JDBC is a popular method used to connect to an Oracle database from Java. 10 contains a complete example of a Java program. JDBC provides a set of interfaces for querying databases and processing SQL data in the Java programming language. Listing A-9 shows a simple JDBC program that connects to an Oracle database and executes a simple SQL query. Listing A-9. A Simple JDBC Program import java.sql.*; public class JDBCExample { public static void main(String args[]) throws SQLException /* Declare the type of Oracle Driver you are using */ {DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver()); /* Create a database connection for the JDBC program */ Connection conn= DriverManager.getConnection( "jdbc:oracle:thin:@nicholas:1521:aparna","hr","hr"); Statement stmt = conn.createStatement(); /* Pass a query to SQL and store the results in the result set rs */ ResultSet rs = stmt.executeQuery("select emp_id, emp_name,salary from employees"); /* Using the while loop, result set rs is accessed row by row */ while({ int number = rs.getInt(1); String name= rs.getString(2); System.out.println(number+" "+name+" "+salary); } /* Close the JDBC result set and close the database connection */ rs.close(); conn.close(); } } JDBC is ideal for dynamic SQL, where the SQL statements aren t known until run time.

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The checkpoint process is discussed in more detail in the The Checkpoint section later in this chapter.

Due to its obvious importance, Oracle recommends that you keep multiple copies of the control file.

Your project is now configured to produce a mixed-code assembly If you build a mixed-code EXE file and the linker property Configuration Properties Linker General Register Output is set to true, your project will fail with the following error message: Registering output.. RegAsm : error RA0000 : Attempt to load an unverifiable executable with fixups (IAT with more than 2 sections or a TLS section) (Exception from HRESULT: 0x80131019) Project : error PRJ0050: Failed to register output Please ensure you have the appropriate permissions to modify the registry As the error message says, this error occurs when the EXE file is registered In native projects, the Register Output linker property is used to register COM servers via the COM registration tool RegSvr32exe However, since the EXE file is a NET assembly, this linker property causes a managed tool called RegAsmexe to be started instead RegAsm.

The Oracle redo log files record all the changes made to the database, and they are vital during the recovery of a database. If you need to restore your database from a backup, you can recover the latest changes made to the database from the redo log files. The set of redo log files that are currently being used to record the changes to the database are called online redo log files. These logs can be archived or copied to a different location before being reused, and the saved logs are called archived redo logs. Oracle writes all final changes made to data (committed data) first to the redo log files, before applying those changes to the actual data files themselves. Thus, if a system failure prevents these data changes from being written to the permanent data files, Oracle will use the redo logs to recover all transactions that committed but couldn t be applied to the data files. Thus, redo log files guarantee that no committed data is never lost. If you have all the archived redo logs since the last database backup, and a set of the current redo logs as well, you can always bring a database up to date.

When such expressions become very complex, it is easy to make logic mistakes that can be difficult to track down. In the following examples, the complexity has been toned down.

Current redo log files are often referred to as online redo logs to distinguish them from the older saved or archived redo log files.

Redo log files consist of redo records, which are groups of change vectors, each referring to a specific change made to a data block in the Oracle database A single transaction may involve multiple changes to data blocks, so it may have more than one redo record Initially, the contents of the log are kept in the redo log buffer (a memory area), but they are transferred to disk very quickly If your database comes down without warning, the redo log can help you determine whether all transactions were committed before the crash or if some were still incomplete Oracle redo log files contain the following information about database changes made by transactions: Indicators specifying when the transaction started The name of the transaction The name of the data object that was being updated (eg.

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