Replication Guide and Reference
- 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.
- application version
- The set of setup, update, and cleanup batches that are associated with a
specific version of an application that runs on the satellites of a
group.
- Apply job table
- An AS/400 specific replication control table at the control server used to
guarantee a unique APPLY_QUAL value for all instances of the Apply program
running at the control server.
- 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 each instance of the Apply program.
- Apply-qualifier-cross-reference table
- An AS/400 specific replication control table at the source server that
contains information to support update-anywhere replication.
- Apply trail table
- A replication control table at the control server that records a history
of the updates performed against target tables.
- 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 or update, 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.
- C
- Capture enqueue table
- This VM and VSE specific control table at the source server is used to
ensure that only one Capture program is running per database.
- 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, multi-byte, 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.
- conflict detection
- In update-anywhere replication configurations, the process of detecting if
the same row was updated in the source and target tables during the same
replication cycle. When a conflict is detected, the transaction that
caused the conflict is rejected. See also enhanced conflict detection, standard conflict detection, and row-replica conflict detection.
- conflict table
- A Microsoft Jet specific table at the target server that contains row data
for DataPropagator for Microsoft Jet-detected conflict losers.
- consistent-change-data (CCD) table
- A replication table that is used for staging data, with four replication
control columns. See also internal CCD table and external CCD table.
- consolidation replication
- A replication model in which the data from multiple source tables is
replicated to a single target table. Contrast with fan-out replication.
- 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 the tasks on database objects.
- 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.
- critical section table
- A replication control table at the source server that is used to prevent
circular replication for update-anywhere subscriptions.
- 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.
- 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.
- Design Master
- The original copy of a Microsoft Jet database. Only the Design
Master supports changes to the database structure (table, query, and form
design).
- differential refresh
- A process in which only changed data is copied to the target table,
replacing existing data.
- 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).
- 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 in the subscription set
against further transactions, and begins detection after all changes made
prior to locking have been captured. See also standard conflict detection, conflict detection, and row-replica conflict detection.
- error information table
- A Microsoft Jet specific table at the target server that contains
additional information to identify the row-replica table and row that caused
an error.
- error messages table
- A Microsoft Jet specific table at the target server that contains error
codes and error messages.
- error-side-information table
- A Microsoft Jet specific table at the target server that contains the
names of the conflict tables.
- external source table
- A non-DB2 table that is manually updated to match the
consistent-change-data table structure and defined as a replication
source. Also called an external CCD table. See also consistent-change-data (CCD) table.
- F
- fan-out replication
- A replication model in which data from one source table is copied to
multiple target tables, thereby distributing the data to multiple
locations. Contrast with consolidation replication.
- 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
- A collection of satellites that share characteristics such as database
configuration and the application that runs on the satellite.
- I
- internal CCD table
- A consistent-change-data table that is a join of the change data table and
the unit-of-work table at the source server.
- 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.
- key string table
- A Microsoft Jet specific table at the target server that maps the
Microsoft Jet table identifiers and row identifiers to primary key values when
the following actions occur:
- Rows are deleted from Microsoft Jet database tables.
- Deleted rows are recorded in MSysTombstone with s_Generation, TableGUID,
and s_GUID (row) identifiers, but without primary key details.
- The primary key values are needed to replicate Microsoft Jet database
deletes to an RDBMS.
- 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
-
- A means of serializing events or access to data
- 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.
- mobile client
- The node, usually a laptop computer, where the mobile replication
enabler and replication source and target tables used in a mobile environment
are located. The mobile replication mode is started from the mobile
client.
- mobile replication enabler
- A replication program that starts the mobile replication mode at the
mobile client.
- mobile replication mode
- A mode of replication in which the Capture and Apply programs operate as
needed rather than continuously. This mode is started from the mobile
client and allows data to be replicated when the mobile client is connected to
the source or target server.
- N
- 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
-
- Anything that can be created or manipulated with SQL--for example,
tables, view, indexes, or packages.
- 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.
- 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 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, used to form a name.
- P
- package
- A control structure produced during program preparation that is used to
execute SQL statements.
- partitioning key
-
- An ordered set of one or more columns in a table. For each row in
the table, the values in the partitioning key columns are used to determine on
which database partition the row belongs.
- In replication, an ordered set of one or more columns in a table.
For each row in the source table, the values in the partitioning key columns
are used to determine in which target table the row belongs.
- 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.
- pruning control table
- A replication control table at the source server that coordinates the
pruning of the change data and unit-of-work control tables. The values
in this table indicate how much data has been replicated by the Apply program
and can be safely pruned by the Capture mechanisms.
- prune lock table
- A replication control table at the source server that is used to serialize
the access of staging tables during cold start and retention limit
pruning.
- R
- RDBMS
- Relational database management system.
- referential integrity
- The state of a database in which all values of all foreign keys are
valid.
- registration
- The process of identifying a source table to DB2 DPROP to make the table
available for subscription. See also replication source.
- register table
- A replication control table at the source server that relates each source
table or view to an associated change data table and consistent-change-data
table, if applicable.
- register extension table
- An AS/400 specific replication control table at the source server that is
an extension of the register table. This table contains additional
information about replication sources, such as the journal name and the remote
source table's RDB entry name.
- register synchronization table
- A replication control table at the source server that contains an update
trigger that initiates an update of the SYNCHPOINT value for all the rows in
the register table before the Apply program reads the information from the
register table. The register synchronization table is used when
replicating from a non-IBM data source.
- 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 replication subscription set. See also subscription set and registration.
- 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.
- row-replica table
- A type of target table used specifically with the Microsoft Jet
database.
- row-replica-target-list table
- A Microsoft Jet specific table at the control server that maintains the
names of the row-replica tables.
- 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 graphical 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
-
- The consecutive ordering of items.
- In DB2 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 consistent-change-data 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 replica's change data
tables. See also conflict detection, enhanced conflict detection, and row-replica conflict detection.
- subscription
- See subscription set.
- subscription columns table
- A replication control table that contains column details of target
tables.
- subscription events table
- A replication control table that defines the events that trigger
replication, including the event name and time.
- subscription-schema-changes table
- A Microsoft Jet specific table that is used to signal when add or delete
modifications are made to a subscription.
- subscription set
- The specification of a group of source tables, target tables, and the
control information that governs the replication of changed data.
- 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.
- subscription set table
- A replication control table that defines the members of a subscription
set.
- subscription statements table
- A replication control table used to store the optional SQL statements that
can be run at the beginning or end of the subscription set cycle.
- subscription-targets-member table
- A replication control table that maps the source and target table
relationships within a subscription set.
- synchronization generations table
- A Microsoft Jet specific table at the target server that prevents cyclic
updates from replicating back to the RDBMS from a Microsoft Jet
database.
- 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.
- trace table
- A table that contains a high-level record of the execution of the Capture
program.
- transaction
- An exchange between a workstation and a program, two workstations, or two
programs that accomplishes a particular action or result. Some 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.
- tuning parameters table
- A table at the source server that contains timing information used by the
Capture program. The information includes:
- How long to keep rows in the change data table.
- How much time can elapse before changes are stored in a database log or
journal.
- How often to commit changed data to the unit-of-work tables.
- 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.
- unit-of-work 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.
- update
- A process in which the changes to data in a source table are used to
refresh a target table. This process is also known as differential
refresh.
- 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 such
as the consistent-change-data, 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.
- warm start table
- A table used by the Capture program to save the position in a DBMS log for
later reference during a warm start.
- work file
- A temporary file used by the Apply program when processing a subscription
set.
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