ASP.NET Web PDF Document Viewer/Editor Control Library

The implementation of n-level undo functionality is quite complex, and involves heavy use of reflection. Fortunately, we can use inheritance to place the implementation in a base class, so that no business object needs to worry about the undo code. In fact, to keep things cleaner, this code is in its own base class, separate from any other business object behaviors, as shown in Figure 2-11.

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update t t2 set x = x+1 call count ------- -----Parse 1 Execute 1 Fetch 0 ------- -----total 2 query current ------ ---------0 0 7 1 0 0 ------ ---------7 1 rows ---------0 1 0 ---------1

So, during just a normal query, we incur seven query (consistent) mode gets During the first UPDATE, we incur the same seven I/Os (the search component of the update involves finding all of the rows that are in the table when the update began, in this case) and three current mode gets as well The current mode gets are performed in order to retrieve the table block as it exists right now, the one with the row on it, to get an undo segment block to begin our transaction, and an undo block The second update has exactly one current mode get; since we did not have to do the undo work again, we had only the one current get on the block with the row we want to update The very presence of the current mode gets tells us that a modification of some sort took place.

ASP.NET comes with a number of built-in application services that you can use and customize as you build your web applications. These encapsulate much of the core functionality common to most websites, such as membership and role management, profiles and personalization, and site navigation, and you can easily plug them into your website logic right out of the box. These services interact with service-specific data (the users registered, the different user roles your site is programmed for, various data associated with the authenticated users, and so on) via providers, which are classes that implement the appropriate interfaces to fulfill contracts for various services. ASP.NET comes with a number of built-in providers; for instance, it has a SQL and an Active Directory membership provider. The provider model allows you to plug in your own providers (simply by specifying them in the appropriate section of your web.config), so you may write an Oracle or a custom membership provider to your existing user/membership database or a role service provider based on simple XML files. Table 14-9 shows some common provider-based services in ASP.NET.

Before Oracle will modify a block with new information, it must get the most current copy of it So, how does read consistency affect a modification Well, imagine you were executing the following UPDATE statement against some database table: Update t set x = x+1 where y = 5; We understand that the WHERE Y=5 component, the read-consistent phase of the query, will be processed using a consistent read (query mode gets in the TKPROF report) The set of WHERE Y=5 records that was committed in the table at the beginning of the statement s execution are the records it will see (assuming READ COMMITTED isolation; if the isolation is SERIALIZABLE, it would be the set of WHERE Y=5 records that existed when the transaction began).

Handles the encryption and decryption of ASP.NET configuration files and sections within Manages users and their accounts Adds user information (for instance, user preferences) that is to be collected and stored for each user Manages roles and their associated access rights Manages session state for a user visit Stores information about each page and its place in the site s structure Allows the monitoring of an application for control purposes Manages a set of controls and their content and appearance that make up a portal

This means if that UPDATE statement were to take five minutes to process from start to finish, and someone added and committed a new record to the table.

with a value of 5 in the Y column, then that UPDATE would not see it because the consistent read would not see it. This is expected and normal. But, the question is, what happens if two sessions execute the following statements in order: Update t set y = 10 where y = 5; Update t Set x = x+1 Where y = 5; Table 7-8 demonstrates the timeline. Table 7-8. Sequence of Updates