C

cardinality

The number of distinct values in a column or a table.

Cartesian product

The query result produced when a join condition is omitted from a query that references two or more tables in the FROM clause.

change vectors

A description of a change made to a single block in the database.

checkpoint

An event during which the dirty data block buffers are flushed to disk and database files are updated to reflect this action. The database is put into a consistent state.

checkpoint (CKPT) process

The Oracle background process that updates the control file and the datafile headers to reflect the last successful transaction by recording the last System Change Number (SCN).

CKPT

See checkpoint (CKPT) process.

column

The vertical space in a table or a view that holds a specific domain of data. In the relational model, an entity has attributes. When this model is implemented in an Oracle database, an entity becomes a table, and an attribute becomes a column.

COMMIT

The SQL command for making permanent the changes effected during a transaction.

connection

The communication channel between the User Process and the Server Process. See also Server Process; User Process.

Connection Manager

See Oracle Connection Manager.

consistent backup

A backup performed while the database is shut down and unavailable. Also referred to as offline backup.

constraint

An optional schema object that restricts values in the dependent table to a specified condition. Constraints enforce business rules about data.

control file

A small binary file that contains metadata about the physical structure of the database such as the database name, locations of the datafiles and redo logs, and recovery information.

cost-based optimizer

The Oracle optimizer mode that uses statistics about the size, selectivity, and dispersion of the tables and indexes in the database to formulate the most efficient execution plan.