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.NET/ASP.NET/C#/VB.NET PDF Document SDKWith the advent of web applications, application servers mediate the interaction between the application and the database. Typically, a web application client uses the HTTP protocol to connect to an application server containing the middle-tier business logic. The application server in turn connects to the database to perform various functions. If we create a separate database account for each end user and maintain a dedicated connection, we run into two problems: Performance: The number of users in a large web application can easily run into the thousands (or more). Maintaining a dedicated connection for each user for the duration of one application session can rapidly exhaust the computing resources (memory and CPU) at the database and application server levels. It can also result in very poor usage of connection resources. Security: Maintaining separate database accounts for each user means that the application may have to know and maintain the database password of each user. This can result in password-management issues. In this chapter, we will focus on tackling the performance issues just outlined using connection pooling. In the next chapter, we will examine how we can use proxy authentication to solve the security problem while maintaining good performance. barcode generator excel template, excel 2010 barcode macro, excel 2010 barcode erstellen freeware, how to make barcodes in excel free, barcode excel, creating barcodes in excel 2003, download barcode font for excel 2010, how to make barcodes from a list of numbers in excel 2010, how to make barcodes in excel 2013, barcode font excel 2016,This is not the case for programming languages such as C that allow functions with a variable number of arguments such as printf When variable arguments are allowed, it is the caller that knows exactly the size of the activation record; therefore, it is its responsibility to free the stack at the end of the function call Apart from being consistent with the chosen convention, it may seem that there is little difference between the two choices, but if the caller is responsible for cleaning the stack, each function invocation requires more instructions, which leads to larger executables; for this reason, Windows uses the stdcall calling convention instead of the C calling convention. To quantify the cost of establishing and tearing down a database connection, I wrote a simple program. The following program, CostOfConnection, extends the JBenchmark class (explained in the section Timing Java Programs of 1) to time the process of creating and closing a connection. First, we import the necessary classes and declare the requisite variables: /** This program times the process of establishing and closing a connection. * COMPATIBLITY NOTE: runs successfully against 9.2.0.1.0 and 10.1.0.2.0 */ import java.sql.Connection; collection could exceed the size of the DataSet So at this point you ve got about a 2X hit on the web server memory (X being the size of your result set) After that, your code is done executing Your DataSet goes out of scope, but the DataGrid won t go out of scope until you re done rendering Furthermore, the DataSet hangs around on the managed heap until the garbage collector does a couple of sweeps, which probably won t happen until after your rendering is complete So as you enter the rendering stage of your Page object, we re still holding onto memory resources of the web server equal to approximately twice the size of the result set When the DataGrid renders, it does a couple of things First, it transforms its DataGridItem collection into HTML. It is important to notice that the CLR uses an array of objects to pass a variable number of arguments, which is very different from the variable arguments of C because the method receives a single pointer to the array that resides in the heap It is important to note that if the memory layout of the activation record is compatible, as it is in Windows, the use of the cdecl convention instead of the stdcall convention leads to a subtle memory leak If the runtime assumes the stdcall convention (that is the default) and the callee assumes the cdecl convention, the arguments pushed on the stack are not freed, and at each invocation the height of the stack grows until a stack overflow happens The CLR supports a number of calling conventions. import oracle.jdbc.pool.OracleDataSource; import book.util.JBenchmark; class CostOfConnection extends JBenchmark { private static int _numOfConnections = 1; private OracleDataSource _ods; Next, we override the method firstMethod() of the JBenchmark class to establish and close a given number of connections. The variable ods points to an initialized OracleDataSource instance, and the variable _numOfConnections points to the number of connections to be established and torn down for each iteration of the loop. _numOfConnections is passed as a command-line parameter: public void firstMethod( ) throws Exception { Connection connections[] = new Connection[ _numOfConnections ]; for( int i=0; i < _numOfConnections; i++ ) { try { connections[i] = _ods.getConnection(); } catch( Exception e ) { System.err.println( "failed in connection number: " + i ); throw e; } } for( int i=0; i < _numOfConnections; i++ ) { if( connections[i] != null ) { connections[i].close(); } } } The following _runBenchmark() method initializes the OracleDataSource instance variable and calls the method timeMethod() inherited from the JBenchmark class to run the benchmark. In this case, we time only one method. private void _runBenchmark() throws Exception { _ods = new OracleDataSource(); _ods.setURL ( "jdbc:oracle:thin:@rmenon-lap:1521:ora10g" ); _ods.setUser("scott"); // username _ods.setPassword("tiger"); // password // time the process of establishing a connection - method 1 String msg = "Establishing " + _numOfConnections + " connection(s) and closing them"; timeMethod( JBenchmark.FIRST_METHOD, null, null, msg ); }
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