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  • Undocumented Query Plans: Equality Comparisons

    - by Paul White
    The diagram below shows two data sets, with differences highlighted: To find changed rows using TSQL, we might write a query like this: The logic is clear: join rows from the two sets together on the primary key column, and return rows where a change has occurred in one or more data columns.  Unfortunately, this query only finds one of the expected four rows: The problem, of course, is that our query does not correctly handle NULLs.  The ‘not equal to’ operators <> and != do not evaluate...(read more)

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  • HTML Maps for DataViz

    - by jamiet
    I don’t talk about data visualisation (#dataviz) much on this blog because, well, because its not something I can claim to be particularly knowledgeable about – that doesn’t stop me from having an opinion about it though. I just stumbled upon an article that compares the media ecosystems of four various technology companies entitled Mapping The Entertainment Ecosystems of Apple, Microsoft, Google & Amazon and apart from being a well-researched and well-written article (not something that the tech press excels in, in my opinion) I was struck by how well the author uses maps to tell a story to the reader. Take the map in this screenshot: Clicking on one of the four icons at the bottom of the map dynamically changes the shaded areas of the map to indicate which countries that company offers their services. Its aesthetically pleasing but moreover it instantly coveys useful information to me. What I love about it most of all though is that its all pure HTML – I don’t need any poxy Silverlight or Flash plugin to view the maps and interact with them – all I need is an up to date web browser (I use Chrome v22 although I tested using IE9 and it worked fine there too). This is how I believe data visualisation should be - conveying useful info in a friction-free way. Maps are a great way of achieving that – I just wish more people agreed with me about calendars as a mechanism for doing the same! @Jamiet

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  • CodePlex Daily Summary for Saturday, March 31, 2012

    CodePlex Daily Summary for Saturday, March 31, 2012Popular ReleasesAuto-LiMPoT: Auto-LiMPoT - v.1.1 - binary: Changelog: +Now patches updater-script with correct packager name and version number +Added option to choose position of java.exe manually if not found automaticallyExtended WPF Toolkit: Extended WPF Toolkit - 1.6.0: Want an easier way to install the Extended WPF Toolkit?The Extended WPF Toolkit is available on Nuget. What's in the 1.6.0 Release?BusyIndicator ButtonSpinner Calculator CalculatorUpDown CheckListBox - Breaking Changes CheckComboBox - New Control ChildWindow CollectionEditor CollectionEditorDialog ColorCanvas ColorPicker DateTimePicker DateTimeUpDown DecimalUpDown DoubleUpDown DropDownButton IntegerUpDown Magnifier MaskedTextBox MessageBox MultiLineTex...ScriptIDE: Release 4.4: ...Media Companion: MC 3.434b Release: General This release should be the last beta for 3.4xx. If there are no major problems, by the end of the week it will upgraded to 3.500 Stable! The latest mc_com.exe should be included too! TV Bug fix - crash when using XBMC scraper for TV episodes. Bug fix - episode count update when adding new episodes. Bug fix - crash when actors name was missing. Enhanced TV scrape progress text. Enhancements made to missing episodes display. Movies Bug fix - hide "Play Trailer" when multisaev...Better Explorer: Better Explorer 2.0.0.831 Alpha: - A new release with: - many bugfixes - changed icon - added code for more failsafe registry usage on x64 systems - not needed regfix anymore - added ribbon shortcut keys - Other fixes Note: If you have problems opening system libraries, a suggestion was given to copy all of these libraries and then delete the originals. Thanks to Gaugamela for that! (see discussion here: 349015 ) Note2: I was upload again the setup due to missing file!XAML Dialect Comparer Tool: Beta 1: This is a first beta version of this tool (as shown at DevConncetions in Vegas, March 2012). Community participation and suggestions are appreciated.LINQ Extensions Library: 1.0.2.7: Append and Prepend extensions (1.0.2.7) IndexOf extensions (1.0.2.7) New Align/Match extensions (1.0.2.6) Ready to use stable code with comprehensive unit tests and samples New Pivot extensions New Filter ExtensionsMonoGame - Write Once, Play Everywhere: MonoGame 2.5: The MonoGame team are pleased to announce that MonoGame v2.5 has been released. This release contains important bug fixes, implements optimisations and adds key features. MonoGame now has the capability to use OpenGLES 2.0 on Android and iOS devices, meaning it now supports custom shaders across mobile and desktop platforms. Also included in this release are native orientation animations on iOS devices and better Orientation support for Android. There have also been a lot of bug fixes since t...callisto: callisto 2.0.23: Patched Script static class and peak user count bug fix.Circuit Diagram: Circuit Diagram 2.0 Alpha 3: New in this release: Added components: Microcontroller Demultiplexer Flip & rotate components Open XML files from older versions of Circuit Diagram Text formatting for components New CDDX syntax Other fixesUmbraco CMS: Umbraco 5.1 CMS (Beta): Beta build for testing - please report issues at issues.umbraco.org (Latest uploaded: 5.1.0.123) What's new in 5.1? The full list of changes is on our http://progress.umbraco.org task tracking page. It shows items complete for 5.1, and 5.1 includes items for 5.0.1 and 5.0.2 listed there too. Here's two headline acts: Members5.1 adds support for backoffice editing of Members. We support the pairing up of our content type system in Hive with regular ASP.NET Membership providers (we ship a def...51Degrees.mobi - Mobile Device Detection and Redirection: 2.1.2.11: One Click Install from NuGet Changes to Version 2.1.2.11Code Changes 1. The project is now licenced under the Mozilla Public Licence 2. 2. User interface control and associated data access layer classes have been added to aid developers integrating 51Degrees.mobi into wider projects such as content management systems or web hosting management solutions. Use the following in a web form or user control to access these new UI components. <%@ Register Assembly="FiftyOne.Foundation" Namespace="...JSON Toolkit: JSON Toolkit 3.1: slight performance improvement (5% - 10%) new JsonException classPicturethrill: Version 2.3.28.0: Straightforward image selection. New clean UI look. Super stable. Simplified user experience.SQL Monitor - managing sql server performance: SQL Monitor 4.2 alpha 16: 1. finally fixed problem with logic fault checking for temporary table name... I really mean finally ...ScintillaNET: ScintillaNET 2.5: A slew of bug-fixes with a few new features sprinkled in. This release also upgrades the SciLexer and SciLexer64 DLLs to version 3.0.4. The official stuff: Issue # Title 32402 32402 27137 27137 31548 31548 30179 30179 24932 24932 29701 29701 31238 31238 26875 26875 30052 30052 Mugen MVVM Toolkit: Mugen MVVM Toolkit ver 1.1: Added Design mode support.Harness: Harness 2.0.2: change to .NET Framework Client Profile bug fix the download dialog auto answer. bug fix setFocus command. add "SendKeys" command. remove "closeAll" command. minor bugs fixed.BugNET Issue Tracker: BugNET 0.9.161: Below is a list of fixes in this release. Bug BGN-2092 - Link in Email "visit your profile" not functional BGN-2083 - Manager of bugnet can not edit project when it is not public BGN-2080 - clicking on a link in the project summary causes error (0.9.152.0) BGN-2070 - Missing Functionality On Feed.aspx BGN-2069 - Calendar View does not work BGN-2068 - Time tracking totals not ok BGN-2067 - Issues List Page Size Bug: Index was out of range. Must be non-negative and less than the si...YAF.NET (aka Yet Another Forum.NET): v1.9.6.1 RTW: v1.9.6.1 FINAL is .NET v4.0 ONLY v1.9.6.1 has: Performance Improvements .NET v4.0 improvements Improved FaceBook Integration KNOWN ISSUES WITH THIS RELEASE: ON INSTALL PLEASE DON'T CHECK "Upgrade BBCode Extensions...". More complete change list and discussion here: http://forum.yetanotherforum.net/yaf_postst14201_v1-9-6-1-RTW-Dated--3-26-2012.aspxNew ProjectsAlloCiné API: API AlloCiné v3 This is a library to use the API of AlloCiné. It covers the version 3 of the AlloCiné service as described here GroWiki API AlloCiné v3. The data-interchange format used behind the scene is JSON. Auto-LiMPoT: An automated tool to convert an N1 MIUI Rom to an AcerLiquid-compatible Rom.Azure Management API (via F#): This lib is a wrapper for Azure Management REST API. Can be used by .Net languages but adapted for F# (used asyncs and other). Supported operations: AffinityGroups (all), HostedServices (all), StorageServices (all), Azure Sql (all = manage server + firewall rules), AsyncOperationCraigsPack: This is a Light weight and Expandable library that helps search through craigslist ads but not bound to only one website. It includes interfaces and base classes to help create custom web providers for other specific websites. Written in c#Cygnus v3: Cygnus internal.DataHelperCS: Porject about DataHelper for rapid development and Simplist Architectur Model.Datewise Picture Arranger: Arranges/Renames pictures based on the date taken. d? án web: Ð? án môn phát tri?n ?ng d?ng webDrawbot: IRC Bot for /r/sketchdaily on reddit.FONIS prezenter: FONIS prezenter je aplikacija koja omogucava korisniku da odredenom kombinacijom sa tastature pozove odgovarajucu PowerPoint prezentaciju. Program je razvijen u C#. Za instaliranje i pokretanje ovog programa, potrebno je instalirati .NET Framework 4. Grammars: Grammars makes it easy to design regular, context-free and context-dependent grammars and apply various tools for parsing and language analysis. It is developed in C# and provides a BNF-like syntax with operator overloading and semantic rules as delegates, allowing you to design and code your grammar right in the middle of your C# code. It fleets with a fully-functional LR parser generator.iConference: Conference Management System.IQCare: IQCare is a Open Source, data capture and reporting system with patient management tools designed to measure patient outcomes. Having the ability to analyze data and then use the resulting analysis to provide improved care is the end goal of IQCare. IQCare has all of the key features needed to collect clean data and to do patient and facility analysis and reporting.Memory Management: General purpose memory management in C++ with policy-based architecture.Metro Style App Study Project: Metro Style App demos from QQ Group 95331609OpenNETCF CAB Installer SDK: The OpenNETCF CAB Installer SDK provides programmatic access to the extraction of CAB files under Windows CE, Windows Mobile, Windows Embedded Compact and Windows Embedded HandheldOrchard Private Content: Allows content items to be displayed by only users with roles that have permission.Pete Brown NETMF and Gadgeteer Code: Module drivers and other code for my .NET Micro Framework projects.QuanLyBanHang-Nhom100: Qu?n lý bán hàng - nhóm 100 Bùi vi?t sang Nguy?n van longRegeXml: This is about a Framework that allow you to transform a bunch of dirty data into a one and well formated XML.SSIS Row Number Component: This Rownumber component allows you to add a rownumber in the case your destination doesn't support auto-increment.Sunburn XNA advanced help custom samples: This project will include samples I do using sunburns engine. If you use it correctly it is a very powerful engine i found out. I will post samples for things that people have been trying to do in xna 4 and above with sunburn for awhile. THE webpage: gffgfgdhhgghdj91Transbin for anyone: Transbin makes it easier to contorl your computer anywhere.Wazzup module for DotNetNuke: Wazzup is a simple module for the DotNetNuke CMS to display the newest content added to your site. It leverage's DNN's search indexer and displays a simple link with publishing date and text summary. Developed in VB. Fits well into narrow vertical content areasWLCompus: WLCompusXNA Game Studio 3.0 Unleashed Book Source Code: C# Source Code and Assets from the XNA Game Studio 3.0 Unleashed book. The code is released under the Ms-PL license.

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  • Learn SSIS from the Authors of SSIS Design Patterns at the PASS Summit 2012!

    - by andyleonard
    Jessica Moss ( blog | @jessicammoss ), Michelle Ufford ( blog | @sqlfool ), Tim Mitchell ( blog | @tim_mitchell ), Matt Masson ( blog | @mattmasson ), and me – we are all presenting the SSIS Design Patterns pre-conference session at the PASS Summit 2012 ! We will be covering material from, and based upon, the book. We will describe and demonstrate patterns for package execution, package logging, loading flat file and XML sources, loading the cloud, dynamic package generation, SSIS Frameworks, data...(read more)

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  • Basket Analysis with #dax in #powerpivot and #ssas #tabular

    - by Marco Russo (SQLBI)
    A few days ago I published a new article on DAX Patterns web site describing how to implement Basket Analysis in DAX. This topic is a very classical one and is also covered in the many-to-many revolution white paper. It has been also discussed in several blog posts, listed here in historical order: Simple Basket Analysis in DAX by Chris Webb PowerPivot, basket analysis and the hidden many to many by Alberto Ferrari Applied Basket Analysis in Power Pivot using DAX by Gerhard Brueckl As usual, in DAX Patterns we try to present the required DAX formulas in a way that is easy to adapt to specific models. We also try to show a good implementation from a performance point of view. Further optimizations are always possible in DAX. However, in order to keep the model simple to adapt in different scenarios, we avoid presenting optimizations that would require particular assumptions or restrictions on the data model. I hope you will find the Basket Analysis pattern useful. Even if you do not need it today, reading the DAX formula is a good exercise to check your knowledge of evaluation contexts in DAX. For example, describing how does it work the following expression is not a trivial task! [Orders with Both Products] := CALCULATE (     DISTINCTCOUNT ( Sales[SalesOrderNumber] ),     CALCULATETABLE (         SUMMARIZE ( Sales, Sales[SalesOrderNumber] ),         ALL ( Product ),         USERELATIONSHIP ( Sales[ProductCode], 'Filter Product'[Filter ProductCode] )     ) ) The good news is that you can use the patterns even if you do not really understand all the details of the DAX formulas you are using! Any feedback on this new pattern is very welcome.

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  • Scaling Out the Distribution Database

    Replication is a great technology for moving data from one server to another, and it has a great many configuration options. David Poole brings us a technique for scaling out with multiple distribution databases.

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  • SSIS - The expression cannot be parsed because it contains invalid elements at the location specifie

    - by simonsabin
    If you get the following error when trying to write an expression there is an easy solution Attempt to parse the expression "@[User::FilePath] + "\" + @[User::FileName] + ".raw"" failed.  The token "." at line number "1", character number "<some position>" was not recognized. The expression cannot be parsed because it contains invalid elements at the location specified. The SSIS expression language is a C based language and the \ is a token, this means you have to escape it with another one. i.e "\" becomes "\\", unlike C# you can't prefix the string with a @, you have to use the escaping route. In summary when ever you want to use \ you need to use two \\

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  • Acommodation deal annoucced for SQLBits 6

    - by simonsabin
    The details of our acommodation deal have been announced. We are going to be using the Park Paza on Westminster Bridge. http://www.parkplaza.com/hotels/gbwestmi The speakers are going to be based there so why not join us, its a short walk from the venue. We have a promotion code SQL6 which gives you a greatly reduced rate of £139 + VAT.  If you want cheaper then consider using Laterooms

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  • Acommodation deal annoucced for SQLBits 6

    - by simonsabin
    The details of our acommodation deal have been announced. We are going to be using the Park Paza on Westminster Bridge. http://www.parkplaza.com/hotels/gbwestmi The speakers are going to be based there so why not join us, its a short walk from the venue. We have a promotion code SQL6 which gives you a greatly reduced rate of £139 + VAT.  If you want cheaper then consider using Laterooms

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  • SSIS Dashboard v0.4

    - by Davide Mauri
    Following the post on SSISDB script on Gist, I’ve been working on a HTML5 SSIS Dashboard, in order to have a nice looking, user friendly and, most of all, useful, SSIS Dashboard. Since this is a “spare-time” project, I’ve decided to develop it using Python since it’s THE data language (R aside), it’s a beautiful & powerful, well established and well documented and with a rich ecosystem around. Plus it has full support in Visual Studio, through the amazing Python Tools For Visual Studio plugin, I decided also to use Flask, a very good micro-framework to create websites, and use the SB Admin 2.0 Bootstrap admin template, since I’m all but a Web Designer. The result is here: https://github.com/yorek/ssis-dashboard and I can say I’m pretty satisfied with the work done so far (I’ve worked on it for probably less than 24 hours). Though there’s some features I’d like to add in t future (historical execution time, some charts, connection with AzureML to do prediction on expected execution times) it’s already usable. Of course I’ve tested it only on my development machine, so check twice before putting it in production but, give the fact that, virtually, there is not installation needed (you only need to install Python), and that all queries are based on standard SSISDB objects, I expect no big problems. If you want to test, contribute and/or give feedback please fell free to do it…I would really love to see this little project become a community project! Enjoy!

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  • Management Reporter Installation – Lessons Learned

    - by Ryan McBee
    After successfully completing several installations of Management Reporter this year, I wanted to share a few lessons learned that should help you. First, you will want to make sure that you install Management Reporter under a domain account as opposed to a local system or network service account. Management Reporter gives you the option to install under these accounts, but it is a be a best practice approach to use a domain account. Upon installation of Management Report, you will want to make sure that Directory Browsing is enabled within the IIS server of your site or you will have problems when you go to use Management Reporter. By default, it will be disabled in Server 2008 R2 and you will need to make the setting change under the Actions pane shown below. Lastly, you will want to make sure that SQL Server is running under a domain account. I have had multiple situations where reports have been stuck in the Queued status rather than Processing status of Management Reporter. After reviewing resolution 5 of KB 2298248, it was determined that running SQL Server under a domain account is the way to go.

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  • It's raining development VirtualBox images again!

    - by pieter.humphrey
                                                The cloud has burst.. forecast is looking like large amounts of VirtualBox images are coming down from OTN.   Are you finding the install for Database, WebLogic, SOA or WebCenter to be complicated when your goal is simply to setup a development sandbox?  Sick of giving your credit card info to cloud vendors, only to be stuck in a walled garden where you can't connect to your own internal systems?   Are you new to Java and just wanted something technical to sink your teeth into?  Or maybe you just want to put some stuff on that new terabyte drive you got? ;) Have no fear.  VirtualBox 4.0 is here.  We've have several development (read: don't use in production) images that were designed for use for in-person events, but we're posting them for your enjoyment.  Some of the images have step by step hands on labs baked into them too!  So get a freeware download manager like BitComet, install VirtualBox, an MD5 checksum utility (if you are on windows) and get wet!   del.icio.us Tags: java,development,java ee,java fx,virtualBox,virtualization,database,soa,weblogic,jdeveloper,eclipse,netbeans,sql developer,times ten,zend,php,SOA,SOA Suite,BPM,BAM,B2B,hudson,maven,subversion,Eclipse,Solaris,OTN Technorati Tags: java,development,java ee,java fx,virtualBox,virtualization,database,soa,weblogic,jdeveloper,eclipse,netbeans,sql developer,times ten,zend,php,SOA,SOA Suite,BPM,BAM,B2B,hudson,maven,subversion,Eclipse,Solaris,OTN

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  • IdentityServer Beta 1 Refresh &amp; Windows Azure Support

    - by Your DisplayName here!
    I just uploaded two new releases to Codeplex. IdentityServer B1 refresh A number of bug fixes and streamlined extensibility interfaces. Mostly a result of adding the Windows Azure support. Nothing has changed with regards to setup. Make sure you watch the intro video on the Codeplex site. IdentityServer B1 (Windows Azure Edition) I have now implemented all repositories for Windows Azure backed data storage. The default setup assumes you use the ASP.NET SQL membership provider database in SQL Azure and Table Storage for relying party, client certificates and delegation settings. The setup is simple: Upload your SSL/signing certificate via the portal Adjust the .cscfg file – you need to insert your storage account, certificate thumbprint and distinguished name There is a setup tool that can automatically insert the certificate distinguished names into your config file Adjust the connection string for the membership database in WebSite\configuration\connectionString.config Deploy Feedback Feature-wise this looks like the V1 release to me. It would be great if you could give me feedback, when you find a bug etc. – especially: Do the built-in repository implementations work for you (both on-premise and Azure)? Are the repository interfaces enough to add you own data store or feature?

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  • Learn more about MDX every day

    - by Marco Russo (SQLBI)
    I started learning MDX in 1999 and after so many years of using it and teaching it to other people, I still discover something new every day. Not only because I use it in strange ways (well, this doesn’t happen every day, at least!) but because there are other interesting information to read. Jeffrey Wang just published another interesting blog about data prefetching in MDX, which explains very well some strange behavior that sometime I observed in some customer cube. I never had a clear explanation...(read more)

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  • Bash script for mysql backup - error handling

    - by Jure1873
    I'm trying to backup a bunch of MyISAM tables in a way that would allow me to rsync/rdiff the backup directory to a remote location. I've came up with a script that dumps only the recently changed tables and sets the date of the file so that rsync can pick up only the changed ones, but now I don't know how to do the error handling - I would like the script to exit with a non 0 value if there are errors. How could I do that? #/bin/bash BKPDIR="/var/backups/db-mysql" mkdir -p $BKPDIR ERRORS=0 FIELDS="TABLE_SCHEMA, TABLE_NAME, UPDATE_TIME" W_COND="UPDATE_TIME >= DATE_ADD(CURDATE(), INTERVAL -2 DAY) AND TABLE_SCHEMA<>'information_schema'" mysql --skip-column-names -e "SELECT $FIELDS FROM information_schema.tables WHERE $W_COND;" | while read db table tstamp; do echo "DB: $db: TABLE: $table: ($tstamp)" mysqldump $db $table | gzip > $BKPDIR/$db-$table.sql.gz touch -d "$tstamp" $BKPDIR/$db-$table.sql.gz done exit $ERRORS

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  • The Excel Column Name assigment problem

    - by Peter Larsson
    Here is a generic algorithm to get the Excel column name according to it's position. By changing the @Base parameter, you can do this for any sequence according to same style as Excel. DECLARE @Value INT = 8839,         @Base TINYINT = 26   ;WITH cteSequence(Value, Delta, Quote, Base, Chr) AS (     SELECT  CAST(@Value AS INT) AS Value,             CAST(1 AS INT) AS Delta,             CAST(@Base AS INT) AS Quote,             CAST(@Base AS INT) AS Base,             CHAR(65 +(@Value - 1) % @Base) AS Chr       UNION ALL       SELECT  Value AS Value,             Quote AS Delta,             26 * Quote AS Quote,             Base AS Base,             CHAR(65 +((Value - Delta)/ Quote - 1) % Base) AS Chr     FROM    cteSequence     WHERE   CHAR(65 +((Value - Delta)/ Quote - 1) % Base) <> '@' ) SELECT  CAST(Msg AS VARCHAR(MAX)) FROM    (             SELECT        '' + Chr             FROM        cteSequence             ORDER BY    Delta DESC             FOR XML        PATH('')         ) AS x(Msg)

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  • Performance Tuning and Query Optimisation–SQLBits Training Day

    - by simonsabin
    I will be doing a training day at SQLbits in April on Performance Tuning and Query Optimisation. This is the outline for the day. Its going to be an intense day, I look forward to seeing you there. To register go to http://www. sqlbits .com/information/registration.aspx . Places are limited so make sure you register soon. Outline of the day. Most database performance issues are due to a combination of bad queries, bad database design or poor indexing. All of them are related to each other. In this...(read more)

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  • Differences in documentation for sys.dm_exec_requests

    - by AaronBertrand
    I've already complained about this on Connect ( see #641790 ), but I just wanted to point out that if you're trying to make sense of the sys.dm_exec_requests document and what it lists as the commands supported by the percent_complete column, you should check which version of the documentation you're reading. I noticed the following discrepancies. I can't explain why certain operations are missing, except that the Denali topic was generated from the 2008 topic (or maybe from the 2008 R2 topic before...(read more)

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  • SQLMidlands & SQLLunch

    - by Dave Ballantyne
    Many thanks to all those that turned out to see my presentation on Thursday (16th of Feb) of “Cursors are Evil” at SQLMidlands.  The scripts i used are here : https://skydrive.live.com/?cid=4004b6a3bc887e2c&id=4004B6A3BC887E2C%21216 You will need the AdventureWorks2008r2 release to run these, feel free to mail me ([email protected]) with any questions.  They are based upon a series of articles I wrote for SQLServerCentral which can be found here and here. Also I am starting ,or at least having an attempt at, a new user group in London.  This is SQLLunch, meeting downstairs at The Golden Fleece , EC4N 1SP which is 2 minutes from Bank Tube , we will have a twice monthly meeting (2nd and 4th Tuesdays) for an ‘All Stuff, No Fluff’ event.  Put plainly, a quick hello followed by a 45 minute presentation , which will ,optimistically, have you there and back to your desk within a lunch hour. Registrations for the first series of dates are at sqlserverfaq.com If you would like to speak, then please get in touch. Hope to see you there. 

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  • Increasing deadlocks with NoLock

    - by Dave Ballantyne
    One on my personnel pet issues is with inappropriate use of the NOLOCK hint (and read uncommitted) .  Dont get me wrong, I have used it in exceptional circumstances , but as a general statement it is a bad thing.  Mostly , when NOLOCK, is used the discussion is around a single statement,  “it runs faster with nolock for XYZ reason”,  however ,IMO, this is quite a shorted sighted view.  What about the Transaction ? What about other concurrent users ?  What is good for one statement in isolation , does not mean that it is good for the system as a whole.  I have seen on a number of occasions deadlocks happen, when tasks that would of(and should of) be blocked continue to execute, only for a deadlock to occur at a later data writing (INSERT,UPDATE,DELETE) statement.  Writers will block writers regardless of isolation level. By Way of (fairly contrived ) example , lets generate some dummy tables and populate with some data drop table a go drop table b go Create Table a ( col1 integer ) go insert into a values(1) insert into a values(2) go Create Table b ( col1 integer ) go insert into b values(1) insert into b values(2) go   Now make two connections. In connection one execute set transaction isolation level read committed BEGIN TRAN Select * from a Select * from b delete from a In connection two execute set transaction isolation level read committed BEGIN TRAN Select * from a Select * from b delete from b Right now the ‘select from a’ in connection two is being blocked by the ‘delete from a’ in connection one.  This is ,IMO, quite a healthy and natural thing to be happening , some see this as a ‘slow down’, a drop in performance.  So, lets reach for our ‘NOLOCK’ magic pill.  Cancel the blocked query and ROLLBACK both transactions, then in connection one execute set transaction isolation level read uncommitted BEGIN TRAN Select * from a Select * from b delete from b and then in connection two execute set transaction isolation level read uncommitted BEGIN TRAN Select * from a Select * from b delete from a We have now solved out performance problem , no more blocking.  Lets finish the work required by the transaction, in connection one , execute delete from a Oh, ‘ performance problem’ again , its now being blocked. Still, lets complete the work in connection two…. delete from b DEADLOCK!!  It is important to be clear about the role of the select statements.  They do not participate within the deadlock, but are preventing code executing that would of.   Additionally, without the select readers to block, a deadlock would occur on the deletes with READ COMMITTED. Naturally, other isolation levels will exhibit different behaviour as to where and when they will and wont block,  and I would encourage you to read BOL and satisfy yourself that you really do NEED to NOLOCK.

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