C

cache

A buffer containing frequently accessed instructions and data. It is used to reduce access time.

caching 3

The process of storing frequently used results from a request to memory for quick retrieval until it is time to refresh the information. DB2 UDB provides many forms of caching, such as directory caching and package caching.

call-level interface (CLI)

A callable API for database access that is an alternative to an embedded SQL API. In contrast to embedded SQL, the CLI does not require precompiling or binding to a database; instead, it provides a standard set of functions to process SQL statements and related services at runtime.

cardinality

The number of rows in a database table.

cascade delete

The way DB2 UDB enforces referential constraints when it deletes all descendent rows of a deleted parent row.

CASE expression

An expression that allows another expression to be selected based on the evaluation of one or more conditions.

case-insensitive search

A search that does not consider the case of the string being searched.

cast function

A function that converts instances of a source data type into instances of a different target data type. In general, a cast function has the name of the target data type and has one argument whose type is the source data type. Its return type is the target data type.

catalog

A set of tables and views maintained by the database manager. These tables and views contain information about the database, such as descriptions of tables, views, and indexes.

catalog node

See [catalog partition]

catalog partition

In a partitioned database environment, the database partition where the catalog tables for the database resides. Each database in a partitioned database environment can have its catalog partition on a different database partition server. The catalog partition for a database is automatically created on the database partition server where the CREATE DATABASE command is run.

catalog table

A table in the DB2 UDB catalog that is automatically created when a database is created. These tables contain information about the database and definitions of database objects, such as user tables, views, and indexes, as well as security information about the authority that users have on these objects. You cannot explicitly create or drop a catalog table, but you can query and view its contents using the catalog views.

catalog view

A SYSCAT or SYSSTAT view on the catalog table.

CDB

See [communications database]

cell

A unique combination of dimension values. Physically, a cell is made up of blocks of pages whose records all share the same values for each clustering column.

character conversion

The process of changing data from one character coding representation to another.

character large object (CLOB)

A sequence of characters (single-byte, multibyte, or both) with a size ranging from 0 bytes to 2GB minus 1 byte. In general, character large object values are used whenever a character string might exceed the limits of the VARCHAR type. Also called character large object string.

character set

A defined set of characters, for example, 26 unaccented letters A through Z.

character string

A sequence of bytes that represent bit data, single-byte characters, or a mixture of single-byte and multi-byte characters.

character string delimiter

The characters enclosing character strings in delimited ASCII files that are imported or exported.

CHECK clause

In SQL, an extension to the CREATE TABLE and ALTER TABLE statements that specifies a table check constraint.

check condition

A restricted form of a search condition used in check constraints.

check constraint

A constraint specifying a check condition that is not false for each row of the table on which the constraint is defined.

check integrity

The condition that exists when each row in a table conforms to the check constraints that are defined on that table. Maintaining check integrity requires DB2 to enforce table check constraints on operations that add or change data.

check pending

A state which a table can be placed in. Only limited activity is allowed on the table, and constraints are not checked when the table is updated.

checkpoint

A point at which the database manager records internal status information on the log. The recovery process uses this information if the subsystem terminates abnormally.

circular log

A database log in which records are overwritten if they are no longer needed by an active database. Consequently, if a failure occurs, lost data cannot be restored during forward recovery.

clause

In SQL, a distinct part of a statement, such as a SELECT clause or a WHERE clause. (e.g., SELECT * FROM employee WHERE empno='000010').

CLI

See [call-level interface]

client

Any program (or workstation that a program is running on) that communicates with and accesses a database server.

client profile

A profile that configures clients using the Import function in the Configuration Assistant. It can contain database connection information, client settings, CLI or ODBC common parameters, and configuration data for local APPC or NetBIOS communication subsystems.

CLOB

See [character large object]

CLP

See [command line processor]

clustered index

An index whose sequence of key values closely corresponds to the sequence of rows stored in a table. The degree to which this correspondence exists is measured by statistics that the optimizer uses. Synonym for partitioning index.

clustering block index

A block index that is automatically created for a particular dimension when the dimension is defined on a multidimensional clustering table. This index maintains the clustering of data along that dimension, together with the other dimensions that are defined on the table. Also known as a dimension block index.

code page

A set of assignments of characters to code points.

code point

A unique bit pattern that represents a character in a code page.

code set

International Organization for Standardization (ISO) term for code page.

See also [code page]

coded character set

A set of unambiguous rules that establishes a character set and the one-to-one relationships between the characters of the set and their coded representations.

collating sequence

The sequence in which the characters are ordered for sorting, merging, comparing, and processing indexed data sequentially.

collocated join

The result of two tables being joined when the tables reside in a single-partition database partition group in the same database partition, or when they are in the same database partition group and have the same number of partitioning columns, the columns are partition-compatible, both tables use the same partitioning function, and pairs of the corresponding partitioning key columns participate in the equijoin predicates.

column data

The data store that is stored in a DB2 column. The type of data can be any data type supported by DB2.

column distribution value

Statistics that describe the most frequent values of some column or the quantile values. These values are used in the DB2 optimizer to help determine the best access plan.

column function

(1) An operation that derives its result using values from one or more rows.

(2) A function that performs a computation on a set of values rather than on a single value.

command

A way to start database administration functions to access and maintain the database manager.

Command Line Processor (CLP)

A character-based interface for entering SQL statements and database manager commands.

commit

The operation that ends a unit of work by releasing locks so the database changes made by that unit of work can be perceived by other processes. This operation makes the data changes permanent.

commit point

A point in time when data is considered to be consistent.

common table expression

An expression that defines a result table with a name (a qualified SQL identifier). The expression can be specified as a table name in any FROM clause in the fullselect that follows the WITH clause.

communications database (CDB)

A set of tables in the DB2 for z/OS and OS/390 catalog that establishes conversations with remote database management systems.

comparison operator

Comparison operators are (not less than), <= (less than or equal to), (not equal to), = (equal to), >= (greater than or equal to), > (greater than), and (not greater than).

composite block index

An index that contains only dimension key columns and maintains the clustering of data over insert and update activity in a multidimensional clustering (MDC) table.

composite key

An ordered set of key columns in the same table.

compound SQL statement

A block of SQL statements that are executed in a single call to the application server.

concurrency

The shared use of resources by multiple interactive users or application processes at the same time.

configurable configuration parameters

A set of configuration parameters containing information that can be changed.

configurable online configuration parameters

A set of configuration parameters whose values can be changed while the database manager is running.

Configuration Advisor

A graphical tool that can be used to obtain an initial set of database configuration parameters. This tool can be run from the command line or in a graphical mode from the Control Center.

Configuration Assistant

A graphical tool that can be used to configure and maintain the database objects that you or your applications will be using. With this tool, you can work with existing database objects, add new ones, bind applications, set Database Manager Configuration parameters, and import and export configuration information.

configuration file

A file that contains the values specified for configuration parameters. These parameters specify the resources that are allocated to the DB2 products and to individual databases as well as the diagnostic level. There are two types of configuration files: the Database Manager Configuration file for each DB2 instance and the database configuration file for each individual database. Database Manager Configuration parameters are stored in a file named db2systm. Database configuration parameters are stored in a file named SQLDBCON. In a partitioned database environment, each database partition has its own database configuration file, but all partitions that participate in the instance use the same Database Manager Configuration file.

configuration parameter

A parameter whose value limits the resources that can be used by the database manager or database. Some configuration parameters are informational and display characteristics about the environment that cannot be changed.

connection

(1) An association between an application process and an application server.

(2) In data communications, an association established between functional units for conveying information.

connection concentrator

A process that allows applications to stay connected without any resources being consumed on the DB2 host server. Thousands of users can be active in applications, while only a few threads are active on the DB2 host server.

constant

A language element that specifies an unchanging value. Constants are classified as string constants or numeric constants.

constraint

A rule that limits the values that can be inserted, deleted, or updated in a table.

container

(1) A physical storage location of the data, for example, a file, directory, or device.

(2)

See also [table space container]

container tag

A container tag uniquely identifies the database and table space that the container (an allocation of physical storage, such as a file or a device) is part of.

contention

A situation in which a transaction attempts to lock a row or table that is already locked.

Control Center

The DB2 graphical interface that shows database objects (such as databases and tables) and their relationship to each other. You can perform the tasks provided by the various tools in the Control Center, such as Replication Center, Health Center, Task Center, and Journal.

Coordinated Universal Time (UTC)

Synonym for Greenwich Mean Time.

coordinator agent

The agent that is started when the database manager receives a request from an application. The agent remains associated with the application during the life of the application. This agent initiates subagents that work for the application.

coordinator node

See [coordinator partition]

coordinator partition

The database partition server to which the application originally connected and on which the coordinating agent resides.

correlated subquery

A subquery that contains a correlated reference to a column in a table that is outside the subquery.

correlation name

An identifier that designates a table or view within a single SQL statement. The name can be defined in any FROM clause or in the first clause of an UPDATE or DELETE statement.

cost

The estimated total resource usage that is necessary to run the access plan for a statement (or the elements of a statement). Cost is derived from a combination of processor cost (in number of instructions) and I/O (in numbers of seeks and page transfers).

counter

A representation of information that is cumulative up until the sample is taken. The counter counts values that increase, such as the number of deadlocks. Counters are reset when you stop and restart an instance or database.

country/region code

The two-character representation for the country or region to establish monetary, date, and numeric formatting.

crash recovery

The process of bringing a database back to a consistent and usable state after a failure.

CS

See [cursor stability]

cumulative backup

See [incremental backup]

current path

An ordered list of schema names that is used to resolve unqualified references to functions and data types. In dynamic SQL, the current function path is set by the CURRENT PATH special register. Static SQL defines it in the FUNCPATH option for the PREP and BIND commands.

current working directory

The default directory of a process from which all relative path names are resolved.

cursor

A named control structure that an application program uses to point to a specific row within some ordered set of rows. The cursor is used to retrieve rows from a set.

cursor blocking

A technique that reduces overhead by retrieving a block of rows in a single operation. These rows are cached while they are processed.

cursor sensitivity

The degree to which database updates are visible to the subsequent FETCH statements in a cursor. A cursor can be sensitive to changes made with positioned UPDATE and DELETE statements that specify the name of the cursor. A cursor can also be sensitive to changes made with searched UPDATE and DELETE statements, or with cursors other than this cursor.

cursor stability (CS)

An isolation level that locks any row accessed by an application's transaction while the cursor is positioned on the row. The lock remains in effect until the next row is fetched or the transaction is terminated. If any data is changed in a row, the lock is held until the change is committed to the database.