Accessing Objects in External Object Storage Using Foreign Table - Teradata Vantage

Teradata® VantageCloud Lake
Deployment
VantageCloud
Edition
Lake
Product
Teradata Vantage
Published
January 2023
Language
English (United States)
Last Update
2024-04-03
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  • Each Native Object Store (NOS) table access requires three steps in the EXPLAIN. The same three steps are required whether the NOS table is accessed using a foreign table or the READ_NOS table operator:
    • A single-AMP step requests object metadata based on the foreign table definition. Path filtering, if the SQL includes it, is applied in this step. Names and sizes of objects to be accessed are returned.
    • A single-AMP step takes the list of filenames and sizes and uses a bin-packing algorithm to assign objects as equitably as possible across all AMPs in the map.
    • An all-AMP step where each AMP connects to and reads its assigned objects, and then transforms the data into relational rows.
  • Row estimates that show up in the single-AMP metadata requests represent the number of objects estimated to be accessed in the all-AMP retrieve step, not the number of rows from the table.