.NET/Java PDF, Tiff, Barcode SDK Library

In a similar way, you can obtain an instance of the MethodInfo class describing the Quit method. Since a method has a signature, you ask for the parameters; there are three of them, and they are optional. Therefore, you can invoke the Quit method by calling the Invoke method and passing the object target of the invocation and an array of arguments that you set to null because arguments are optional. How can the runtime interact with COM components The basic approach is based on the so-called COM callable wrapper (CCW) and the runtime callable wrapper (RCW), as shown in Figure 17-3. The former is a chunk of memory dynamically generated with a layout compatible with the one expected from COM components so that external programs, even legacy Visual Basic 6 applications, can access services implemented as managed components. The latter is more common and creates a .NET type dealing with the COM component, taking care of all the interoperability issues. It is worth noting that although the CCW can always be generated because the .NET runtime has full knowledge about assemblies, the opposite is not always possible. Without IDispatch or type libraries, there is no description of a COM component at run time. Moreover, if a component uses custom marshalling, it cannot be wrapped by an RCW. Fortunately, for the majority of COM components, it is possible to generate the RCW.

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The clustering column for this cluster will be the DEPTNO column The columns in the tables do not have to be called DEPTNO but they must be NUMBER(2) to match this definition We have, on the cluster definition, a SIZE 1024 option This is used to tell Oracle that we expect about 1,024 bytes of data to be associated with each cluster key value Oracle will use that to compute the maximum number of cluster keys that could fit per block Given that we have an 8KB block size, Oracle will fit up to seven cluster keys (but maybe less if the data is larger than expected) per database block For example, the data for departments 10, 20, 30, 40, 50, 60, and 70 would tend to go onto one block, and as soon as we insert department 80, a new block will be used.

Figure 17-3. The wrappers generated by the CLR to interact with COM components Programming patterns based on event-driven programming are widely adopted, and COM components have a programming pattern to implement callbacks based on the notion of sink. The programming pattern is based on the delegate event model, and the sink is where a listener can register a COM interface that should be invoked by a component to notify an event. The Internet Explorer Web Browser COM component (implemented by shdocvw.dll), for instance, provides a number of events to notify its host about the various events such as loading a page or clicking a hyperlink. The RCW generated by the runtime exposes these events in the form of delegates and takes care of handling all the details required to perform the communication between managed and unmanaged code. Although COM components can be accessed dynamically using .NET reflection, explicitly relying on the ability of the CLR to generate CCW and RCW, it is desirable to use a less verbose

This does not mean that the data is stored in a sorted manner; it just means that if we inserted the departments in that order, they would naturally tend to be put together If we inserted the departments in the order 10, 80, 20, 30, 40, 50, 60, and then 70, the final department (70) would tend to be on the newly added block As we ll see below, both the size of the data and the order in which the data is inserted will affect the number of keys we can store per block The SIZE parameter therefore controls the maximum number of cluster keys per block It is the single largest influence on the space utilization of our cluster Set the size too high, and we ll get very few keys per block and we ll use more space than we need.

Set the size too low, and we ll get excessive chaining of data, which offsets the purpose of the cluster to store all of the data together on a single block It is the most important parameter for a cluster..

Table 10-2. Namespaces in the DLLs from Table 10-1, with MSDN Descriptions (Continued)

This is one of the most highly touted reasons for using shared server: it reduces the amount of required memory. It does, but not as significantly as you might think, especially given the new automatic PGA memory management discussed in 4, Memory Structures, where work areas are allocated to a process, used, and released and their size varies based on the concurrent workload. So, this was a fact that was truer in older releases of Oracle but is not as meaningful today. Also, remember that when you use shared server, the UGA is located in the SGA. This means that when switching over to shared server, you must be able to accurately determine your expected UGA memory needs and allocate appropriately in the SGA via the LARGE_POOL_SIZE parameter. The SGA requirements for the shared server configuration are typically very large. This memory must typically be preallocated and thus can only be used by the database instance.

Note It is true that with a resizable SGA, you may grow and shrink this memory over time, but for the most part,