Down-AMP Recovery Journal:-
Recovery journal provides the capability to continue normal write operation like insert, update, create and delete on a table even if a logical AMP goes down in the same cluster.
Suppose we have activated the fallback option for a table and an AMP goes down in a cluster. As soon as AMP goes down the down-amp recovery journal will be activated and captures all the changes made on the fallback protected table. This means during the downtime, down-amp recovery journal is the representative for the down amp until AMP comes back.
Once the AMP comes back, all the changes will be applied back to the original table. Recovery journal is discarded once down AMP is recovered and fully functional.
Transient Journal:-
Transient journal is the mechanism to capture before image of data during transaction processing. It helps to roll back to the previous state of data if transaction fails for any reason.
A Transient journal is used during transaction processing to keep before-snapshot of changed rows. This helps to restore previous state of data if a transaction fails. At the starting point of any transaction, Teradata software activates the transient journal and starts to capture the affected rows for a transaction.
Once the transaction is successful, before images will be discarded for the particular transaction from the transient journal log.