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  • Settings what-opens-what once and for all (Backing up File Associations)

    - by ldigas
    Every time I switch machines (as in, get a new one, or reinstall an OS or something like that) my precious file associations get lost. And the next six months pass slowly until I again set them up right. Is there a program that allows me to: Set all the extensions I would like to open with let's say, Vim, without setting each one of them individually. Something of a kind: Vim opens: .... list of extensions ... and/or A program which lets me backup my current settings, and when I copy those to a new machine it lets me just modify the paths where I putted the applications in question, and it does the rest (again, associates that program with all the extensions it opened before).

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  • CentOS running inside VMware as WebServer times out on outside connection [migrated]

    - by Tom Hart
    I have a CentOS machine running inside VMware, and I have got PHP and Apache set up on it, so if I open a browser (on the VM) and go to either localhost, or 192.168.0.3, I get a phpinfo page I made in /var/www/html/index.php, but, if on the host (Windows 7), in my browser I go to 192.168.0.3, it times out. I can ping the IP address from Windows and get a response, I just can't through the browser. Does anyone have any ideas what I need to do to get this working? This is my first time using a VM and I'm getting lost in the network settings.

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  • websites resolving in browser but not resolving in CLI. Can ping IP but not domain name (unknown host)

    - by tjkoding
    Hi guys I'm currently developing using rails and for some reason bundle install is returning the following output Error Bundler::HTTPError during request to dependency API Fetching full source index from https://rubygems.org/ Could not reach https://rubygems.org/ I've discovered that pinging by domain name keeps returning an unknown host. The browser is still resolving web pages just fine and I've managed to confirm that the problem is localized (i.e. the rubygems page isn't down). I'm completely lost so any help would be much appreciated. Thanks in advance!

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  • MS Outlook 2010 Folder Strucruture Search

    - by SaUce
    Ok I feel very dumb to ask this question. I would consider myself to be smart but i cannot figure this out. I work at helpdesk and today i received a call from user who lost folder in Outlook. When I connected to user's PC I discovered that user has several hundreds of folders. She had the same name folder in several different locations. When we did advance find for the messages we found them. It said that messages are located in folder X the only problem we could not locate the folder X in the list. Does anyone know of any way to quickly and easily browsing all the folders or looking up a folder in Outlook 2010?

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  • nginx location pathing issue

    - by Michael Jefferys
    I've got a pretty much default sites-enabled set up in my nginx on debian squeeze and i'm now trying to get it to serve up my munin graphs on myhost/munin/ Heres the location i've added to the config location /munin { root /var/cache/munin/www/; index index.htm index.html; } And here is the error I recieve: 2012/07/09 23:52:03 [error] 3598#0: *13 "/var/cache/munin/www/munin/index.htm" is not found (2: No such file or directory), client: 93.*.*.*, server: , request: "GET /munin/ HTTP/1.1", host: "" This set up used to 'just work' in apache. I'm new to nginx so a bit lost as to why its adding the extra /munin when looking for the path. Any advice?

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  • Android chess development design [on hold]

    - by Plejo
    I want to develop human vs human android chess game and I have bunch of new questions. I would like to have screen where online players are shown(nickname, rating) and when player challenge antoher player and he accpet it game begins. These are my questions: When player install application, does he have to create account/login or does every instance of installed application have some kind of ID so I can recognize it on server side? I want to have also ratings of players saved in my DB so login procedure will probably be necessary. When player connects to server server updates online players list. When he challenge another player and he accept server exchange ip`s(and ports? which port to use?) between players. Then they connect to each other and game begins. What is best practice for connection between server-android and android-android? Probably sockets, right? Is there any library for handling lost connection etc.? Which server do you recommend?

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  • Microsoft .NET Web Programming: Web Sites versus Web Applications

    - by SAMIR BHOGAYTA
    In .NET 2.0, Microsoft introduced the Web Site. This was the default way to create a web Project in Visual Studio 2005. In Visual Studio 2008, the Web Application has been restored as the default web Project in Visual Studio/.NET 3.x The Web Site is a file/folder based Project structure. It is designed such that pages are not compiled until they are requested ("on demand"). The advantages to the Web Site are: 1) It is designed to accommodate non-.NET Applications 2) Deployment is as simple as copying files to the target server 3) Any portion of the Web Site can be updated without requiring recompilation of the entire Site. The Web Application is a .dll-based Project structure. ASP.NET pages and supporting files are compiled into assemblies that are then deployed to the target server. Advantages of the Web Application are: 1) Precompiled files do not expose code to an attacker 2) Precompiled files run faster because they are binary data (the Microsoft Intermediate Language, or MSIL) executed by the CLR (Common Language Runtime) 3) References, assemblies, and other project dependencies are built in to the compiled site and automatically managed. They do not need to be manually deployed and/or registered in the Global Assembly Cache: deployment does this for you If you are planning on using automated build and deployment, such as the Team Foundation Server Team Build engine, you will need to have your code in the form of a Web Application. If you have a Web Site, it will not properly compile as a Web Application would. However, all is not lost: it is possible to work around the issue by adding a Web Deployment Project to your Solution and then: a) configuring the Web Deployment Project to precompile your code; and b) configuring your Team Build definition to use the Web Deployment Project as its source for compilation. https://msevents.microsoft.com/cui/WebCastEventDetails.aspx?culture=en-US&EventID=1032380764&CountryCode=US

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  • displaying python's autodoc to the user (python 3.3)

    - by Plotinus
    I'm writing a simple command line math game, and I'm using python's autodoc for my math algorithms to help me remember, for example, what a proth number is while i'm writing the algorithm, but later on I'll want to tell that information to the user as well, so they'll know what the answer was. So, for example I have: def is_proth(): """Proth numbers and numbers that fit the formula k×2^n + 1, where k are odd positive integers, and 2^n > k.""" [snip] return proths and then I tried to make a dictionary, like so: definitions = {"proths" : help(is_proth)} But it doesn't work. It prints this when I start the program, one for each item in the dictionary, and then it errors out on one of them that returns a set. And anyway, I don't want it displayed to the user until after they've played the game. Help on function is_proth in module __main__: is_proth() Proth numbers and numbers that fit the formula k×2^n + 1, where k are odd positive integers, and 2^n > k. (END) I understand the purpose of autodoc is more for helping programmers who are calling a function than for generating userdoc, but it seems inefficient to have to type out the definition of what a proth number is twice, once in a comment to help me remember what an algorithm does and then once to tell the user the answer to the game they were playing after they've won or lost.

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  • Wireless doesn't work on a Lenovo V570

    - by Stephen
    I've had Ubuntu installed on my HD for about 3 months but ever since I ran into this wireless issue I kinda lost my lust of Ubuntu. I have zero experience getting around with/ using the console command. I have a Lenovo V570. I got the driver update for the broadcom networking card via the Additional Drivers application but that did nothing. I love the look and feel of using Ubuntu but I have no technological experience for the matter. Any help would be awesome. When I scan for wireless connections while in Ubuntu, my computer picks up nothing, while on Win7 it will pick up the handful of wireless networks around my area. My wired connection is fine, but the use of not having wireless on a laptop is rather contradictory to it as a feature. Cheers! Also, I just installed 11.10, if that helps any. Yes, I used the search before I posted this, but again I have ZERO understanding of the command stuff and need a meat and potatoes answer(s). stephen@ubuntu:~$ sudo lshw -class network [sudo] password for stephen: *-network UNCLAIMED description: Network controller product: BCM4313 802.11b/g/n Wireless LAN Controller vendor: Broadcom Corporation physical id: 0 bus info: pci@0000:03:00.0 version: 01 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list configuration: latency=0 resources: memory:f1900000-f1903fff *-network description: Ethernet interface product: RTL8111/8168B PCI Express Gigabit Ethernet controller vendor: Realtek Semiconductor Co., Ltd. physical id: 0 bus info: pci@0000:04:00.0 logical name: eth0 version: 06 serial: f0:de:f1:63:98:14 size: 100Mbit/s capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full firmware=rtl_nic/rtl8168e-2.fw ip=192.168.1.78 latency=0 link=yes multicast=yes port=MII speed=100Mbit/s resources: irq:41 ioport:2000(size=256) memory:f1804000-f1804fff memory:f1800000-f1803fff stephen@ubuntu:~$ rfkill list all 0: ideapad_wlan: Wireless LAN Soft blocked: yes Hard blocked: no 1: acer-wireless: Wireless LAN Soft blocked: yes Hard blocked: no

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  • SQL SERVER – CTRL+SHIFT+] Shortcut to Select Code Between Two Parenthesis

    - by pinaldave
    Every weekend brings creative ideas and accidents brings best unknown secrets in front of us. Just a day while working with complex SQL Server code in SSMS I came across very interesting shortcut which I have never used before and instantly fell in love with it. It is totally possible that you are familiar with this but for me it was the first time and I was surprised that I did know know this short cut so far. Shortcut key is CTRL+SHIFT+]. This key can be very useful when dealing with multiple subqueries, CTE or query with multiple parentheses. When exercised this shortcut key it selects T-SQL code between two parentheses. Let us see the examples to understand the same. In each of the examples I have put the cursor at the position displayed and pressed CTRL+SHIFT+] and it has selected the code between two corresponding parentheses. Cursor position 1 Cursor position 2 Cursor position 3 If you are a developer and have to code with complex queries, you will totally appreciate that this feature can save so much of the time for development. I often remember my experience as a developer when I have lost a lot of hours to just balance parentheses. As I said yesterday I found this shortcut accidently. How many of you were aware of this feature? Is there any other useful feature you would like to share with us? Please leave a comment and if I have not covered it earlier, I will share it due credit on this blog. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Shortcut

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  • sudo: /usr/lib/sudo/sudoers.so must be owned by uid 0

    - by 7UR7L3
    Whenever I try to do anything at all that requires my password it returns this: u7ur7l3@ubuntu:~$ sudo sudo: /usr/lib/sudo/sudoers.so must be owned by uid 0 sudo: fatal error, unable to load plugins u7ur7l3@ubuntu:~$ So I can't install anything from the Software Center / package manager or run any commands in terminal that require my password. I can log in, but that's pretty much it. I accidentally changed the permissions of some files, then changed some more trying to fix it :/. Now I'm completely lost as to what to do. This is what happened when I tried to get sudo working again using pkexec: u7ur7l3@ubuntu:~$ pkexec chown root /usr/lib/sudo/sudoers.so Error getting authority: Error initializing authority: Error calling StartServiceByName for org.freedesktop.PolicyKit1: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ExecFailed: Failed to execute program /usr/lib/dbus-1.0/dbus-daemon-launch-helper: Success u7ur7l3@ubuntu:~$ sudo ls sudo: /usr/lib/sudo/sudoers.so must be owned by uid 0 sudo: fatal error, unable to load plugins And to change permissions I was using Root Actions as a dolphin service/ plugin thing, so history doesn't show me the permission changes. I just realized that sounds don't work at all anymore. When I go into Phonon my default settings and playback devices aren't even there. Also I don't have the option to shutdown, I can only log out or leave.

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  • Desktop Fun: Adventure Icon Packs

    - by Asian Angel
    Do you long for adventure and excitement? If so you can add some of that goodness to your desktop with our adventure icon packs collection. A Sneak Peak To give you an idea of how these icons could look on your desktop we have an example set up here using the “LOTR – Armoury of the Third Age” set shown below. Note: Wallpaper can be found here. A close-up look at the icons… Indiana Jones and the Raiders of the Lost Ark Download Indiana Jones and the Temple of Doom Download Indiana Jones and the Last Crusade Download Indiana Jones and the Kingdom of the Crystal Skull Download Adventure Icons Note: This icon set in “.png” format only. Download Climb On Download Hieroglyphica Vol. 1 Download Hieroglyphica Vol. 2 Download Tribal Masks Download Kong Download Jolly Roger Vol. 1 Download Jolly Roger Vol. 2 Download Pirates Theme Icon Collection Note: This icon set contains both “.ico” and “.png” files. Download Vampire Hunter Kit 1 Note: This icon set contains both “.ico” and “.png” files. Download LOTR – Armoury of the Third Age Download If you enjoyed this icon collection then make certain to visit our new Desktop Fun section for more customization goodness! Similar Articles Productive Geek Tips Restore Missing Desktop Icons in Windows 7 or VistaAdd Home Directory Icon to the Desktop in Windows 7 or VistaQuick Help: Downloadable Show Desktop Icon for XPDesktop Customization: Sci-Fi Icon PacksDisplay My Computer Icon on the Desktop in Windows 7 or Vista TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Google Maps Place marks – Pizza, Guns or Strip Clubs Monitor Applications With Kiwi LocPDF is a Visual PDF Search Tool Download Free iPad Wallpapers at iPad Decor Get Your Delicious Bookmarks In Firefox’s Awesome Bar Manage Photos Across Different Social Sites With Dropico

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  • How to do I build and install the gspca webcam driver?

    - by sam
    I tried to install gspca to run Orite webcam. But I failed to install gspca on ubuntu 12.04 64 bits. It lost a lot of headers,here are my instructions but failed. wget http://mxhaard.free.fr/spca50x/Download/gspcav1-20071224.tar.gz tar zxvf gspcav1-20071224.tar.gz cd gspcav1-20071224/ sudo ./gspca_build sudo touch /usr/src/linux-headers-3.2.0-25-generic/include/linux/config.h sudo mkdir /usr/src/linux-headers-3.2.0-25-generic/include/asm sudo touch /usr/src/linux-headers-3.2.0-25-generic/include/asm/semaphore.h sudo touch /usr/src/linux-headers-3.2.0-25-generic/include/linux/videodev.h sudo touch /usr/src/linux-headers-3.2.0-25-generic/include/linux/smp_lock.h How to solve it? Thank you~ I move to /usr/src and make sam@sam:/usr/src/gspcav1-20071224$ sudo make make -C /lib/modules/`uname -r`/build SUBDIRS=/usr/src/gspcav1-20071224 CC=cc modules make[1]: Entering directory `/usr/src/linux-headers-3.2.0-25-generic' CC [M] /usr/src/gspcav1-20071224/gspca_core.o /usr/src/gspcav1-20071224/gspca_core.c:37:26: fatal error: linux/config.h: No such file or directory compilation terminated. make[2]: *** [/usr/src/gspcav1-20071224/gspca_core.o] Error 1 make[1]: *** [_module_/usr/src/gspcav1-20071224] Error 2 make[1]: Leaving directory `/usr/src/linux-headers-3.2.0-25-generic' make: *** [default] Error 2 sam@sam:/usr/src/gspcav1-20071224$

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  • Are you aware of .NET Reflector Pro?

    I'm sure many of my readers know Reflector, that tool to decompile the assemblies to see what it contains, maybe investigating what Microsoft has done with the base assemblies in .NET or maybe trying to understand 3rd party assemblies (or maybe just trying to recover the lost source code ;-) ) It's invaluable tool to have in your tool box. One nice scenario where it helps a lot is Sharepoint development in case you are in problems with the API. But are you aware that MS gave the product to Red Gate Software (http://www.red-gate.com) which released a Pro version of Reflector (http://www.red-gate.com/products/reflector/index.htm) a couple of months ago? Have a look at the feature set on top of the free version.Full support for .NET 1.0, 1.1, 2.0, 3.0, 3.5, and 4.0Decompile an entire assembly to either C# or VB to view and debug in Visual Studio Step-through debugging of any assembly in Visual Studio (as long as it's not obfuscated): Step into and set breakpoints anywhere in any assemblyWatch variables in the decompiled codeUse Visual Studio's advanced debugging features in decompiled code: Set Next Statement, modify variable values, and dynamic expression evaluation in the immediate window I strongly encourage you to have a look at .NET Reflector in case you haven't done so already. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Incrementing Assembly Version in TFS Builds and its affect over Other Build Definitions

    - by ssmantha
    A very common scenario while performing TFS builds is to increment version number of the assemblies. There are quite a few approaches of which I would like to share two links: Ewald Hofman’s Approach: http://www.ewaldhofman.nl/post/2010/05/13/Customize-Team-Build-2010-e28093-Part-5-Increase-AssemblyVersion.aspx#id_02e7b082-ce95-49a9-92e9-7dc88887b377 Richard Bank’s Approach : http://www.richard-banks.org/2010/07/how-to-versioning-builds-with-tfs-2010.html   Both these approaches work well, however there are scenarios where Editing and Checking–in the Assembly version information can create problems with Build Definitions meant for Continuous Integration, or gated Check-ins. You can suppress the Continuous Integration Builds while checking in the Assembly info file by just putting a comment “***NO_CI***” as specified by Ewald in his blog. However, if you have Gated Checkin in place, this can turn out to be difficult to suppress, I myself tried to suppress the Build Trigger during the check in process but things doesn’t turn out well. That’s where Richard’s solution comes as handy. Both the solutions have their own pros and cons, which I believe can only be experienced over a period of time. In case of Richard’s solution I believe that we don’t have any history of the Assembly Version Info file and when you take latest of the solution the information will be lost. If you notice closely, that suppressing the Continuous Integration (the NO_CI approach in check in comments) is a workaround provided by Microsoft, however I didn’t find anything to suppress the gated Checkin so far. Suggestions or Findings are most welcome.

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  • Can notes/to-dos in code comments sent to code-reviews result in an effective refactoring process?

    - by dukeofgaming
    I want to start/improve a culture of collective code ownership at my company but at a geographically distributed level... I'd say there is some current collective code-ownership mentality, but only at single geographical sites. This is a follow-up to this question: What is the politically correct way of refactoring other's code? I'm just wondering if submitting *just code comments* for code reviews (we have ReviewBoard, possibly upgrading to Crucible) could actually be an effective mechanism to get the conversation started on improving code, without having others feel territorial about their code. For example, if I add: //ToDo: Refactor this code and that code because of reasons X and Y Then, submit it for code review, and it gets accepted... it could be considered as an agreement (which I think is sometimes harder to get with new code up front). At the same time, the author (and others) might have an easier time digesting and accepting the proposal; rejecting a proposal because it might break things will not longer be a valid reason and therefore the fear of making a change is lost... and at the same time, do not invest 10 hours optimizing something that no one thinks it is worth it and opposes to it just out of fear. This is all conjecture, but I'm feeling something like this (submitting refactoring notes in code comments at the code-review process) would work. Has anyone done something like this in practice?, if so, what have been the results?

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  • SQL SERVER – Concurrency Basics – Guest Post by Vinod Kumar

    - by pinaldave
    This guest post is by Vinod Kumar. Vinod Kumar has worked with SQL Server extensively since joining the industry over a decade ago. Working on various versions from SQL Server 7.0, Oracle 7.3 and other database technologies – he now works with the Microsoft Technology Center (MTC) as a Technology Architect. Let us read the blog post in Vinod’s own voice. Learning is always fun when it comes to SQL Server and learning the basics again can be more fun. I did write about Transaction Logs and recovery over my blogs and the concept of simplifying the basics is a challenge. In the real world we always see checks and queues for a process – say railway reservation, banks, customer supports etc there is a process of line and queue to facilitate everyone. Shorter the queue higher is the efficiency of system (a.k.a higher is the concurrency). Every database does implement this using checks like locking, blocking mechanisms and they implement the standards in a way to facilitate higher concurrency. In this post, let us talk about the topic of Concurrency and what are the various aspects that one needs to know about concurrency inside SQL Server. Let us learn the concepts as one-liners: Concurrency can be defined as the ability of multiple processes to access or change shared data at the same time. The greater the number of concurrent user processes that can be active without interfering with each other, the greater the concurrency of the database system. Concurrency is reduced when a process that is changing data prevents other processes from reading that data or when a process that is reading data prevents other processes from changing that data. Concurrency is also affected when multiple processes are attempting to change the same data simultaneously. Two approaches to managing concurrent data access: Optimistic Concurrency Model Pessimistic Concurrency Model Concurrency Models Pessimistic Concurrency Default behavior: acquire locks to block access to data that another process is using. Assumes that enough data modification operations are in the system that any given read operation is likely affected by a data modification made by another user (assumes conflicts will occur). Avoids conflicts by acquiring a lock on data being read so no other processes can modify that data. Also acquires locks on data being modified so no other processes can access the data for either reading or modifying. Readers block writer, writers block readers and writers. Optimistic Concurrency Assumes that there are sufficiently few conflicting data modification operations in the system that any single transaction is unlikely to modify data that another transaction is modifying. Default behavior of optimistic concurrency is to use row versioning to allow data readers to see the state of the data before the modification occurs. Older versions of the data are saved so a process reading data can see the data as it was when the process started reading and not affected by any changes being made to that data. Processes modifying the data is unaffected by processes reading the data because the reader is accessing a saved version of the data rows. Readers do not block writers and writers do not block readers, but, writers can and will block writers. Transaction Processing A transaction is the basic unit of work in SQL Server. Transaction consists of SQL commands that read and update the database but the update is not considered final until a COMMIT command is issued (at least for an explicit transaction: marked with a BEGIN TRAN and the end is marked by a COMMIT TRAN or ROLLBACK TRAN). Transactions must exhibit all the ACID properties of a transaction. ACID Properties Transaction processing must guarantee the consistency and recoverability of SQL Server databases. Ensures all transactions are performed as a single unit of work regardless of hardware or system failure. A – Atomicity C – Consistency I – Isolation D- Durability Atomicity: Each transaction is treated as all or nothing – it either commits or aborts. Consistency: ensures that a transaction won’t allow the system to arrive at an incorrect logical state – the data must always be logically correct.  Consistency is honored even in the event of a system failure. Isolation: separates concurrent transactions from the updates of other incomplete transactions. SQL Server accomplishes isolation among transactions by locking data or creating row versions. Durability: After a transaction commits, the durability property ensures that the effects of the transaction persist even if a system failure occurs. If a system failure occurs while a transaction is in progress, the transaction is completely undone, leaving no partial effects on data. Transaction Dependencies In addition to supporting all four ACID properties, a transaction might exhibit few other behaviors (known as dependency problems or consistency problems). Lost Updates: Occur when two processes read the same data and both manipulate the data, changing its value and then both try to update the original data to the new value. The second process might overwrite the first update completely. Dirty Reads: Occurs when a process reads uncommitted data. If one process has changed data but not yet committed the change, another process reading the data will read it in an inconsistent state. Non-repeatable Reads: A read is non-repeatable if a process might get different values when reading the same data in two reads within the same transaction. This can happen when another process changes the data in between the reads that the first process is doing. Phantoms: Occurs when membership in a set changes. It occurs if two SELECT operations using the same predicate in the same transaction return a different number of rows. Isolation Levels SQL Server supports 5 isolation levels that control the behavior of read operations. Read Uncommitted All behaviors except for lost updates are possible. Implemented by allowing the read operations to not take any locks, and because of this, it won’t be blocked by conflicting locks acquired by other processes. The process can read data that another process has modified but not yet committed. When using the read uncommitted isolation level and scanning an entire table, SQL Server can decide to do an allocation order scan (in page-number order) instead of a logical order scan (following page pointers). If another process doing concurrent operations changes data and move rows to a new location in the table, the allocation order scan can end up reading the same row twice. Also can happen if you have read a row before it is updated and then an update moves the row to a higher page number than your scan encounters later. Performing an allocation order scan under Read Uncommitted can cause you to miss a row completely – can happen when a row on a high page number that hasn’t been read yet is updated and moved to a lower page number that has already been read. Read Committed Two varieties of read committed isolation: optimistic and pessimistic (default). Ensures that a read never reads data that another application hasn’t committed. If another transaction is updating data and has exclusive locks on data, your transaction will have to wait for the locks to be released. Your transaction must put share locks on data that are visited, which means that data might be unavailable for others to use. A share lock doesn’t prevent others from reading but prevents them from updating. Read committed (snapshot) ensures that an operation never reads uncommitted data, but not by forcing other processes to wait. SQL Server generates a version of the changed row with its previous committed values. Data being changed is still locked but other processes can see the previous versions of the data as it was before the update operation began. Repeatable Read This is a Pessimistic isolation level. Ensures that if a transaction revisits data or a query is reissued the data doesn’t change. That is, issuing the same query twice within a transaction cannot pickup any changes to data values made by another user’s transaction because no changes can be made by other transactions. However, this does allow phantom rows to appear. Preventing non-repeatable read is a desirable safeguard but cost is that all shared locks in a transaction must be held until the completion of the transaction. Snapshot Snapshot Isolation (SI) is an optimistic isolation level. Allows for processes to read older versions of committed data if the current version is locked. Difference between snapshot and read committed has to do with how old the older versions have to be. It’s possible to have two transactions executing simultaneously that give us a result that is not possible in any serial execution. Serializable This is the strongest of the pessimistic isolation level. Adds to repeatable read isolation level by ensuring that if a query is reissued rows were not added in the interim, i.e, phantoms do not appear. Preventing phantoms is another desirable safeguard, but cost of this extra safeguard is similar to that of repeatable read – all shared locks in a transaction must be held until the transaction completes. In addition serializable isolation level requires that you lock data that has been read but also data that doesn’t exist. Ex: if a SELECT returned no rows, you want it to return no. rows when the query is reissued. This is implemented in SQL Server by a special kind of lock called the key-range lock. Key-range locks require that there be an index on the column that defines the range of values. If there is no index on the column, serializable isolation requires a table lock. Gets its name from the fact that running multiple serializable transactions at the same time is equivalent of running them one at a time. Now that we understand the basics of what concurrency is, the subsequent blog posts will try to bring out the basics around locking, blocking, deadlocks because they are the fundamental blocks that make concurrency possible. Now if you are with me – let us continue learning for SQL Server Locking Basics. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Concurrency

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  • Does a site's bounce rate influence Google rankings?

    - by Joel Spolsky
    Does Google consider bounce rate or something similar in ranking sites? Background: here at Stack Exchange we noticed that the latest Google algorithm changes resulted in about a 20% dip in traffic to Server Fault (and a much smaller dip in traffic to Super User). Stack Overflow traffic was not affected. There was an article on WebProNews which hypothesized that bounce rate might be a ranking signal in Google's latest Panda update. According to Google Analytics, these are our bounce rates over the last month: Site Bounce Rate Avg Time on Site ------------- ----------- ---------------- SuperUser 84.67% 01:16 ServerFault 83.76% 00:53 Stack Overflow 63.63% 04:12 Now, technically, Google has no way to know the bounce rate. If you go to Google, search for something, and click on the first result, Google can't tell the difference between: a user who turns off their computer a user who goes to a completely different web site a user who spends hours clicking around on the website they landed on What Google does know is how long it takes the user to come back to Google and do another search. According to the book In The Plex (page 47), Google distinguishes between what they call "short clicks" and "long clicks": A short click is a search where the user quickly comes back to Google and does another search. Google interprets this as a signal that the first search results were unsatisfactory. A long click is a search where the user doesn't search again for a long time. The book says that Google uses this information internally, to judge the quality of their own algorithms. It also said that short click data in which someone retypes a slight variation of the search is used to fuel the "Did you mean...?" spell checking algorithm. So, my hypothesis is that Google has recently decided to use long click rates as a signal of a high quality site. Does anyone have any evidence of this? Have you seen any high-bounce-rate sites which lost traffic (or vice-versa)?

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  • Recover Data Like a Forensics Expert Using an Ubuntu Live CD

    - by Trevor Bekolay
    There are lots of utilities to recover deleted files, but what if you can’t boot up your computer, or the whole drive has been formatted? We’ll show you some tools that will dig deep and recover the most elusive deleted files, or even whole hard drive partitions. We’ve shown you simple ways to recover accidentally deleted files, even a simple method that can be done from an Ubuntu Live CD, but for hard disks that have been heavily corrupted, those methods aren’t going to cut it. In this article, we’ll examine four tools that can recover data from the most messed up hard drives, regardless of whether they were formatted for a Windows, Linux, or Mac computer, or even if the partition table is wiped out entirely. Note: These tools cannot recover data that has been overwritten on a hard disk. Whether a deleted file has been overwritten depends on many factors – the quicker you realize that you want to recover a file, the more likely you will be able to do so. Our setup To show these tools, we’ve set up a small 1 GB hard drive, with half of the space partitioned as ext2, a file system used in Linux, and half the space partitioned as FAT32, a file system used in older Windows systems. We stored ten random pictures on each hard drive. We then wiped the partition table from the hard drive by deleting the partitions in GParted. Is our data lost forever? Installing the tools All of the tools we’re going to use are in Ubuntu’s universe repository. To enable the repository, open Synaptic Package Manager by clicking on System in the top-left, then Administration > Synaptic Package Manager. Click on Settings > Repositories and add a check in the box labelled “Community-maintained Open Source software (universe)”. Click Close, and then in the main Synaptic Package Manager window, click the Reload button. Once the package list has reloaded, and the search index rebuilt, search for and mark for installation one or all of the following packages: testdisk, foremost, and scalpel. Testdisk includes TestDisk, which can recover lost partitions and repair boot sectors, and PhotoRec, which can recover many different types of files from tons of different file systems. Foremost, originally developed by the US Air Force Office of Special Investigations, recovers files based on their headers and other internal structures. Foremost operates on hard drives or drive image files generated by various tools. Finally, scalpel performs the same functions as foremost, but is focused on enhanced performance and lower memory usage. Scalpel may run better if you have an older machine with less RAM. Recover hard drive partitions If you can’t mount your hard drive, then its partition table might be corrupted. Before you start trying to recover your important files, it may be possible to recover one or more partitions on your drive, recovering all of your files with one step. Testdisk is the tool for the job. Start it by opening a terminal (Applications > Accessories > Terminal) and typing in: sudo testdisk If you’d like, you can create a log file, though it won’t affect how much data you recover. Once you make your choice, you’re greeted with a list of the storage media on your machine. You should be able to identify the hard drive you want to recover partitions from by its size and label. TestDisk asks you select the type of partition table to search for. In most cases (ext2/3, NTFS, FAT32, etc.) you should select Intel and press Enter. Highlight Analyse and press enter. In our case, our small hard drive has previously been formatted as NTFS. Amazingly, TestDisk finds this partition, though it is unable to recover it. It also finds the two partitions we just deleted. We are able to change their attributes, or add more partitions, but we’ll just recover them by pressing Enter. If TestDisk hasn’t found all of your partitions, you can try doing a deeper search by selecting that option with the left and right arrow keys. We only had these two partitions, so we’ll recover them by selecting Write and pressing Enter. Testdisk informs us that we will have to reboot. Note: If your Ubuntu Live CD is not persistent, then when you reboot you will have to reinstall any tools that you installed earlier. After restarting, both of our partitions are back to their original states, pictures and all. Recover files of certain types For the following examples, we deleted the 10 pictures from both partitions and then reformatted them. PhotoRec Of the three tools we’ll show, PhotoRec is the most user-friendly, despite being a console-based utility. To start recovering files, open a terminal (Applications > Accessories > Terminal) and type in: sudo photorec To begin, you are asked to select a storage device to search. You should be able to identify the right device by its size and label. Select the right device, and then hit Enter. PhotoRec asks you select the type of partition to search. In most cases (ext2/3, NTFS, FAT, etc.) you should select Intel and press Enter. You are given a list of the partitions on your selected hard drive. If you want to recover all of the files on a partition, then select Search and hit enter. However, this process can be very slow, and in our case we only want to search for pictures files, so instead we use the right arrow key to select File Opt and press Enter. PhotoRec can recover many different types of files, and deselecting each one would take a long time. Instead, we press “s” to clear all of the selections, and then find the appropriate file types – jpg, gif, and png – and select them by pressing the right arrow key. Once we’ve selected these three, we press “b” to save these selections. Press enter to return to the list of hard drive partitions. We want to search both of our partitions, so we highlight “No partition” and “Search” and then press Enter. PhotoRec prompts for a location to store the recovered files. If you have a different healthy hard drive, then we recommend storing the recovered files there. Since we’re not recovering very much, we’ll store it on the Ubuntu Live CD’s desktop. Note: Do not recover files to the hard drive you’re recovering from. PhotoRec is able to recover the 20 pictures from the partitions on our hard drive! A quick look in the recup_dir.1 directory that it creates confirms that PhotoRec has recovered all of our pictures, save for the file names. Foremost Foremost is a command-line program with no interactive interface like PhotoRec, but offers a number of command-line options to get as much data out of your had drive as possible. For a full list of options that can be tweaked via the command line, open up a terminal (Applications > Accessories > Terminal) and type in: foremost –h In our case, the command line options that we are going to use are: -t, a comma-separated list of types of files to search for. In our case, this is “jpeg,png,gif”. -v, enabling verbose-mode, giving us more information about what foremost is doing. -o, the output folder to store recovered files in. In our case, we created a directory called “foremost” on the desktop. -i, the input that will be searched for files. This can be a disk image in several different formats; however, we will use a hard disk, /dev/sda. Our foremost invocation is: sudo foremost –t jpeg,png,gif –o foremost –v –i /dev/sda Your invocation will differ depending on what you’re searching for and where you’re searching for it. Foremost is able to recover 17 of the 20 files stored on the hard drive. Looking at the files, we can confirm that these files were recovered relatively well, though we can see some errors in the thumbnail for 00622449.jpg. Part of this may be due to the ext2 filesystem. Foremost recommends using the –d command-line option for Linux file systems like ext2. We’ll run foremost again, adding the –d command-line option to our foremost invocation: sudo foremost –t jpeg,png,gif –d –o foremost –v –i /dev/sda This time, foremost is able to recover all 20 images! A final look at the pictures reveals that the pictures were recovered with no problems. Scalpel Scalpel is another powerful program that, like Foremost, is heavily configurable. Unlike Foremost, Scalpel requires you to edit a configuration file before attempting any data recovery. Any text editor will do, but we’ll use gedit to change the configuration file. In a terminal window (Applications > Accessories > Terminal), type in: sudo gedit /etc/scalpel/scalpel.conf scalpel.conf contains information about a number of different file types. Scroll through this file and uncomment lines that start with a file type that you want to recover (i.e. remove the “#” character at the start of those lines). Save the file and close it. Return to the terminal window. Scalpel also has a ton of command-line options that can help you search quickly and effectively; however, we’ll just define the input device (/dev/sda) and the output folder (a folder called “scalpel” that we created on the desktop). Our invocation is: sudo scalpel /dev/sda –o scalpel Scalpel is able to recover 18 of our 20 files. A quick look at the files scalpel recovered reveals that most of our files were recovered successfully, though there were some problems (e.g. 00000012.jpg). Conclusion In our quick toy example, TestDisk was able to recover two deleted partitions, and PhotoRec and Foremost were able to recover all 20 deleted images. Scalpel recovered most of the files, but it’s very likely that playing with the command-line options for scalpel would have enabled us to recover all 20 images. These tools are lifesavers when something goes wrong with your hard drive. If your data is on the hard drive somewhere, then one of these tools will track it down! Similar Articles Productive Geek Tips Recover Deleted Files on an NTFS Hard Drive from a Ubuntu Live CDUse an Ubuntu Live CD to Securely Wipe Your PC’s Hard DriveReset Your Ubuntu Password Easily from the Live CDBackup Your Windows Live Writer SettingsAdding extra Repositories on Ubuntu TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Awe inspiring, inter-galactic theme (Win 7) Case Study – How to Optimize Popular Wordpress Sites Restore Hidden Updates in Windows 7 & Vista Iceland an Insurance Job? Find Downloads and Add-ins for Outlook Recycle !

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  • Davicom Semiconductor, Inc. 21x4x DEC-Tulip not detected by Wireshark but IP operational

    - by deepsix86
    Recently flipped to Ubuntu 11.10 on a Dell 4300 (Intel). Getting IP address and no issues (ping/surf) but Wireshark unable to detect eth0 interface. I see references in forums to blacklist tulip but looks like I am running dmfe. Not sure if the blacklist is required and where to go from here. Maybe Driver update? Got a little lost looking in that area. Some h/w details below (IP/MAC/HOSTNAME removed) Linux xxxxxx 3.0.0-17-generic #30-Ubuntu SMP Thu Mar 8 17:34:21 UTC 2012 i686 i686 i386 GNU/Linux network-admin (HOSTS TAB) does not list eth0, only loopback and bunch of IPv6 interfaces ifconfig eth0 Link encap:Ethernet HWaddr xxxxxxxx inet addr:192.168.x.xx Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: xxxxxxxxxxx 64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:36662 errors:0 dropped:1 overruns:0 frame:0 TX packets:24975 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:42115779 (42.1 MB) TX bytes:3056435 (3.0 MB) Interrupt:18 Base address:0xe800 lspci 02:09.0 Ethernet controller: Davicom Semiconductor, Inc. 21x4x DEC-Tulip compatible 10/100 Ethernet (rev 31) Subsystem: Device 4554:434e Flags: bus master, medium devsel, latency 64, IRQ 18 I/O ports at e800 [size=256] Memory at fe1ffc00 (32-bit, non-prefetchable) [size=256] Expansion ROM at fe200000 [disabled] [size=256K] Capabilities: [50] Power Management version 2 Kernel driver in use: dmfe Kernel modules: dmfe hwinfo --netcard 20: PCI 209.0: 0200 Ethernet controller [Created at pci.318] Unique ID: rBUF.0NgK5ZS9c0D Parent ID: 6NW+.siohrLUzzI4 SysFS ID: /devices/pci0000:00/0000:00:1e.0/0000:02:09.0 SysFS BusID: 0000:02:09.0 Hardware Class: network Model: "Davicom 21x4x DEC-Tulip compatible 10/100 Ethernet" Vendor: pci 0x1282 "Davicom Semiconductor, Inc." Device: pci 0x9102 "21x4x DEC-Tulip compatible 10/100 Ethernet" SubVendor: pci 0x4554 SubDevice: pci 0x434e Revision: 0x31 Driver: "dmfe" Driver Modules: "dmfe" Device File: eth0 I/O Ports: 0xe800-0xe8ff (rw) Memory Range: 0xfe1ffc00-0xfe1ffcff (rw,non-prefetchable) Memory Range: 0xfe200000-0xfe23ffff (ro,non-prefetchable,disabled) IRQ: 18 (61379 events) HW Address: 00:08:a1:01:35:70 Link detected: yes Module Alias: "pci:v00001282d00009102sv00004554sd0000434Ebc02sc00i00" Driver Info #0: Driver Status: dmfe is active Driver Activation Cmd: "modprobe dmfe" Config Status: cfg=new, avail=yes, need=no, active=unknown Attached to: #11 (PCI bridge)

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  • Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

    - by Bakhtiyor
    I have mailserver configure using dovecot+postfix+mysql and it was runnig fine in the server(Ubuntu Server). But during last week it stopped working correctly. It doesn't send email. When I try to telnet localhost smtp I'm connecting successfully but when I do mail from:<[email protected]> and hit Enter it hangs on, nothing happen. Having reviewed /var/log/mail.log file I've found out that probably(99%) the problem is on postfix when it is trying to connect to MySQL server. If you see the log file given below you can see that it says Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2). Nov 14 21:54:36 ns1 dovecot: dovecot: Killed with signal 15 (by pid=7731 uid=0 code=kill) Nov 14 21:54:36 ns1 dovecot: Dovecot v1.2.9 starting up (core dumps disabled) Nov 14 21:54:36 ns1 dovecot: auth-worker(default): mysql: Connected to localhost (mailserver) Nov 14 21:54:44 ns1 postfix/postfix-script[7753]: refreshing the Postfix mail system Nov 14 21:54:44 ns1 postfix/master[1670]: reload -- version 2.7.0, configuration /etc/postfix Nov 14 21:54:52 ns1 postfix/trivial-rewrite[7759]: warning: connect to mysql server localhost: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) Nov 14 21:54:52 ns1 postfix/trivial-rewrite[7759]: fatal: mysql:/etc/postfix/mysql-virtual-alias-maps.cf(0,lock|fold_fix): table lookup problem Nov 14 21:54:53 ns1 postfix/master[1670]: warning: process /usr/lib/postfix/trivial-rewrite pid 7759 exit status 1 Nov 14 21:54:53 ns1 postfix/cleanup[7397]: warning: problem talking to service rewrite: Connection reset by peer Nov 14 21:54:53 ns1 postfix/master[1670]: warning: /usr/lib/postfix/trivial-rewrite: bad command startup -- throttling Nov 14 21:54:53 ns1 postfix/smtpd[7071]: warning: problem talking to service rewrite: Success I tried netstat -ln | grep mysql and it returns unix 2 [ ACC ] STREAM LISTENING 5817 /var/run/mysqld/mysqld.sock. The content of /etc/postfix/mysql-virtual-alias-maps.cf file is here: user = stevejobs password = apple hosts = localhost dbname = mailserver query = SELECT destination FROM virtual_aliases WHERE source='%s' Here I tried to change hosts = 127.0.0.1 but it says warning: connect to mysql server 127.0.0.1: Can't connect to MySQL server on '127.0.0.1' (110) So, I am lost and don't know where else to change in order to solve the problem. Any help would be appreciated highly. Thank you.

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  • Why can I not map a dynamic texture in D3D?

    - by sebf
    I am trying to map a Texture2D resource in DirectX11 via SharpDX. The resource is declared as a ShaderResource, with Dynamic usage and the 'Write' CPU flag specified. My call however fails with a generic exception from SharpDX: _Parent.Context.MapSubresource( _Resource, 0, SharpDX.Direct3D11.MapMode.Write, SharpDX.Direct3D11.MapFlags.None, out stream ); I see from this question that it is supported. The MSDN docs and this other question hint that instead of using Context.MapSubresource() I should be using Texture2D.Map(), however, the DirectX11 Texture2D class does not define Map() (though it does for the D3D 10 equivalent). If I call the above with MapMode.WriteDiscard, the call succeeds but in this case the previous content of the texture is lost, which is no good when I only want to update a section of it. Has the Map() method been removed in Direct3D 11 or am I looking in the wrong place? Is the MapSubresource() method unsuitable or am I using it wrong? EDIT: I declared my resource as Dynamic with CPU Write Flags - not Default as I originaly wrote - sorry for the fairly huge 'typo' that changes the entire question!

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  • SQL SERVER – Introduction to PERCENTILE_CONT() – Analytic Functions Introduced in SQL Server 2012

    - by pinaldave
    SQL Server 2012 introduces new analytical function PERCENTILE_CONT(). The book online gives following definition of this function: Computes a specific percentile for sorted values in an entire rowset or within distinct partitions of a rowset in Microsoft SQL Server 2012 Release Candidate 0 (RC 0). For a given percentile value P, PERCENTILE_DISC sorts the values of the expression in the ORDER BY clause and returns the value with the smallest CUME_DIST value (with respect to the same sort specification) that is greater than or equal to P. If you are clear with understanding of the function – no need to read further. If you got lost here is the same in simple words – it is lot like finding median with percentile value. Now let’s have fun following query: USE AdventureWorks GO SELECT SalesOrderID, OrderQty, ProductID, PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY ProductID) OVER (PARTITION BY SalesOrderID) AS MedianCont FROM Sales.SalesOrderDetail WHERE SalesOrderID IN (43670, 43669, 43667, 43663) ORDER BY SalesOrderID DESC GO The above query will give us the following result: You can see that I have used PERCENTILE_COUNT(0.5) in query, which is similar to finding median. Let me explain above diagram with little more explanation. The defination of median is as following: In case of Even Number of elements = In ordered list add the two digits from the middle and devide by 2 In case of Odd Numbers of elements = In ordered list select the digits from the middle I hope this example gives clear idea how PERCENTILE_CONT() works. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • How to penetrate the QA industry after layoffs, next steps...

    - by Erik
    Briefly, my background is in manual black box testing of websites and applications within the Agile/waterfall context. Over the past four years I was a member of two web development firms' small QA teams dedicated to testing the deployment of websites for national/international non profits, governmental organizations, and for profit business, to name a few: -Brookings Institution -Senate -Tyco Electronics -Blue Cross/Blue Shield -National Geographic -Discover Channel I have a very strong understanding of the: -SDLC -STLC of bugs and website deployment/development -Use Case & Test Case development In March of this year, my last firm downsized and lost my job as a QA tester. I have been networking and doing a very detailed job search, but have had a very difficult time getting my next job within the QA industry, even with my background as a manual black box QA tester in the website development context. My direct question to all of you: What are some ways I can be more competitive and get hired? Options that could get me competitive: Should I go back to school and learn some more 'hard' skills in website development and client side technologies, e.g.: -HTML -CSS -JavaScript Learn programming: -PHP -C# -Ruby -SQL -Python -Perl -?? Get Certified as a QA Tester, there are a countless numbers of programs to become a Certified Tester. Most, if not all jobs, being advertised now require Automated Testing experience, in: -QTP -Loadrunner -Selenium -ETC. Should I learn, Automated testing skills, via a paid course, or teach myself? --Learn scripting languages to understand the automated testing process better? Become a Certified "Project Management Professional" (PMP) to prove to hiring managers that I 'get' the project development life cycle? At the end of the day I need to be competitive and get hired as a QA tester and want to build upon my skills within the QA web development field. How should I do this, without reinventing the wheel? Any help in this regard would be fabulous. Thanks! .erik

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  • Hello Operator, My Switch Is Bored

    - by Paul White
    This is a post for T-SQL Tuesday #43 hosted by my good friend Rob Farley. The topic this month is Plan Operators. I haven’t taken part in T-SQL Tuesday before, but I do like to write about execution plans, so this seemed like a good time to start. This post is in two parts. The first part is primarily an excuse to use a pretty bad play on words in the title of this blog post (if you’re too young to know what a telephone operator or a switchboard is, I hate you). The second part of the post looks at an invisible query plan operator (so to speak). 1. My Switch Is Bored Allow me to present the rare and interesting execution plan operator, Switch: Books Online has this to say about Switch: Following that description, I had a go at producing a Fast Forward Cursor plan that used the TOP operator, but had no luck. That may be due to my lack of skill with cursors, I’m not too sure. The only application of Switch in SQL Server 2012 that I am familiar with requires a local partitioned view: CREATE TABLE dbo.T1 (c1 int NOT NULL CHECK (c1 BETWEEN 00 AND 24)); CREATE TABLE dbo.T2 (c1 int NOT NULL CHECK (c1 BETWEEN 25 AND 49)); CREATE TABLE dbo.T3 (c1 int NOT NULL CHECK (c1 BETWEEN 50 AND 74)); CREATE TABLE dbo.T4 (c1 int NOT NULL CHECK (c1 BETWEEN 75 AND 99)); GO CREATE VIEW V1 AS SELECT c1 FROM dbo.T1 UNION ALL SELECT c1 FROM dbo.T2 UNION ALL SELECT c1 FROM dbo.T3 UNION ALL SELECT c1 FROM dbo.T4; Not only that, but it needs an updatable local partitioned view. We’ll need some primary keys to meet that requirement: ALTER TABLE dbo.T1 ADD CONSTRAINT PK_T1 PRIMARY KEY (c1);   ALTER TABLE dbo.T2 ADD CONSTRAINT PK_T2 PRIMARY KEY (c1);   ALTER TABLE dbo.T3 ADD CONSTRAINT PK_T3 PRIMARY KEY (c1);   ALTER TABLE dbo.T4 ADD CONSTRAINT PK_T4 PRIMARY KEY (c1); We also need an INSERT statement that references the view. Even more specifically, to see a Switch operator, we need to perform a single-row insert (multi-row inserts use a different plan shape): INSERT dbo.V1 (c1) VALUES (1); And now…the execution plan: The Constant Scan manufactures a single row with no columns. The Compute Scalar works out which partition of the view the new value should go in. The Assert checks that the computed partition number is not null (if it is, an error is returned). The Nested Loops Join executes exactly once, with the partition id as an outer reference (correlated parameter). The Switch operator checks the value of the parameter and executes the corresponding input only. If the partition id is 0, the uppermost Clustered Index Insert is executed, adding a row to table T1. If the partition id is 1, the next lower Clustered Index Insert is executed, adding a row to table T2…and so on. In case you were wondering, here’s a query and execution plan for a multi-row insert to the view: INSERT dbo.V1 (c1) VALUES (1), (2); Yuck! An Eager Table Spool and four Filters! I prefer the Switch plan. My guess is that almost all the old strategies that used a Switch operator have been replaced over time, using things like a regular Concatenation Union All combined with Start-Up Filters on its inputs. Other new (relative to the Switch operator) features like table partitioning have specific execution plan support that doesn’t need the Switch operator either. This feels like a bit of a shame, but perhaps it is just nostalgia on my part, it’s hard to know. Please do let me know if you encounter a query that can still use the Switch operator in 2012 – it must be very bored if this is the only possible modern usage! 2. Invisible Plan Operators The second part of this post uses an example based on a question Dave Ballantyne asked using the SQL Sentry Plan Explorer plan upload facility. If you haven’t tried that yet, make sure you’re on the latest version of the (free) Plan Explorer software, and then click the Post to SQLPerformance.com button. That will create a site question with the query plan attached (which can be anonymized if the plan contains sensitive information). Aaron Bertrand and I keep a close eye on questions there, so if you have ever wanted to ask a query plan question of either of us, that’s a good way to do it. The problem The issue I want to talk about revolves around a query issued against a calendar table. The script below creates a simplified version and adds 100 years of per-day information to it: USE tempdb; GO CREATE TABLE dbo.Calendar ( dt date NOT NULL, isWeekday bit NOT NULL, theYear smallint NOT NULL,   CONSTRAINT PK__dbo_Calendar_dt PRIMARY KEY CLUSTERED (dt) ); GO -- Monday is the first day of the week for me SET DATEFIRST 1;   -- Add 100 years of data INSERT dbo.Calendar WITH (TABLOCKX) (dt, isWeekday, theYear) SELECT CA.dt, isWeekday = CASE WHEN DATEPART(WEEKDAY, CA.dt) IN (6, 7) THEN 0 ELSE 1 END, theYear = YEAR(CA.dt) FROM Sandpit.dbo.Numbers AS N CROSS APPLY ( VALUES (DATEADD(DAY, N.n - 1, CONVERT(date, '01 Jan 2000', 113))) ) AS CA (dt) WHERE N.n BETWEEN 1 AND 36525; The following query counts the number of weekend days in 2013: SELECT Days = COUNT_BIG(*) FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; It returns the correct result (104) using the following execution plan: The query optimizer has managed to estimate the number of rows returned from the table exactly, based purely on the default statistics created separately on the two columns referenced in the query’s WHERE clause. (Well, almost exactly, the unrounded estimate is 104.289 rows.) There is already an invisible operator in this query plan – a Filter operator used to apply the WHERE clause predicates. We can see it by re-running the query with the enormously useful (but undocumented) trace flag 9130 enabled: Now we can see the full picture. The whole table is scanned, returning all 36,525 rows, before the Filter narrows that down to just the 104 we want. Without the trace flag, the Filter is incorporated in the Clustered Index Scan as a residual predicate. It is a little bit more efficient than using a separate operator, but residual predicates are still something you will want to avoid where possible. The estimates are still spot on though: Anyway, looking to improve the performance of this query, Dave added the following filtered index to the Calendar table: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear) WHERE isWeekday = 0; The original query now produces a much more efficient plan: Unfortunately, the estimated number of rows produced by the seek is now wrong (365 instead of 104): What’s going on? The estimate was spot on before we added the index! Explanation You might want to grab a coffee for this bit. Using another trace flag or two (8606 and 8612) we can see that the cardinality estimates were exactly right initially: The highlighted information shows the initial cardinality estimates for the base table (36,525 rows), the result of applying the two relational selects in our WHERE clause (104 rows), and after performing the COUNT_BIG(*) group by aggregate (1 row). All of these are correct, but that was before cost-based optimization got involved :) Cost-based optimization When cost-based optimization starts up, the logical tree above is copied into a structure (the ‘memo’) that has one group per logical operation (roughly speaking). The logical read of the base table (LogOp_Get) ends up in group 7; the two predicates (LogOp_Select) end up in group 8 (with the details of the selections in subgroups 0-6). These two groups still have the correct cardinalities as trace flag 8608 output (initial memo contents) shows: During cost-based optimization, a rule called SelToIdxStrategy runs on group 8. It’s job is to match logical selections to indexable expressions (SARGs). It successfully matches the selections (theYear = 2013, is Weekday = 0) to the filtered index, and writes a new alternative into the memo structure. The new alternative is entered into group 8 as option 1 (option 0 was the original LogOp_Select): The new alternative is to do nothing (PhyOp_NOP = no operation), but to instead follow the new logical instructions listed below the NOP. The LogOp_GetIdx (full read of an index) goes into group 21, and the LogOp_SelectIdx (selection on an index) is placed in group 22, operating on the result of group 21. The definition of the comparison ‘the Year = 2013’ (ScaOp_Comp downwards) was already present in the memo starting at group 2, so no new memo groups are created for that. New Cardinality Estimates The new memo groups require two new cardinality estimates to be derived. First, LogOp_Idx (full read of the index) gets a predicted cardinality of 10,436. This number comes from the filtered index statistics: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH STAT_HEADER; The second new cardinality derivation is for the LogOp_SelectIdx applying the predicate (theYear = 2013). To get a number for this, the cardinality estimator uses statistics for the column ‘theYear’, producing an estimate of 365 rows (there are 365 days in 2013!): DBCC SHOW_STATISTICS (Calendar, theYear) WITH HISTOGRAM; This is where the mistake happens. Cardinality estimation should have used the filtered index statistics here, to get an estimate of 104 rows: DBCC SHOW_STATISTICS (Calendar, Weekends) WITH HISTOGRAM; Unfortunately, the logic has lost sight of the link between the read of the filtered index (LogOp_GetIdx) in group 22, and the selection on that index (LogOp_SelectIdx) that it is deriving a cardinality estimate for, in group 21. The correct cardinality estimate (104 rows) is still present in the memo, attached to group 8, but that group now has a PhyOp_NOP implementation. Skipping over the rest of cost-based optimization (in a belated attempt at brevity) we can see the optimizer’s final output using trace flag 8607: This output shows the (incorrect, but understandable) 365 row estimate for the index range operation, and the correct 104 estimate still attached to its PhyOp_NOP. This tree still has to go through a few post-optimizer rewrites and ‘copy out’ from the memo structure into a tree suitable for the execution engine. One step in this process removes PhyOp_NOP, discarding its 104-row cardinality estimate as it does so. To finish this section on a more positive note, consider what happens if we add an OVER clause to the query aggregate. This isn’t intended to be a ‘fix’ of any sort, I just want to show you that the 104 estimate can survive and be used if later cardinality estimation needs it: SELECT Days = COUNT_BIG(*) OVER () FROM dbo.Calendar AS C WHERE theYear = 2013 AND isWeekday = 0; The estimated execution plan is: Note the 365 estimate at the Index Seek, but the 104 lives again at the Segment! We can imagine the lost predicate ‘isWeekday = 0’ as sitting between the seek and the segment in an invisible Filter operator that drops the estimate from 365 to 104. Even though the NOP group is removed after optimization (so we don’t see it in the execution plan) bear in mind that all cost-based choices were made with the 104-row memo group present, so although things look a bit odd, it shouldn’t affect the optimizer’s plan selection. I should also mention that we can work around the estimation issue by including the index’s filtering columns in the index key: CREATE NONCLUSTERED INDEX Weekends ON dbo.Calendar(theYear, isWeekday) WHERE isWeekday = 0 WITH (DROP_EXISTING = ON); There are some downsides to doing this, including that changes to the isWeekday column may now require Halloween Protection, but that is unlikely to be a big problem for a static calendar table ;)  With the updated index in place, the original query produces an execution plan with the correct cardinality estimation showing at the Index Seek: That’s all for today, remember to let me know about any Switch plans you come across on a modern instance of SQL Server! Finally, here are some other posts of mine that cover other plan operators: Segment and Sequence Project Common Subexpression Spools Why Plan Operators Run Backwards Row Goals and the Top Operator Hash Match Flow Distinct Top N Sort Index Spools and Page Splits Singleton and Range Seeks Bitmaps Hash Join Performance Compute Scalar © 2013 Paul White – All Rights Reserved Twitter: @SQL_Kiwi

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