GCP Professional Data Engineer Practice Question

A retailer maintains an unpartitioned BigQuery table that receives frequent streaming inserts with new transactions. Analysts complain that their daily dashboard loads slowly because it runs an expensive aggregation over the last 7 days of data. You are asked to speed up the dashboard while keeping the data no more than 30 minutes behind the source. You create a BigQuery materialized view that pre-aggregates the last 7 days of sales by store and product. Which statement correctly describes how this materialized view will stay up-to-date once it is in production?

BigQuery automatically performs incremental refreshes of the materialized view shortly after new rows are written to the underlying transactions table; no manual job or scheduler is required.
The materialized view refreshes only once per day at 00:00 UTC, so you should partition the base table and use partition decorators to shorten lag.
BigQuery refreshes the materialized view only when you explicitly run a query against it; until then it remains stale regardless of incoming data.
You must create a Cloud Scheduler job that calls the BigQuery Jobs API to rewrite the view every 30 minutes, because BigQuery materialized views do not refresh on their own.

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Answer Description

BigQuery maintains materialized views automatically. When new rows are appended to the base table-through streaming inserts, batch loads, or DML-the service triggers an incremental refresh that processes only the changes since the previous refresh and writes the updated results to the view's cached storage. Refresh typically occurs within a few minutes and never more than every 30 minutes. No external scheduler or manual job is required. If a query requests data newer than the cached results, BigQuery can transparently read the base table instead. Therefore, the statement that the materialized view refreshes itself incrementally as new data arrives best reflects the default behavior, whereas the other options either require unnecessary manual work, assume a daily schedule, or incorrectly state that queries are needed to trigger refresh.

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