Oracle® Database PL/SQL Packages and Types Reference 10g Release 2 (10.2) Part Number B14258-01 |
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The DBMS_CDC_SUBSCRIBE
package, one of a set of Change Data Capture packages, lets subscribers view and query change data that was captured and published with the DBMS_CDC_PUBLISH
package.
A Change Data Capture system usually has one publisher and many subscribers. The subscribers (applications or individuals), use the Oracle supplied package, DBMS_CDC_SUBSCRIBE
, to access published data.
Note:
In previous releases, this package was namedDBMS_LOGMNR_CDC_SUBSCRIBE
. Beginning with Oracle Database 10g, the LOGMNR
string has been removed from the name, resulting in the name DBMS_CDC_SUBSCRIBE
. Although both variants of the name are still supported, the variant with the LOGMNR
string has been deprecated and may not be supported in a future release.See Also:
Oracle Database Data Warehousing Guide for information regarding Oracle Change Data Capture.This chapter contains the following topics:
Overview
Deprecated Subprograms
Security Model
Views
This section contains the following topics, which relate to using the DBMS_CDC_SUBSCRIBE
package:
The primary role of the subscriber is to use the change data. Through the DBMS_CDC_SUBSCRIBE
package, each subscriber registers interest in source tables by subscribing to them.
Once the publisher sets up the system to capture data into change tables (which are viewed as publications by subscribers) and grants subscribers access to the change tables, subscribers can access and query the published change data for any of the source tables of interest. Using the subprograms in the DBMS_CDC_SUBSCRIBE
package, the subscriber accomplishes the following main objectives:
Indicates the change data of interest by creating a subscription and associated subscriber views on published source tables and source columns
Activates the subscription to indicate that the subscriber is ready to receive change data
Extends the subscription window to receive a new set of change data
Uses SQL SELECT
statements to retrieve change data from the subscriber views
Purges the subscription window when finished processing a block of changes
Figure 22-1 provides a graphical flowchart of the order in which subscribers most typically use the subprograms in the DBMS_CDC_SUBSCRIBE
package (which are listed in Table 22-1). A subscriber would typically create a subscription, subscribe to one or more source tables and columns, activate the subscription, extend the subscription window, query the subscriber views, purge the subscription window, and then either extend the subscription window again or drop the subscription.
Note:
If a subscriber uses thePURGE_WINDOW
procedure immediately after using an EXTEND_WINDOW
procedure, then change data may be lost without ever being processed.See Also:
Chapter 21, "DBMS_CDC_PUBLISH" for information on the package for publishing change data.Note:
Oracle Corporation recommends that you do not use deprecated procedures in new applications. Support for deprecated features is for backward compatibility only.The following subprograms are deprecated with Oracle Database 10g:
Subscribers no longer need to drop subscriber views. This work is now done automatically by Change Data Capture.
Subscribers no longer explicitly specify subscription handles. Subscribers should use the CREATE_SUBSCRIPTION
procedure instead to specify a subscription name.
Subscribers no longer need to prepare subscriber views. This work is now done automatically by Change Data Capture.
Changes in Behavior
If an existing application uses these deprecated DBMS_CDC_SUBSCRIBE
subprograms with Oracle Database 10g, note the following changes in behavior:
Subscriber views are persistent for the life of the subscription.
Some error conditions, particularly with regard to subscriber view management, no longer occur.
If a publisher alters a publication such that it contains different control columns, the subscriber must call DBMS_CDC_SUBSCRIBE.EXTEND_WINDOW
to see the new column structure.
Deprecated Parameters
The use of the subscription_handle
parameter with the following DBMS_CDC_SUBSCRIBE
procedures has been deprecated beginning with Oracle Database 10g:
SUBSCRIBE
ACTIVATE_SUBSCRIPTION
EXTEND_WINDOW
PURGE_WINDOW
DROP_SUBSCRIPTION
Change Data Capture grants EXECUTE
privileges to PUBLIC
on the DBMS_CDC_SUBSCRIBE
package.
The DBMS_CDC_SUBSCRIBE
package uses the views listed in the section on Getting Information About the Change Data Capture Environment in Oracle Database Data Warehousing Guide.
Table 22-1 DBMS_CDC_SUBSCRIBE Package Subprograms
Subprogram | Description |
---|---|
ACTIVATE_SUBSCRIPTION Procedure |
Indicates that a subscription is ready to start accessing change data |
CREATE_SUBSCRIPTION Procedure | Creates a subscription and associates it with one change set |
DROP_SUBSCRIPTION Procedure |
Drops a subscription that was created with a prior call to the CREATE_SUBSCRIPTION procedure |
EXTEND_WINDOW Procedure | Sets a subscription window high boundary so that new change data can be seen |
PURGE_WINDOW Procedure |
Sets the low boundary for a subscription window to notify Change Data Capture that the subscriber is finished processing a set of change data |
SUBSCRIBE Procedure |
Specifies a source table and the source columns for which the subscriber wants to access change data and specifies the subscriber view through which the subscriber sees change data for the source table |
This procedure indicates that a subscription is ready to start accessing change data.
Syntax
DBMS_CDC_SUBSCRIBE.ACTIVATE_SUBSCRIPTION ( subscription_name IN VARCHAR2);
Parameters
Table 22-2 ACTIVATE_SUBSCRIPTION Procedure Parameters
Parameter | Description |
---|---|
subscription_name |
The name of the subscription that was specified for a previous call to the CREATE_SUBSCRIPTION procedure. Subscription names follow the Oracle schema object naming rules. |
Exceptions
Table 22-3 ACTIVATE_SUBSCRIPTION Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31425 |
Subscription does not exist |
ORA-31426 |
Cannot modify active subscriptions |
ORA-31469 |
Cannot enable Change Data Capture for change set |
ORA-31514 |
Change set disabled due to capture error |
Usage Notes
The ACTIVATE_SUBSCRIPTION
procedure indicates that the subscriber is finished subscribing to tables, and the subscription is ready to start accessing change data.
Once the subscriber activates the subscription:
No additional source tables can be added to the subscription.
Change Data Capture holds the available data for the source tables and sets the subscription window to empty.
The subscriber must use the EXTEND_WINDOW
procedure to see the initial set of change data.
The subscription cannot be activated again.
A subscription cannot be activated if the underlying change set has reached its end_date
parameter value.
This procedure creates a subscription that is associated with one change set. This procedure replaces the deprecated GET_SUBSCRIPTION_HANDLE
procedure.
Syntax
DBMS_CDC_SUBSCRIBE.CREATE_SUBSCRIPTION ( change_set_name IN VARCHAR2, description IN VARCHAR2, subscription_name IN VARCHAR2);
Parameters
Table 22-4 CREATE_SUBSCRIPTION Procedure Parameters
Parameter | Description |
---|---|
change_set_name |
The name of an existing change set to which the subscriber subscribes |
description |
A description of the subscription (which might include, for example, the purpose for which it is used). The description must be specified using 255 or fewer characters. |
subscription_name |
A unique name for a subscription that must consist of 30 characters or fewer and cannot have a prefix of CDC$ . Subscription names follow the Oracle schema object naming rules. |
Exceptions
Table 22-5 CREATE_SUBSCRIPTION Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31415 |
Specified change set does not exist |
ORA-31449 |
Invalid value for change_set_name |
ORA-31457 |
Maximum length of description field exceeded |
ORA-31469 |
Cannot enable Change Data Capture for change set |
ORA-31506 |
Duplicate subscription name specified |
ORA-31510 |
Name uses reserved prefix CDC$ |
ORA-31511 |
Name exceeds maximum length of 30 characters |
Usage Notes
The
CREATE_SUBSCRIPTION
procedure allows a subscriber to register interest in a change set associated with source tables of interest.
A subscriber can query the ALL_PUBLISHED_COLUMNS
view to see all the published source tables for which the subscriber has privileges and the change sets in which the source table columns are published.
Subscriptions are not shared among subscribers; rather, each subscription name is validated against a given subscriber's login ID.
Subscriptions cannot be created if the underlying change set has reached its end_date
parameter value.
This procedure drops a subscription.
Syntax
DBMS_CDC_SUBSCRIBE.DROP_SUBSCRIPTION ( subscription_name IN VARCHAR2);
Parameters
Table 22-6 DROP_SUBSCRIPTION Procedure Parameters
Parameter | Description |
---|---|
subscription_name |
The name of the subscription that was specified for a previous call to the CREATE_SUBSCRIPTION procedure. Subscription names follow the Oracle schema object naming rules. |
Exceptions
Table 22-7 DROP_SUBSCRIPTION Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31425 |
Subscription does not exist |
Usage Notes
Subscribers should be diligent about dropping subscriptions that are no longer needed so that change data will not be held in the change tables unnecessarily.
This procedure sets the subscription window high boundary so that new change data can be seen.
Syntax
DBMS_CDC_SUBSCRIBE.EXTEND_WINDOW ( subscription_name IN VARCHAR2);
Parameters
Table 22-8 EXTEND_WINDOW Procedure Parameters
Parameter | Description |
---|---|
subscription_name |
The unique name of the subscription that was specified by a previous call to the CREATE_SUBSCRIPTION procedure. Subscription names follow the Oracle schema object naming rules. |
Exceptions
Table 22-9 EXTEND_WINDOW Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31425 |
Subscription does not exist |
ORA-31429 |
Subscription has not been activated |
ORA-31432 |
Invalid source table |
ORA-31469 |
Cannot enable Change Data Capture for change set |
ORA-31509 |
Publication does not exist |
ORA-31514 |
Change set disabled due to capture error |
Usage Notes
Until the subscriber calls the EXTEND_WINDOW
procedure to begin receiving change data, the subscription window remains empty.
The first time that the subscriber calls the EXTEND_WINDOW
procedure, it establishes the initial boundaries for the subscription window.
Subsequent calls to the EXTEND_WINDOW
procedure extend the high boundary of the subscription window so that new change data can be seen.
Oracle recommends that subscribers not view change tables directly. Instead, subscribers should use the DBMS_CDC_SUBSCRIBE
package and access data through subscriber views only. Control column values are guaranteed to be consistent only when viewed through subscriber views that have been updated with a call to the EXTEND_WINDOW
procedure.
When the underlying change set for a subscription has reached its end_date
parameter value, subsequent calls to the EXTEND_WINDOW
procedure will not raise the high boundary.
This procedure sets the low boundary of the subscription window so that the subscription no longer sees any change data, effectively making the subscription window empty. The subscriber calls this procedure to notify Change Data Capture that the subscriber is finished processing a block of change data.
Syntax
DBMS_CDC_SUBSCRIBE.PURGE_WINDOW ( subscription_name IN VARCHAR2);
Parameters
Table 22-10 PURGE_WINDOW Procedure Parameters
Parameter | Description |
---|---|
subscription_name |
The name of the subscription that was specified for a previous call to the CREATE_SUBSCRIPTION procedure. Subscription names follow the Oracle schema object naming rules. |
Exceptions
Table 22-11 PURGE_WINDOW Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31425 |
Subscription does not exist |
ORA-31429 |
Subscription has not been activated |
ORA-31432 |
Invalid source table |
ORA-31469 |
Cannot enable Change Data Capture for change set |
ORA-31514 |
Change set disabled due to capture error |
Usage Notes
When finished with a set of changes, the subscriber purges the subscription window with the PURGE_WINDOW
procedure. By this action, the subscriber performs the following functions:
Informs Change Data Capture that the subscriber is finished with the current set of change data.
Enables Change Data Capture to remove change data that is no longer needed by any subscribers.
Change Data Capture manages the change data to ensure that it is available as long as there are subscribers who need it.
When the underlying change set for a subscription has reached its end_date
parameter value, subsequent calls to the PURGE_WINDOW
procedure will not move the low boundary.
This procedure specifies a source table and the source columns for which the subscriber wants to access change data. In addition, it specifies the subscriber view through which the subscriber sees change data for the source table.
Syntax
There are two versions of syntax for the SUBSCRIBE
procedure, as follow:
Using source schema and source table
When this syntax is used, Change Data Capture will attempt to find a single publication ID that contains the specified source_table
and column_list
. If such a publication cannot be found, then Change Data Capture returns an error.
DBMS_CDC_SUBSCRIBE.SUBSCRIBE ( subscription_name IN VARCHAR2, source_schema IN VARCHAR2, source_table IN VARCHAR2, column_list IN VARCHAR2, subscriber_view IN VARCHAR2);
Using publication IDs
When this syntax is used, Change Data Capture will use the publication ID to identify the change table. If the columns specified in the column_list
parameter are not in the identified change table, then Change Data Capture returns an error.
DBMS_CDC_SUBSCRIBE.SUBSCRIBE ( subscription_name IN VARCHAR2, publication_id IN NUMBER, column_list IN VARCHAR2, subscriber_view IN VARCHAR2);
Parameters
Table 22-12 SUBSCRIBE Procedure Parameters
Parameter | Description |
---|---|
subscription_name |
The name of a subscription that was specified for, or returned by, a previous call to the CREATE_SUBSCRIPTION procedure. Subscription names follow the Oracle schema object naming rules. |
source_schema |
The name of the schema where the source table resides |
source_table |
The name of a published source table |
column_list |
A comma-delimited list of columns from the published source table or publication |
subscriber_view |
Unique name for the subscriber view for this source table or publication that must consist of 30 or fewer characters and must not have a prefix of CDC$ . Subscriber view names follow the Oracle schema object naming rules. |
publication_id |
A valid publication_id , which the subscriber can obtain from the ALL_PUBLISHED_COLUMNS view. |
Exceptions
Table 22-13 SUBSCRIBE Procedure Exceptions
Exception | Description |
---|---|
ORA-31409 |
One or more values for input parameters are incorrect |
ORA-31425 |
Subscription does not exist |
ORA-31426 |
Cannot modify active subscriptions |
ORA-31427 |
Specified source table already subscribed |
ORA-31428 |
No publication contains all the specified columns |
ORA-31432 |
Invalid source table |
ORA-31466 |
No publications found |
ORA-31469 |
Cannot enable Change Data Capture for change set |
ORA-31510 |
Name uses reserved prefix CDC$ |
ORA-31511 |
Name exceeds maximum length of 30 characters |
Usage Notes
The SUBSCRIBE
procedure allows a subscriber to subscribe to one or more published source tables and to specific columns in each source table. Each call to the SUBSCRIBE
procedure can specify only a single source table or publication ID. The subscriber can make multiple calls to the SUBSCRIBE
procedure to include multiple source tables or publications IDs in a subscription.
If the columns of interest are all in a single publication, the subscriber can call the SUBSCRIBE
procedure using the source_schema
and source_table
parameters or using the publication_id
parameter. However, if there are multiple publications on a single source table and these publications share some columns, and if any of the shared columns will be used by a single subscription, then the subscriber should call the SUBSCRIBE
procedure using the publication_id
parameter.
The subscriber can subscribe to any valid publication ID on which the subscriber has privileges to access. The subscriber can find valid publication IDs on which the subscriber has access by querying the ALL_PUBLISHED_COLUMNS
view.
A subscriber can query the ALL_PUBLISHED_COLUMNS
view to see all the published source table columns accessible to the subscriber.
Subscriptions must be created before a subscriber calls the SUBSCRIBE
procedure. Change Data Capture does not guarantee that there will be any change data available at the moment the subscription is created.
Subscribers can subscribe only to published columns from the source table. All of the columns specified in a single call to the SUBSCRIBE
procedure must come from the same publication. Any control columns associated with the underlying change table are added to the subscription automatically.
All specified source tables or publications must be in the change set that is associated with the named subscription.
A single source table can have more than one publication defined on it. A subscriber can subscribe to one or more of these publications. However a subscriber can subscribe to a particular publication only once.
Each publication in a subscription has its own subscriber view. Subscriber views are used to query the change data encompassed by the subscription's current window. Subscriber views are created in the schema of the subscriber.
A subscriber cannot subscribe to a publication within a change set that has reached its end_date
parameter value.