ASP.NET Web PDF Document Viewer/Editor Control Library

The application was built without a single consideration for scaling at the database level. The application was performing functionality (the queue table) that the database already supplied in a highly concurrent and scalable fashion. I m referring to the Advance Queuing (AQ) software that is burned into the database, functionality they were trying to reinvent. Experience shows that 80 to 90 percent of all tuning is done at the application level, not at the database level. The developers had no idea what the beans did in the database or where to look for potential problems.

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Typed datasets are derived from ordinary datasets and allow you to work with data in a typesafe manner. This means that instead of (row.Item "FirstName" : > string), you can simply write row.FirstName. Typed datasets can be created using the xsd.exe command-line tool included in the .NET SDK. This tool generates source code from XML schema documents, so to use it you must obtain an XSD document for the tables you want data objects for. (You can quickly generate an XML schema document using Visual Studio; select File New File XML Schema, and drag the needed data tables onto the design canvas.) Alternatively, we can extract this schema definition using code: open System.IO let dataSet2 = buildDataSet conn "SELECT * FROM Employees" let file name = Path.Combine(@"c:\fsharp", name) do File.WriteAllText(file "employees.xsd", dataSet2.GetXmlSchema()) Using this extracted XSD document, we can now fire up xsd.exe from the command-line shell:

This was hardly the end of the problems on this project. We also had to figure out How to tune SQL without changing the SQL. In general, that is very hard to do. Oracle10g and above do permit us to accomplish this magic feat for the first time to some degree with SQL Profiles, and 11g and above with extended statistics. But inefficient SQL will remain inefficient SQL. How to measure performance. How to see where the bottlenecks were. How and what to index. And so on.

At the end of the week the developers, who had been insulated from the database, were amazed at what the database could actually provide for them and how easy it was to get that information. Most importantly, they saw how big of a difference taking advantage of database features could make to the performance of their application. In the end, they were successful just behind schedule by a couple of weeks. My point about the power of database features is not a criticism of tools or technologies like Hibernate, EJBs, and container-managed persistence. It is a criticism of purposely remaining ignorant of the database and how it works and how to use it. The technologies used in this case worked well after the developers got some insight into the database itself. The bottom line is that the database is typically the cornerstone of your application. If it does not work well, nothing else really matters. If you have a black box and it does not work, what are you going to do about it About the only thing you can do is look at it and wonder why it is not working very well. You can t fix it, you can t tune it. Quite simply, you do not understand how it works and you made the decision to be in this position. The alternative is the approach that I advocate: understand your database, know how it works, know what it can do for you, and use it to its fullest potential.

C:\fsharp> xsd.exe employees.xsd /d /l:CS /n:Employees.Data Writing file 'C:\fsharp\Employees.cs'. C:\fsharp> csc /target:library Employees.cs This generates a C# file Employees.cs in the Employees.Data namespace containing a typed dataset for the Employees table, which we then compile to Employees.dll. We can now reference this DLL and create an instance of a typed dataset: > #r @"employees.dll";; Binding session to 'C:\fsharp\Employees.dll'... > let employeesTable = new Employees.Data.NewDataSet();; val employeesTable : Employees.Data.NewDataSet > dataAdapter.Fill(employeesTable) |> ignore;; val it : unit = () // ignore the number of records

That s enough hypothesizing, for now at least. In the remainder of this chapter, I will take a more empirical approach, discussing why knowledge of the database and its workings will definitely go a long way towards a successful implementation (without having to write the application twice!). Some problems are simple to fix as long as you understand how to find them. Others require drastic rewrites. One of the goals of this book is to help you avoid the problems in the first place.

Note In the following sections, I discuss certain core Oracle features without delving into exactly what these