In Oracle Data Integrator (ODI), what's the role of C$ tables? Under what circumstances does ODI create them?

 In Oracle Data Integrator (ODI), C$ tables are temporary tables used for staging data during the data integration process. They play a crucial role in facilitating data manipulation and transformation before loading it into the target system.

• Purpose: C$ tables serve as a temporary storage area for data extracted from source systems. ODI utilizes these tables to perform transformations, filtering, and other operations before loading the final data set into the target.

• Creation: ODI automatically creates C$ tables under specific circumstances during the data integration flow. This typically occurs when:

  • Knowledge Module (CKM) Usage: If your integration scenario involves data manipulation using the CKM, ODI might create C$ tables to hold intermediate data results.
  • Heterogeneous Data Sources: When dealing with data from multiple source systems with different structures, ODI often leverages C$ tables to stage and unify the data before further processing.
  • Specific Loading Strategies: Certain loading strategies within ODI, like using the "File to SQL" Knowledge Module (LKM) or performing joins on data from different sources, might trigger the creation of C$ tables.

C$ tables are created whenever ODI needs a temporary workspace to manipulate data before loading it to the target.

Some additional details about C$ tables:

• Naming Convention: C$ tables follow a specific naming pattern typically starting with "C$" followed by an underscore ("_") and a unique identifier. This identifier can be a combination of numbers and letters depending on the context.
• Structure: The structure of C$ tables generally reflects the columns and data types of the source data being processed. However, in some cases, ODI might add additional columns for internal processing purposes.
• Lifetime: C$ tables are temporary and exist only for the duration of the current data integration session. Once the data is loaded into the target and the session completes, ODI automatically drops the C$ tables.

In simpler terms, C$ tables act as a behind-the-scenes mechanism for ODI to manage data during transformations and ensure smooth data flow to the target system.