CDC Redo/Archive log mode - 6.3

Talend Real-time Big Data Platform Studio User Guide

Talend Real-Time Big Data Platform
Data Quality and Preparation
Design and Development
Talend Studio

The Redo/Archive log mode is only available for Oracle v11 and previous versions and AS/400 databases. It is equivalent to the archive log mode for Oracle and to the journal mode for AS/400.

In an Oracle database, a Redo log is a file which logs the history of changes made to data. In an AS/400 database, these changes are logged automatically in the database's internal logbook (journal). These changes include the insert, update and delete operations which data may undergo.

Redo/Archive log mode is less intrusive than Trigger mode because in contrast to Trigger mode, it does not require modifications to the database structure.

When setting up this Redo/Archive log mode for Oracle, only one subscriber can have access rights to the change table. This subscriber must be a database user who holds the subscription rights. Also, there is a subscription table which controls access to the subscriber change table. The subscription change table is a comprehensive, internal table which reflects the state of the Oracle database at the moment at which the Redo/Archive log option was activated.

When setting up this mode for AS/400, a save file, called fitcdc.savf and provided in your Studio, is restored on AS/400 and used to install a program called RUNCDC. When the subscriber views the changes made (View all changes) or consumes them for reuse (using a tAS400CDC component), the RUNCDC program reads and analyzes the logbook (journal) and the attached receiver from the source table and updates the change table accordingly. The AS/400 CDC Redo/Archive log mode (journal) creates subscription tables to prevent unauthorized target systems from accessing the data in the change tables. A target system means any application which tries to use data captured in the source system.

In this example, the CDC monitors the changes made to a Product table, thanks to the data contained in the database's logbook (journal). The CDC reads the logbook and records the changes which have been made to the data. These changes are collected and published in a table of changes to which two subscribers have access, a CRM application and an Accounting application. These two systems fetch the changes and use them to update their data.