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Oracle® Streams Concepts and Administration
11g Release 1 (11.1)

B28321-03
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Glossary

action context

Optional information associated with a rule that is interpreted by the client of the rules engine when the rule is evaluated for a message.

ANYDATA queue

A queue of type ANYDATA. These queues can stage messages of different types wrapped in an ANYDATA wrapper.

See Also: typed queue

applied SCN

A system change number (SCN) relating to a capture process that corresponds to the most recent message dequeued by an apply process that applies changes captured by the capture process.

apply forwarding

A directed network in which messages being forwarded at an intermediate database are first processed by an apply process. These messages are then recaptured by a capture process at the intermediate database and forwarded.

See Also: queue forwarding

apply handler

A user-defined procedure used by an apply process for customized processing of messages. Apply handlers include message handlers, DML handlers, DDL handlers, precommit handlers, and error handlers.

apply process

An optional Oracle background process that dequeues messages from a specific queue and either applies each message directly, discards it, passes it as a parameter to an apply handler, or re-enqueues it. An apply process is an Oracle Streams client.

See Also: logical change record (LCR)

apply servers

A component of an apply process that includes one or more processes that apply LCRs to database objects as DML or DDL statements or pass the LCRs to their appropriate apply handlers. For user messages, the apply servers pass the messages to the message handler. Apply servers can also enqueue logical change record (LCR) and non-LCR messages specified by the DBMS_APPLY_ADM.SET_ENQUEUE_DESTINATION procedure. If an apply server encounters an error, then it tries to resolve the error with a user-specified error handler. If an apply server cannot resolve an error, then it places the entire transaction, including all of its LCRs, in the error queue.

See Also: logical change record (LCR)

apply user

The user in whose security domain an apply process dequeues messages that satisfy its rule sets, applies messages directly to database objects, runs custom rule-based transformations configured for apply process rules, and runs apply handlers configured for the apply process.

approximate commit system change number (approximate CSCN)

An SCN value based on the current SCN of the database when a transaction that has enqueued messages into a commit-time queue is committed.

archived-log downstream capture process

A downstream capture process that captures changes in archived redo log files copied from the source database to the downstream database.

barrier transaction

A DDL transaction or a transaction that includes a row logical change record (row LCR) for which an apply process cannot identify the table rows or the database object by using the destination database data dictionary and virtual dependency definitions.

builder server

A component of a capture process that is a process that merges redo records from the preparer server. These redo records either evaluated to TRUE during partial evaluation or partial evaluation was inconclusive for them. The builder server preserves the system change number (SCN) order of these redo records and passes the merged redo records to the capture process.

buffered LCR

A logical change record (LCR) that is constructed explicitly by an application and enqueued into the buffered queue portion of an ANYDATA queue.

buffered queue

The portion of a queue that uses the Oracle Streams pool to store messages in memory and a queue table to store messages that have spilled from memory.

buffered user message

A non-LCR message of a user-defined type that is created explicitly by an application and enqueued into a buffered queue. A buffered user message can be enqueued into the buffered queue portion of an ANYDATA queue or a typed queue.

capture process

An optional Oracle background process that scans the database redo log to capture DML and DDL changes made to database objects. A capture process is an Oracle Streams client.

capture user

Either the user in whose security domain a capture process captures changes that satisfy its rule sets and runs custom rule-based transformations configured for capture process rules, or the user in whose security domain a synchronous capture captures changes that satisfy its rule set and runs custom rule-based transformations configured for synchronous capture rules.

captured LCR

A logical change record (LCR) that was captured implicitly by a capture process and enqueued into the buffered queue portion of an ANYDATA queue.

See Also: user message

captured SCN

The system change number (SCN) that corresponds to the most recent change scanned in the redo log by a capture process.

change cycling

Sending a change back to the database where it originated. Typically, change cycling should be avoided in an information sharing environment by using tags and by using the LCR member function GET_SOURCE_DATABASE_NAME in rule conditions.

See Also: logical change record (LCR)

checkpoint

Information about the current state of a capture process that is stored persistently in the data dictionary of the database running the capture process.

checkpoint interval

A regular interval at which a capture process attempts to record a checkpoint.

checkpoint retention time

The amount of time that a capture process retains checkpoints before purging them automatically.

column list

A list of columns for which an update conflict handler is called when an update conflict occurs for one or more of the columns in the list.

See Also: conflict resolution

commit-time queue

A queue in which messages are ordered by their approximate commit system change number (approximate CSCN) values.

conditional log group

A supplemental log group that logs the before images of all specified columns only if at least one of the columns in the supplemental log group is modified.

See Also: unconditional log group

conflict

A mismatch between the old values in an LCR and the expected data in a table. Conflicts are detected by an apply process when it attempts to apply an LCR. Conflicts typically result when two different databases that are sharing data in a table modify the same row in the table at nearly the same time.

See Also: logical change record (LCR)

conflict resolution

Handling a conflict to avoid an apply error. Either prebuilt update conflict handlers or custom conflict handlers can resolve conflicts.

consumption

The process of dequeuing an message from a queue.

coordinator process

A component of an apply process that is an Oracle background process that gets transactions from the reader server and passes them to apply servers.

custom apply

An apply process passes an LCR as a parameter to a user procedure for processing. The user procedure can process the LCR in a customized way.

See Also: logical change record (LCR)

custom rule-based transformation

A rule-based transformation that requires a user-defined PL/SQL function to perform the transformation.

See Also: declarative rule-based transformation

database supplemental logging

The type of supplemental logging that can apply to the primary key, foreign key, and unique key columns in an entire database.

DDL handler

An apply handler that processes DDL LCRs.

See Also: DDL logical change record (DDL LCR)

DDL logical change record (DDL LCR)

A logical change record (LCR) that describes a data definition language (DDL) change.

declarative rule-based transformation

A rule-based transformation that covers one of a common set of transformation scenarios for row LCRs. Declarative rule-based transformations are run internally without using PL/SQL.

See Also: row logical change record (row LCR) and custom rule-based transformation

dequeue

To retrieve a message from a queue.

destination database

A database where messages are consumed. Messages can be consumed when they are dequeued implicitly from a queue by a propagation or apply process, or messages can be consumed when they are dequeued explicitly by an application, a messaging client, or a user.

See Also: consumption

destination queue

The queue that receives the messages propagated by a propagation from a source queue.

direct apply

An apply process applies an LCR without running a user procedure.

See Also: logical change record (LCR)

directed network

A network in which propagated messages pass through one or more intermediate databases before arriving at a destination database.

DML handler

An apply handler that processes row LCRs.

See Also: row logical change record (row LCR)

downstream capture process

A capture process that runs on a database other than its source database.

downstream database

The database on which a downstream capture process runs.

enqueue

To place a message in a queue.

error handler

An apply handler that tries to resolve apply errors. An error handler is invoked only when a row logical change record (row LCR) raises an apply process error. Such an error might result from a conflict if no conflict handler is specified or if the update conflict handler cannot resolve the conflict.

evaluation context

A database object that defines external data that can be referenced in rule conditions. The external data can exist as variables, table data, or both.

exception queue

Messages are transferred to an exception queue if they cannot be retrieved and processed for some reason.

explicit capture

The messages are enqueued into a queue by an application or a user.

explicit consumption

The messages in a queue are dequeued either by a messaging client when it is invoked by a user or application or by an application or user directly.

expression

A combination of one or more values and operators that evaluate to a value.

file

In the context of a file group, a reference to a file stored on hard disk. A file is composed of a file name, a directory object, and a file type. The directory object references the directory in which the file is stored on hard disk.

file group

A collection of versions.

file group repository

A collection of all of the file groups in a database.

first SCN

The lowest system change number (SCN) in the redo log from which a capture process can capture changes.

global rule

A rule that is relevant either to an entire database or an entire queue.

heterogeneous information sharing

Sharing information between Oracle and non-Oracle databases.

high-watermark

The system change number (SCN) beyond which no messages have been applied by an apply process.

See Also: low-watermark

ignore SCN

The system change number (SCN) specified for a table below which changes cannot be applied by an apply process.

implicit capture

The messages are captured automatically by a capture process or by synchronous capture and enqueued into a queue.

implicit consumption

The messages in a queue are dequeued automatically by an apply process.

instantiation

The process of preparing database objects for instantiation at a source database, optionally copying the database objects from a source database to a destination database, and setting the instantiation SCN for each instantiated database object.

instantiation SCN

The system change number (SCN) for a table which specifies that only changes that were committed after the SCN at the source database are applied by an apply process.

LCR

See logical change record (LCR).

LOB assembly

An option for DML handlers and error handlers that assembles multiple row LCRs resulting from a change to a single row with LOB columns into a single row LCR. LOB assembly simplifies processing of row LCRs with LOB columns in DML handlers and error handlers.

local capture process

A capture process that runs on its source database.

logical change record (LCR)

A message with a specific format that describes a database change.

See Also: row logical change record (row LCR) and DDL logical change record (DDL LCR)

LogMiner data dictionary

A separate data dictionary used by a capture process to determine the details of a change that it is capturing. The LogMiner data dictionary is necessary because the primary data dictionary of the source database might not be synchronized with the redo data being scanned by a capture process.

low-watermark

The system change number (SCN) up to which all messages have been applied by an apply process.

See Also: high-watermark

maximum checkpoint SCN

The system change number (SCN) that corresponds to the last checkpoint interval recorded by a capture process.

message

A unit of shared information in an Oracle Streams environment.

message handler

An apply handler that processes persistent user messages.

See Also: logical change record (LCR)

message rule

A rule that is relevant only for a user message of a specific message type.

messaging client

An optional Oracle Streams client that dequeues persistent LCRs or persistent user messages when it is invoked by an application or a user.

negative rule set

A rule set for an Oracle Streams client that results in the Oracle Streams client discarding a message when a rule in the rule set evaluates to TRUE for the message. The negative rule set for an Oracle Streams client always is evaluated before the positive rule set.

nonpersistent queue

Nonpersistent queues store messages in memory. They are generally used to provide an asynchronous mechanism to send notifications to all users that are currently connected. Nonpersistent queues were deprecated in Oracle Database 10g Release 2. Oracle recommends that you use buffered messaging instead.

nontransactional queue

A queue in which each message is its own transaction.

See Also: transactional queue

object dependency

A virtual dependency definition that defines a parent-child relationship between two objects at a destination database.

oldest SCN

For a running apply process, the earliest system change number (SCN) of the transactions currently being dequeued and applied. For a stopped apply process, the oldest SCN is the earliest SCN of the transactions that were being applied when the apply process was stopped.

Oracle Streams client

A mechanism that performs work in an Oracle Streams environment and is a client of the rules engine (when the mechanism is associated with one or more rule sets). The following are Oracle Streams clients: capture process, propagation, apply process, and messaging client.

Oracle Streams data dictionary

A separate data dictionary used by propagations and apply processes to keep track of the database objects from a particular source database.

Oracle Streams pool

A portion of memory in the System Global Area (SGA) that is used by Oracle Streams. The Oracle Streams pool stores buffered queue messages in memory, and it provides memory for capture processes and apply processes.

Oracle Streams topology

A representation of the databases in an Oracle Streams environment, the Oracle Streams components configured in these databases, and the flow of messages between these components.

persistent LCR

A logical change record (LCR) that is enqueued into the persistent queue portion of an ANYDATA queue. A persistent LCR can be enqueued in one of the following ways:

persistent queue

The portion of a queue that only stores messages on hard disk in a queue table, not in memory.

persistent user message

A non-LCR message of a user-defined type that is enqueued into a persistent queue. A persistent user message can be enqueued in one of the following ways:

A persistent user message can be enqueued into the persistent queue portion of an ANYDATA queue or a typed queue.

positive rule set

A rule set for an Oracle Streams client that results in the Oracle Streams client performing its task for a message when a rule in the rule set evaluates to TRUE for the message. The negative rule set for an Oracle Streams client always is evaluated before the positive rule set.

precommit handler

An apply handler that can receive the commit information for a transaction and process the commit information in any customized way.

prepared table

A table that has been prepared for instantiation.

preparer server

A component of a capture process that scans a region defined by the reader server and performs prefiltering of changes found in the redo log. A reader server is a process, and multiple reader servers can run in parallel. Prefiltering entails sending partial information about changes, such as schema and object name for a change, to the rules engine for evaluation, and receiving the results of the evaluation.

propagation

An optional Oracle Streams client that uses an Oracle Scheduler job to send messages from a source queue to a destination queue.

propagation job

An Oracle Scheduler job used by a propagation to propagate messages.

propagation schedule

A schedule that specifies how often a propagation job propagates messages.

queue

The abstract storage unit used by a messaging system to store messages.

queue forwarding

A directed network in which the messages being forwarded at an intermediate database are the messages received by the intermediate database, so that the source database for a message is the database where the message originated.

See Also: apply forwarding

queue table

A database table where queues are stored. Each queue table contains a default exception queue.

reader server

  1. A component of a capture process that is a process that reads the redo log and divides the redo log into regions.

  2. A component of an apply process that dequeues messages. The reader server is a process that computes dependencies between LCRs and assembles messages into transactions. The reader server then returns the assembled transactions to the coordinator process, which assigns them to idle apply servers.

See Also: logical change record (LCR)

real-time downstream capture process

A downstream capture process that can capture changes made at the source database before the changes are archived in an archived redo log file.

required checkpoint SCN

The system change number (SCN) that corresponds to the lowest checkpoint interval for which a capture process requires redo data.

replication

The process of sharing database objects and data at multiple databases.

resolution column

The column used to identify a prebuilt update conflict handler.

See Also: conflict resolution

row logical change record (row LCR)

A logical change record (LCR) that describes a change to the data in a single row or a change to a single LONG, LONG RAW, or LOB column in a row that results from a data manipulation language (DML) statement or a piecewise update to a LOB. One DML statement can result in multiple row LCRs.

row migration

An automatic conversion performed by an internal rule-based transformation when a subset rule evaluates to TRUE in which an UPDATE operation might be converted into an INSERT or DELETE operation.

rule

A database object that enables a client to perform an action when an event occurs and a condition is satisfied.

rule condition

A component of a rule which combines one or more expressions and conditions and returns a Boolean value, which is a value of TRUE, FALSE, or NULL (unknown).

rule set

A group of rules.

rule-based transformation

Any modification to a message when a rule in a positive rule set evaluates to TRUE.

rules engine

A built-in part of Oracle that evaluates rule sets.

schema rule

A rule that is relevant only to a particular schema.

secure queue

A queue for which Oracle Streams Advanced Queuing (AQ) agents must be associated explicitly with one or more database users who can perform queue operations, such as enqueue and dequeue.

source database

The database where changes captured by a capture process are generated in a redo log, or the database where a synchronous capture that generated LCRs is configured.

source queue

The queue from which a propagation propagates messages to a destination queue.

start SCN

The system change number (SCN) from which a capture process begins to capture changes.

subset rule

A rule that is relevant only to a subset of the rows in a particular table.

supplemental log group

A group of columns in a table that is supplementally logged.

See Also: supplemental logging

supplemental logging

Additional column data placed in a redo log whenever an operation is performed. A capture process captures this additional information and places it in LCRs, and the additional information might be needed for an apply process to apply LCRs properly at a destination database.

See Also: logical change record (LCR)

synchronous capture

An optional Oracle Streams client that uses an internal mechanism to capture DML changes made to tables immediately after the changes are made.

system-created rule

A rule with a system-generated name that was created using the DBMS_STREAMS_ADM package.

table rule

A rule that is relevant only to a particular table.

table supplemental logging

The type of supplemental logging that applies to columns in a particular table.

tablespace repository

A collection of the tablespace sets in a file group.

tag

Data of RAW data type that appears in each redo entry and LCR. Tags can be used to modify the behavior of Oracle Streams clients and to track LCRs. Tags can also be used to prevent change cycling.

See Also: logical change record (LCR)

topology

See Oracle Streams topology.

transactional queue

A queue in which messages can be grouped into a set that are applied as one transaction.

See Also: nontransactional queue

typed queue

A queue that can stage messages of one specific type only.

See Also: ANYDATA queue

unconditional log group

A supplemental log group that logs the before images of specified columns when the table is changed, regardless of whether the change affected any of the specified columns.

See Also: conditional log group

user message

A non-LCR message of a user-defined type. A user message can be a buffered user message or a persistent user message.

See Also: logical change record (LCR)

value dependency

A virtual dependency definition that defines a table constraint, such as a unique key, or a relationship between the columns of two or more tables.

version

A collection of related files.

virtual dependency definition

A description of a dependency that is used by an apply process to detect dependencies between transactions being applied at a destination database.