ASP.NET PDF Viewer using C#, VB/NET

From Table 8-1, we can draw the following performance-related conclusions: In general, the relational tables based solution outperforms the other two solutions (in many cases by orders of magnitudes, both in terms of elapsed times and latches). The object views based solution performs rather poorly when compared to the nested tables based solution when it comes to inserts, deletes, and updates. This can be attributed to the overhead of the instead of triggers that do all the work behind the scenes. When it comes to selects, object views perform much better than the nested tables based solution. From the discussion we have had so far in this chapter, we can conclude the following about the code maintenance of all three approaches: In general, the code written on top of the relational schema is much more maintainable and also more open to be accessed from various tools that work using SQL as compared to schema that uses objects as storage mechanism. The code complexity increases tremendously for both object views and the nested tables based schema. On the whole, it is a good idea to always give preference to a pure relational tables based approach given the performance benefits and the other benefits, as discussed in the earlier sections. If you do have a good reason to choose otherwise, then the second choice, in general, may be the object views based solution, especially if the inserts, deletes, and updates are done directly on the underlying tables and only selects, when required, are done on the object view itself.

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Note how each individual Async program hops between threads; the MOMA request started on .NET thread 12 and finished life on .NET thread 8. Each asynchronous computation in Listing 13-5 executes in the following way: Each asynchronous computation starts life as a work item in the .NET thread pool. (The .NET thread pool is explained in the What Is the .NET Thread Pool sidebar.) These are processed by a number of .NET threads. When the asynchronous computations reach the GetResponseAsync and ReadToEndAsync calls, the requests are made and the continuations are registered as I/O completion actions in the .NET thread pool. No thread is used while the request is in progress. When the requests complete, they trigger a callback in the .NET thread pool. These may be serviced by different threads than those that originated the calls.

Summary

as we focus on larger issues of architecture and design in an n-tiered application. You can find feature-level coverage in Beginning ASP.NET 2.0 in C# by Matthew MacDonald (Apress, 2005).

.NET objects such as BackgroundWorker use a single .NET background thread, which corresponds to a single Windows or other OS thread. OS threads have supporting resources such as an execution stack that consume memory and are relatively expensive resources to create and run. However, many concurrent processing tasks require only the ability to schedule short-lived tasks that then suspend, waiting for further input. To simplify the process of creating and managing these tasks, the .NET Framework provides the System.Threading.ThreadPool class. The thread pool consists of two main sets of suspended tasks: a queue containing user work items and a pool of I/O completion callbacks, each waiting for a signal from the operating system. The number of threads in the thread pool is automatically tuned, and items can be either queued asynchronously or registered against a .NET WaitHandle synchronization object (for example, a lock, a semaphore, or an I/O request). This is how to queue a work item in the .NET thread pool: open System.Threading ThreadPool.QueueUserWorkItem(fun _ -> printf "Hello!") |> ignore

In this chapter, you learned about different ways in which objects are useful in Oracle. In particular, you learned about three different ways in which objects are useful: Purely as a programming construct As a mechanism to store data in object tables In the form of object views that work on top of relational tables You discovered that it is best to use objects as a programming construct to enhance the power of your PL/SQL code. Storing data in object tables that contain varrays or nested table columns can lead to complex code that does not perform well, as you learned from the performance study done at the end of the chapter. In particular, you discovered that DMLs on relational tables perform much better in general when compared to DMLs carried out on object views and tables containing nested tables. In the next chapter, we will look at how to access objects from JDBC.

Async<'a> values are essentially a way of writing continuation-passing or callback programs explicitly Continuations themselves were described in 8 along with techniques to pass them explicitly Async<'a> are computations that call a success continuation when the asynchronous computation completes and an exception continuation if it fails They provide a form of managed asynchronous computation, where managed means that several aspects of asynchronous programming are handled automatically: Exception propagation is added for free : If an exception is raised during an asynchronous step, then the exception terminates the entire asynchronous computation and cleans up any resources declared using use, and the exception value is then handed to a continuation Exceptions may also be caught and managed within the asynchronous workflow by using try/with/finally Cancellation checking is added for free : The execution of an Async<'a> workflow automatically checks a cancellation flag at each asynchronous operation.