Pythian Group

Most people think Windows administrators make a living with their right-hand—you know, right-clicking and left-clicking the user interface to get things done. While anybody can do that in Windows, the real value comes in when you no longer need to rely so much on the user interface but instead write scripts. Lower total cost of ownership is achieved when the administrative costs are kept low, and this is where Windows PowerShell comes in.

I’ve spent a fair amount of time writing VBScript scripts to administer Windows servers and workstations and automating repetitive tasks. One reason for me moving into Windows PowerShell is its roots in the Microsoft .NET Framework, as I have done a fair amount of .NET programming. But what is Windows PowerShell anyway?

Windows PowerShell is an extensible command-line shell and an associated scripting language built on top of the .NET Framework v2.0. It was released in 2006 and is currently available for Windows XP SP2/SP3, Windows Server 2003, Windows Vista, and is included in Windows Server 2008.

PowerShell will be included as a common engineering criteria (CEC) in future releases of Microsoft server products, making it a must-learn for Microsoft server administrators.

Administrators (DBAs included) have been using scripting to automate administrative tasks with scripting languages like DOS batch, VBScript, Perl, and a few third-party tools like KiXtart and WinScript. Windows PowerShell complements the administrators’ existing scripting toolkit to easily manage and administer Windows workstations and servers and other Microsoft server products as THEY are being built using the .NET Framework.

Although it is designed for operating systems, Windows PowerShell can be used to administer SQL Server 2005 instances and higher, as Server Management Objects—the object model used to manage SQL Server 2005—are built using the .NET Framework, thus exposing the object model in PowerShell. And since SMO is compatible with SQL Server 2000, you can administer SQL Server 2000 instances using Windows PowerShell. SQL Server 2008 even ships with its own PowerShell snap-in.

No wonder it makes sense to learn a thing or two about Windows PowerShell. Besides, I’ve seen Windows administrators being “forced” to do SQL Server DBA tasks even without knowing what T-SQL is. Windows PowerShell makes it a level playing field.

I will be posting a series of blog posts on getting started with Windows PowerShell, and how any Windows administrator can use it for their day-to-day tasks. In the process, I’ll also cover how to use Windows PowerShell for administering SQL Server instances.

Contemporary software engineering models include many loosely-defined layers. Database developers might help with other layers, but for the most part a database administrator’s domain is the persistence layer.

• Presentation


• Application


• Business Logic


• Persistence (also called Storage)

The Daily WTF has an article on The Mythical Business Layer makes the case for not separating the business layer and the application layer:

A good system (as in, one that’s maintainable by other people) has no choice but to duplicate, triplicate, or even-more-licate business logic. If Account_Number is a seven-digit required field, it should be declared as CHAR(7) NOT NULL in the database and have some client-side code to validate it was entered as seven digits. If the system allows data entry in other places by other means, that means more duplication of the Account_Number logic is required.

It almost goes without saying that business logic changes frequently and in unpredictable ways. The solution to this problem is not a cleverly coded business layer. Unfortunately, it’s much more boring than that. Accommodating change can only be accomplished through careful analysis and thorough testing.

I will call this merged business/application layer the “functional layer.”

The serious scaling requirements posed by most applications these days call for partitioning, clustering, sharding or some other term for “dividing up the data so it does not become the bottleneck”. Enter the “architecture layer”.

“Wait a minute,” I hear you asking. “Isn’t that just the persistence layer?”

Yes and no. To me, there’s a difference between the storage and the architecture of said storage. The database schema for storing a user profile is a persistence layer issue. Figuring out which database instance to go to is an architecture layer issue.

This is an important distinction for me. Many folks are coding the architecture layer directly into the functional layer. A “save_profile()” API function might call an ORM to deal with the persistence, or it will have MySQL (or other database) connection handling and queries. However, the database will grow, and at some point you will find yourself wanting to split the data [more].

This type of information, like the presentation layer, needs to be separate. Why should the application care whether save_profile(‘Sheeri’,'hair color’,'blonde’) accesses database1 or database2? More importantly, why should there be major code changes to the functional layer if the architecture changes? Just like no functionality has changed when you change your website color from blue to red, there is no functionality change when you go from splitting data between 2 database servers to splitting among 3, or 10.

For me, the persistence layer is about how the data is stored. Which, explicitly and for the record, I also believe should be separate from the functional layer — if you store hair color and eye color in one table or 2, the functionality of the application has not changed; all that’s needed is a change in how that data is stored and retrieved.

The architecture layer is all about where the data is stored. Early forms of the architecture layer are configuration files, though most would not call that a “layer”. Database administrators should be able to change the architecture of the database system without requiring mucking about in the application’s functional code.

Thoughts?