Replication Guide and Reference

Glossary

A

after-image
The updated content of a source table column that is recorded in a change data table, or in a database log or journal. Contrast with before-image.

Apply program
A program that is used to refresh or update a target table, depending on the applicable source-to-target rules. Contrast with Capture program and Capture trigger.

Apply qualifier
A case-sensitive character string that identifies subscription sets that are unique to an instance of the Apply program.

archive log
The set of log files that are closed and are no longer needed for normal processing. These files are retained for use in roll-forward recovery. Contrast with active log.

audit trail
Data, in the form of a logical path linking a sequence of events, used for tracing the transactions that affected the contents of a record.

B

base aggregate table
A type of target table that contains data aggregated from a source table or a point-in-time table at intervals.

before-image
The content of a source table column prior to a refresh, as recorded in a change data table, or in a database log or journal. Contrast with after-image.

binary large object (BLOB)
A sequence of bytes, where the size of the sequence ranges from 0 to 2 gigabytes. This string does not have an associated code page and character set. Image, audio, and video objects are stored in BLOBs.

BLOB
Binary large object.

blocking
An option that is specified when binding an application. It allows caching of multiple rows of information by the communications subsystem so that each FETCH statement does not require the transmission of one row for each request across the network. Contrast with data blocking.

C

Capture program
A program that reads database log or journal records to capture data about changes made to DB2 source tables. Contrast with Apply program and Capture trigger.

Capture trigger
A mechanism that captures delete, update, and insert operations performed on non-IBM source tables. Contrast with Capture program and Apply program.

cascade rejection
The process of rejecting a replication transaction because it is associated with a transaction that had a conflict detected and was itself rejected.

CCD table
Consistent-change-data table.

CD table
Change data table.

change aggregate table
A type of target table that contains data aggregations based on changes recorded for a source table.

change data (CD) table
A replication control table at the source server that contains changed data for a replication source table.

character large object (CLOB)
A sequence of characters (single-byte, multibyte, or both) where the length can be up to 2 gigabytes. This data type can be used to store large text objects. Also called character large object string.

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

CLOB
Character large object.

cold start
The process of starting the Capture program using an initial program load procedure. Contrast with warm start.

complete CCD table
A CCD table that contains all the rows that satisfy the source view and predicates from the source table or view. Contrast with noncomplete CCD table.

condensed
A table attribute indicating that the table contains current data rather than a history of changes to the data. A condensed table includes no more than one row for each primary key value in the table. As a result, a condensed table can be used to supply current information for a refresh.

condensed CCD table
A CCD table that contains only the most current value for a row. This type of table is useful for staging changes to remote locations and for summarizing hot-spot updates. Contrast with noncondensed CCD table.

conflict detection
In update-anywhere replication configurations;

consistent-change-data (CCD) table
A type of target table that is used for auditing or staging data or both. See also complete CCD table, condensed CCD table, external CCD table, internal CCD table, noncomplete CCD table, and noncondensed CCD table.

Control Center
A graphical user interface that shows database objects (such as databases and tables) and their relationship to each other. From the Control Center you can perform tasks on DB2 database objects. Contrast with DJRA tool.

control server
The database location of the applicable subscription definitions and Apply program control tables.

control table
A table in which replication source and subscription definitions or other replication control information is stored.

D

database log
A set of primary and secondary log files consisting of log records that record all changes to a database. The database log is used to roll back changes for transactions that are not committed and to recover a database to a consistent state.

database management system (DBMS)
Synonym for database manager.

database manager
A computer program that manages data by providing the services of centralized control, data independence, and complex physical structures for efficient access, integrity, recovery, data currency control, privacy, and security.

database server
A functional unit that provides database services for databases.

data blocking
The process of specifying how many minutes worth of change data will be replicated during a subscription cycle. Contrast with blocking.

DataJoiner Replication Administration (DJRA) tool
DJRA tool.

DBCLOB
Double-byte character large object.

DBMS
Database management system.

delimited identifier
A sequence of characters enclosed within quotation marks ("). The sequence must consist of a letter followed by zero or more characters, each of which is a letter, a digit, or the underscore character.

differential refresh
A process in which only changed data is copied to the target table, replacing existing data. Contrast with full refresh.

distinct type
A user-defined data type that is internally represented as an existing type (its source type), but is considered to be a separate and incompatible type for semantic purposes. See also user-defined type (UDT).

DJRA tool
A database administration tool that you can use to perform various replication administration tasks. Unlike the Control Center, the DJRA tool can also be used to administer replication for non-IBM databases. Contrast with Control Center.

double-byte character large object (DBCLOB)
A sequence of double-byte characters, where the size can be up to 2 gigabytes. This data type can be used to store large double-byte text objects. Also called double-byte character large object string. Such a string always has an associated code page.

E

enhanced conflict detection
Conflict detection that guarantees data integrity among all replicas and the source table. The Apply program locks all replicas or user tables in the subscription set against further transactions, and begins detection after all changes made prior to locking have been captured. See also conflict detection, standard conflict detection, and row-replica conflict detection.

event timing
The most precise method of controlling when to start a subscription cycle. Requires that you specify an event and the time when you want the event processed. Contrast with interval timing and on-demand timing.

external CCD table
A CCD table that can be subscribed to directly. It has its own row in the register table, where it is referenced as SOURCE_OWNER and SOURCE_TABLE. Contrast with internal CCD table.

F

full refresh
A process in which all of the data of interest in a user table is copied to the target table, replacing existing data. Contrast with differential refresh.

G

gap
A situation in which the Capture program is not able to read a range of log or journal records, so there is potential loss of change data.

group
In Satellite Edition, a collection of satellites that share characteristics such as database configuration and the application that runs on the satellite.

H

hot-spot updates
Updates made repeatedly to the same rows over a short period of time.

I

internal CCD table
A CCD table that cannot be subscribed to directly. It does not have its own row in the register table; it is referenced as CCD_OWNER and CCD_TABLE in the row for the associated replication source. Contrast with external CCD table.

interval timing
The simplest method of controlling when to start a subscription cycle. You must specify a date and a time for a subscription cycle to start, and set a time interval that describes how frequently you want the subscription cycle to run. Contrast with event timing and on-demand timing.

J

join
A relational operation that allows for retrieval of data from two or more tables based on matching column values.

K

key
A column or an ordered collection of columns that are identified in the description of a table, index, or referential constraint.

L

large object (LOB)
A sequence of bytes, where the length can be up to 2 gigabytes. It can be any of three types: BLOB (binary), CLOB (single-byte character or mixed) or DBCLOB (double-byte character).

LOB
Large object.

local database
A database that is physically located on the workstation in use. Contrast with remote database.

lock
(1) A means of serializing events or access to data
(2) A means of preventing uncommitted changes made by one application process from being perceived by another application process and for preventing one application process from updating data that is being accessed by another process

locking
The mechanism used by the database manager to ensure the integrity of data. Locking prevents concurrent users from accessing inconsistent data.

M

member
See subscription-set member.

N

nickname
A name that is defined in a DB2 DataJoiner database to represent a physical database object (such as a table or stored procedure) in a non-IBM database.

noncomplete CCD table
A CCD table that is empty when it is created and has rows appended to it as changes are made to the source. Contrast with complete CCD table.

noncondensed CCD table
A CCD table that contains the history of changes to the values for a row. This type of table is useful for auditing purposes. Contrast with condensed CCD table.

nullable
The condition where a value for a column, function parameter, or result can have an absence of a value. For example, a field for a person's middle initial does not require a value.

null value
A parameter for which no value is specified.

O

object
(1) Anything that can be created or manipulated with SQL--for example, tables, views, indexes, or packages.
(2) In object-oriented design or programming, an abstraction consisting of data and operations associated with that data.

ODBC
Open Database Connectivity.

ODBC driver
A driver that implements ODBC function calls and interacts with a data source.

on-demand timing
A method for controlling the timing of replication for occasionally connected systems. Requires that you use the ASNSAT program to operate the Capture and Apply programs. Contrast with event timing and interval timing.

Open Database Connectivity (ODBC)
An API that allows access to database management systems using callable SQL, which does not require the use of an SQL preprocessor. The ODBC architecture allows users to add modules, called database drivers, that link the application to their choice of database management systems at run time. Applications do not need to be linked directly to the modules of all the supported database management systems.

ordinary identifier
In SQL, a name that is made up of a letter, which might be followed by zero or more characters, each of which is a letter (a-z and A-Z), a symbol, a number, or the underscore character.

P

package
A control structure produced during program preparation that is used to execute SQL statements.

point-in-time table
A type of target table whose content matches all or part of a source table, with an added system column that identifies the approximate time when the particular row was inserted or updated at the source system.

predicate
An element of a search condition that expresses or implies a comparison operation.

primary key
A unique key that is part of the definition of a table. A primary key is the default parent key of a referential constraint definition.

R

RDBMS
Relational database management system.

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.

refresh
A process in which all of the data of interest in a user table is copied to the target table, replacing existing data. See also full refresh and differential refresh.

registration
See replication source.

registration process
The process of defining a replication source. Contrast with subscription process.

rejected transaction
A transaction containing one or more updates from replica tables that are out of date in comparison to the source table.

replica target table
A replication table at the target server that is a type of update-anywhere target table.

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

replication source
A database table or view that is defined as a source for replication. This type of table can accept copy requests and is the source table in a subscription set. See also subscription set.

remote database
A database that is physically located on a workstation other than the one in use. Contrast with local database.

row-replica
A type of update-anywhere replica maintained by DataPropagator for Microsoft Jet without transaction semantics.

row-replica conflict detection
Conflict detection done row by row, not transaction by transaction, as is done for DB2 replicas.

S

satellite
An occasionally connected client machine that has a DB2 server that synchronizes with its group at the satellite control database.

Satellite Administration Center
A user interface that provides centralized administrative support for satellites.

satellite control server
A DB2 Universal Database system that contains the satellite control database, SATCTLDB.

serialization
(1) The consecutive ordering of items.
(2) In DB2 Universal Database for AS/400, the process of controlling access to a resource to protect the integrity of the resource.

source server
The database location of the replication source and the Capture program.

source table
A table that contains the data that is to be copied to a target table. The source table can be a replication source table, a change data table, or a consistent-change-data table. Contrast with target table.

spill file
A temporary file created by the Apply program that is used as the source for updating data to multiple target tables.

staging table
A CCD table that can be used as the source for updating data to multiple target tables.

standard conflict detection
Conflict detection in which the Apply program searches for conflicts in rows that are already captured in the change data tables of the replica or user table. See also conflict detection, enhanced conflict detection, and row-replica conflict detection.

subscription
See subscription set.

subscription cycle
A process in which the Apply program retrieves changed data for a given subscription set, replicates the changes to the target table, and updates the appropriate replication control tables to reflect the progress it made.

subscription process
A process in which you define subscription sets and subscription-set members. Contrast with registration process.

subscription set
The specification of a group of source tables, target tables, and the control information that governs the replication of changed data. See also subscription-set member.

subscription-set member
A member of a subscription set. There is one member for each source-target pair. Each member defines the structure of the target table and which rows and columns will be replicated from the source table.

T

target server
The database location of the target table. Normally this is also the location of the Apply program.

target table
The table on the target server to which data is copied. It can be a user copy table, a point-in-time table, a base aggregate table, a change aggregate table, a consistent-change-data table, or a replica table.

temporary table
A table created during the processing of an SQL statement to hold intermediate results.

transaction
An exchange between a workstation and a program, two workstations, or two programs that accomplishes a particular action or result. Examples are the entry of a customer's deposit and the updating of the customer's balance.

trigger
In DB2, an object in a database that is invoked indirectly by the database manager when a particular SQL statement is run.

two-phase commit
A two-step process by which recoverable resources and an external subsystem are committed. During the first step, the database manager subsystems are polled to ensure that they are ready to commit. If all subsystems respond positively, the database manager instructs them to commit.

U

UDT
User-defined type.

uncommitted read (UR)
An isolation level that allows an application to access uncommitted changes of other transactions. The application does not lock other applications out of the row that it is reading unless the other application attempts to drop or alter the table.

Unicode
An international character encoding scheme that is a subset of the ISO 10646 standard. Each character supported is defined using a unique 2-byte code.

unit-of-work (UOW) table
A replication control table at the source server that contains commit records read from the database log or journal. The records include a unit-of-recovery ID that can be used to join the unit-of-work table and the change data table to produce transaction-consistent change data. For DB2, the unit-of-work table optionally includes the correlation ID, which can be useful for auditing purposes.

UR
Uncommitted read.

user copy table
A target table whose content matches all or part of a source table and contains only user data columns.

user-defined type (UDT)
A data type that is not native to the database manager and was created by a user. See also distinct type.

user table
A table created for and used by an application before it is defined as a replication source. It is used as the source for updates to read-only target tables, consistent-change-data tables, replicas, and row-replica tables.

V

view
A logical table that consists of data that is generated by a query.

W

warm start
A start of the Capture program that allows reuse of previously initialized input and output work queues. Contrast with cold start.

work file
A temporary file used by the Apply program when processing a subscription set.

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