ASP.NET Web PDF Document Viewer/Editor Control Library

Oracle finds this method scalable enough to run all of their TPC-Cs (an industry standard OLTP benchmark; see http://wwwtpcorg for details) In many other implementations, you will find this being achieved with shared read locks and their corresponding deadlocks, and blocking In Oracle, we do not get any blocking, but we will get the ORA-08177 error if other sessions change the data we want to change as well However, we will not get the error as frequently as we will get deadlocks and blocks in the other systems But there is always a but you must take care to understand these different isolation levels and their implications Remember, with isolation set to SERIALIZABLE, you will not see any changes made in the database after the start of your transaction, until you commit.

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InitialValue MinimumValue, MaximumValue, Type ValidationExpression ControlToCompare, Operator, ValueToCompare, Type ClientValidationFunction, ServerValidate (event) DisplayMode, HeaderText, ValidationGroup

Applications that attempt to enforce their own data integrity constraints, such as the resource scheduler described in 1 Developing Successful Oracle Applications , must take extra care in this regard If you recall, the problem in 1 was that we could not enforce our integrity constraint in a multiuser system since we could not see changes made by other uncommitted sessions Using SERIALIZABLE, we would still not see the uncommitted changes, but we would also not see the committed changes made after our transaction began! As a final point, be aware that SERIALIZABLE does not mean that all transactions executed by users will behave as if they were executed one right after another in a serial fashion It does not imply that there is some serial ordering of the transactions that will result in the same outcome The phenomena previously described by the SQL standard do not make this happen.

This last point is a frequently misunderstood concept, and a small demonstration will clear it up The following table represents two sessions performing work over time The database tables A and B start out empty and are created as follows: ops$tkyte@ORA11GR2> create table a ( x int ); Table created ops$tkyte@ORA11GR2> create table b ( x int ); Table created..

You may end up working with complex web pages that have many, even dozens, of input controls that belong to different forms on the page (for instance, a web page with a search form, a user registration form, and a contact form). By default, all validators defined on the page would be run and most likely prohibit your end user from moving onto the next page because of validation errors that are seemingly unrelated to the chosen action of the user. To solve this problem, you can turn to using validation groups, which specify a set of related controls and their validators. A validation group is formed by specifying a common group name (as a string) for the ValidationGroup property of each validator and the input control that triggers a page submission. This will ensure that only the validators that are related to the control initiating the page submission will be run. Finally, you can disable any validation by setting the CausesValidation property of a postback control to false.

Alter session set isolation_level=serializable; --

Alter session set isolation_level=serializable; -Insert into b select count(*) from a; -Commit;

Debugging ASP.NET applications is easy when using a tool such as Visual Studio. You can set breakpoints in your F# code, and these will allow you to break into the middle of code executing when server requests are performed. We discuss debugging techniques for regular F# code in 18. During development, it is often necessary to trace what happens on a page, as well as during the process of serving that page. You can enable page tracing by adding the Trace="true" page attribute to your web form. This will append information shown in Table 14-8 to the page displayed. Figure 14-3 shows an example of this information for the application from Listing 14-4.

Insert into a select count(*) from b; -Commit; --

Now, when this is all said and done, tables A and B will each have a row with the value 0 in it. If there were some serial ordering of the transactions, we could not possibly have both tables containing the value 0 in them. If session 1 executed in its entirety before session 2, then table B would have a row with the value 1 in it. If session 2 executed is its entirety before session 1, then table A would have a row with the value 1 in it. As executed here, however, both tables will have rows with a value of 0. They just executed as if they were the only transaction in the database at that point in time. No matter how many times session 1 queries table B and no matter the committed state of session 2, the count will be the count that was committed in the database at time T1. Likewise, no matter how many times session 2 queries table A, the count will be the same as it was at time T2.