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  • Your Next IT Job

    - by BuckWoody
    Some data professionals have worked (and plan to work) in the same place for a long time. In organizations large and small, the turnover rate just isn’t that high. This has not been my experience. About every 3-5 years I’ve changed either roles or companies. That might be due to the IT environment or my personality (or a mix of the two), but the point is that I’ve had many roles and worked for many companies large and small throughout my 27+ years in IT. At one point this might have been a detriment – a prospective employer looks at the resume and says “it seems you’ve moved around quite a bit.” But I haven’t found that to be the case all the time –in fact, in some cases the variety of jobs I’ve held has been an asset because I’ve seen what works (and doesn’t) in other environments, which can save time and money. So if you’re in the first camp – great! Stay where you are, and continue doing the work you love. but if you’re in the second, then this post might be useful. If you are planning on making a change, or perhaps you’ve hit a wall at your current location, you might start looking around for a better paying job – and there’s nothing wrong with that. We all try to make our lives better, and for some that involves more money. Money, however, isn’t always the primary motivator. I’ve gone to another job that doesn’t have as many benefits or has the same salary as the current job I’m working to gain more experience, get a better work/life balance and so on. It’s a mix of factors that only you know about. So I thought I would lay out a few advantages and disadvantages in the shops I’ve worked at. This post isn’t aimed at a single employer, but represents a mix of what I’ve experienced, and of course the opinions here are my own. You will most certainly have a different take – if so, please post a response! I also won’t mention a specific industry – I’ve worked everywhere from medical firms, legal offices, retail, billing centers, manufacturing, government, even to NASA. I’m focusing here mostly on size and composition. And I’m making some very broad generalizations here – I am fully aware that a small company might have great benefits and a large company might allow a lot of role flexibility.  your mileage may vary – and again, post those comments! Small Company To me a “small company” means around 100 people or less – sometimes a lot less. These can be really fun, frustrating places to to work. Advantages: a great deal of flexibility, a wide range of roles (often at the same time), a large degree of responsibility, immediate feedback, close relationships with co-workers, work directly with your customer. Disadvantages: Too much responsibility, little work/life balance, immature political structure, few (if any) benefits. If the business is family-owned, they can easily violate work/life boundaries. Medium Size company In my experience the next size company I would work for involves from a few hundred people to around five thousand. Advantages: Good mobility – fairly easy to get promoted, acceptable benefits, more defined responsibilities, better work/life balance, balanced load for expertise, but still the organizational structure is fairly simple to understand. Disadvantages: Pay is not always highest, rapid changes in structure as the organization grows, transient workforce. You may not be given the opportunity to work with another technology if someone already “owns” it. Politics are painful at this level as people try to learn how to do it. Large Company When you get into the tens of thousands of folks employed around the world, you’re in a large company. Advantages: Lots of room to move around – sometimes you can work (as I have) multiple jobs through the years and yet stay at the same company, building time for benefits, very defined roles, trained managers (yes, I know some of them are still awful – trust me – I DO know that), higher-end benefits, long careers possible, discounts at retailers and other “soft” benefits, prestige. For some, a higher level of politics (done professionally) is a good thing. Disadvantages: You could become another faceless name in the crowd, might not allow a great deal of flexibility,  large organizational changes might take away any control you have of your career. I’ve also seen large layoffs happen, and good people get let go while “dead weight” is retained. For some, a higher level of politics is distasteful. So what are your experiences? Share with the group! Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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  • Oracle Index Skip Scan

    - by jchang
    There is a feature, called index skip scan that has been in Oracle since version 9i. When I across this, it seemed like a very clever trick, but not a critical capability. More recently, I have been advocating DW on SSD in approrpiate situations, and I am thinking this is now a valuable feature in keeping the number of nonclustered indexes to a minimum. Briefly, suppose we have an index with key columns: Col1 , Col2 , in that order. Obviously, a query with a search argument (SARG) on Col1 can use...(read more)

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  • Two free SQL Server events I'll be presenting at in UK. Come and say hi!

    - by Mladen Prajdic
    SQLBits: April 7th - April 9th 2011 in Brighton, UK Free community event on Saturday (April 9th) with a paid conference day on Friday (April 8th) and a Pre Conference day full of day long seminars (April 7th). It'll be a huge event with over 800 attendees and over 20 MVPs. I'll be presenting on Saturday April 9th.     SQL in the City: July 15th 2011 in London, UK One day of free SQL Server training sponsored by Redgate. Other MVP's that'll be presenting there are Steve Jones (website|twitter), Brad McGehee (blog|twitter) and Grant Fritchey (blog|twitter)   At both conferences I'll be presenting about database testing. In the sessions I'll cover a few things from my book The Red Gate Guide to SQL Server Team based Development like what do we need for testing, how to go about it, what are some of the obstacles we have to overcome, etc… If you're around there come and say Hi!

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  • 24 Hours of PASS: 15 Powerful Dynamic Management Objects - Deck and Demos

    - by Adam Machanic
    Thank you to everyone who attended today's 24 Hours of PASS webcast on Dynamic Management Objects! I was shocked, awed, and somewhat scared when I saw the attendee number peak at over 800. I really appreciate your taking time out of your day to listen to me talk. It's always interesting presenting to people I can't see or hear, so I relied on Twitter for a form of nearly real-time feedback. I would like to especially thank everyone who left me tweets both during and after the presentation. Your feedback...(read more)

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  • Intel Server Strategy Shift with Sandy Bridge EN & EP

    - by jchang
    The arrival of the Sandy Bridge EN and EP processors, expected in early 2012, will mark the completion of a significant shift in Intel server strategy. For the longest time 1995-2009, the strategy had been to focus on producing a premium processor designed for 4-way systems that might also be used in 8-way systems and higher. The objective for 2-way systems was use the desktop processor that later had a separate brand and different package & socket to leverage the low cost structure in driving...(read more)

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  • Managed code and the Shell – Do?

    Back in 2006 I wrote a blog post titled: Managed code and the Shell – Don't!. Please visit that post to see why that advice was given.The crux of the issue has been addressed in the latest CLR via In-Process Side-by-Side Execution. In addition to the MSDN documentation I just linked, there is also an MSDN article on the topic: In-Process Side-by-Side.Now, even though the major technical impediment seems to be removed, I don’t know if Microsoft is now officially supporting managed extensions to the shell. Either way, I noticed a CodePlex project that is marching ahead to enable exactly that: Managed Mini Shell Extension Framework. Not much activity there, but maybe it will grow once .NET 4 is released... Comments about this post welcome at the original blog.

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  • Silverlight as a Transmedia Platform (Silverlight TV #33)

    In this mini episode Jesse Liberty explains Transmedia Storytelling and why he believes that Silverlight may be the ideal platform for creating Transmedia applications on the web, Windows Phone 7 and eventually set-top boxes. Relevant links: John's Blog and on Twitter (@john_papa) Jesse's blog and on Twitter (@jesseliberty) Jesses mini-tutorial on Silverlight and Transmedia Follow us on Twitter @SilverlightTV or on the web at http://silverlight.tv/     ...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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  • Real tortoises keep it slow and steady. How about the backups?

    - by Maria Zakourdaev
      … Four tortoises were playing in the backyard when they decided they needed hibiscus flower snacks. They pooled their money and sent the smallest tortoise out to fetch the snacks. Two days passed and there was no sign of the tortoise. "You know, she is taking a lot of time", said one of the tortoises. A little voice from just out side the fence said, "If you are going to talk that way about me I won't go." Is it too much to request from the quite expensive 3rd party backup tool to be a way faster than the SQL server native backup? Or at least save a respectable amount of storage by producing a really smaller backup files?  By saying “really smaller”, I mean at least getting a file in half size. After Googling the internet in an attempt to understand what other “sql people” are using for database backups, I see that most people are using one of three tools which are the main players in SQL backup area:  LiteSpeed by Quest SQL Backup by Red Gate SQL Safe by Idera The feedbacks about those tools are truly emotional and happy. However, while reading the forums and blogs I have wondered, is it possible that many are accustomed to using the above tools since SQL 2000 and 2005.  This can easily be understood due to the fact that a 300GB database backup for instance, using regular a SQL 2005 backup statement would have run for about 3 hours and have produced ~150GB file (depending on the content, of course).  Then you take a 3rd party tool which performs the same backup in 30 minutes resulting in a 30GB file leaving you speechless, you run to management persuading them to buy it due to the fact that it is definitely worth the price. In addition to the increased speed and disk space savings you would also get backup file encryption and virtual restore -  features that are still missing from the SQL server. But in case you, as well as me, don’t need these additional features and only want a tool that performs a full backup MUCH faster AND produces a far smaller backup file (like the gain you observed back in SQL 2005 days) you will be quite disappointed. SQL Server backup compression feature has totally changed the market picture. Medium size database. Take a look at the table below, check out how my SQL server 2008 R2 compares to other tools when backing up a 300GB database. It appears that when talking about the backup speed, SQL 2008 R2 compresses and performs backup in similar overall times as all three other tools. 3rd party tools maximum compression level takes twice longer. Backup file gain is not that impressive, except the highest compression levels but the price that you pay is very high cpu load and much longer time. Only SQL Safe by Idera was quite fast with it’s maximum compression level but most of the run time have used 95% cpu on the server. Note that I have used two types of destination storage, SATA 11 disks and FC 53 disks and, obviously, on faster storage have got my backup ready in half time. Looking at the above results, should we spend money, bother with another layer of complexity and software middle-man for the medium sized databases? I’m definitely not going to do so.  Very large database As a next phase of this benchmark, I have moved to a 6 terabyte database which was actually my main backup target. Note, how multiple files usage enables the SQL Server backup operation to use parallel I/O and remarkably increases it’s speed, especially when the backup device is heavily striped. SQL Server supports a maximum of 64 backup devices for a single backup operation but the most speed is gained when using one file per CPU, in the case above 8 files for a 2 Quad CPU server. The impact of additional files is minimal.  However, SQLsafe doesn’t show any speed improvement between 4 files and 8 files. Of course, with such huge databases every half percent of the compression transforms into the noticeable numbers. Saving almost 470GB of space may turn the backup tool into quite valuable purchase. Still, the backup speed and high CPU are the variables that should be taken into the consideration. As for us, the backup speed is more critical than the storage and we cannot allow a production server to sustain 95% cpu for such a long time. Bottomline, 3rd party backup tool developers, we are waiting for some breakthrough release. There are a few unanswered questions, like the restore speed comparison between different tools and the impact of multiple backup files on restore operation. Stay tuned for the next benchmarks.    Benchmark server: SQL Server 2008 R2 sp1 2 Quad CPU Database location: NetApp FC 15K Aggregate 53 discs Backup statements: No matter how good that UI is, we need to run the backup tasks from inside of SQL Server Agent to make sure they are covered by our monitoring systems. I have used extended stored procedures (command line execution also is an option, I haven’t noticed any impact on the backup performance). SQL backup LiteSpeed SQL Backup SQL safe backup database <DBNAME> to disk= '\\<networkpath>\par1.bak' , disk= '\\<networkpath>\par2.bak', disk= '\\<networkpath>\par3.bak' with format, compression EXECUTE master.dbo.xp_backup_database @database = N'<DBName>', @backupname= N'<DBName> full backup', @desc = N'Test', @compressionlevel=8, @filename= N'\\<networkpath>\par1.bak', @filename= N'\\<networkpath>\par2.bak', @filename= N'\\<networkpath>\par3.bak', @init = 1 EXECUTE master.dbo.sqlbackup '-SQL "BACKUP DATABASE <DBNAME> TO DISK= ''\\<networkpath>\par1.sqb'', DISK= ''\\<networkpath>\par2.sqb'', DISK= ''\\<networkpath>\par3.sqb'' WITH DISKRETRYINTERVAL = 30, DISKRETRYCOUNT = 10, COMPRESSION = 4, INIT"' EXECUTE master.dbo.xp_ss_backup @database = 'UCMSDB', @filename = '\\<networkpath>\par1.bak', @backuptype = 'Full', @compressionlevel = 4, @backupfile = '\\<networkpath>\par2.bak', @backupfile = '\\<networkpath>\par3.bak' If you still insist on using 3rd party tools for the backups in your production environment with maximum compression level, you will definitely need to consider limiting cpu usage which will increase the backup operation time even more: RedGate : use THREADPRIORITY option ( values 0 – 6 ) LiteSpeed : use  @throttle ( percentage, like 70%) SQL safe :  the only thing I have found was @Threads option.   Yours, Maria

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  • NomCom Time

    - by RickHeiges
    Well, it is official... there is a race for the community seats on the PASS NomCom. I am very pleased to see that we have 12 people who decided to put their names forward for this task. This is largely a thankless job that takes a great deal of time, judgement, and consideration. I have put my name forward as one of those people who would like to take on this task and serve PASS (and the greater SQL Community) in this effort. You can find out more about me and the other candidates for the NomCom...(read more)

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  • Be the surgeon

    - by Rob Farley
    It’s a phrase I use often, especially when teaching, and I wish I had realised the concept years earlier. (And of course, fits with this month’s T-SQL Tuesday topic, hosted by Argenis Fernandez) When I’m sick enough to go to the doctor, I see a GP. I used to typically see the same guy, but he’s moved on now. However, when he has been able to roughly identify the area of the problem, I get referred to a specialist, sometimes a surgeon. Being a surgeon requires a refined set of skills. It’s why they often don’t like to be called “Doctor”, and prefer the traditional “Mister” (the history is that the doctor used to make the diagnosis, and then hand the patient over to the person who didn’t have a doctorate, but rather was an expert cutter, typically from a background in butchering). But if you ask the surgeon about the pain you have in your leg sometimes, you’ll get told to ask your GP. It’s not that your surgeon isn’t interested – they just don’t know the answer. IT is the same now. That wasn’t something that I really understood when I got out of university. I knew there was a lot to know about IT – I’d just done an honours degree in it. But I also knew that I’d done well in just about all my subjects, and felt like I had a handle on everything. I got into developing, and still felt that having a good level of understanding about every aspect of IT was a good thing. This got me through for the first six or seven years of my career. But then I started to realise that I couldn’t compete. I’d moved into management, and was spending my days running projects, rather than writing code. The kids were getting older. I’d had a bad back injury (ask anyone with chronic pain how it affects  your ability to concentrate, retain information, etc). But most of all, IT was getting larger. I knew kids without lives who knew more than I did. And I felt like I could easily identify people who were better than me in whatever area I could think of. Except writing queries (this was before I discovered technical communities, and people like Paul White and Dave Ballantyne). And so I figured I’d specialise. I wish I’d done it years earlier. Now, I can tell you plenty of people who are better than me at any area you can pick. But there are also more people who might consider listing me in some of their lists too. If I’d stayed the GP, I’d be stuck in management, and finding that there were better managers than me too. If you’re reading this, SQL could well be your thing. But it might not be either. Your thing might not even be in IT. Find out, and then see if you can be a world-beater at it. But it gets even better, because you can find other people to complement the things that you’re not so good at. My company, LobsterPot Solutions, has six people in it at the moment. I’ve hand-picked those six people, along with the one who quit. The great thing about it is that I’ve been able to pick people who don’t necessarily specialise in the same way as me. I don’t write their T-SQL for them – generally they’re good enough at that themselves. But I’m on-hand if needed. Consider Roger Noble, for example. He’s doing stuff in HTML5 and jQuery that I could never dream of doing to create an amazing HTML5 version of PivotViewer. Or Ashley Sewell, a guy who does project management far better than I do. I could go on. My team is brilliant, and I love them to bits. We’re all surgeons, and when we work together, I like to think we’re pretty good! @rob_farley

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  • SQL Azure and Trust Services

    - by BuckWoody
    Microsoft is working on a new Windows Azure service called “Trust Services”. Trust Services takes a certificate you upload and uses it to encrypt and decrypt sensitive data in the cloud. Of course, like any security service, there’s a bit more to it than that. I’ll give you a quick overview of how you can use this product to protect data you send to SQL Azure. The primary issue with storing data in the cloud is that you are in an environment that isn’t under your control – in fact, that’s the benefit of being in a distributed computing environment in the first place. On premises you’re able to encrypt data you don’t want anyone else to see, using various methods such as passwords (not very strong) or certificates (stronger). When you use a certificate, it’s vital that you create (or procure) and protect it yourself. When you store data remotely, regardless of IaaS, PaaS or SaaS, you don’t own the machines where the data lives. That means if you use a certificate from the cloud vendor to encrypt the data, you have to trust that the data won’t be accessed by the vendor. In some cases having a signed agreement with the vendor that they won’t access your data is sufficient, in other cases that doesn’t meet the requirements your system has for security. With the new Trust Services service, the basic process is that you use a Portal to create a Trust Server using policies and other controls. You place a X.509 Certificate you create or procure in that server. Using the Software development Kit (SDK), the developer has access to an Application Layer Encryption Framework to set fields of data they want to encrypt. From there, the data can be stored in SQL Azure as a standard field – only it is encrypted before it ever arrives. The portion of the client software that decrypts the data uses the same service, so the authenticated user sees the data if they are allowed to do so. The data remains encrypted “at rest”.  You can learn more about this product and check it out in the SQL Azure labs at Microsoft Codename "Trust Services"

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  • Less Useful Soft Skills

    - by andyleonard
    Introduction This post is the fifty-sixth part of a ramble-rant about the software business. The current posts in this series can be found on the series landing page . Over a career that spans decades, one encounters useful and “less useful” soft skills in the modern enterprise. I thought I would share a few of the less useful variety: Free Advice If someone asks another for advice, that’s a cool compliment. The person asking has seen something that compels them to seek information about how-another-does-or-sees-things....(read more)

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  • Disqus Comment Form Missing from Posts

    - by Saad
    I decided to transition from IntenseDebate to Disqus for the blog. So I uninstalled ID via their uninstall process (you upload the template to them, they remove code, you reupload your new template onto the site). Then I went to install Disqus into the site through their Blogger widget method. The problem is that there is no comment form present on any of the blog posts' pages. For example, when you click on the 'Comments' link it jumps to #disqus-thread but there is no thread there. So is there any fix that I can do in order to make the comment form appear? I checked Disqus' knowledgebase for Blogger installation but as far as I can tell my template should be compatible.

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  • Oracle Linked Servers on Windows Server 2008 R2

    - by John Paul Cook
    Oracle hasn’t yet released versions of its client software for Windows Server 2008 R2. If you need to create an Oracle linked server, that’s a problem. You’ll see this installation block when attempting to install the Oracle client software for Windows Server 2008: It’s very simple to fix. Check the first checkbox to make the installer ignore the version check. Click Next and ignore the warning you’ll see. The installation should complete successfully. Windows does offer various strategies for mitigating...(read more)

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  • Is your TRY worth catching?

    - by Maria Zakourdaev
      A very useful error handling TRY/CATCH construct is widely used to catch all execution errors  that do not close the database connection. The biggest downside is that in the case of multiple errors the TRY/CATCH mechanism will only catch the last error. An example of this can be seen during a standard restore operation. In this example I attempt to perform a restore from a file that no longer exists. Two errors are being fired: 3201 and 3013: Assuming that we are using the TRY and CATCH construct, the ERROR_MESSAGE() function will catch the last message only: To workaround this problem you can prepare a temporary table that will receive the statement output. Execute the statement inside the xp_cmdshell stored procedure, connect back to the SQL Server using the command line utility sqlcmd and redirect it's output into the previously created temp table.  After receiving the output, you will need to parse it to understand whether the statement has finished successfully or failed. It’s quite easy to accomplish as long as you know which statement was executed. In the case of generic executions you can query the output table and search for words like“Msg%Level%State%” that are usually a part of the error message.Furthermore, you don’t need TRY/CATCH in the above workaround, since the xp_cmdshell procedure always finishes successfully and you can decide whether to fire the RAISERROR statement or not. Yours, Maria

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  • Microsoft Assessment and Planning (MAP) Toolkit 5.0 Beta

    - by Lara Rubbelke
    Do you know where SQL Server is installed - everywhere it is installed? Do you really know where SQL Server is installed? Are you looking for a tool that will help you discover any rogue instances so you can better manage these instances? The Beta 2 for the Microsoft Assessment and Planning (MAP) Toolkit 5.0 is now open. Join the beta review program and help influence the development of the toolkit. To participate, register for the MAP Toolkit 5.0 Beta 2 at Microsoft Connect. The MAP Toolkit 5.0...(read more)

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  • OT: Thank You, Microsoft

    - by andyleonard
    cross-posted from AndyLeonard.me … Each April 1st for the past five years, I have been honored to receive an email from Microsoft informing me I have been recognized as a SQL Server MVP. Tomorrow will be different. Back in January – when I wrote this – I requested Microsoft not consider me for renewal. I have enjoyed serving as a Microsoft MVP. I only got to see what it is like to be a SQL Server MVP, and I think we are part of a special community that makes being an MVP even more special. I have...(read more)

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  • Possible SWITCH Optimization in DAX – #powerpivot #dax #tabular

    - by Marco Russo (SQLBI)
    In one of the Advanced DAX Workshop I taught this year, I had an interesting discussion about how to optimize a SWITCH statement (which could be frequently used checking a slicer, like in the Parameter Table pattern). Let’s start with the problem. What happen when you have such a statement? Sales :=     SWITCH (         VALUES ( Period[Period] ),         "Current", [Internet Total Sales],         "MTD", [MTD Sales],         "QTD", [QTD Sales],         "YTD", [YTD Sales],          BLANK ()     ) The SWITCH statement is in reality just syntax sugar for a nested IF statement. When you place such a measure in a pivot table, for every cell of the pivot table the IF options are evaluated. In order to optimize performance, the DAX engine usually does not compute cell-by-cell, but tries to compute the values in bulk-mode. However, if a measure contains an IF statement, every cell might have a different execution path, so the current implementation might evaluate all the possible IF branches in bulk-mode, so that for every cell the result from one of the branches will be already available in a pre-calculated dataset. The price for that could be high. If you consider the previous Sales measure, the YTD Sales measure could be evaluated for all the cells where it’s not required, and also when YTD is not selected at all in a Pivot Table. The actual optimization made by the DAX engine could be different in every build, and I expect newer builds of Tabular and Power Pivot to be better than older ones. However, we still don’t live in an ideal world, so it could be better trying to help the engine finding a better execution plan. One student (Niek de Wit) proposed this approach: Selection := IF (     HASONEVALUE ( Period[Period] ),     VALUES ( Period[Period] ) ) Sales := CALCULATE (     [Internet Total Sales],     FILTER (         VALUES ( 'Internet Sales'[Order Quantity] ),         'Internet Sales'[Order Quantity]             = IF (                 [Selection] = "Current",                 'Internet Sales'[Order Quantity],                 -1             )     ) )     + CALCULATE (         [MTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "MTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [QTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "QTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     )     + CALCULATE (         [YTD Sales],         FILTER (             VALUES ( 'Internet Sales'[Order Quantity] ),             'Internet Sales'[Order Quantity]                 = IF (                     [Selection] = "YTD",                     'Internet Sales'[Order Quantity],                     -1                 )         )     ) At first sight, you might think it’s impossible that this approach could be faster. However, if you examine with the profiler what happens, there is a different story. Every original IF’s execution branch is now a separate CALCULATE statement, which applies a filter that does not execute the required measure calculation if the result of the FILTER is empty. I used the ‘Internet Sales’[Order Quantity] column in this example just because in Adventure Works it has only one value (every row has 1): in the real world, you should use a column that has a very low number of distinct values, or use a column that has always the same value for every row (so it will be compressed very well!). Because the value –1 is never used in this column, the IF comparison in the filter discharge all the values iterated in the filter if the selection does not match with the desired value. I hope to have time in the future to write a longer article about this optimization technique, but in the meantime I’ve seen this optimization has been useful in many other implementations. Please write your feedback if you find scenarios (in both Power Pivot and Tabular) where you obtain performance improvements using this technique!

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  • Fun with Aggregates

    - by Paul White
    There are interesting things to be learned from even the simplest queries.  For example, imagine you are given the task of writing a query to list AdventureWorks product names where the product has at least one entry in the transaction history table, but fewer than ten. One possible query to meet that specification is: SELECT p.Name FROM Production.Product AS p JOIN Production.TransactionHistory AS th ON p.ProductID = th.ProductID GROUP BY p.ProductID, p.Name HAVING COUNT_BIG(*) < 10; That query correctly returns 23 rows (execution plan and data sample shown below): The execution plan looks a bit different from the written form of the query: the base tables are accessed in reverse order, and the aggregation is performed before the join.  The general idea is to read all rows from the history table, compute the count of rows grouped by ProductID, merge join the results to the Product table on ProductID, and finally filter to only return rows where the count is less than ten. This ‘fully-optimized’ plan has an estimated cost of around 0.33 units.  The reason for the quote marks there is that this plan is not quite as optimal as it could be – surely it would make sense to push the Filter down past the join too?  To answer that, let’s look at some other ways to formulate this query.  This being SQL, there are any number of ways to write logically-equivalent query specifications, so we’ll just look at a couple of interesting ones.  The first query is an attempt to reverse-engineer T-SQL from the optimized query plan shown above.  It joins the result of pre-aggregating the history table to the Product table before filtering: SELECT p.Name FROM ( SELECT th.ProductID, cnt = COUNT_BIG(*) FROM Production.TransactionHistory AS th GROUP BY th.ProductID ) AS q1 JOIN Production.Product AS p ON p.ProductID = q1.ProductID WHERE q1.cnt < 10; Perhaps a little surprisingly, we get a slightly different execution plan: The results are the same (23 rows) but this time the Filter is pushed below the join!  The optimizer chooses nested loops for the join, because the cardinality estimate for rows passing the Filter is a bit low (estimate 1 versus 23 actual), though you can force a merge join with a hint and the Filter still appears below the join.  In yet another variation, the < 10 predicate can be ‘manually pushed’ by specifying it in a HAVING clause in the “q1” sub-query instead of in the WHERE clause as written above. The reason this predicate can be pushed past the join in this query form, but not in the original formulation is simply an optimizer limitation – it does make efforts (primarily during the simplification phase) to encourage logically-equivalent query specifications to produce the same execution plan, but the implementation is not completely comprehensive. Moving on to a second example, the following query specification results from phrasing the requirement as “list the products where there exists fewer than ten correlated rows in the history table”: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) < 10 ); Unfortunately, this query produces an incorrect result (86 rows): The problem is that it lists products with no history rows, though the reasons are interesting.  The COUNT_BIG(*) in the EXISTS clause is a scalar aggregate (meaning there is no GROUP BY clause) and scalar aggregates always produce a value, even when the input is an empty set.  In the case of the COUNT aggregate, the result of aggregating the empty set is zero (the other standard aggregates produce a NULL).  To make the point really clear, let’s look at product 709, which happens to be one for which no history rows exist: -- Scalar aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709;   -- Vector aggregate SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = 709 GROUP BY th.ProductID; The estimated execution plans for these two statements are almost identical: You might expect the Stream Aggregate to have a Group By for the second statement, but this is not the case.  The query includes an equality comparison to a constant value (709), so all qualified rows are guaranteed to have the same value for ProductID and the Group By is optimized away. In fact there are some minor differences between the two plans (the first is auto-parameterized and qualifies for trivial plan, whereas the second is not auto-parameterized and requires cost-based optimization), but there is nothing to indicate that one is a scalar aggregate and the other is a vector aggregate.  This is something I would like to see exposed in show plan so I suggested it on Connect.  Anyway, the results of running the two queries show the difference at runtime: The scalar aggregate (no GROUP BY) returns a result of zero, whereas the vector aggregate (with a GROUP BY clause) returns nothing at all.  Returning to our EXISTS query, we could ‘fix’ it by changing the HAVING clause to reject rows where the scalar aggregate returns zero: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID HAVING COUNT_BIG(*) BETWEEN 1 AND 9 ); The query now returns the correct 23 rows: Unfortunately, the execution plan is less efficient now – it has an estimated cost of 0.78 compared to 0.33 for the earlier plans.  Let’s try adding a redundant GROUP BY instead of changing the HAVING clause: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY th.ProductID HAVING COUNT_BIG(*) < 10 ); Not only do we now get correct results (23 rows), this is the execution plan: I like to compare that plan to quantum physics: if you don’t find it shocking, you haven’t understood it properly :)  The simple addition of a redundant GROUP BY has resulted in the EXISTS form of the query being transformed into exactly the same optimal plan we found earlier.  What’s more, in SQL Server 2008 and later, we can replace the odd-looking GROUP BY with an explicit GROUP BY on the empty set: SELECT p.Name FROM Production.Product AS p WHERE EXISTS ( SELECT * FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ); I offer that as an alternative because some people find it more intuitive (and it perhaps has more geek value too).  Whichever way you prefer, it’s rather satisfying to note that the result of the sub-query does not exist for a particular correlated value where a vector aggregate is used (the scalar COUNT aggregate always returns a value, even if zero, so it always ‘EXISTS’ regardless which ProductID is logically being evaluated). The following query forms also produce the optimal plan and correct results, so long as a vector aggregate is used (you can probably find more equivalent query forms): WHERE Clause SELECT p.Name FROM Production.Product AS p WHERE ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) < 10; APPLY SELECT p.Name FROM Production.Product AS p CROSS APPLY ( SELECT NULL FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () HAVING COUNT_BIG(*) < 10 ) AS ca (dummy); FROM Clause SELECT q1.Name FROM ( SELECT p.Name, cnt = ( SELECT COUNT_BIG(*) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID GROUP BY () ) FROM Production.Product AS p ) AS q1 WHERE q1.cnt < 10; This last example uses SUM(1) instead of COUNT and does not require a vector aggregate…you should be able to work out why :) SELECT q.Name FROM ( SELECT p.Name, cnt = ( SELECT SUM(1) FROM Production.TransactionHistory AS th WHERE th.ProductID = p.ProductID ) FROM Production.Product AS p ) AS q WHERE q.cnt < 10; The semantics of SQL aggregates are rather odd in places.  It definitely pays to get to know the rules, and to be careful to check whether your queries are using scalar or vector aggregates.  As we have seen, query plans do not show in which ‘mode’ an aggregate is running and getting it wrong can cause poor performance, wrong results, or both. © 2012 Paul White Twitter: @SQL_Kiwi email: [email protected]

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  • Oracle Product Leader Named a Leader in Gartner MQ for MDM of Product Data Solutions

    - by Mala Narasimharajan
    Gartner recently Oracle as a leader in the MQ report for MDM of Product Data Solutions.  They named Oracle as a leader with the following key points:  Strong MDM portfolio covering multiple data domains, industries and use cases Oracle PDH can be a good fit for Oracle EBS customers and can form part of a multidomain solution: Deep MDM of product data functionality Evolving support for information stewardship For  more information on the report visit Oracle's Analyst Relations blog at  http://blog.us.oracle.com/dimdmar/.  To learn more about Oracle's product information solutions for master data management click here. 

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  • Reproducing a Conversion Deadlock

    - by Alexander Kuznetsov
    Even if two processes compete on only one resource, they still can embrace in a deadlock. The following scripts reproduce such a scenario. In one tab, run this: CREATE TABLE dbo.Test ( i INT ) ; GO INSERT INTO dbo.Test ( i ) VALUES ( 1 ) ; GO SET TRANSACTION ISOLATION LEVEL SERIALIZABLE ; BEGIN TRAN SELECT i FROM dbo.Test ; --UPDATE dbo.Test SET i=2 ; After this script has completed, we have an outstanding transaction holding a shared lock. In another tab, let us have that another connection have...(read more)

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  • Windows 8 SDK and Orca

    - by John Paul Cook
    The Windows 8 SDK has a new version of Orca for those of us who edit msi files. The download is for a small executable, sdksetup.exe which causes the following dialog box to appear. If you only want Orca and you don’t want to install the SDK, override the default and download all of the files to the location of your choice. In this example, the files are downloaded to D:\Media\Windows8\SDK Figure 1. Downloading the Windows 8 SDK to D:\Media\Windows8\SDK instead of installing it. Click the D ownload...(read more)

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  • The updated Survey pattern for Power Pivot and Tabular #powerpivot #tabular #ssas #dax

    - by Marco Russo (SQLBI)
    One of the first models I created for the many-to-many revolution white paper was the Survey one. At the time, it was in Analysis Services Multidimensional, and then we implemented it in Analysis Services Tabular and in Power Pivot, using the DAX language. I recently reviewed the data model and published it in the Survey article on DAX Patterns site. The Survey pattern is the foundation for others, such as the Basket Analysis, and it is widely used in many different business scenario. I was particularly happy to know it has been using to perform data analysis for cancer research! In this article I did some maintenance on the DAX formulas, checking that the proper error handling is part of the formulas, and highlighting some differences in slicers behavior between Excel 2010 and Excel 2013, which could be particularly important for the Survey scenario. As usual, we provide sample workbooks for both Excel 2010 and Excel 2013, and we use DAX Formatter to make the DAX code easier to read. Any feedback will be appreciated!

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  • Update from Ola Hallengren: Target multiple devices during SQL Server backup

    - by Greg Low
    Ola has produced another update of his database management scripts. If you haven't taken a look at them, you should. At the very least, they'll give you good ideas about what to implement and how others have done so. The latest update allows targeting multiple devices during backup. This is available in native SQL Server backup and can be helpful with very large databases. Ola's scripts now support it as well.Details are here: http://ola.hallengren.com/sql-server-backup.html http://ola.hallengren.com/versions.html The following example shows it backing up to 4 files on 4 drives, one file on each drive:EXECUTE dbo.DatabaseBackup@Databases = 'USER_DATABASES',@Directory = 'C:\Backup, D:\Backup, E:\Backup, F:\Backup',@BackupType = 'FULL',@Compress = 'Y',@NumberOfFiles = 4And this example shows backing up to 16 files on 4 drives, 4 files on each drive: EXECUTE dbo.DatabaseBackup@Databases = 'USER_DATABASES',@Directory = 'C:\Backup, D:\Backup, E:\Backup, F:\Backup',@BackupType = 'FULL',@Compress = 'Y',@NumberOfFiles = 16Ola mentioned that you can now back up to up to 64 drives. 

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