.NET/ASP.NET/C#/VB.NET PDF Document SDK

Component Object Model (COM) is a technology that Microsoft introduced in the 1990s to support interoperability among different programs possibly developed by different vendors The Object Linking and Embedding (OLE) technology that allows embedding arbitrary content in a Microsoft Word document, for instance, relies on this infrastructure COM is a binary standard that allows code written in different languages to interoperate, assuming that the programming language supports this infrastructure Most of the Windows operating system and its applications are based on COM components The CLR was initially conceived as an essential tool to develop COM components, being that COM was the key technology at the end of 1990s It is no surprise that the Microsoft implementation of CLR interoperates easily and efficiently with the COM infrastructure.

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Rows ------4 1 1 4

Row Source Operation --------------------------------------------------NESTED LOOPS (cr=7 pr=3 pw=0 time=9 us cost=4 size=280 card=4) TABLE ACCESS BY INDEX ROWID EMP (cr=3 pr=0 pw=0 time=0 us cost=2 size=30 ) INDEX UNIQUE SCAN EMP_PK (cr=2 pr=0 pw=0 time=0 us cost=1 size=0 ) INDEX RANGE SCAN SYS_IOT_TOP_93124 (cr=4 pr=3 pw=0 time=3 us cost=2 )

In this section, we briefly review the main concepts of the COM infrastructure and its goals in order to show you how COM components can be consumed from F# (and vice versa) and how F# components can be exposed as COM components A COM component is a binary module with a well-defined interface that can be dynamically loaded at run time by a running program The COM design was influenced by CORBA and the Interface Definition Language (IDL) to describe a component as a set of interfaces In the case of COM, however, components are always loaded inside the process using the dynamic loading of DLLs Even when a component runs in a different process, a stub is loaded as a DLL, and it is responsible for interprocess communication.

Both queries fetched exactly the same number of rows, but the HEAP table performed considerably more logical I/O. As the degree of concurrency on the system goes up, we would likewise expect the CPU used by the HEAP table to go up more rapidly as well, while the query possibly waits for latches into the buffer cache. Using runstats (a utility of my own design; refer to the introductory section Setting Up Your Environment for This Book for details), we can measure the difference in latching. On my system, I observed the following STAT...consistent gets STAT...consistent gets from ca STAT...no work - consistent re STAT...session logical reads STAT...consistent gets from ca STAT...table fetch by rowid STAT...buffer is not pinned co LATCH.cache buffers chains STAT...physical read total byt STAT...physical read bytes STAT...cell physical IO interc 723,073 723,073 362,683 723,131 359,225 360,385 648,695 1,090,022 30,703,616 30,703,616 30,703,616 438,048 438,048 77,651 438,086 72,982 72,085 288,324 523,161 40,747,008 40,747,008 40,747,008 -285,025 -285,025 -285,032 -285,045 -286,243 -288,300 -360,371 -566,861 10,043,392 10,043,392 10,043,392

Run1 latches total versus runs -- difference and pct Run1 Run2 Diff Pct 1,204,593 624,834 -579,759 192.79% where Run1 was the HEAP_ADDRESSES table and Run2 was the IOT_ADDRESSES table. As you can see, there was a dramatic and repeatable decrease in the latching taking place, mostly due to the cache buffers chains latch (the one that protects the buffer cache). The IOT in this case would provide the following benefits: Increased buffer cache efficiency, as any given query needs to have fewer blocks in the cache. Decreased buffer cache access, which increases scalability. Less overall work to retrieve our data, as it is faster. Less physical I/O per query possibly, as fewer distinct blocks are needed for any given query and a single physical I/O of the addresses most likely retrieves all of them (not just one of them, as the heap table implementation does).

When you create an instance of a COM component, you obtain a pointer to an IUnknown interface that acts as the entry point to all interfaces implemented by the component The QueryInterface method of this interface allows you to get pointers to additional interfaces Interface pointers in COM are pointers to tables of pointers defining the method s location The program must know the layout of the table in order to read the desired pointer and invoke the corresponding method This knowledge can be compiled into the program (interfaces.

The same would be true if you frequently use BETWEEN queries on a primary or unique key. Having the data stored physically sorted will increase the performance of those queries as well. For example, I maintain a table of stock quotes in my database. Every day, for hundreds of stocks, I gather together the stock ticker, date, closing price, days high, days low, volume, and other related information. The table looks like this: ops$tkyte@ORA11GR2> create table stocks 2 ( ticker varchar2(10), 3 day date,