All 7 Amazon Redshift & Data Warehousing questions
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What is columnar storage, and why does Redshift use it?

Beginner

Answer

Columnar storage organizes and stores data by column rather than by row, meaning that when a query only needs a few specific columns out of a table with dozens of columns, Redshift only needs to read the data for those specific columns, dramatically reducing the amount of data scanned and improving performance for the kind of aggregation heavy analytical queries data warehouses commonly run.
SELECT SUM(sales_amount) FROM transactions WHERE region = 'US';
Real-world example A retail analytics query that only needs the sales amount and region columns from a table with fifty columns runs significantly faster in Redshift than it would in a traditional row based database, since Redshift only reads the two relevant columns.

Common follow-ups: How does columnar storage compare to row based storage for transactional workloads?;What compression benefits come from columnar storage?

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All 7 Amazon Redshift & Data Warehousing questions