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  • Databases and Beer

    - by Johnm
    It is a bit of a no-brainer: Include the word "beer" in a subject line of an e-mail or blog post title and you can be certain that it will be read. While there are times this practice might be a ploy to increase readership, it is not the case for this blog post. There is inspiration that can be drawn from other industries to which we, as database professionals, can apply in our industry. In this post I will highlight one of my favorite participants of the brewing industry. The Boston Beer Company started in the 1970s in Boston, Massachusetts. Others may be more familiar with this company through their Samuel Adams Boston Lager and other various seasonal beers. I am continually inspired by their commitment to mastery of the brewing process to which they evangelize frequently in their commercials. They also are continually in pursuit of pushing the boundaries of beer as we know it while working within traditional constraints. A recent example of this is their collaboration with Weihenstephan Brewery of Munich, Germany to produce the soon to be released Infinium beer. This beer, while brewed as an ale, is touted as something closer to something like Champaign - all while complying with the Reinheitsgebot. The Reinheitsgebot is also known as the "German Beer Purity Law" which was originated in 1516. This law states that beer is to consist of water, barley, hops and yeast. That's it. Quite a limiting constraint indeed. and yet, The Boston Beer Company pushed forward. Much like the process of brewing, the discipline of database design and architecture is one that is continually in process and driven by the pursuit of mastery. While we do not have purity laws to constrain us, we have many other types: best practices, company policies, government regulations, security and budgets. Through our fellow comrades, we discuss the challenges and constraints in which we operate. We boil down the principles and theories that define our profession. We reassemble these into something that is complementary to the business needs that we must fulfill. As a result, it is not uncommon to see something amazingly innovative in a small business who is pushing the boundaries of their database well beyond its intended state. It is equally common to see innovation in the use of features available in the more advanced features of databases that are found in large businesses. The tag line for The Boston Beer Company is: "Take Pride In Your Beer.", I would like to offer an alternative and say "Take Pride In Your Database." So, As you pour your next Boston Lager into a frosted glass, consider those who spend their lives mastering the craft of brewing and strive to interject their spirit into everything that you do as a database professional. Cheers!

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  • Subterranean IL: Compiling C# exception handlers

    - by Simon Cooper
    An exception handler in C# combines the IL catch and finally exception handling clauses into a single try statement: try { Console.WriteLine("Try block") // ... } catch (IOException) { Console.WriteLine("IOException catch") // ... } catch (Exception e) { Console.WriteLine("Exception catch") // ... } finally { Console.WriteLine("Finally block") // ... } How does this get compiled into IL? Initial implementation If you remember from my earlier post, finally clauses must be specified with their own .try clause. So, for the initial implementation, we take the try/catch/finally, and simply split it up into two .try clauses (I have to use label syntax for this): StartTry: ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndTry: StartIOECatch: ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndIOECatch: StartECatch: ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End EndECatch: StartFinally: ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally EndFinally: End: // ... .try StartTry to EndTry catch [mscorlib]System.IO.IOException handler StartIOECatch to EndIOECatch catch [mscorlib]System.Exception handler StartECatch to EndECatch .try StartTry to EndTry finally handler StartFinally to EndFinally However, the resulting program isn't verifiable, and doesn't run: [IL]: Error: Shared try has finally or fault handler. Nested try blocks What's with the verification error? Well, it's a condition of IL verification that all exception handling regions (try, catch, filter, finally, fault) of a single .try clause have to be completely contained within any outer exception region, and they can't overlap with any other exception handling clause. In other words, IL exception handling clauses must to be representable in the scoped syntax, and in this example, we're overlapping catch and finally clauses. Not only is this example not verifiable, it isn't semantically correct. The finally handler is specified round the .try. What happens if you were able to run this code, and an exception was thrown? Program execution enters top of try block, and exception is thrown within it CLR searches for an exception handler, finds catch Because control flow is leaving .try, finally block is run The catch block is run leave.s End inside the catch handler branches to End label. We're actually running the finally before the catch! What we do about it What we actually need to do is put the catch clauses inside the finally clause, as this will ensure the finally gets executed at the correct time (this time using scoped syntax): .try { .try { ldstr "Try block" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.IO.IOException { ldstr "IOException catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } catch [mscorlib]System.Exception { ldstr "Exception catch" call void [mscorlib]System.Console::WriteLine(string) // ... leave.s End } } finally { ldstr "Finally block" call void [mscorlib]System.Console::WriteLine(string) // ... endfinally } End: ret Returning from methods There is a further semantic mismatch that the C# compiler has to deal with; in C#, you are allowed to return from within an exception handling block: public int HandleMethod() { try { // ... return 0; } catch (Exception) { // ... return -1; } } However, you can't ret inside an exception handling block in IL. So the C# compiler does a leave.s to a ret outside the exception handling area, loading/storing any return value to a local variable along the way (as leave.s clears the stack): .method public instance int32 HandleMethod() { .locals init ( int32 retVal ) .try { // ... ldc.i4.0 stloc.0 leave.s End } catch [mscorlib]System.Exception { // ... ldc.i4.m1 stloc.0 leave.s End } End: ldloc.0 ret } Conclusion As you can see, the C# compiler has quite a few hoops to jump through to translate C# code into semantically-correct IL, and hides the numerous conditions on IL exception handling blocks from the C# programmer. Next up: catch-all blocks, and how the runtime deals with non-Exception exceptions.

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  • SQL Monitor and "The Cloud"

    - by Richard Mitchell
    So, how can we demo this thing? In the beginning there was a product, and it was a good product for the testers had decreed it so, and nobody argues with a tester. But then comes the inevitable question of how can somebody test it out without risk. Red Gate prides itself on the tools being easy for people to trial before they buy, and no cut down trial for you sir, oh no, for you sir only the best will do - a fully functional trial - suits you sir. The problem The problem comes when you get a...(read more)

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  • The SQL Beat Podcast-Capturing a SQL Rockstar

    - by SQLBeat
      This is the first permissible (waiting for signed disclaimers) episode of the SQL Beat Podcast featuring the gracious and famous Thomas La Rock. We talk about gay marriage, abortion, SQL community and a 9 inch pipe with a hole in it at the tip. No really. If there ever was a gentleman, SQL Rockstar is one and I want to thank him from the bottom of my digital recorder for agreeing to talk to me and my audience. All forty of them will appreciate the candor. Enjoy World. I did. Oh and a special rock start drum intro from me to you. CLICK HERE TO PLAY >>

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  • SQL Azure Down - how I got labs.red-gate.com back up

    - by Richard Mitchell
    11:06am - Currently SQL Azure in western europe is down How do I know this? Well on labs.red-gate.com (my Azure website) I have elmah installed which started sending me e-mails about connection failures from 10:40am when trying to get the dynamic content from the database (I was too busy playing with my new Eee Pad transformer to notice immediately). Going to the website confirmed the failure and trying to connect to SQL Azure from SQL Server Management studio and the Management confirmed bad...(read more)

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  • Virtual Machine Storage Provisioning and best practises

    If you're using Virtualization technology, then at some point you'll have run out of (or will run out of) virtual disk space, & had to provision extra storage; are you confident that you know how to do that? Sean Duffy makes sure you're doing it right, sharing his recommendations and tips in this step-by-step guide to Virtual Machine Storage provisioning for VMware. Follow this advice, and you'll be a Virtualization Veteran in no time.

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  • ReSharper C# Live Template for Dependency Property and Property Change Routed Event Boilerplate Code

    - by Bart Read
    I don't know about you but it took me about 5 seconds to get royally fed up of typing the boilerplate code necessary for creating WPF (and Silverlight) dependency properties and, if you want them, their associated property change routed events. Being a ReSharper user, I wondered if there was any live template for doing this. It turns out there's nothing built in, but there are many examples of templates for creating dependency properties out there on the web, such as this excellent one from Roy...(read more)

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  • Anatomy of a .NET Assembly - CLR metadata 2

    - by Simon Cooper
    Before we look any further at the CLR metadata, we need a quick diversion to understand how the metadata is actually stored. Encoding table information As an example, we'll have a look at a row in the TypeDef table. According to the spec, each TypeDef consists of the following: Flags specifying various properties of the class, including visibility. The name of the type. The namespace of the type. What type this type extends. The field list of this type. The method list of this type. How is all this data actually represented? Offset & RID encoding Most assemblies don't need to use a 4 byte value to specify heap offsets and RIDs everywhere, however we can't hard-code every offset and RID to be 2 bytes long as there could conceivably be more than 65535 items in a heap or more than 65535 fields or types defined in an assembly. So heap offsets and RIDs are only represented in the full 4 bytes if it is required; in the header information at the top of the #~ stream are 3 bits indicating if the #Strings, #GUID, or #Blob heaps use 2 or 4 bytes (the #US stream is not accessed from metadata), and the rowcount of each table. If the rowcount for a particular table is greater than 65535 then all RIDs referencing that table throughout the metadata use 4 bytes, else only 2 bytes are used. Coded tokens Not every field in a table row references a single predefined table. For example, in the TypeDef extends field, a type can extend another TypeDef (a type in the same assembly), a TypeRef (a type in a different assembly), or a TypeSpec (an instantiation of a generic type). A token would have to be used to let us specify the table along with the RID. Tokens are always 4 bytes long; again, this is rather wasteful of space. Cutting the RID down to 2 bytes would make each token 3 bytes long, which isn't really an optimum size for computers to read from memory or disk. However, every use of a token in the metadata tables can only point to a limited subset of the metadata tables. For the extends field, we only need to be able to specify one of 3 tables, which we can do using 2 bits: 0x0: TypeDef 0x1: TypeRef 0x2: TypeSpec We could therefore compress the 4-byte token that would otherwise be needed into a coded token of type TypeDefOrRef. For each type of coded token, the least significant bits encode the table the token points to, and the rest of the bits encode the RID within that table. We can work out whether each type of coded token needs 2 or 4 bytes to represent it by working out whether the maximum RID of every table that the coded token type can point to will fit in the space available. The space available for the RID depends on the type of coded token; a TypeOrMethodDef coded token only needs 1 bit to specify the table, leaving 15 bits available for the RID before a 4-byte representation is needed, whereas a HasCustomAttribute coded token can point to one of 18 different tables, and so needs 5 bits to specify the table, only leaving 11 bits for the RID before 4 bytes are needed to represent that coded token type. For example, a 2-byte TypeDefOrRef coded token with the value 0x0321 has the following bit pattern: 0 3 2 1 0000 0011 0010 0001 The first two bits specify the table - TypeRef; the other bits specify the RID. Because we've used the first two bits, we've got to shift everything along two bits: 000000 1100 1000 This gives us a RID of 0xc8. If any one of the TypeDef, TypeRef or TypeSpec tables had more than 16383 rows (2^14 - 1), then 4 bytes would need to be used to represent all TypeDefOrRef coded tokens throughout the metadata tables. Lists The third representation we need to consider is 1-to-many references; each TypeDef refers to a list of FieldDef and MethodDef belonging to that type. If we were to specify every FieldDef and MethodDef individually then each TypeDef would be very large and a variable size, which isn't ideal. There is a way of specifying a list of references without explicitly specifying every item; if we order the MethodDef and FieldDef tables by the owning type, then the field list and method list in a TypeDef only have to be a single RID pointing at the first FieldDef or MethodDef belonging to that type; the end of the list can be inferred by the field list and method list RIDs of the next row in the TypeDef table. Going back to the TypeDef If we have a look back at the definition of a TypeDef, we end up with the following reprensentation for each row: Flags - always 4 bytes Name - a #Strings heap offset. Namespace - a #Strings heap offset. Extends - a TypeDefOrRef coded token. FieldList - a single RID to the FieldDef table. MethodList - a single RID to the MethodDef table. So, depending on the number of entries in the heaps and tables within the assembly, the rows in the TypeDef table can be as small as 14 bytes, or as large as 24 bytes. Now we've had a look at how information is encoded within the metadata tables, in the next post we can see how they are arranged on disk.

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  • Subterranean IL: Generics and array covariance

    - by Simon Cooper
    Arrays in .NET are curious beasts. They are the only built-in collection types in the CLR, and SZ-arrays (single dimension, zero-indexed) have their own commands and IL syntax. One of their stranger properties is they have a kind of built-in covariance long before generic variance was added in .NET 4. However, this causes a subtle but important problem with generics. First of all, we need to briefly recap on array covariance. SZ-array covariance To demonstrate, I'll tweak the classes I introduced in my previous posts: public class IncrementableClass { public int Value; public virtual void Increment(int incrementBy) { Value += incrementBy; } } public class IncrementableClassx2 : IncrementableClass { public override void Increment(int incrementBy) { base.Increment(incrementBy); base.Increment(incrementBy); } } In the CLR, SZ-arrays of reference types are implicitly convertible to arrays of the element's supertypes, all the way up to object (note that this does not apply to value types). That is, an instance of IncrementableClassx2[] can be used wherever a IncrementableClass[] or object[] is required. When an SZ-array could be used in this fashion, a run-time type check is performed when you try to insert an object into the array to make sure you're not trying to insert an instance of IncrementableClass into an IncrementableClassx2[]. This check means that the following code will compile fine but will fail at run-time: IncrementableClass[] array = new IncrementableClassx2[1]; array[0] = new IncrementableClass(); // throws ArrayTypeMismatchException These checks are enforced by the various stelem* and ldelem* il instructions in such a way as to ensure you can't insert a IncrementableClass into a IncrementableClassx2[]. For the rest of this post, however, I'm going to concentrate on the ldelema instruction. ldelema This instruction pops the array index (int32) and array reference (O) off the stack, and pushes a pointer (&) to the corresponding array element. However, unlike the ldelem instruction, the instruction's type argument must match the run-time array type exactly. This is because, once you've got a managed pointer, you can use that pointer to both load and store values in that array element using the ldind* and stind* (load/store indirect) instructions. As the same pointer can be used for both input and output to the array, the type argument to ldelema must be invariant. At the time, this was a perfectly reasonable restriction, and maintained array type-safety within managed code. However, along came generics, and with it the constrained callvirt instruction. So, what happens when we combine array covariance and constrained callvirt? .method public static void CallIncrementArrayValue() { // IncrementableClassx2[] arr = new IncrementableClassx2[1] ldc.i4.1 newarr IncrementableClassx2 // arr[0] = new IncrementableClassx2(); dup newobj instance void IncrementableClassx2::.ctor() ldc.i4.0 stelem.ref // IncrementArrayValue<IncrementableClass>(arr, 0) // here, we're treating an IncrementableClassx2[] as IncrementableClass[] dup ldc.i4.0 call void IncrementArrayValue<class IncrementableClass>(!!0[],int32) // ... ret } .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } And the result: Unhandled Exception: System.ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array. at IncrementArrayValue[T](T[] arr, Int32 index) at CallIncrementArrayValue() Hmm. We're instantiating the generic method as IncrementArrayValue<IncrementableClass>, but passing in an IncrementableClassx2[], hence the ldelema instruction is failing as it's expecting an IncrementableClass[]. On features and feature conflicts What we've got here is a conflict between existing behaviour (ldelema ensuring type safety on covariant arrays) and new behaviour (managed pointers to object references used for every constrained callvirt on generic type instances). And, although this is an edge case, there is no general workaround. The generic method could be hidden behind several layers of assemblies, wrappers and interfaces that make it a requirement to use array covariance when calling the generic method. Furthermore, this will only fail at runtime, whereas compile-time safety is what generics were designed for! The solution is the readonly. prefix instruction. This modifies the ldelema instruction to ignore the exact type check for arrays of reference types, and so it lets us take the address of array elements using a covariant type to the actual run-time type of the array: .method public static void IncrementArrayValue<(IncrementableClass) T>( !!T[] arr, int32 index) { // arr[index].Increment(1) ldarg.0 ldarg.1 readonly. ldelema !!T ldc.i4.1 constrained. !!T callvirt instance void IIncrementable::Increment(int32) ret } But what about type safety? In return for ignoring the type check, the resulting controlled mutability pointer can only be used in the following situations: As the object parameter to ldfld, ldflda, stfld, call and constrained callvirt instructions As the pointer parameter to ldobj or ldind* As the source parameter to cpobj In other words, the only operations allowed are those that read from the pointer; stind* and similar that alter the pointer itself are banned. This ensures that the array element we're pointing to won't be changed to anything untoward, and so type safety within the array is maintained. This is a typical example of the maxim that whenever you add a feature to a program, you have to consider how that feature interacts with every single one of the existing features. Although an edge case, the readonly. prefix instruction ensures that generics and array covariance work together and that compile-time type safety is maintained. Tune in next time for a look at the .ctor generic type constraint, and what it means.

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  • The Fast Guide to Application Profiling

    In this sample chapter from his recently released book (co-Authored with Paul Glavich) Chris Farrell gives us a fast overview of performance profiling, memory profiling, profiling tools, and in fact everything we need to know when it comes to profiling our applications. This is a great first step, and The Complete Guide to .NET Performance Testing and Optimization is crammed with even more indispensable knowledge.

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  • Sweet and Sour Source Control

    - by Tony Davis
    Most database developers don't use Source Control. A recent anonymous poll on SQL Server Central asked its readers "Which Version Control system do you currently use to store you database scripts?" The winner, with almost 30% of the vote was...none: "We don't use source control for database scripts". In second place with almost 28% of the vote was Microsoft's VSS. VSS? Given its reputation for being buggy, unstable and lacking most of the basic features required of a proper source control system, answering VSS is really just another way of saying "I don't use Source Control". At first glance, it's a surprising thought. You wonder how database developers can work in a team and find out what changed, when the system worked before but is now broken; to work out what happened to their changes that now seem to have vanished; to roll-back a mistake quickly so that the rest of the team have a functioning build; to find instantly whether a suspect change has been deployed to production. Unfortunately, the survey didn't ask about the scale of the database development, and correlate the two questions. If there is only one database developer within a schema, who has an automated approach to regular generation of build scripts, then the need for a formal source control system is questionable. After all, a database stores far more about its metadata than a traditional compiled application. However, what is meat for a small development is poison for a team-based development. Here, we need a form of Source Control that can reconcile simultaneous changes, store the history of changes, derive versions and builds and that can cope with forks and merges. The problem comes when one borrows a solution that was designed for conventional programming. A database is not thought of as a "file", but a vast, interdependent and intricate matrix of tables, indexes, constraints, triggers, enumerations, static data and so on, all subtly interconnected. It is an awkward fit. Subversion with its support for merges and forks, and the tolerance of different work practices, can be made to work well, if used carefully. It has a standards-based architecture that allows it to be used on all platforms such as Windows Mac, and Linux. In the words of Erland Sommerskog, developers should "just do it". What's in a database is akin to a "binary file", and the developer must work only from the file. You check out the file, edit it, and save it to disk to compile it. Dependencies are validated at this point and if you've broken anything (e.g. you renamed a column and broke all the objects that reference the column), you'll find out about it right away, and you'll be forced to fix it. Nevertheless, for many this is an alien way of working with SQL Server. Subversion is the powerhouse, not the GUI. It doesn't work seamlessly with your existing IDE, and that usually means SSMS. So the question then becomes more subtle. Would developers be less reluctant to use a fully-featured source (revision) control system for a team database development if they had a turn-key, reliable system that fitted in with their existing work-practices? I'd love to hear what you think. Cheers, Tony.

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  • The SQL Beat Podcast–Capturing a SQL Rockstar

    - by SQLBeat
      This is the first permissible (waiting for signed disclaimers) episode of the SQL Beat Podcast featuring the gracious and famous Thomas La Rock. We talk about gay marriage, abortion, SQL community and a 9 inch pipe with a hole in it at the tip. No really. If there ever was a gentleman, SQL Rockstar is one and I want to thank him from the bottom of my digital recorder for agreeing to talk to me and my audience. All forty of them will appreciate the candor. Enjoy World. I did. Oh and a special rock start drum intro from me to you. CLICK BELOW TO LISTEN >>>>>>>>>CLICK HERE TO PLAY >>>>>>>>> CLICK ABOVE TO SPEAR A FISH INSTEAD

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  • Statistical Sampling for Verifying Database Backups

    A DBA's huge workload can start to threaten best practices for data backup and recovery, but ingenuity, and an eye for a good tactic, can usually find a way. For Tom, the revelation about a solution came from eating crabs. Statistical sampling can be brought to bear to minimise the risk of faliure of an emergency database restore.

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  • Exporting PowerPoint Slides with Specific Heights and Widths

    - by Damon Armstrong
    I found myself in need of exporting PowerPoint slides from a presentation and was fairly excited when I found that you could save them off in standard image formats. The problem is that Microsoft conveniently exports all images with a resolution of 960 x 720 pixels, which is not the resolution I wanted.  You can, however, specify the resolution if you are willing to put a macro into your project: Sub ExportSlides()   For i = 1 To ActiveWindow.Selection.SlideRange.Count     Dim fileName As String     If (i < 10) Then       fileName = "C:\PowerPoint Export\Slide" & i & ".png"     Else       fileName = "C:\PowerPoint Export\Slide0" & i & ".png"     End If     ActiveWindow.Selection.SlideRange(i).Export fileName, "PNG", 1280, 720   Next End Sub When you call the Export method you can specify the file type as well as the dimensions to use when creating the image.  If the macro approach is not your thing, then you can also modify the default settings through the registry: http://support.microsoft.com/kb/827745

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  • Hello, can you just send me all your data please?

    - by fatherjack
    LiveJournal Tags: Security,SQL Server Our house phone rang on Saturday night and Mrs Fatherjack answered. I was in the other room but I heard her trying to explain to the caller that they were in some way mistaken. Eventually, as she got more irate with the caller, I went out and started to catch up with the events so far. The caller was trying to convince my wife that our computer was infected with a virus. She was confident that it wasn't. Her patience expired after almost 10 minutes...(read more)

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  • Restoring Databases

    - by Grant Fritchey
    I like the way Mike Walsh phrased it: You're Only As Good as Your Ability To Restore. Ain't it the truth. You may be taking backups, incrementals, and log backups of your databases. You may have DBCC in place, and all that fun stuff. But if you haven't restored the database, what do you have? You don't know. The trick is, restoring databases takes up a heck of a lot of space on your servers. To test all your productions backups, you'd need a system with as much space as production. unless.. Ever heard of SQL Virtual Restore? Check it out. With this, you answer Mike's questions and validate your backups without having to have twice the amount of space. That's a win, and we all know, winning is better than losing.

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  • Planning for Disaster

    There is a certain paradox in being advised to expect the unexpected, but the DBA must plan and prepare in advance to protect their organisation's data assets in the event of an unexpected crisis, and return them to normal operating conditions. To minimise downtime in such circumstances should be the aim of every effective DBA. To plan for recovery, It pays to have the mindset of a pessimist.

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  • ANTS Profiler Saves Me From A Sordid Fate

    A bit of string concatenation never hurt anybody, right? Think again. Carl Niedner has been designing software since 1983, and was shocked to find his latest and greatest creation suddenly plagued with long loading times. After trying ANTS Profiler, he discovered one tiny line of forgotten concept code was causing his pain.

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  • How to Create Features for Windows SharePoint Services 3.0

    To customise a SharePoint (WSS 3.0) site, you'll need to understand 'Features'. The 'Feature' framework has become the most important method of customising a SharePoint site, because it is now defined by a list of Features, a layout page and a master page. One templated site can be turned into another by toggling Features and maybe switching the layout page or master page. Charles Lee explains.

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  • Developing Schema Compare for Oracle (Part 1)

    - by Simon Cooper
    SQL Compare is one of Red Gate's most successful SQL Server tools; it allows developers and DBAs to compare and synchronize the contents of their databases. Although similar tools exist for Oracle, they are quite noticeably lacking in the usability and stability that SQL Compare is known for in the SQL Server world. We could see a real need for a usable schema comparison tools for Oracle, and so the Schema Compare for Oracle project was born. Over the next few weeks, as we come up to release of v1, I'll be doing a series of posts on the development of Schema Compare for Oracle. For the first post, I thought I would start with the main pitfalls that we stumbled across when developing the product, especially from a SQL Server background. 1. Schemas and Databases The most obvious difference is that the concept of a 'database' is quite different between Oracle and SQL Server. On SQL Server, one server instance has multiple databases, each with separate schemas. There is typically little communication between separate databases, and most databases are no more than about 1000-2000 objects. This means SQL Compare can register an entire database in a reasonable amount of time, and cross-database dependencies probably won't be an issue. It is a quite different scene under Oracle, however. The terms 'database' and 'instance' are used interchangeably, (although technically 'database' refers to the datafiles on disk, and 'instance' the running Oracle process that reads & writes to the database), and a database is a single conceptual entity. This immediately presents problems, as it is infeasible to register an entire database as we do in SQL Compare; in my Oracle install, using the standard recommended options, there are 63975 system objects. If we tried to register all those, not only would it take hours, but the client would probably run out of memory before we finished. As a result, we had to allow people to specify what schemas they wanted to register. This decision had quite a few knock-on effects for the design, which I will cover in a future post. 2. Connecting to Oracle The next obvious difference is in actually connecting to Oracle – in SQL Server, you can specify a server and database, and off you go. On Oracle things are slightly more complicated. SIDs, Service Names, and TNS A database (the files on disk) must have a unique identifier for the databases on the system, called the SID. It also has a global database name, which consists of a name (which doesn't have to match the SID) and a domain. Alternatively, you can identify a database using a service name, which normally has a 1-to-1 relationship with instances, but may not if, for example, using RAC (Real Application Clusters) for redundancy and failover. You specify the computer and instance you want to connect to using TNS (Transparent Network Substrate). The user-visible parts are a config file (tnsnames.ora) on the client machine that specifies how to connect to an instance. For example, the entry for one of my test instances is: SC_11GDB1 = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = simonctest)(PORT = 1521)) ) (CONNECT_DATA = (SID = 11gR1db1) ) ) This gives the hostname, port, and SID of the instance I want to connect to, and associates it with a name (SC_11GDB1). The tnsnames syntax also allows you to specify failover, multiple descriptions and address lists, and client load balancing. You can then specify this TNS identifier as the data source in a connection string. Although using ODP.NET (the .NET dlls provided by Oracle) was fine for internal prototype builds, once we released the EAP we discovered that this simply wasn't an acceptable solution for installs on other people's machines. Due to .NET assembly strong naming, users had to have installed on their machines the exact same version of the ODP.NET dlls as we had on our build server. We couldn't ship the ODP.NET dlls with our installer as the Oracle license agreement prohibited this, and we didn't want to force users to install another Oracle client just so they can run our program. To be able to list the TNS entries in the connection dialog, we also had to locate and parse the tnsnames.ora file, which was complicated by users with several Oracle client installs and intricate TNS entries. After much swearing at our computers, we eventually decided to use a third party Oracle connection library from Devart that we could ship with our program; this could use whatever client version was installed, parse the TNS entries for us, and also had the nice feature of being able to connect to an Oracle server without having any client installed at all. Unfortunately, their current license agreement prevents us from shipping an Oracle SDK, but that's a bridge we'll cross when we get to it. 3. Running synchronization scripts The most important difference is that in Oracle, DDL is non-transactional; you cannot rollback DDL statements like you can on SQL Server. Although we considered various solutions to this, including using the flashback archive or recycle bin, or generating an undo script, no reliable method of completely undoing a half-executed sync script has yet been found; so in this case we simply have to trust that the DBA or developer will check and verify the script before running it. However, before we got to that stage, we had to get the scripts to run in the first place... To run a synchronization script from SQL Compare we essentially pass the script over to the SqlCommand.ExecuteNonQuery method. However, when we tried to do the same for an OracleConnection we got a very strange error – 'ORA-00911: invalid character', even when running the most basic CREATE TABLE command. After much hair-pulling and Googling, we discovered that Oracle has got some very strange behaviour with semicolons at the end of statements. To understand what's going on, we need to take a quick foray into SQL and PL/SQL. PL/SQL is not T-SQL In SQL Server, T-SQL is the language used to interface with the database. It has DDL, DML, control flow, and many other nice features (like Turing-completeness) that you can mix and match in the same script. In Oracle, DDL SQL and PL/SQL are two completely separate languages, with different syntax, different datatypes and different execution engines within the instance. Oracle SQL is much more like 'pure' ANSI SQL, with no state, no control flow, and only the basic DML commands. PL/SQL is the Turing-complete language, but can only do DML and DCL (i.e. BEGIN TRANSATION commands). Any DDL or SQL commands that aren't recognised by the PL/SQL engine have to be passed back to the SQL engine via an EXECUTE IMMEDIATE command. In PL/SQL, a semicolons is a valid token used to delimit the end of a statement. In SQL, a semicolon is not a valid token (even though the Oracle documentation gives them at the end of the syntax diagrams) . When you execute the command CREATE TABLE table1 (COL1 NUMBER); in SQL*Plus the semicolon on the end is a command to SQL*Plus to execute the preceding statement on the server; it strips off the semicolon before passing it on. SQL Developer does a similar thing. When executing a PL/SQL block, however, the syntax is like so: BEGIN INSERT INTO table1 VALUES (1); INSERT INTO table1 VALUES (2); END; / In this case, the semicolon is accepted by the PL/SQL engine as a statement delimiter, and instead the / is the command to SQL*Plus to execute the current block. This explains the ORA-00911 error we got when trying to run the CREATE TABLE command – the server is complaining about the semicolon on the end. This also means that there is no SQL syntax to execute more than one DDL command in the same OracleCommand. Therefore, we would have to do a round-trip to the server for every command we want to execute. Obviously, this would cause lots of network traffic and be very slow on slow or congested networks. Our first attempt at a solution was to wrap every SQL statement (without semicolon) inside an EXECUTE IMMEDIATE command in a PL/SQL block and pass that to the server to execute. One downside of this solution is that we get no feedback as to how the script execution is going; we're currently evaluating better solutions to this thorny issue. Next up: Dependencies; how we solved the problem of being unable to register the entire database, and the knock-on effects to the whole product.

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  • Opportunity Nokia's

    - by Andrew Clarke
    Nokia’s alliance with Microsoft is likely to be good news for anyone using Microsoft technologies, and particularly for .NET developers. Before the announcement, the future wasn’t looking so bright for the ‘mobile’ version of Windows, Windows Phone. Microsoft currently has only 3.1% of the Smartphone market, even though it has been involved in it for longer than its main rivals. Windows Phone has now got the basics right, but that is hardly sufficient by itself to change its predicament significantly. With Nokia's help, it is possible. Despite the promise of multi-tasking for third party apps, integration with Microsoft platforms such as Xbox and Office, direct integration of Twitter support, and the introduction of IE 9 “later this year”, there have been frustratingly few signs of urgency on Microsoft’s part in improving the Windows Phone  product. Until this happens, there seems little prospect of reward for third-party developers brave enough to support the platform with applications. This is puzzling when one sees how well SQL Server and Microsoft’s other server technologies have thrived in recent years, under good leadership from a management that understands the technology. The same just hasn’t been true for some of the consumer products. In consequence, iPads and Android tablets have already exposed diehard Windows users, for the first time, to an alternative GUI for consumer Tablet PCs, and the comparisons aren’t always in Windows’ favour. Nokia’s problem is obvious: Android’s meteoric rise. Android now has 33% of the worldwide market for smartphones, while the market share of Nokia’s Symbian has dropped from 44% to 31%. As details of the agreement emerge, it would seem that Nokia will bring a great deal of expertise, such as imaging and Nokia Maps, to Windows Phone that should make it more competitive. It is wrong to assume that Nokia’s decline will continue: the shock of Android’s sudden rise could be enough to sting them back to their previous form, and they have Microsoft’s huge resources and marketing clout to help them. For the sake of the whole Windows stack, I really hope the alliance succeeds.

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