R

raw device

A disk that does not contain an operating system managed file system. Instead of a file system managing the reading and writing activities, Oracle does so.

reactive monitoring

Monitoring the Oracle server for issues after they have occurred, too late to avoid impacting the database's performance, availability, or manageability.

read consistency

Oracle's read consistency uses undo data to ensure that a statement (or a transaction) sees a set of data that does not change during its execution.

recycle bin

A logical container in each tablespace holding dropped tables that can be retrieved by a database user as long as the space occupied by the deleted object is not required for new objects in the tablespace.

redo entry

A group of change vectors. Redo entries record data that you can use to reconstruct all changes made to the database, including the undo segments. Also referred to as redo record.

redo log

The physical files on disk that store the transaction recovery information written from the Redo Log Buffer by the LGWR (log writer) process. See also log writer (LGWR).

Redo Log Buffer

The portion of the SGA (System Global Area) where transaction recovery information is stored until it can be written to the redo log files. See also System Global Area (SGA).

redo log file

One of the files that constitutes a redo log group. Also referred to as redo log member.

redo log group

A collection of multiplexed (mirrored) redo log files that contain information about changes in the database.

redo log group member

One of the redo logs within a redo log group.

referential integrity

Enforcing business rules within or between tables using primary key and foreign key constraints.

refuse packet

A packet sent via TCP/IP that acknowledges the refusal of some network request.

request queue

A location in the SGA (System Global Area) in an Oracle Shared Server environment in which the dispatcher process places client requests. The shared server process then processes these requests. See also System Global Area (SGA).

response queue

The location in the SGA (System Global Area) in an Oracle Shared Server environment where a shared server process places a completed client request. The dispatcher process then picks up the completed request and sends it back to the client.

response time

The time it takes for a single user's request to return the desired result while using an application. Frequently used as a performance measure in data warehouse systems.

role

A mechanism for grouping privileges for ease in administering them

ROLLBACK

The SQL statement to undo a transaction.

rollback

The second phase of instance recovery during which uncommitted transactions are backed out from the datafiles.

rollback segments

Manually managed segments for storing undo information. This information is used for read consistency and recovery purposes. Rollback segments were replaced by system-managed undo segments when automatic undo management was used.

roll forward

The first phase of instance recovery during which information in the online redo log files is applied to the datafiles (including the undo tablespace) to bring the datafiles up to their state before the instance failed.

rolling back

The process of undoing one or more changes to data within a transaction.

row

A single instance of data in a table. In the relational model, a row is analogous to a tupple.