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

exactly The reason is that the act of taking a snapshot is not atomic; a series of queries are executed gathering statistics into tables during a statspack snapshot, and each query is as of a slightly different point in time. So, the wait event metrics were gathered at a time slightly before the latching details were.

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Our Latch Sleep Breakdown report shows us the number of times we tried to get a latch and failed in the spin loop That means the Top 5 report is showing us only the tip of the iceberg with regard to latching issues the 133,507 misses (which means we spun trying to get the latch) are not revealed in the Top 5 report for us After examination of the Top 5 report, we might not be inclined to think we have a hard parse problem here, even though we have a very serious one To perform 2 units of work, we needed to use 3 units of CPU This was due entirely to the fact that we need that shared resource, the shared pool Such is the nature of latching.

This has the effect of making simple website projects seem quite complex. To help you through this, Table 14-1 shows the most common file types used when writing web applications using F# and ASP.NET. Table 14-2 shows some additional file types that are useful to be aware of.

You can see that it can be very hard to diagnose a latching-related issue, unless you understand the mechanics of how they are implemented A quick glance at a statspack report, using the Top 5 section, might cause us to miss the fact that we have a fairly bad scaling issue on our hands Only by deeper investigation in the latching section of the statspack report will we see the problem at hand Additionally, it is not normally possible to determine how much of the CPU time used by the system is due to this spinning all we know in looking at the two-user test is that we used 102 seconds of CPU time and that we missed getting a latch on the shared pool 133,507 times.

We don t know how many times we spun trying to get the latch each time we missed, so we have no real way of gauging how much of the CPU time was spent spinning and how much was spent processing We need multiple data points to derive that information In our tests, because we have the single-user example for comparison, we can conclude that about 39 CPU seconds or so was spent spinning on the latch, waiting for that resource We can come to this conclusion because we know that a single user needs only 32 seconds of CPU time so two single users would need 64 seconds, and 103 (total CPU seconds)minus 64 is 39..

Web form (web page)

Now I d like to look at the same situation as presented in the previous section, but this time using a program that uses significantly less latches during its processing. We ll take that Java program and code it using bind variables. To accomplish this, we ll change the Statement into a PreparedStatement, parse a single INSERT statement, and then bind and execute that PreparedStatement repeatedly in the loop:

import java.sql.*; public class instest { static public void main(String args[]) throws Exception { System.out.println( "start" ); DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver()); Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@localhost:1521:ora11gr2", "scott","tiger"); conn.setAutoCommit( false ); PreparedStatement pstmt = conn.prepareStatement ("insert into "+ args[0] + " (x) values( )" ); for( int i = 0; i < 25000; i++ ) { pstmt.setInt( 1, i ); pstmt.executeUpdate(); } conn.commit(); conn.close(); System.out.println( "done" ); } } Let s look at the single and dual user statspack reports, as we did for the no bind variable example. We ll see dramatic differences here. Here is the single-user report: Elapsed: DB time: 0.17 (mins) Av Act Sess: 0.10 (mins) DB CPU: 0.6 0.10 (mins)

The presentation layer, often authored using visual editing tools. These files include ASP.NET control declarations and embedded HTML tags. They may also include fragments of other languages such as CSS and scripts written in F#. Similar to the .aspx file but is used for writing elementary building blocks that can be reused on multiple pages in the application. The programmatic portion of the website logic. Typically makes extensive use of the System.Data and System.Web namespaces. Compiled DLLs referenced by your server-side code. Configuration files that may be located in every application directory and are used to specify aspects such as security or compilation options.