens 99% of the time), then the system will fake its way through. It will create a symbolic link in your /Volumes directory which has the same name as your swap partition, but points back to the default swapfile location (/private/var/vm). Then, when your actual swap partition mounts, it will be given the name Swap 1 (or YourDriveName 1). You can see the problem by opening up Terminal and listing the contents of your /Volumes directory: $ cd /Volumes $ ls -l You will see something like this: drwxrwxrwx 11 yourUser staff 442 16 Sep 12:13 Swap -> private/var/vm drwxrwxrwx 14 yourUser staff 5 16 Sep 12:13 Swap 1 lrwxr-xr-x 1 root admin 1 17 Sep 12:01 System -> / Note that this failure can be very hard to spot. If you were to check for the swapfiles as I show in step 12, you would still see them! The symbolic link would make it seem as though your swapfiles had been moved, even though they were actually being stored in the default location. Note 2 I was originally unable to get this to work in Snow Leopard because com.apple.dynamic_pager.plist was stored in binary format. I made a copy of the original file and opened it with Apple's Property List Editor (available with Xcode) in order to make changes, but this process added some extended attributes to the plist file which caused the system to ignore it and just use the defaults. As dblu pointed out, using plutil to convert the file to plain XML works like a charm. Note 3 You can check the Console application to see any messages that dynamic_pager_init echos to the screen. If you see the following lines repeated over and over again, there is a problem with the setup. I ran into these messages because I forgot to create the '.vm' directory that I specified in dynamic_pager_init. com.apple.launchd[1] (com.apple.dynamic_pager[176]) Exited with exit code: 1 com.apple.launchd[1] (com.apple.dynamic_pager) Throttling respawn: Will start in 10 seconds When everything is working properly, you may see the above message a couple of times, but you should also see the following message, and then no more of the "Throttling respawn" messages afterwards. com.apple.dynamic_pager[???] Launching dynamic pager on volume Swap This means that the script did have to wait for the partition to load, but in the end it was successful.

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  • Why OS X use swap when there is lots of "inactive memory"?

    - by Balchev
    I am using OS X from few months (Lion and now Mountain Lion). I have 8 GB on my mini and almost daily now it get close to that. On Windows 7 machine with 8 GB I never had that kind of problem. Anyway, I read over the net, that the inactive memory is app cache of the programs that are recently closed and can be used for faster reopening.And this inactive memory can be released to a new app if needed. It is not released. Instead OS X starts swapping. So my question is why OS X use swap when there is lots of "inactive memory"? Here a screen that shows what I mean: I really hope there is a away to make OS X to use those 2.69 GB before start swapping.I really do.

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  • Deleting Unused Swaps Partions

    - by Nikita Kononov
    Good evening everyone , I got a little issue with Swap Partitions. Due to some issues after installing Ubuntu first time, I reinstalled it and now I have 3 Swaps. Here is sudo fdisk -l result Disk /dev/sda: 750.2 GB, 750156374016 bytes 255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0xaa9693fe Device Boot Start End Blocks Id System /dev/sda1 2048 52430847 26214400 1c Hidden W95 FAT32 (LBA) /dev/sda2 * 52430848 540677076 244123114+ 7 HPFS/NTFS/exFAT /dev/sda3 540678142 1465147391 462234625 5 Extended Partition 3 does not start on physical sector boundary. /dev/sda5 1452750848 1465147391 6198272 82 Linux swap / Solaris /dev/sda6 1440352256 1452742655 6195200 82 Linux swap / Solaris /dev/sda7 540678144 1427951615 443636736 83 Linux /dev/sda8 1427953664 1440339967 6193152 82 Linux swap / Solaris So Swaps in /dev/sda5 and /dev/sda6 are no longer in use as far as I understand and thus I was planning to delete them, however faced a problem. What I did is download and burn Gparted Live CD and boot it up, tried to delete those partitions but I have no idea how to add 12GB unallocated memory to the existing OS partition in this case to /dev/sda7 Is there anyway I can delete 2 swaps and extend unallocated memory to /dev/sda7 partion? Thank you in advance!

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  • How do I prevent my computer from freezing when it starts to swap?

    - by cdauth
    I work as a Java programmer, so I often have to run several programs at the same time that consume a lot of memory. When my memory is full and Linux starts swapping, my computer almost completely freezes. I can see that it is heavily writing on the hard-disk and everything reacts really slowly, often not at all. Moving the mouse in X sometimes doesn’t work at all, sometimes it has a delay of several seconds, clicking usually has a delay of several minutes. Sometimes it is possible to change to the TTY (with a long delay), there I can usually type without delay, but when I try to log in, it takes several minutes after typing in the user name until the password prompt appears, and usually an error message appears that tells me that the login timed out. So the only possibility is usually to restart the computer. I noticed that other intensive writing to the hard disk also significantly slows down my computer. Sometimes, I used rsync to limit the bandwidth when I copied files around on my own computer, as else the system would be almost unusable. How can this be? At the moment it seems more useful to me to completely turn off swapping. That might crash some processes, which is unfortunate, but the alternative at the moment is to crash all processes by turning off my computer. I am using Gentoo Linux with kernel 3.6.2-gentoo, I have a 10 GB swap partition on a HDD.

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  • SQL SERVER – Solution of Puzzle – Swap Value of Column Without Case Statement

    - by pinaldave
    Earlier this week I asked a question where I asked how to Swap Values of the column without using CASE Statement. Read here: SQL SERVER – A Puzzle – Swap Value of Column Without Case Statement. I have proposed 3 different solutions in the blog posts itself. I had requested the help of the community to come up with alternate solutions and honestly I am stunned and amazed by the qualified entries. I will be not able to cover every single solution which is posted as a comment, however, I would like to for sure cover few interesting entries. However, I am selecting 5 solutions which are different (not necessary they are most optimal or best – just different and interesting). Just for clarity I am involving the original problem statement here. USE tempdb GO CREATE TABLE SimpleTable (ID INT, Gender VARCHAR(10)) GO INSERT INTO SimpleTable (ID, Gender) SELECT 1, 'female' UNION ALL SELECT 2, 'male' UNION ALL SELECT 3, 'male' GO SELECT * FROM SimpleTable GO -- Insert Your Solutions here -- Swap value of Column Gender SELECT * FROM SimpleTable GO DROP TABLE SimpleTable GO Here are the five most interesting and different solutions I have received. Solution by Roji P Thomas UPDATE S SET S.Gender = D.Gender FROM SimpleTable S INNER JOIN SimpleTable D ON S.Gender != D.Gender I really loved the solutions as it is very simple and drives the point home – elegant and will work pretty much for any values (not necessarily restricted by the option in original question ‘male’ or ‘female’). Solution by Aneel CREATE TABLE #temp(id INT, datacolumn CHAR(4)) INSERT INTO #temp VALUES(1,'gent'),(2,'lady'),(3,'lady') DECLARE @value1 CHAR(4), @value2 CHAR(4) SET @value1 = 'lady' SET @value2 = 'gent' UPDATE #temp SET datacolumn = REPLACE(@value1 + @value2,datacolumn,'') Aneel has very interesting solution where he combined both the values and replace the original value. I personally liked this creativity of the solution. Solution by SIJIN KUMAR V P UPDATE SimpleTable SET Gender = RIGHT(('fe'+Gender), DIFFERENCE((Gender),SOUNDEX(Gender))*2) Sijin has amazed me with Difference and Soundex function. I have never visualized that above two functions can resolve the problem. Hats off to you Sijin. Solution by Nikhildas UPDATE St SET St.Gender = t.Gender FROM SimpleTable St CROSS Apply (SELECT DISTINCT gender FROM SimpleTable WHERE St.Gender != Gender) t I was expecting that someone will come up with this solution where they use CROSS APPLY. This is indeed very neat and for sure interesting exercise. If you do not know how CROSS APPLY works this is the time to learn. Solution by mistermagooo UPDATE SimpleTable SET Gender=X.NewGender FROM (VALUES('male','female'),('female','male')) AS X(OldGender,NewGender) WHERE SimpleTable.Gender=X.OldGender As per author this is a slow solution but I love how syntaxes are placed and used here. I love how he used syntax here. I will say this is the most beautifully written solution (not necessarily it is best). Bonus: Solution by Madhivanan Somehow I was confident Madhi – SQL Server MVP will come up with something which I will be compelled to read. He has written a complete blog post on this subject and I encourage all of you to go ahead and read it. Now personally I wanted to list every single comment here. There are some so good that I am just amazed with the creativity. I will write a part of this blog post in future. However, here is the challenge for you. Challenge: Go over 50+ various solutions listed to the simple problem here. Here are my two asks for you. 1) Pick your best solution and list here in the comment. This exercise will for sure teach us one or two things. 2) Write your own solution which is yet not covered already listed 50 solutions. I am confident that there is no end to creativity. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Function, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • SQL SERVER – A Puzzle – Swap Value of Column Without Case Statement

    - by pinaldave
    For the last few weeks, I have been doing Friday Puzzles and I am really loving it. Yesterday I received a very interesting question by Navneet Chaurasia on Facebook Page. He was asked this question in one of the interview questions for job. Please read the original thread for a complete idea of the conversation. I am presenting the same question here. Puzzle Let us assume there is a single column in the table called Gender. The challenge is to write a single update statement which will flip or swap the value in the column. For example if the value in the gender column is ‘male’ swap it with ‘female’ and if the value is ‘female’ swap it with ‘male’. Here is the quick setup script for the puzzle. USE tempdb GO CREATE TABLE SimpleTable (ID INT, Gender VARCHAR(10)) GO INSERT INTO SimpleTable (ID, Gender) SELECT 1, 'female' UNION ALL SELECT 2, 'male' UNION ALL SELECT 3, 'male' GO SELECT * FROM SimpleTable GO The above query will return following result set. The puzzle was to write a single update column which will generate following result set. There are multiple answers to this simple puzzle. Let me show you three different ways. I am assuming that the column will have either value ‘male’ or ‘female’ only. Method 1: Using CASE Statement I believe this is going to be the most popular solution as we are all familiar with CASE Statement. UPDATE SimpleTable SET Gender = CASE Gender WHEN 'male' THEN 'female' ELSE 'male' END GO SELECT * FROM SimpleTable GO Method 2: Using REPLACE  Function I totally understand it is the not cleanest solution but it will for sure work in giving situation. UPDATE SimpleTable SET Gender = REPLACE(('fe'+Gender),'fefe','') GO SELECT * FROM SimpleTable GO Method 3: Using IIF in SQL Server 2012 If you are using SQL Server 2012 you can use IIF and get the same effect as CASE statement. UPDATE SimpleTable SET Gender = IIF(Gender = 'male', 'female', 'male') GO SELECT * FROM SimpleTable GO You can read my article series on SQL Server 2012 various functions over here. SQL SERVER – Denali – Logical Function – IIF() – A Quick Introduction SQL SERVER – Detecting Leap Year in T-SQL using SQL Server 2012 – IIF, EOMONTH and CONCAT Function Let us clean up. DROP TABLE SimpleTable GO Question to you: I came up with three simple tricks where there is a single UPDATE statement which swaps the values in the column. Do you know any other simple trick? If yes, please post here in the comments. I will pick two random winners from all the valid answers. Winners will get 1) Print Copy of SQL Server Interview Questions and Answers 2) Free Learning Code for Online Video Courses I will announce the winners on coming Monday. Reference:  Pinal Dave (http://blog.SQLAuthority.com) Filed under: CodeProject, PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology

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  • Is Updating double operation atomic

    - by Yan Cheng CHEOK
    In Java, updating double and long variable may not be atomic, as double/long are being treated as two separate 32 bits variables. http://java.sun.com/docs/books/jls/second_edition/html/memory.doc.html#28733 In C++, if I am using 32 bit Intel Processor + Microsoft Visual C++ compiler, is updating double (8 byte) operation atomic? I cannot find much specification mention on this behavior. When I say "atomic variable", here is what I mean : Thread A trying to write 1 to variable x. Thread B trying to write 2 to variable x. We shall get value 1 or 2 out from variable x, but not an undefined value.

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  • Libgdx Palette Swap

    - by Haedrian
    I'm developing a game using the Libgdx library. I'm trying to implement a very simple palette swap functionality (basically just complete recolouring of some areas, I don't even need to have various shades), but I don't have any idea where to begin. The closest I've come is trying to draw the picture myself using a Pixmap, but that appears to be horrible unmaintainable and produces oodles of code.

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  • Order of partitions for root, home and swap with respect to Windows partitions

    - by Tim
    I am installing Ubuntu on the same hard drive as Windows 7. The partitions of Windows 7 have already occupied the left part of the hard drive. I was wondering how to arrange the order of partitions of root, home and swap, i.e. which is on the left just besides one Windows partition, which is in the middle and which is on the far right? Is there some consideration regarding about this arrangement? Thanks and regards!

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  • Is there a way to exclude a specific drive vdi from "snapshots" in VirtualBox?

    - by Graza
    ...or is there another space-efficient way of dealing with the page/swap file of the Guest O/S? I've realised that its quite possible/likely that one of the things which "bloats" the snapshot/diff vdi's when a snapshot is taken is the guest operating system's pagefile. For example, say I have a 2Gb swap-file in a Windows guest OS, and over the course of a few weeks the usage of the swap file has gone over 1Gb a couple of times. When I next create a snapshot, it seems likely that I'd be almost guaranteed around 1Gb of space taken up in the new differencing disk just because of changes in the swap file. Obviously (provided I never did "live" snapshots on running or paused machines, and only ever did them when the machine was shut down), I would not need any of the information in the swap file to be saved. So this would simply be a waste of 1Gb. I'm wondering if there's a way to attach a vdi to a VM and flag it as "exclude from snapshots" - which would mean I could put the swap file on a different vdi which would never be included in a snapshot. Or if anyone has any other suggestions. Or an explanation about why it might not be an issue. I could obviously delete and recreate a swap drive vdi every time I did a snapshot to achieve the same effect, but this is a little more effort than simply clicking "create snapshot"....

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  • Another hibernation question

    - by GeekOfTheWeek
    I installed Ubuntu on my Windows 7 Sager laptop using Wubi. Hibernate (i.e. suspend to disc) is not an option from the power icon, only suspend, shutdown, etc. Hibernate is also not an option from my battery/lid close options. I understand that hibernation is disabled by default in Ubuntu 12.04. I tried running pm-hibernate but I get the following message: Looking for splash system... none s2disk: Snapshotting system and then the computer just hangs with a black screen. According to the documentation here if this fails then I can't enable hibernate but it offers no help in making pm-hibernate succeed. Could swap be my problem? It looks like I have very small swap: user@ubuntu:~$ cat /proc/swaps Filename Type Size Used Priority /host/ubuntu/disks/swap.disk file 262140 0 -1 The advice on SwapFaq is only for the author's set up (e.g. I don't have an Ubuntu install disk since I used Wubi) and he says that 'INFO: This will not work for 12.04, resume from hibernate work differently in 12.04.' Any advice? I really need to get hibernate working to use my laptop as a, er, laptop. Thanks

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  • [C++][OpenMP] Proper use of "atomic directive" to lock STL container

    - by conradlee
    I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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