The following types of files although related to the database are separate from the data files. These files include:
•Trace files and the Alert Log
Redo log are used to recover the database’s transactions in their proper order in the event of database cache. The Redo log information is stored external to the database’s data files.
When a transaction occurs in the database it is entered in the Redo log buffers, while the data blocks affects by the transactions are not immediately written to disk. This allows the database to perform batch writes to disks thus optimizing the performance of this function.
Each ORACLE database will have two or more online Redo log files. ORACLE writes to online Redo log files in a cyclical fashion: after the first log file is filled, it writes to the second log file, until that one is filled. When all the online Redo log files have been filled, it returns to the first log file and begins overwriting its contents with new transaction data. If the database is running in ARCHIVE LOG mode, then the database will make a copy of the online Redo log files before overwriting them. These Archived Redo log files can then be used to recover any part of the database to any point in time.
Control files record control information about all of the files within the database. A database’s overall physical architecture is maintained by its control files. They are used to maintain internal consistency and guide recovery operations.
Since the control files are critical to the database, multiple copies are stored online these files are typically stored on separate disks to minimize the potential damage due to disk failures. The database will create and maintain the control files specified at database creation.
Trace files and Alert log:
Each of the background process running in an instance has a trace file associated with it. The trace file will contain information about significant event encountered by the background process.
In addition to the trace files ORACLE maintains a file called the Alert Log. The Alert log records the commands and command result of major events in the life of the database.
Alert log is a vital source of information for day to day management of the database; trace files are most useful when attempting to discover the cause of a major failure. In the simplest from an ORACLE database consists of
•One or more Data files
•One or more Control files
•Two or more online Redo Log
•Multiple Users / Schema.
•One or more Rollback Segments.
•One or more Table spaces.
•Data Dictionary Tables.
•User objects (Tables, Indexes, and Views etc).
•An SGA (includes the Data block buffer cache, Redo log buffer cache and shared SQL pool)
•The SMON Background process
•The PMON Background process
•The DBWR Background process
•The LGWR Background process
•User processes with associated PGAs.