Which layer is primarily responsible for merging answer sets back to the Parsing Engine (PE)?

The layer primarily responsible for merging answer sets back to the Parsing Engine (PE) is the Message Parsing Layer. This layer plays a crucial role in the Teradata architecture by managing the communication between the Parsing Engine and the various nodes where query processing occurs. Once a query is executed, the Message Parsing Layer collects the results from different nodes and merges them into a single result set before sending it back to the Parsing Engine.

This integration is vital for ensuring that the results reflect all the calculations and aggregations performed across the system, allowing the PE to provide a coherent and complete answer to the original query. The effective management of this layer is essential for maintaining data integrity and performance in Teradata's parallel processing environment.

In contrast, the other layers mentioned do not perform this function. Virtual Disk Space pertains to storage management rather than query result handling; Parallel Database Extensions allow for optimizations and extensions but do not directly deal with merging results; and Archiving Utilities focus on data backup and restoration rather than real-time query processing.