VACUUM and its importance in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the VACUUM command do in PostgreSQL?

VACUUM cleans up dead rows left behind after updates or deletes to free space and maintain database performance.

beginner

Why is VACUUM important for database performance?

Because it removes dead rows, VACUUM prevents table bloat and keeps queries fast by allowing PostgreSQL to reuse space efficiently.

intermediate

What is the difference between VACUUM and VACUUM FULL?

VACUUM reclaims space but does not lock tables fully; VACUUM FULL rewrites the entire table and locks it, freeing more space but with more impact.

beginner

How does PostgreSQL handle dead rows before VACUUM runs?

Dead rows remain in the table and can slow down queries until VACUUM removes them and frees space.

beginner

What is autovacuum in PostgreSQL?

Autovacuum is a background process that automatically runs VACUUM to keep the database clean without manual intervention.

What problem does VACUUM solve in PostgreSQL?

A Creates new tables

B Indexes all columns

C Backs up the database

D Removes dead rows to free space

VACUUM removes dead rows left by updates or deletes to free space and improve performance.

Which VACUUM type locks the table fully and reclaims more space?

A VACUUM FULL

B ANALYZE

C Autovacuum

D VACUUM

VACUUM FULL rewrites the entire table and locks it to reclaim more space.

What is the role of autovacuum in PostgreSQL?

A Manually run VACUUM commands

B Automatically run VACUUM in the background

C Create backups

D Optimize queries

Autovacuum automatically runs VACUUM to maintain database health without manual work.

What happens if you never run VACUUM on a PostgreSQL database?

A Dead rows accumulate and slow queries

B Database size shrinks

C Tables get deleted

D Indexes are rebuilt automatically

Without VACUUM, dead rows build up causing table bloat and slower queries.

Which command reclaims space but does not lock the table fully?

A DROP TABLE

B VACUUM FULL

C VACUUM

D CREATE INDEX

VACUUM reclaims space without fully locking the table, allowing normal operations.

Explain what VACUUM does in PostgreSQL and why it is important.

Think about how updates and deletes affect storage and how VACUUM cleans that up.

Describe the difference between VACUUM and VACUUM FULL.

Consider how much space is freed and the impact on table availability.