Exam AWS Certified Data Engineer - Associate DEA-C01 topic 1 question 127 discussion

When you TRUNCATE a materialized view in Amazon Redshift, it removes all rows from the view and reclaims the most storage space because the operation does not log individual row deletions. This is far more efficient in terms of both time and space than a DELETE operation.

the key is "reclaim database storage space" Delete does not reclaim disk space

in AWS Redshift, you can use the "TRUNCATE" command to delete all rows from a materialized view, effectively "truncating" it, especially when the materialized view is configured for streaming ingestion; this is a faster way to clear the data compared to a "DELETE" statement.

(B) TRUNCATE is invalid for materialized views, so it is excluded. In actual operations, to most effectively reuse storage, you need to delete all rows with a DELETE statement and then run VACUUM, as shown in (A) or (D). If you want to delete everything, option (A) is the most straightforward approach.

Why this is the best option: Efficiency: By using "WHERE 1=1", the database doesn't need to iterate through each row individually to check a specific condition, resulting in faster deletion of all data. Storage reclamation: Deleting all rows using this method will free up the most storage space within the materialized view. Important Considerations: TRUNCATE vs DELETE: While "TRUNCATE" can also be used to remove all data from a table, it is not recommended for materialized views in Redshift as it might not always reclaim all the storage space effectively. VACUUM command: "VACUUM" is used to reclaim space within a table after deletions, but it's not necessary when deleting all rows using "DELETE FROM ... WHERE 1=1;" as the entire table will be emptied.

B is the correct answer. Here is why: TRUNCATE is the most efficient way to remove all rows from a table or materialized view in Amazon Redshift. It's faster than DELETE and immediately reclaims disk space. TRUNCATE removes all rows in a table without scanning them individually. This makes it much faster than DELETE operations, especially for large tables. TRUNCATE automatically performs a VACUUM operation, which sorts the table and reclaims space. TRUNCATE resets any auto-increment columns.

Answer:B TRUNCATE Command: The TRUNCATE command is the most efficient way to delete all rows from a table or materialized view. It does not scan the table, does not generate individual row delete actions, and effectively frees up space immediately by removing all data at once. It also resets any identity columns, if applicable.