A segment is a set of extents allocated for a certain logical structure.
What are the different types of segments?
Data segment, index segment, rollback segment and temporary segment.
What is a data segment?
Each non-clustered table has a data segment. All of the table's data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.
What is an index segment?
Each index has an index segment that stores all of its data.
A database contains one or more rollback segments to temporarily store "undo" information.
What are the uses of rollback segment?
To generate read-consistent database information during database recovery and to rollback uncommitted transactions by the users.
What is a temporary segment?
Temporary segments are created by Oracle when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.
What is a datafile?
Every Oracle database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.
What is a redo log?
The set of redo log files for a database is collectively known as the database redo log.
What is the function of redo log?
The primary function of the redo log is to record all changes made to data.
What is the use of redo log information?
The information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files.