Max_Staleness parameters

Google Cloud Database
4

Here is clarification on better understanding Refresh Frequency and Max Staleness in BigQuery Materialized Views:

Refresh Frequency:

  • Correct: Setting the materialized view to refresh every 15 minutes is accurately described. This means the view will attempt to update its data from the base tables at this interval.

Max Staleness:

  • Clarification: Max staleness does not trigger automatic refreshes but controls the behavior of queries against the materialized view.
  • Function: It determines whether BigQuery uses the cached data in the view or re-queries the base tables.
  • Your Setup: With max_staleness = INTERVAL "0:30:0" HOUR_TO_SECOND, BigQuery will:
    • Use cached data if the last successful refresh was within the past 30 minutes.
    • Query the base tables for fresh data if the last refresh was more than 30 minutes ago, which may affect query performance.

Key Point:

  • Max staleness is solely about the age of the cached data at the time of a query. It does not initiate data refreshes in the materialized view.

Clarification on Data Handling:

  • BigQuery does not mix cached and fresh data. It will use either the cached data (if within the max staleness period) or re-query the base tables for fresh data (if beyond the max staleness period).

Recommendations:

  • Set max_staleness to at least the same duration as the refresh interval (15 minutes or more) to ensure efficient use of cached data between scheduled refreshes.
  • For critical data freshness, consider a shorter max staleness duration, but be aware of potential performance impacts and increased costs.

Additional Considerations:

  • Data Change Frequency: A shorter max staleness might be necessary for datasets with rapid changes to ensure accuracy.
  • Query Performance Impact: Direct queries to base tables can impact performance, especially for large datasets.
  • Cost Implications: Frequent refreshes and base table queries can lead to higher BigQuery costs.

Best Practices:

  • Regularly monitor the materialized view’s usage and query performance to fine-tune the refresh intervals and max staleness settings for optimal balance.
  • Consider partitioning for large datasets to improve efficiency. However, note that max_staleness is not compatible with partitioning in BigQuery-managed storage.
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