R

RDB

See [relational database]

RDBMS

See [relational database management system]

read-ahead prefetching

A method of prefetching pages by looking ahead in a scan, which results in an asynchronous retrieval of pages even though those pages are not located sequentially on disk.

read-only

Pertaining to data that can be read but not modified or deleted.

read stability (RS)

An isolation level that locks only the rows that an application retrieves within a transaction. Read stability ensures that any qualifying row that is read during a transaction is not changed by other application processes until the transaction is completed, and that any row changed by another application process is not read until the change is committed by that process.

rebind

To create a package for an application program that was previously bound. For example, if an index is added for a table that is accessed by a program, the package must be rebound for it to take advantage of the new index.

record

The storage representation of a single row of a table or other data.

record identifier (RID)

A 3-byte page number followed by a 1-byte slot number that is used internally by DB2 to uniquely identify a record in a table. The RID contains enough information to address the page in which the record is stored.

record identifier pool

In DB2 UDB for z/OS and OS/390, an area of main storage above the 16MB line that is reserved for sorting record identifiers during list prefetch processing.

record length

The sum of a length of all the columns in a table, which is the length of the data as it is physically stored in the database. Records can be fixed or variable in length, depending on how the columns are defined. If all columns are fixed-length columns, the record is a fixed-length record. If one or more columns are variable-length columns, the record is a variable-length column.

recoverable log

A database log in which all log records are retained, so if there is a failure, lost data can be recovered during forward recovery.

recovery

The process of rebuilding a database or table space that has become unusable because of a hardware or software failure, or both. The process includes restoring a backup image and can also include rolling database logs forward in time.

recovery log

See [database log]

recovery pending

A state of the database or table space when it is restored from a backup. While the database or table space is in this state, its data cannot be accessed.

recursive common table expression

A common table expression that refers to itself in a FROM clause from the fullselect. Recursive common table expressions are used to write recursive queries.

recursive query

A fullselect that uses a recursive common table expression.

referential constraint

The referential integrity rule that the nonnull values of the foreign key are valid only if they also appear as values of a parent key.

referential integrity

The state of a database in which all values of all foreign keys are valid. Maintaining referential integrity requires the enforcement of a referential constraint on all operations that change the data in a table where the referential constraints are defined.

regular table space

A table space that can store any nontemporary data.

relational database

A database that can be perceived as a set of tables and manipulated in accordance with the relational model of data. Each database includes a set of system catalog tables that describe the logical and physical structure of the data, a configuration file containing the parameter values allocated for the database, and a recovery log with ongoing transactions and archivable transactions.

relational database management system (RDBMS)

A collection of hardware and software that organizes and provides access to a relational database.

remote database

A database that is physically located on a system other than the one in use.

remote unit of work (RUOW)

A unit of work that lets a user or application program read or update data at one location per unit of work. Remote unit of work supports access to one database within a unit of work. An application program can update several remote databases, but it can only access one database within a unit of work.

repeatable read (RR)

An isolation level that locks all the rows in an application that are referenced within a transaction. When a program uses repeatable read protection, rows referenced by the program cannot be changed by other programs until the program ends the current transaction.

replication

The process of maintaining a defined set of data in more than one location. It involves copying designated changes from one location (a source) to another (a target) and synchronizing the data in both locations.

Replication Center

A graphical interface that lets you define, operate, maintain, and monitor the replication environment. It is part of the DB2 Administration Client tool suite.

Request For Comments (RFC)

A set of technical and organizational notes about the Internet (originally the ARPANET), beginning in 1969. Memos in the RFC series discuss many aspects of computer networking, including protocols, procedures, programs, and concepts, as well as meeting notes, opinions, and sometimes humor.

requester

The source of a request to access data at a remote server. Also, the system that requests the data.

reserved word

(1) A word that is used in a source program to describe an action to be taken by the program or compiler. It must not appear in the program as a user-defined name or a system name.

(2) A word that has been set aside for special use in the SQL standard.

resource limit facility (RLF)

A portion of DB2 UDB for z/OS and OS/390 code that prevents dynamic manipulative SQL statements from exceeding specified time limits. Also known as the governor.

response file

An ASCII file customized with the setup and configuration data that will automate an installation. The setup and configuration data must be entered during an interactive install, but with a response file, the installation can proceed without any intervention.

response file generator

A utility that creates a response file from an existing installed and configured DB2 UDB product. You can use the generated response file to recreate the same setup on other computers.

restore

To rebuild a damaged or corrupted database or table space from a backup image produced with the BACKUP utility.

restore set

A backup copy of a database or table space plus zero or more log files which, when restored and rolled forward, bring the database or table space back to a consistent state.

result set

The set of rows that a stored procedure returns.

result table

The set of rows produced by the evaluation of a SELECT statement.

revoke

To remove a privilege or authority from an authorization identifier.

RID

See [record identifier]

RID pool

See [record identifier pool]

right outer join

The result of a join operation that includes the matched rows of both tables being joined and preserves the unmatched rows of the second join operand.

roll back

To restore data changed by SQL statements to the state at its last commit point.

roll forward

To update the data in a restored database or table space by applying changes recorded in the database log files.

roll forward recovery

A process started by the roll forward utility to recover a database by applying transactions recorded in the database recovery log file.

routine

A user-defined method, user-defined function, or stored procedure.

row

The horizontal component of a table that consists of a sequence of values, one for each column of the table.

row lock

A lock on a single row of data.

RR

See [repeatable read]

RS

See [read stability]

RUOW

See [remote unit of work]