During an Update job, the Update operator loads database tables. Each instance retrieves rows from the Teradata PT data streams and sends them to the database. Multiple parallel instances can be used to improve the performance of the update.
The Update operator reads a data block only once. The operator reads rows from a data stream, writes that data to a buffer, then sends that buffer of data across sessions to the available AMPs.
This process is dependent on all changes to tables being keyed on the primary index. Thus, all transactions must be primary index operations when using the Update operator. An exception to this rule is the use of the Delete Task. For more information, see Delete Task Option.