MVCC Concurrency & The VACUUM Process

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Understand Multi-Version Concurrency Control (MVCC), transaction snapshots, dead tuple garbage collection, and autovacuum.

Readers Never Block Writers

Under MVCC, when a row is updated, PostgreSQL does not overwrite the old bytes in place; it marks the old row as dead and writes a new row version. VACUUM reclaims this space.

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Test Yourself With Exercise

+15 XP

Which maintenance command cleans dead row versions (tuples) and reclaims disk space in PostgreSQL?

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