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• July, the 31 Days of SQL Server DMO’s – Day 25 (sys.dm_db_missing_index_details)

  - by Tamarick Hill

  The sys.dm_db_missing_index_details Dynamic Management View is used to return information about missing indexes on your SQL Server instances. These indexes are ones that the optimizer has identified as indexes it would like to use but did not have. You may also see these same indexes indicated in other tools such as query execution plans or the Database tuning advisor. Let’s execute this DMV so we can review the information it provides us. I do not have any missing index information for my AdventureWorks2012 database, but for the purposes of illustrating the result set of this DMV, I will present the results from my msdb database. SELECT * FROM sys.dm_db_missing_index_details The first column presented is the index_handle which uniquely identifies a particular missing index. The next two columns represent the database_id and the object_id for the particular table in question. Next is the ‘equality_columns’ column which gives you a list of columns (comma separated) that would be beneficial to the optimizer for equality operations. By equality operation I mean for any queries that would use a filter or join condition such as WHERE A = B. The next column, ‘inequality_columns’, gives you a comma separated list of columns that would be beneficial to the optimizer for inequality operations. An inequality operation is anything other than A = B. For example, “WHERE A != B”, “WHERE A > B”, “WHERE A < B”, and “WHERE A <> B” would all qualify as inequality. Next is the ‘included_columns’ column which list all columns that would be beneficial to the optimizer for purposes of providing a covering index and preventing key/bookmark lookups. Lastly is the ‘statement’ column which lists the name of the table where the index is missing. This DMV can help you identify potential indexes that could be added to improve the performance of your system. However, I will advise you not to just take the output of this DMV and create an index for everything you see. Everything listed here should be analyzed and then tested on a Development or Test system before implementing into a Production environment. For more information on this DMV, please see the below Books Online link: http://msdn.microsoft.com/en-us/library/ms345434.aspx Follow me on Twitter @PrimeTimeDBA

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• Application Performance: The Best of the Web

  - by Michaela Murray

  Wisdom A deep understanding and realization […] resulting in the ability to apply perceptions, judgements and actions. It is also the comprehension of what is true coupled with optimum judgment as to action. - Wikipedia We’re writing a book for ASP.NET developers, and we want you to be a part of it. We know that there’s a huge amount of web developer wisdom that never gets shared, and we want to find those golden nuggets of knowledge and experience, and make sure everyone can learn from them. Right now, we want to find out about your top tips, hard-won lessons, and sage advice for avoiding, finding, and fixing application performance problems. If you work with .NET and SQL, even better – a lot of application performance relies on the interaction with the database, so we want to hear from you! “How Do You Want Me To Be Involved?” Right! Details! We want you, our most excellent readers, to email us with the Best Advice you would give to other developers for getting the best performance out of their applications. It doesn’t matter if your advice is for newbies or veterans, .NET or SQL – so long as it’s about application performance, we want to hear from you. (And if you think that there’s developer wisdom out there that “everyone knows”, a) I’m willing to bet you could find someone who doesn’t know about it, and b) it probably bears repeating anyway!) “I’m Interested. What Can You Do For Me?” Excellent question. For starters, there’s a chance to win a Microsoft Surface (the tablet, not the table-top). Once all the ASP.NET Wisdom has been collected, tallied, and labelled, it will then be weighed and measured by a team of expert judges (whose identities are still a closely-guarded secret).  The top tip in both SQL & .NET categories will each win their author their very own MS Surface. But that’s not all! We can also give you… immortality! More details? Ok. We’ll be collecting all of the tips sent in by our readers (and we can’t wait to learn from you all,) and with the help of our Simple-Talk editors, we will publish and distribute your combined and documented knowledge as a free, community-created, professionally typeset eBook. You will naturally be credited by name / pseudonym / twitter handle / GitHub username / StackOverflow profile / Whatever, as the clearly ingenious author of hot performance tips. The Not-Very-Fine Print Here’s the breakdown: We want to bring together the best application performance knowledge from ASP.NET developers. Closing date for submissions will be 9am GMT, December 4th. Submissions should be made by email – [email protected] Submissions will be judged by a panel of expert judges (who will be revealed soon). The top submission in both the SQL & .NET categories will each win a Microsoft Surface. ALL the tips which make it through the judging process will be polished by Simple-Talk editors, and turned into a professionally typeset eBook, which will be freely available, and promoted alongside the ANTS Performance Profiler tool. Anyone whose entry makes it into the book will be clearly and profusely credited in the method of their choice (or can remain anonymous.) The really REALLY short version Share what you know about ASP.NET application performance for a chance to win a Microsoft Surface, and then get your name credited in a slick eBook with top-notch production values. For more details, see above. We can’t wait to learn from you!

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• Failing report subscriptions

  - by DavidWimbush

  We had an interesting problem while I was on holiday. (Why doesn't this stuff ever happen when I'm there?) The sysadmin upgraded our Exchange server to Exchange 2010 and everone's subscriptions stopped. My Subscriptions showed an error message saying that the email address of one of the recipients is invalid. When you create a subscription, Reporting puts your Windows user name into the To field and most users have no permissions to edit it. By default, Reporting leaves it up to exchange to resolve that into an email address. This only works if Exchange is set up to translate aliases or 'short names' into email addresses. It turns out this leaves Exchange open to being used as a relay so it is disabled out of the box. You now have three options: Open up Exchange. That would be bad. Give all Reporting users the ability to edit the To field in a subscription. a) They shouldn't have to, it should just work. b) They don't really have any business subscribing anyone but themselves. Fix the report server to add the domain. This looks like the right choice and it works for us. See below for details. Pre-requisites: A single email domain name. A clear relationship between the Windows user name and the email address. eg. If the user name is joebloggs, then joebloggs@domainname needs to be the email address or an alias of it. Warning: Saving changes to the rsreportserver.config file will restart the Report Server service which effectively takes Reporting down for around 30 seconds. Time your action accordingly. Edit the file rsreportserver.config (most probably in the folder ..\Program Files[ (x86)]\Microsoft SQL Server\MSRS10_50[.instancename]\Reporting Services\ReportServer). There's a setting called DefaultHostName which is empty by default. Enter your email domain name without the leading '@'. Save the file. This domain name will be appended to any destination addresses that don't have a domain name of their own.

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• SQL Server Date Comparison Functions

  - by HighAltitudeCoder

  A few months ago, I found myself working with a repetitive cursor that looped until the data had been manipulated enough times that it was finally correct.  The cursor was heavily dependent upon dates, every time requiring the earlier of two (or several) dates in one stored procedure, while requiring the later of two dates in another stored procedure. In short what I needed was a function that would allow me to perform the following evaluation: WHERE MAX(Date1, Date2) < @SomeDate The problem is, the MAX() function in SQL Server does not perform this functionality.  So, I set out to put these functions together.  They are titled: EarlierOf() and LaterOf(). /**********************************************************                               EarlierOf.sql   **********************************************************/ /**********************************************************   Return the later of two DATETIME variables.   Parameter 1: DATETIME1 Parameter 2: DATETIME2   Works for a variety of DATETIME or NULL values. Even though comparisons with NULL are actually indeterminate, we know conceptually that NULL is not earlier or later than any other date provided.   SYNTAX: SELECT dbo.EarlierOf('1/1/2000','12/1/2009') SELECT dbo.EarlierOf('2009-12-01 00:00:00.000','2009-12-01 00:00:00.521') SELECT dbo.EarlierOf('11/15/2000',NULL) SELECT dbo.EarlierOf(NULL,'1/15/2004') SELECT dbo.EarlierOf(NULL,NULL)   **********************************************************/ USE AdventureWorks GO   IF EXISTS       (SELECT *       FROM sysobjects       WHERE name = 'EarlierOf'       AND xtype = 'FN'       ) BEGIN             DROP FUNCTION EarlierOf END GO   CREATE FUNCTION EarlierOf (       @Date1                              DATETIME,       @Date2                              DATETIME )   RETURNS DATETIME   AS BEGIN       DECLARE @ReturnDate     DATETIME         IF (@Date1 IS NULL AND @Date2 IS NULL)       BEGIN             SET @ReturnDate = NULL             GOTO EndOfFunction       END         ELSE IF (@Date1 IS NULL AND @Date2 IS NOT NULL)       BEGIN             SET @ReturnDate = @Date2             GOTO EndOfFunction       END         ELSE IF (@Date1 IS NOT NULL AND @Date2 IS NULL)       BEGIN             SET @ReturnDate = @Date1             GOTO EndOfFunction       END         ELSE       BEGIN             SET @ReturnDate = @Date1             IF @Date2 < @Date1                   SET @ReturnDate = @Date2             GOTO EndOfFunction       END         EndOfFunction:       RETURN @ReturnDate   END -- End Function GO   ---- Set Permissions --GRANT SELECT ON EarlierOf TO UserRole1 --GRANT SELECT ON EarlierOf TO UserRole2 --GO                                                                                             The inverse of this function is only slightly different. /**********************************************************                               LaterOf.sql   **********************************************************/ /**********************************************************   Return the later of two DATETIME variables.   Parameter 1: DATETIME1 Parameter 2: DATETIME2   Works for a variety of DATETIME or NULL values. Even though comparisons with NULL are actually indeterminate, we know conceptually that NULL is not earlier or later than any other date provided.   SYNTAX: SELECT dbo.LaterOf('1/1/2000','12/1/2009') SELECT dbo.LaterOf('2009-12-01 00:00:00.000','2009-12-01 00:00:00.521') SELECT dbo.LaterOf('11/15/2000',NULL) SELECT dbo.LaterOf(NULL,'1/15/2004') SELECT dbo.LaterOf(NULL,NULL)   **********************************************************/ USE AdventureWorks GO   IF EXISTS       (SELECT *       FROM sysobjects       WHERE name = 'LaterOf'       AND xtype = 'FN'       ) BEGIN             DROP FUNCTION LaterOf END GO   CREATE FUNCTION LaterOf (       @Date1                              DATETIME,       @Date2                              DATETIME )   RETURNS DATETIME   AS BEGIN       DECLARE @ReturnDate     DATETIME         IF (@Date1 IS NULL AND @Date2 IS NULL)       BEGIN             SET @ReturnDate = NULL             GOTO EndOfFunction       END         ELSE IF (@Date1 IS NULL AND @Date2 IS NOT NULL)       BEGIN             SET @ReturnDate = @Date2             GOTO EndOfFunction       END         ELSE IF (@Date1 IS NOT NULL AND @Date2 IS NULL)       BEGIN             SET @ReturnDate = @Date1             GOTO EndOfFunction       END         ELSE       BEGIN             SET @ReturnDate = @Date1             IF @Date2 > @Date1                   SET @ReturnDate = @Date2             GOTO EndOfFunction       END         EndOfFunction:       RETURN @ReturnDate   END -- End Function GO   ---- Set Permissions --GRANT SELECT ON LaterOf TO UserRole1 --GRANT SELECT ON LaterOf TO UserRole2 --GO                                                                                             The interesting thing about this function is its simplicity and the built-in NULL handling functionality.  Its interesting, because it seems like something should already exist in SQL Server that does this.  From a different vantage point, if you create this functionality and it is easy to use (ideally, intuitively self-explanatory), you have made a successful contribution. Interesting is good.  Self-explanatory, or intuitive is FAR better.  Happy coding! Graeme

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• Advanced Record-Level Business Intelligence with Inner Queries

  - by gt0084e1

  While business intelligence is generally applied at an aggregate level to large data sets, it's often useful to provide a more streamlined insight into an individual records or to be able to sort and rank them. For instance, a salesperson looking at a specific customer could benefit from basic stats on that account. A marketer trying to define an ideal customer could pull the top entries and look for insights or patterns. Inner queries let you do sophisticated analysis without the overhead of traditional BI or OLAP technologies like Analysis Services. Example - Order History Constancy Let's assume that management has realized that the best thing for our business is to have customers ordering every month. We'll need to identify and rank customers based on how consistently they buy and when their last purchase was so sales & marketing can respond accordingly. Our current application may not be able to provide this and adding an OLAP server like SSAS may be overkill for our needs. Luckily, SQL Server provides the ability to do relatively sophisticated analytics via inner queries. Here's the kind of output we'd like to see. Creating the Queries Before you create a view, you need to create the SQL query that does the calculations. Here we are calculating the total number of orders as well as the number of months since the last order. These fields might be very useful to sort by but may not be available in the app. This approach provides a very streamlined and high performance method of delivering actionable information without radically changing the application. It's also works very well with self-service reporting tools like Izenda. SELECT CustomerID,CompanyName, ( SELECT COUNT(OrderID) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID ) As Orders, DATEDIFF(mm, ( SELECT Max(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) ,getdate() ) AS MonthsSinceLastOrder FROM Customers Creating Views To turn this or any query into a view, just put CREATE VIEW AS before it. If you want to change it use the statement ALTER VIEW AS. Creating Computed Columns If you'd prefer not to create a view, inner queries can also be applied by using computed columns. Place you SQL in the (Formula) field of the Computed Column Specification or check out this article here. Advanced Scoring and Ranking One of the best uses for this approach is to score leads based on multiple fields. For instance, you may be in a business where customers that don't order every month require more persistent follow up. You could devise a simple formula that shows the continuity of an account. If they ordered every month since their first order, they would be at 100 indicating that they have been ordering 100% of the time. Here's the query that would calculate that. It uses a few SQL tricks to make this happen. We are extracting the count of unique months and then dividing by the months since initial order. This query will give you the following information which can be used to help sales and marketing now where to focus. You could sort by this percentage to know where to start calling or to find patterns describing your best customers. Number of orders First Order Date Last Order Date Percentage of months order was placed since last order. SELECT CustomerID, (SELECT COUNT(OrderID) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) As Orders, (SELECT Max(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) AS LastOrder, (SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) AS FirstOrder, DATEDIFF(mm,(SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID),getdate()) AS MonthsSinceFirstOrder, 100*(SELECT COUNT(DISTINCT 100*DATEPART(yy,OrderDate) + DATEPART(mm,OrderDate)) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID) / DATEDIFF(mm,(SELECT Min(OrderDate) FROM Orders WHERE Orders.CustomerID = Customers.CustomerID),getdate()) As OrderPercent FROM Customers

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• Good DBAs Do Baselines

  - by Louis Davidson

  One morning, you wake up and feel funny. You can’t quite put your finger on it, but something isn’t quite right. What now? Unless you happen to be a hypochondriac, you likely drag yourself out of bed, get on with the day and gather more “evidence”. You check your symptoms over the next few days; do you feel the same, better, worse? If better, then great, it was some temporal issue, perhaps caused by an allergic reaction to some suspiciously spicy chicken. If the same or worse then you go to the doctor for some health advice, but armed with some data to share, and having ruled out certain possible causes that are fixed with a bit of rest and perhaps an antacid. Whether you realize it or not, in comparing how you feel one day to the next, you have taken baseline measurements. In much the same way, a DBA uses baselines to gauge the gauge health of their database servers. Of course, while SQL Server is very willing to share data regarding its health and activities, it has almost no idea of the difference between good and bad. Over time, experienced DBAs develop “mental” baselines with which they can gauge the health of their servers almost as easily as their own body. They accumulate knowledge of the daily, natural state of each part of their database system, and so know instinctively when one of their databases “feels funny”. Equally, they know when an “issue” is just a passing tremor. They see their SQL Server with all of its four CPU cores running close 100% and don’t panic anymore. Why? It’s 5PM and every day the same thing occurs when the end-of-day reports, which are very CPU intensive, are running. Equally, they know when they need to respond in earnest when it is the first time they have heard about an issue, even if it has been happening every day. Nevertheless, no DBA can retain mental baselines for every characteristic of their systems, so we need to collect physical baselines too. In my experience, surprisingly few DBAs do this very well. Part of the problem is that SQL Server provides a lot of instrumentation. If you look, you will find an almost overwhelming amount of data regarding user activity on your SQL Server instances, and use and abuse of the available CPU, I/O and memory. It seems like a huge task even to work out which data you need to collect, let alone start collecting it on a regular basis, managing its storage over time, and performing detailed comparative analysis. However, without baselines, though, it is very difficult to pinpoint what ails a server, just by looking at a single snapshot of the data, or to spot retrospectively what caused the problem by examining aggregated data for the server, collected over many months. It isn’t as hard as you think to get started. You’ve probably already established some troubleshooting queries of the type SELECT Value FROM SomeSystemTableOrView. Capturing a set of baseline values for such a query can be as easy as changing it as follows: INSERT into BaseLine.SomeSystemTable (value, captureTime) SELECT Value, SYSDATETIME() FROM SomeSystemTableOrView; Of course, there are monitoring tools that will collect and manage this baseline data for you, automatically, and allow you to perform comparison of metrics over different periods. However, to get yourself started and to prove to yourself (or perhaps the person who writes the checks for tools) the value of baselines, stick something similar to the above query into an agent job, running every hour or so, and you are on your way with no excuses! Then, the next time you investigate a slow server, and see x open transactions, y users logged in, and z rows added per hour in the Orders table, compare to your baselines and see immediately what, if anything, has changed!

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• Pay in the future should make you think in the present

  - by BuckWoody

  Distributed Computing - and more importantly “-as-a-Service” models of computing have a different cost model. This is something that sounds obvious on the surface but it’s often forgotten during the design and coding phase of a project. In on-premises computing, we’re used to purchasing a server and all of the hardware infrastructure and software licenses needed not only for one project, but several. This is an up-front or “sunk” cost that we consume by running code the organization needs to perform its function. Using a direct connection over wires you’ve already paid for, we don’t often have to think about bandwidth, hits on the data store or the amount of compute we use - we just know more is better. In a pay-as-you-go model, however, each of these architecture decisions has a potential cost impact. The amount of data you store, the number of times you access it, and the amount you send back all come with a charge. The offset is that you don’t buy anything at all up-front, so that sunk cost is freed up. And financial professionals know that money now is worth more than money later. Saving that up-front cost allows you to invest it in other things. It’s not just that you’re using things that now cost money - it’s that the design itself in distributed computing has a cost impact. That can be a really good thing, such as when you dynamically add capacity for paying customers. If you can tie back the cost of a series of clicks to what a user will pay to do so, you can set a profit margin that is easy to track. Here’s a case in point: Assume you are using a large instance in Windows Azure to compute some data that you retrieve from a SQL Azure database. If you don’t monitor the path of the application, you may not know what you are really using. Since you’re paying by the size of the instance, it’s best to maximize it all the time. Recently I evaluated just this situation, and found that downsizing the instance and adding another one where needed, adding a caching function to the application, moving part of the data into Windows Azure tables not only increased the speed of the application, but reduced the cost and more closely tied the cost to the profit. The key is this: from the very outset - the design - make sure you include metrics to measure for the cost/performance (sometimes these are the same) for your application. Windows Azure opens up awesome new ways of doing things, so make sure you study distributed systems architecture before you try and force in the application design you have on premises into your new application structure.

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• When a problem is resolved

  - by Rob Farley

  This month’s T-SQL Tuesday is hosted by Jen McCown, and she’s picked the topic of Resolutions. It’s a new year, and she’s thinking about what people have resolved to do this year. Unfortunately, I’ve never really done resolutions like that. I see too many people resolve to quit smoking, or lose weight, or whatever, and fail miserably. I’m not saying I don’t set goals, but it’s not a thing for New Year. The obvious joke is “1920x1080” as a resolution, but I’m not going there. I think Resolving is a strange word. It makes it sound like I’m having to solve a problem a second time, when actually, it’s more along the lines of solving a problem well enough for it to count as finished. If something has been resolved, a solution has been provided. There is a resolution, through the provision of a solution. It’s a strangeness of English. When I look up the word resolution at dictionary.com, it has 12 options, including “settling of a problem”. There’s a finality about resolution. If you resolve to do something, you’re saying “Yes. This is a done thing. I’m resolving to do it, which means that it may as well be complete already.” I like to think I resolve problems, rather than just solving them. I want my solving to be final and complete. If I tune a query, I don’t want to find that I’m back in there, re-tuning it at some point. Strangely, if I re-solve a problem, that implies that I didn’t resolve it in the first place. I only solved it. Temporarily. We “data-folk” live in a world where the most common answer is “It depends.” Frustratingly, the thing an answer depends on may still be changing in the system in question. That probably means that any solution that is put in place may need reinvestigating at some point later. So do I resolve things? Yes. Am I Chuck Norris, and solve things so well the world would break first? No. Do these two claims happily sit beside each other? No, unfortunately not. But I happily take responsibility for things, and let my clients depend on me to see it through. As far as they are concerned, it is resolved. And so I resolve to keep resolving, right through 2011.

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• Sampling SQL server batch activity

  - by extended_events

  Recently I was troubleshooting a performance issue on an internal tracking workload and needed to collect some very low level events over a period of 3-4 hours.  During analysis of the data I found that a common pattern I was using was to find a batch with a duration that was longer than average and follow all the events it produced.  This pattern got me thinking that I was discarding a substantial amount of event data that had been collected, and that it would be great to be able to reduce the collection overhead on the server if I could still get all activity from some batches. In the past I’ve used a sampling technique based on the counter predicate to build a baseline of overall activity (see Mikes post here).  This isn’t exactly what I want though as there would certainly be events from a particular batch that wouldn’t pass the predicate.  What I need is a way to identify streams of work and select say one in ten of them to watch, and sql server provides just such a mechanism: session_id.  Session_id is a server assigned integer that is bound to a connection at login and lasts until logout.  So by combining the session_id predicate source and the divides_by_uint64 predicate comparator we can limit collection, and still get all the events in batches for investigation. CREATE EVENT SESSION session_10_percent ON SERVER ADD EVENT sqlserver.sql_statement_starting(     WHERE (package0.divides_by_uint64(sqlserver.session_id,10))), ADD EVENT sqlos.wait_info (        WHERE (package0.divides_by_uint64(sqlserver.session_id,10))), ADD EVENT sqlos.wait_info_external (        WHERE (package0.divides_by_uint64(sqlserver.session_id,10))), ADD EVENT sqlserver.sql_statement_completed(     WHERE (package0.divides_by_uint64(sqlserver.session_id,10))) ADD TARGET ring_buffer WITH (MAX_DISPATCH_LATENCY=30 SECONDS,TRACK_CAUSALITY=ON) GO   There we go; event collection is reduced while still providing enough information to find the root of the problem.  By the way the performance issue turned out to be an IO issue, and the session definition above was more than enough to show long waits on PAGEIOLATCH*.        

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• Testing and Validation – You Really Do Have The Time

  - by BuckWoody

  One of the great advantages in my role as a Technical Specialist here at Microsoft is that I get to work with so many great clients. I get to see their environments and how they use them, and the way they work with SQL Server. I’ve been a data professional myself for many years. Over that time I’ve worked with many database platforms, lots of client applications, and written a lot of code in many industries. For a while I was also a consultant, so I got to see how other shops did things as well. But because I now focus on a “set” base of clients (over 500 professionals in over 150 companies) I get to see them over a longer period of time. Many of them help me understand how they use the product in their projects, and I even attend some DBA regular meetings. I see the way the product succeeds, and I see when it fails. Something that has really impacted my way of thinking is the level of importance any given shop is able to place on testing and validation. I’ve always been a big proponent of setting up a test system and following a very disciplined regimen to make sure it will work in production for any new projects, and then taking the lessons learned into production as standards. I know, I know – there’s never enough time to do things right like this. Yet the shops I see that do it have the same level of work that they output as the shops that don’t. They just make the time to do the testing and validation and create a standard that they will follow in production. And what I’ve found (surprise surprise) is that they have fewer production problems. OK, that might seem obvious – but I’ve actually tracked it and those places that do the testing and best practices really do save stress, time and trouble from that effort. We all think that’s a good idea, but we just “don’t have time”. OK – but from what I’m seeing, you can gain time if you spend a little up front. You may find that you’re actually already spending the same amount of time that you would spend in doing the testing, you’re just doing it later, at night, under the gun. Food for thought.  Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Multitenancy in SQL Azure

  - by cibrax

  If you are building a SaaS application in Windows Azure that relies on SQL Azure, it’s probably that you will need to support multiple tenants at database level. This is short overview of the different approaches you can use for support that scenario, A different database per tenant A new database is created and assigned when a tenant is provisioned. Pros Complete isolation between tenants. All the data for a tenant lives in a database only he can access. Cons It’s not cost effective. SQL Azure databases are not cheap, and the minimum size for a database is 1GB.  You might be paying for storage that you don’t really use. A different connection pool is required per database. Updates must be replicated across all the databases You need multiple backup strategies across all the databases Multiple schemas in a database shared by all the tenants A single database is shared among all the tenants, but every tenant is assigned to a different schema and database user. Pros You only pay for a single database. Data is isolated at database level. If the credentials for one tenant is compromised, the rest of the data for the other tenants is not. Cons You need to replicate all the database objects in every schema, so the number of objects can increase indefinitely. Updates must be replicated across all the schemas. The connection pool for the database must maintain a different connection per tenant (or set of credentials) A different user is required per tenant, which is stored at server level. You have to backup that user independently. Centralizing the database access with store procedures in a database shared by all the tenants A single database is shared among all the tenants, but nobody can read the data directly from the tables. All the data operations are performed through store procedures that centralize the access to the tenant data. The store procedures contain some logic to map the database user to an specific tenant. Pros You only pay for a single database. You only have a set of objects to maintain and backup. Cons There is no real isolation. All the data for the different tenants is shared in the same tables. You can not use traditional ORM like EF code first for consuming the data. A different user is required per tenant, which is stored at server level. You have to backup that user independently. SQL Federations A single database is shared among all the tenants, but a different federation is used per tenant. A federation in few words, it’s a mechanism for horizontal scaling in SQL Azure, which basically uses the idea of logical partitions to distribute data based on certain criteria. Pros You only have a single database with multiple federations. You can use filtering in the connections to pick the right federation, so any ORM could be used to consume the data. Cons There is no real isolation at that database level. The isolation is enforced programmatically with federations.

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• VSDB to SSDT Part 2 : SQL Server 2008 Server Project &hellip; with SSDT

  - by Etienne Giust

  With Visual Studio 2012 and the use of SSDT technology, there is only one type of database project : SQL Server Database Project. With Visual Studio 2010, we used to have SQL Server 2008 Server Project which we used to define server-level objects, mostly logins and linked servers. A convenient wizard allowed for creation of this type of projects. It does not exists anymore. Here is how to create an equivalent of the SQL Server 2008 Server Project  with Visual Studio 2012: Create a new SQL Server Database Project : it will be created empty Create a new SQL Schema Compare ( SQL menu item > Schema Compare > New Schema Comparison ) As a source, select any database on the SQL server you want to mimic Set the target to be your newly Database Project In the Schema Compare options (cog-like icon), Object Types pane, set the options as below. You might want to tweak those and select only the object types you want. Then, run the comparison, review and select your changes and apply them to the project.

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• How do I filter out NaN FLOAT values in Teradata SQL?

  - by Paul Hooper

  With the Teradata database, it is possible to load values of NaN, -Inf, and +Inf into FLOAT columns through Java. Unfortunately, once those values get into the tables, they make life difficult when writing SQL that needs to filter them out. There is no IsNaN() function, nor can you "CAST ('NaN' as FLOAT)" and use an equality comparison. What I would like to do is, SELECT SUM(VAL**2) FROM DTM WHERE NOT ABS(VAL) > 1e+21 AND NOT VAL = CAST ('NaN' AS FLOAT) but that fails with error 2620, "The format or data contains a bad character.", specifically on the CAST. I've tried simply "... AND NOT VAL = 'NaN'", which also fails for a similar reason (3535, "A character string failed conversion to a numeric value."). I cannot seem to figure out how to represent NaN within the SQL statement. Even if I could represent NaN successfully in an SQL statement, I would be concerned that the comparison would fail. According to the IEEE 754 spec, NaN = NaN should evaluate to false. What I really seem to need is an IsNaN() function. Yet that function does not seem to exist.

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• iPhone Keychain Questions

  - by AO

  Some questions: * Is there some way to view the data present in the iPhone keychain? * The items an application adds, cannot be accessed by any other application, can it? * What is the purpose of the identifier and access group in the initialization? My guess is that the identifier is simply used to find items but I'm a little bit unsure of the access group. If the access group is assigned nil, all applications can access the items? If the access group is assigned X, could the items be accessed by another application with the same string X as access group or what is the purpose of the access group in this case? * Is the data in the keychain removed when the application is removed? If not, how do I achieve that? And finally: I can't get the KeychainItemWrapper (Apple example) to work. I've added the KeychainItemWrapper files to my project and when running it on the phone, an exception is thrown by SecItemAdd, saying that one or more parameters were not valid (result code -50). The code triggering the SecItemAdd follows: KeychainItemWrapper* wrapper = [[KeychainItemWrapper alloc] initWithIdentifier:@"something" accessGroup:@"com.company.whatever"]; [wrapper setObject:@"this is my password" forKey:@"password"]; NSLog(@"Password: %@", [wrapper objectForKey:@"password"]); The code can be found at http://developer.apple.com/iphone/library/samplecode/GenericKeychain/index.html

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• 2 spss and mrInterview template questions

  - by Donnied

  How can I align the mrProgress bar to be the same size as the image at the top of the table? (I'd like it below the image.) How can I edit the .xml tables for the grid to show grid lines (preferably alternating colors)? (I do not have permissions to write actual scripts - I can only alter the .htm and .xml templates.) The current code: ` BODY {font-family:Verdana,Arial; font-size:10pt; color:000000} TABLE {font-family:Verdana,Arial; font-size:10pt; color:000000} .mrQuestionTable {BORDER-COLLAPSE: collapse} .mrEdit {font-family:Verdana,Arial; font-size:10pt; color:000000} .mrDropDown {font-family:Verdana,Arial; font-size:10pt; color:000000} .mrListBox {font-family:Verdana,Arial; font-size:10pt; color:000000} .mrErrorText {font-family:Verdana,Arial; font-size:10pt; color:red; font-weight:bold} .mrNext {font-family:Verdana,Arial; font-size:8pt; color:000000} .mrPrev {font-family:Verdana,Arial; font-size:8pt; color:000000} mrBannerText Questions here << Back Next >> mrBannerText `

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• Swapping two variable value without using 3rd variable

  - by Muhammad Akhtar

  One of the very tricky question asked in an interview... we need to swap the values of two variables like a=10 and b=15 Generaly to swap two variables values, we need 3rd variable like.. temp=a a=b b=temp Now the requirement is, swaping value of two variable values without using 3rd variable? How can be accopmplish this?

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• Some questions about slugs in ASP.NET MVC content system

  - by mare

  In my application I'm currently using forms which allow to enter Title and Slug fields. Now I've been struggling with the slugs thing for a while because I can never decide once and for all how to handle them. 1) Make Title and Slug indenpendent Should I allow users to enter both Title and Slug separetely? This is what I had first. I also had an option that if user did not enter the Slug it was derived from the Title. If both were enter, the Slug field took precedence. 2) Derive Slug from Title, when content is inserted that's it for the Slug, no more changes Then, I switched to only Title field and derive Slug from title. While doing it I found out that now I have to change all the forms that allowed user to enter a slug. This way of doing it also prevents users to change Slugs - they can change the Title but it has no effect on the Slug. You can think of it like Slug is uniqued ID. 3) Now I'm thinking again of allowing users to change slug Though I don't think it is all that useful. How many times does the content that someone already added, spent time on writing it, even require a change of either Title or slug? I don't think it is that many times. The biggest problem with the 3rd option is that If I use Slugs as IDs, I need to update the reference all over the place when Slug changes. Or maintain a table that would contain somekind of Slug history. What are you thoughts on these, I hope, valid questions?

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• Using SQL Alchemy and pyodbc with IronPython 2.6.1

  - by beargle

  I'm using IronPython and the clr module to retrieve SQL Server information via SMO. I'd like to retrieve/store this data in a SQL Server database using SQL Alchemy, but am having some trouble loading the pyodbc module. Here's the setup: IronPython 2.6.1 (installed at D:\Program Files\IronPython) CPython 2.6.5 (installed at D:\Python26) SQL Alchemy 0.6.1 (installed at D:\Python26\Lib\site-packages\sqlalchemy) pyodbc 2.1.7 (installed at D:\Python26\Lib\site-packages) I have these entries in the IronPython site.py to import CPython standard and third-party libraries: # Add CPython standard libs and DLLs import sys sys.path.append(r"D:\Python26\Lib") sys.path.append(r"D:\Python26\DLLs") sys.path.append(r"D:\Python26\lib-tk") sys.path.append(r"D:\Python26") # Add CPython third-party libs sys.path.append(r"D:\Python26\Lib\site-packages") # sqlite3 sys.path.append(r"D:\Python26\Lib\sqlite3") # Add SQL Server SMO sys.path.append(r"D:\Program Files\Microsoft SQL Server\100\SDK\Assemblies") import clr clr.AddReferenceToFile('Microsoft.SqlServer.Smo.dll') clr.AddReferenceToFile('Microsoft.SqlServer.SqlEnum.dll') clr.AddReferenceToFile('Microsoft.SqlServer.ConnectionInfo.dll') SQL Alchemy imports OK in IronPython, put I receive this error message when trying to connect to SQL Server: IronPython 2.6.1 (2.6.10920.0) on .NET 2.0.50727.3607 Type "help", "copyright", "credits" or "license" for more information. >>> import sqlalchemy >>> e = sqlalchemy.MetaData("mssql://") Traceback (most recent call last): File "<stdin>", line 1, in <module> File "D:\Python26\Lib\site-packages\sqlalchemy\schema.py", line 1780, in __init__ File "D:\Python26\Lib\site-packages\sqlalchemy\schema.py", line 1828, in _bind_to File "D:\Python26\Lib\site-packages\sqlalchemy\engine\__init__.py", line 241, in create_engine File "D:\Python26\Lib\site-packages\sqlalchemy\engine\strategies.py", line 60, in create File "D:\Python26\Lib\site-packages\sqlalchemy\connectors\pyodbc.py", line 29, in dbapi ImportError: No module named pyodbc This code works just fine in CPython, but it looks like the pyodbc module isn't accessible from IronPython. Any suggestions? I realize that this may not be the best way to approach the problem, so I'm open to tackling this a different way. Just wanted to get some experience with using SQL Alchemy and pyodbc.

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• Python for a hobbyist programmer ( a few questions)

  - by Matt

  I'm a hobbyist programmer (only in TI-Basic before now), and after much, much, much debating with myself, I've decided to learn Python. I don't have a ton of free time to teach myself a hundred languages and all programming I do will be for personal use or for distributing to people who need them, so I decided that I needed one good, strong language to be good at. My questions: Is python powerful enough to handle most things that a typical programmer might do in his off-time? I have in mind things like complex stat generators based on user input for tabletop games, making small games, automate install processes, and build interactive websites, but probably a hundred things along those lines Does python handle networking tasks fairly well? Can python source be obscufated (mispelled I think), or is it going to be open-source by nature? The reason I ask this is because if I make something cool and distribute it, I don't want some idiot script kiddie to edit his own name in and say he wrote it And how popular is python, compared to other languages. Ideally, my language would be good and useful with help found online without extreme difficulty, but not so common that every idiot with computer knows python. I like the idea of knowing a slightly obscure language. Thanks a ton for any help you can provide.

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• java RMI newbie-- some basic questions about SSL and auth/.rate limiting an RMI service

  - by Arvind

  I am trying to work to secure a java based RMI service using SSL. I have some basic questions about the capabilities of using SSL. Specifically, from what I understand, the client and server connecting via SSL will need to have appropriate credential certificates in both client and server, for a client to be granted access to the server. Am I correct in my understanding? Also, what I want to know is, can a person who is already using my RMI service and has access to a client machine , make a copy of the certificate in the client machine to other client machines-- and then invoke my RMI service from those other machines as well? How do I prevent such a situation from occurring? I mean, in a REST API you can use OAuth authentication, can we have some kind of authentication in an RMI Service? Also, can I possibly limit usage of the RMI service? For eg, a specific client may be allowed to make only 5000 calls per day to my RMI service, and if he makes more calls the calls occurring after the 5000 calls limit are all denied? How do I do such rate limiting and/or authentication for my RMI Service?

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• Trying to build a Drupal-like CMS in ASP.NET MVC - Newbie Questions

  - by user252160

  I am new to ASP.NET MVC, and the ASP.NET technology in general, so, please, excuse the stupidity of my questions. I have a lot of experience with php development and CMS customization (Drupal and Wordpress mainly), and I wanted to know whether some techniques could be applied in asp.net mvc. I want to know what exactly could be modified without recompiling an already built application Can I edit the views without recompiling the app. Can I create custom themes ? Can I add plugins compiled as dlls and use them at runtime. Can I "mark" the assembly in such a way that the web application will check on the next request and will reference it, without me manually adding it to the project and recompiling. I've heard that this is possible. I will make sure to add more when something comes up. The reason I am asking is because I'd like to try and develop a Drupal-like CMS (custom types, views, etc) in asp.net mvc. The dynamism of php will be quite a challenge to replicate in a compiled technology, yet I am ready to try.

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• Mercurial: a few questions all related to .hgignore

  - by WizardOfOdds

  I've been working for a long time with a .hgignore file that was fine and recently added one new type of files to ignore. When running "hg status", I noticed this: M .hgignore So Mercurial considers the .hgignore to be a file that needs to be tracked (if it's a the root of the project). Now I've read various docs but my points weren't specifically adressed so here are some very detailed questions which hopefully can help me figure this out (it would be great is someone answering could quote and address these three points [even with a simply yes/no answer for each question]): Should .hgignore be at the root of the project? (I guess it should, seen that a developer can potentially be working on several projects which would all have different .hgignore requirements) Can .hgignore be ignored be Mercurial? If it can be ignored, should .hgignore be ignored by Mercurial (which is different than the previous question) In the case where .hgignore should not be ignored, can't some really bad thing happens if you suddenly rollback way earlier, when a really old and incomplete .hgignore was used? I think I saw weird things happening with certain per-user IDE project files (I'm not saying all IDEs project files are per-user only, but some definitely are) that were supposed to be ignored, but then the user rolls back to an old version, where an old .hgignore gets used, and then suddenly files supposed to be ignored are committed because the old .hgignore didn't exclude these.

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• WCF Double Hop questions about Security and Binding.

  - by Ken Maglio

  Background information: .Net Website which calls a service (aka external service) facade on an app server in the DMZ. This external service then calls the internal service which is on our internal app server. From there that internal service calls a stored procedure (Linq to SQL Classes), and passes the serialized data back though to the external service, and from there back to the website. We've done this so any communication goes through an external layer (our external app server) and allows interoperability; we access our data just like our clients consuming our services. We've gotten to the point in our development where we have completed the system and it all works, the double hop acts as it should. However now we are working on securing the entire process. We are looking at using TransportWithMessageCredentials. We want to have WS2007HttpBinding for the external for interoperability, but then netTCPBinding for the bridge through the firewall for security and speed. Questions: If we choose WS2007HttpBinding as the external services binding, and netTCPBinding for the internal service is this possible? I know WS-* supports this as does netTCP, however do they play nice when passing credential information like user/pass? If we go to Kerberos, will this impact anything? We may want to do impersonation in the future. If you can when you answer post any reference links about why you're answering the way you are, that would be very helpful to us. Thanks!

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• SQL Server CLR stored procedures in data processing tasks - good or evil?

  - by Gart

  In short - is it a good design solution to implement most of the business logic in CLR stored procedures? I have read much about them recently but I can't figure out when they should be used, what are the best practices, are they good enough or not. For example, my business application needs to parse a large fixed-length text file, extract some numbers from each line in the file, according to these numbers apply some complex business rules (involving regex matching, pattern matching against data from many tables in the database and such), and as a result of this calculation update records in the database. There is also a GUI for the user to select the file, view the results, etc. This application seems to be a good candidate to implement the classic 3-tier architecture: the Data Layer, the Logic Layer, and the GUI layer. The Data Layer would access the database The Logic Layer would run as a WCF service and implement the business rules, interacting with the Data Layer The GUI Layer would be a means of communication between the Logic Layer and the User. Now, thinking of this design, I can see that most of the business rules may be implemented in a SQL CLR and stored in SQL Server. I might store all my raw data in the database, run the processing there, and get the results. I see some advantages and disadvantages of this solution: Pros: The business logic runs close to the data, meaning less network traffic. Process all data at once, possibly utilizing parallelizm and optimal execution plan. Cons: Scattering of the business logic: some part is here, some part is there. Questionable design solution, may encounter unknown problems. Difficult to implement a progress indicator for the processing task. I would like to hear all your opinions about SQL CLR. Does anybody use it in production? Are there any problems with such design? Is it a good thing?

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• pass username and password to get-credential or run sql query without using invoke-sqlcmd in Powersh

  - by Emo

  I am trying to connect to a remote sql database and simply run the "select @@servername" query in Powershell. I'm trying to do this without using integrated security. I've been struggling with "get-credential" and "invoke-sqlcmd", only to find (I think), that you can't pass the password from "get-credential" to another Powershell cmdlets. Here's the code I'm using: add-pssnapin sqlserverprovidersnapin100 add-pssnapin sqlservercmdletsnapin100 load assemblies [Reflection.Assembly]::Load("Microsoft.SqlServer.Smo, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91") [Reflection.Assembly]::Load("Microsoft.SqlServer.SqlEnum, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91") [Reflection.Assembly]::Load("Microsoft.SqlServer.SmoEnum, Version=9.0.242.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91") [Reflection.Assembly]::Load("Microsoft.SqlServer.ConnectionInfo, Version=9.0.242.0, Culture=neutral,PublicKeyToken=89845dcd8080cc91") connect to SQL Server $serverName = "HLSQLSRV03" $server = New-Object -typeName Microsoft.SqlServer.Management.Smo.Server -argumentList $serverName login using SQL authentication $server.ConnectionContext.LoginSecure=$false; $credential = Get-Credential $userName = $credential.UserName -replace("\","") $pass = $credential.Password $server.ConnectionContext.set_Login($userName) $server.ConnectionContext.set_SecurePassword($credential.Password) $DB = "Master" invoke-sqlcmd -query "select @@Servername" -database $DB -serverinstance $servername -username $username -password $pass If if just hardcode the password in at the end of the "invoke-sqlcmd" line, it works. Is this because you can't use "get-credential" with "invoke-sqlcmd"? If so...what are my alternatives? Thanks so much for you help Emo

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