, an application table) The before image of the transaction (the data as it was before the changes were made) The after image of the transaction (the data as it was after the transaction made the changes) Commit indicators that indicate whether and when the transaction completed When a database crashes, all transactions, both uncommitted as well as committed, have to be applied to the data files on disk, using the information in the redo log files All redo log transactions that have both a begin and a commit entry must be redone, and all transactions that have a begin entry but no commit entry must be undone (Redoing a transaction in this context simply means that you apply the information in the redo log files to the database; you do not rerun the transaction itself.

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) Committed transactions are thus re-created by applying the after image records in the redo log files to the database, and incomplete transactions are undone by using the before image records in the undo tablespace Redo log files are an essential part of database management, and they are one of the main ways you enforce database consistency Oracle requires that every database have at least two redo log groups, each group consisting of at least one individual log file member Oracle writes to one redo log file until it gets to the end of the redo log file, at which point it performs a log switch and starts writing to the second log file (and then to the third, if it exists)..

You can use this code to determine whether variables have been defined. The first example of the two applies to string variables, since the -n operation evaluates to true if the length of the supplied string variable is nonzero. However, this method also works for determining whether a numeric variable has been defined, as its value is then treated as a string. The second example simply tests a variable. Once the variable has been assigned a value, the expression will evaluate to true. Thus, both expressions determine if a variable has been assigned a value. The following expressions are similar to the previous ones; they determine if a variable is undefined:

By default, Oracle will write over the contents of a redo log file, unless you choose to archive your redo files. Oracle recommends that you archive the filled-up redo log files, so you can maintain a complete record of all the changes made to the database since the last backup. If you archive your redo log files, you are said to be running your database in the archivelog mode. Otherwise, you re running in noarchivelog mode. Because of the critical importance of the redo log files in helping recover from database crashes, Oracle recommends multiplexing (maintaining multiple copies of) the redo log files. Multiplexing the online redo log files by placing two or more copies of the redo logs on different disk drives will ensure that you won t easily lose data changes that haven t been recorded in your data files.

exe is a tool that is supposed to register managed types as COM types so that native clients can use these types To perform the COM registration, RegAsmexe uses the NET Reflection API When it tries to load the mixed-code EXE assembly via Assembly::LoadFrom, it fails, because mixed-code EXE files cannot be loaded dynamically, as discussed earlier in this chapter This problem can simply be resolved by setting the Register Output linker property to false When you have successfully rebuilt the project, the generated DLL or EXE file is a mixedcode assembly This significantly changes the startup and the shutdown Therefore, you should do some tests with your mixed-code assembly These tests should be run on a developer machine as well as on typical client machines These tests should also include execution of some native and some managed code parts.

When you create a new database, you specify the initialization parameters for the Oracle instance in a special configuration file called the server parameter file (SPFILE). You can also use an older version of the configuration file called the init.ora file, but Oracle recommends the use of the more sophisticated SPFILE. In the SPFILE, you specify the memory limits for the instance, the locations of the control files, whether and where the archived logs are saved, and other settings that determine the behavior of the Oracle database server. You can t, however, edit the SPFILE manually, as you could the init.ora file, since the SPFILE is a binary file. The SPFILE is always stored on the database server, thus preventing the proliferation of parameter files that sometimes occurs with the use of the init.ora file. By default, the SPFILE (and the init.ora file) is placed in the ORACLE_HOME/dbs directory in UNIX systems and the ORACLE_HOME\database directory in Windows systems. The ORACLE_HOME directory is the standard location for the Oracle executables.

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