Journaling is data protection and disaster recovery mechanism for Teradata database. It maintains Pre-Image and Post-image of any DML Transaction.
There are 3 different types of journals available in Teradata. They are
1. Transient Journal - This maintains current transaction history. Once the query is successful it deletes entries from its table. If the current query transaction fails, It rolls back data from this table.
2. Permanent Journal - This is defined when a table is created. It can store BEFORE or AFTER image of tables. Both BEFORE and AFTER copy can also be maintained as DUAL Journal.
Permanent Journal maintains complete history of table. Permanent journal is maintained for critical table and a database can have one permanent journal, Permanent journal is used basically for Point-in-time recovery in case of accidental data loss, and this resembles redo mechanism in oracle.
3. Down AMP recovery Journal (DARJ) - Down AMP recovery Journal activates automatically when a AMP goes down. It is used with fallback protected table to maintain any change made on table during AMP is unavailable. When failed AMP is brought online the restart process applies all the changes to recovered AMP using DARJ.