Why Pre-Aggregate?

Concepts: dmPreAggregation

The Performance Problem A fact table with 500 million rows. A dashboard with 10 tiles. Each tile runs a GROUP BY query that scans the entire table. Ten full-table scans every time someone opens the dashboard. At $5 per TB scanned (BigQuery pricing), that is real money. At 30 seconds per query, that is a terrible user experience. Pre-aggregation solves this by computing the answer ahead of time. Instead of scanning 500 million rows to get daily revenue, create a daily_revenue summary table with 365 rows per year. The dashboard reads 365 rows instead of 500 million. Load time drops from 30 seconds to milliseconds. The Tradeoff Pre-aggregation is a deliberate tradeoff between freshness and performance. The summary table is only as current as its last refresh. If the daily_revenue table is ref