R

RACF

Resource Access Control Facility.

RDB

Relational database.

RDBMS

Relational database management system.

RDBNAM

Relational database name.

read stability (RS)

An isolation level that is similar to repeatable read but does not completely isolate an application process from all other concurrently executing application processes. Under level RS, an application that issues the same query more than once might read additional rows that were inserted and committed by a concurrently executing application process.

rebind

The creation of a new application plan for an application program that has been bound previously. If, for example, you have added an index for a table that your application accesses, you must rebind the application in order to take advantage of that index.

rebuild

The process of reallocating a coupling facility structure. For the shared communications area (SCA) and lock structure, the structure is repopulated; for the group buffer pool, changed pages are usually cast out to disk, and the new structure is populated only with changed pages that were not successfully cast out.

record

The storage representation of a row or other data.

record length

The sum of the 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 length or varying 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 varying-length columns, the record is a varying-length column.

Recoverable Resource Manager Services attachment facility (RRSAF)

A DB2 subcomponent that uses Resource Recovery Services to coordinate resource commitment between DB2 and all other resource managers that also use RRS in a z/OS system.

recovery

The process of rebuilding databases after a system failure.

recovery log

A collection of records that describes the events that occur during DB2 execution and indicates their sequence. The recorded information is used for recovery in the event of a failure during DB2 execution.

recovery manager

(1) A subcomponent that supplies coordination services that control the interaction of DB2 resource managers during commit, abort, checkpoint, and restart processes. The recovery manager also supports the recovery mechanisms of other subsystems (for example, IMS) by acting as a participant in the other subsystem's process for protecting data that has reached a point of consistency. (2) A coordinator or a participant (or both), in the execution of a two-phase commit, that can access a recovery log that maintains the state of the logical unit of work and names the immediate upstream coordinator and downstream participants.

referential constraint

The requirement that nonnull values of a designated foreign key are valid only if they equal values of the primary key of a designated table.

referential integrity

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

referential structure

A set of tables and relationships that includes at least one table and, for every table in the set, all the relationships in which that table participates and all the tables to which it is related.

refresh age

The duration between the current time and the time during which a materialized query table was last refreshed.

relational database (RDB)

A database that can be perceived as a set of tables and manipulated in accordance with the relational model of data.

relational database management system (RDBMS)

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

relational database name (RDBNAM)

A unique identifier for an RDBMS within a network. In DB2, this must be the value in the LOCATION column of table SYSIBM.LOCATIONS in the communications database. DB2 publications refer to the name of another RDBMS as a LOCATION value or a location name.

relationship

A defined connection between the rows of a table or the rows of two tables. A relationship is the internal representation of a referential constraint.

remote

Any object that is maintained by a remote DB2 subsystem (that is, by a DB2 subsystem other than the local one). A remote view, for example, is a view that is maintained by a remote DB2 subsystem. Contrast with local.

remote attach request

A request by a remote location to attach to the local DB2 subsystem. Specifically, the request that is sent is an SNA Function Management Header 5.

remote subsystem

Any relational DBMS, except the local subsystem, with which the user or application can communicate. The subsystem need not be remote in any physical sense and might even operate on the same processor under the same z/OS system.

reoptimization

The DB2 process of reconsidering the access path of an SQL statement at run time. During reoptimization, DB2 uses the values of host variables, parameter markers, or special registers.

REORG pending (REORP)

A condition that restricts SQL access and most utility access to an object that must be reorganized.

REORP

REORG pending.

repeatable read (RR)

The isolation level that provides maximum protection from other executing application programs. When an application program executes with repeatable read protection, rows that the program references cannot be changed by other programs until the program reaches a commit point.

repeating group

A situation in which an entity includes multiple attributes that are inherently the same. The presence of a repeating group violates the requirement of first normal form. In an entity that satisfies the requirement of first normal form, each attribute is independent and unique in its meaning and its name.

See also [normalization]

requester

The source of a request to access data at a remote server. In the DB2 environment, the requester function is provided by the distributed data facility.

resource

The object of a lock or claim, which could be a table space, an index space, a data partition, an index partition, or a logical partition.

Resource Access Control Facility (RACF)

A component of the z/OS Security Server.

resource limit facility (RLF)

A portion of DB2 code that prevents dynamic manipulative SQL statements from exceeding specified time limits. The resource limit facility is sometimes called the governor.

resource manager

(1) A function that is responsible for managing a particular resource and that guarantees the consistency of all updates made to recoverable resources within a logical unit of work. The resource that is being managed can be physical (for example, disk or main storage) or logical (for example, a particular type of system service). (2) A participant, in the execution of a two-phase commit, that has recoverable resources that could have been modified. The resource manager has access to a recovery log so that it can commit or roll back the effects of the logical unit of work to the recoverable resources.

result set

The set of rows that a stored procedure returns to a client application.

result table

The set of rows that are specified by a SELECT statement.

right outer join

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

See also [join]

RLF

Resource limit facility.

rollback

The process of restoring data that was changed by SQL statements to the state at its last commit point. All locks are freed. Contrast with commit.

routine

A term that refers to either a user-defined function or a stored procedure.

row

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

ROWID

Row identifier.

row identifier (ROWID)

A value that uniquely identifies a row. This value is stored with the row and never changes.

row lock

A lock on a single row of data.

row-positioned access

The ability to retrieve a single row from a single FETCH statement.

rowset

A set of rows for which a cursor position is established.

rowset cursor

A cursor that is defined so that one or more rows can be returned as a rowset for a single FETCH statement, and so that the cursor is positioned on the set of rows that is fetched.

rowset-positioned access

The ability to retrieve multiple rows from a single FETCH statement.

row trigger

A trigger that is defined with the trigger granularity FOR EACH ROW.

RR

Repeatable read.

RRSAF

Recoverable Resource Manager Services attachment facility.

RS

Read stability.