When the physical structure of a database is created or altered which means changing of data files and redo log files then corresponding changing of instances of control files have been done completely. Oracle database structure has been changed in accordance with changing of corresponding structures of data files and redo log files. In short, control files are used to recover Oracle databases.
Redo log files and rolling forward:
Redo logs files consist of a set of two or more redo log files. A redo log file has to redo log records inside it. These are redo log for the database. As the name suggests those who has been very much familiar with basic functioning of Microsoft Word Processor, it has been already cleared that redo log files records number of changes occurring to particular data files and it keep entire history of change that has been undergoing for each and every data.
If any previous changes need to be installed then, it can be done easily from retrieving from redo log files which keep all records of changes of data files. Again like control files, in order to prevent multiple instances of data files, Oracle Database creates and saves multiple instances of redo log files in order to control the functioning of redo log files entirely.
When there is unexpected data loss arising out of sudden outrage or imminent arrival of natural calamities, there is always an easier way to retrieve those data loss from cache files on the logical structure of the database. When database is again started after clearing up all such disturbing situation, then data can be obtained from multiple instances of redo log files.It acts similarly as that of control files, but it works in a logical structure of the database.
Oracle restores data to the time when the power broke down in entire application process environment. This process is termed as rolling forward. It is the process of applying redo log during the process of recovering the Oracle database. Oracle database gives the option of automatically achieving redo log files when any such modification of data files is performed. When the database is in ARCHIEVELOG mode, all redo log files are automatically achieved for better safeguarding of Oracle Database.
Parameter files are a list of configuration parameters for instance and database. It is always advisable for the system administrator to create a server parameter file so that for every instance and database entry from the logical structure of database dynamic mechanisms of constantly creating newer parameter files can be originated from the server. When any instance is created, due to presence of configuration of parameter files. The oracle database must read initialization parameter files for the application process of server parameter files in the physical structure of the server.