Maintaining and Monitoring Your Database : Change Data Capture : Change Data Capture highlights
Change Data Capture highlights
The strengths of OpenEdge CDC, include its flexibility and scalability.
OpenEdge CDC is flexible because:
Captured data is maintained in the same database
Captured data is maintained in relational form
Captured data is accessible with SQL and ABL
No changes are required in your application
OpenEdge CDC is scalable because you can define CDC policies such that:
The amount of data captured is variable by table
You can capture no data, some data, or the whole record
You can index the data for easier retrieval
The amount of data captured is controlled through policies defined at the table and field level.
Change Data Capture is a licensed product. It requires either a combination of an RDBMS license (Workgroup or Enterprise) and the corresponding CDC license, or the Advanced Enterprise RDBMS license.
CDC Policies
Defining the data captured by CDC is done through policies. CDC policies are created to define the tables and fields to be tracked. Create policies in OpenEdge Management or OpenEdge Explorer. For details on creating policies in OpenEdge Management, see OpenEdge Management and OpenEdge Explorer: Managing Change Data Capture in databases.
CDC tables in your database
CDC tracks and records the data and changes in tables within your database.
Schema tables
There are two metadata tables: _Cdc-Table-Policy and _Cdc-Field-Policy. These tables are created in the source database when you enable Change Data Capture for the database. The metadata tables contain information about CDC policies for tables and their associated fields. You do not have to allocate space for the metadata tables; these tables reside in the schema storage area of the database. You should not manage these tables, they are managed by OpenEdge RDBMS.
The relationship between the CDC Table Policy Table and the Field Policy Table is a 1- to-many relationship. The hierarchy consists of two levels: Table policy (_Cdc-Table-Policy) and Field policy (_Cdc-Field-Policy). The table policy is a parent and the field policies are its children.
The CDC Table policy describes the policy attributes such as filename of the source table reporting to this policy, area the table resides in, active status of policy, and coverage level of the policy. This policy can point to a number of CDC Field policy records that identify the fields to be captured in the change table for this table. Once the new policy is defined, created, and committed, the policy becomes active. Each time a CUD record operation is executed, a record is written to the Change Tracking Table and the Change Table assigned to the policy.
Data tables
There are CDC data tables: the _Cdc-Change-Tracking table, and an individual CDC change table for each source table for which you want to capture change data. Database administrators are responsible for allocating space for all CDC data tables, and specifiying the area when enabling CDC.
A CDC change table is created in the source database when you define and activate a CDC policy for a source table. Note that a CDC change table is created only when the policy level is higher than minimal. CDC policies with the minimal level do not have a change table; their data is written only to the _Cdc-Change-Tracking table.
The _Cdc-Change-Tracking table maintains a record of all change capture activities for all tables with CDC policies. This table is created in the source database when you enable Change Data Capture for the database.
For details on these tables, their uses, and their schema, see OpenEdge Getting Started: OpenEdge Change Data Capture Guide.
Captured data is maintained in the same database