The database has logical structure and physical structures. Physical and logical structures are separate, the physical storage of data can be managed without affecting the access to logical storage structures.
Physical Database Structure includes datafiles, redo log files and control files.
Data files
Every oracle database has one or more physical datafiles. The datafiles contain all the database data. The data of logical database structures, such as tables and indexes, is physically stored in the datafiles allocated for a database. The datafiels are located in the $ORACLE_BASE/oradata directory
A data file can be associated with only one database. Datafiles can be set to automatically extend when the database runs out of space. One or more datafiles form a logical unit of database storage called a tablespace. .
Modified or new data is not necessarily written to a datafile immediately. Data is pooled in memory and written to the appropriate detafiles all at once, as determined by the database writer process (DBWn) background process.
Control Files
Every oracle database has a control file. A control file contains entries that specify the physical structure of the database. Every time, an instance of an Oracle database is started, its control file identifies the database and redo log files that must be opened for database operation to proceed.
Redo log file
Parameter files
Alert and trace log file
backup files
Logical database structures
Table spaces
A database is divided into logical storage units called tablespaces, which group related logical structures together. One or more datafiles are explicitly created for each tablespace to physically store the data of all the logical structure. The combined size of the datafiles in a tablespace is the total storage capacity of the tablespace.
Every Oracle database contains a SYSTEM tablespace and a SYSAUX tablespace. Oracle creates them automatically when the database is created. Each of this two tablespaces has a datafiles, named system01.dbf and sysaux01.dbf.
Bigfile tablespaces and smallfile tablespace.
Online and offline tablespaces.
Data Blocks: At the finest level of granularity, oracle database data is stored in data blocks.
Extents: A specific number of contiguous data blocks,obtained in a single allocation, used to store a specific type of information.
Segments: A segment is a set of extents allocated for a certain logical structure. Type of segments include: Data Segment, Index Segment, Temporary segment for temporary tables, Rollback segment for undo,