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Data & Analytics · Intermediate

Columnar Storage

Storing each column's values together on disk rather than storing whole rows, which speeds analytic scans and improves compression.

Definition

Queries read only the columns they reference, and similar values compress well with dictionary and run-length encoding. Columnar storage is used by Parquet, ORC, Snowflake micro-partitions, BigQuery Capacitor and VertiPaq. Row storage remains better for OLTP single-row operations.

Exam tip

Avoid SELECT * in columnar systems; it forces every column to be read.

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