VACUUM and its importance in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run a basic VACUUM command on the table named 'users'.

PostgreSQL

VACUUM [1];

Drag options to blanks, or click blank then click option'

ASELECT

BTABLE

Cusers

DDATABASE

Attempts:

3 left

💡 Hint

Common Mistakes

Using keywords like SELECT or TABLE instead of the actual table name.

Trying to vacuum the whole database without specifying it properly.

The VACUUM command followed by the table name 'users' cleans up that specific table.

2fill in blank

medium

Complete the code to perform a VACUUM FULL on the 'orders' table to reclaim disk space.

PostgreSQL

VACUUM FULL [1];

Drag options to blanks, or click blank then click option'

Aorders

BDATABASE

CINDEX

DANALYZE

Attempts:

3 left

💡 Hint

Common Mistakes

Using DATABASE, ANALYZE, or INDEX instead of the table name.

Inserting unnecessary keywords like TABLE.

VACUUM FULL followed by the table name reclaims all available disk space by compacting the table into a minimal contiguous area.

3fill in blank

hard

Fix the error in the VACUUM command to analyze the 'products' table after vacuuming.

PostgreSQL

VACUUM ANALYZE [1];

Drag options to blanks, or click blank then click option'

Aproducts

BDATABASE

CINDEX

DFULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using INDEX, DATABASE, or FULL instead of the table name.

Adding extra keywords like TABLE.

The correct syntax is VACUUM ANALYZE followed by the table name to vacuum and update statistics.

4fill in blank

hard

Fill the blank to create a command that vacuums and analyzes the 'customers' table.

PostgreSQL

VACUUM [1] customers;

Drag options to blanks, or click blank then click option'

ADATABASE

BANALYZE

CFULL

DTABLE

Attempts:

3 left

💡 Hint

Common Mistakes

Using TABLE, FULL, or DATABASE instead of ANALYZE.

Adding extra unnecessary keywords.

VACUUM ANALYZE table_name vacuums the table and updates query planner statistics.

5fill in blank

hard

Fill both blanks to vacuum full and analyze the 'invoices' table.

PostgreSQL

VACUUM [1] [2] invoices;

Drag options to blanks, or click blank then click option'

ATABLE

BFULL

CANALYZE

DDATABASE

Attempts:

3 left

💡 Hint

Common Mistakes

Using TABLE or DATABASE instead of FULL/ANALYZE.

Mixing up the order of FULL and ANALYZE.

The correct command is VACUUM FULL ANALYZE table_name to fully reclaim space and update statistics.

Practice

1. What is the main purpose of the VACUUM command in PostgreSQL?

easy

A. To backup the database

B. To create new tables automatically

C. To clean up old, deleted data and free space

D. To increase the size of the database

Solution

1. Step 1: Understand what happens to deleted data

   When rows are deleted or updated, old versions remain and take space.

2. Step 2: Role of VACUUM

   VACUUM cleans these old rows to free space and keep the database efficient.

3. Final Answer:

   To clean up old, deleted data and free space -> Option C

4. Quick Check:

   VACUUM cleans old data = A [OK]

Hint: VACUUM removes old data to keep DB fast [OK]

Common Mistakes:

• Thinking VACUUM creates tables
• Confusing VACUUM with backup
• Believing VACUUM increases DB size

2. Which of the following is the correct syntax to run a basic VACUUM on a table named users?

easy

A. VACUUM TABLE users;

B. VACUUM users;

C. RUN VACUUM ON users;

D. CLEAN users VACUUM;

Solution

1. Step 1: Recall PostgreSQL VACUUM syntax

   The correct command is simply VACUUM followed by the table name.

2. Step 2: Check each option

   VACUUM users; matches the correct syntax: VACUUM users;

3. Final Answer:

   VACUUM users; -> Option B

4. Quick Check:

   Correct VACUUM syntax = C [OK]

Hint: VACUUM followed by table name, no TABLE keyword [OK]

Common Mistakes:

• Adding TABLE keyword incorrectly
• Using RUN or CLEAN commands
• Wrong order of keywords

3. Consider a table orders where many rows were deleted recently. After running VACUUM on it, what is the expected effect?

medium

A. The table size on disk will increase

B. The database will create a backup of the table

C. The table will be locked and unavailable during VACUUM

D. The deleted rows' space will be freed for reuse

Solution

1. Step 1: Understand what VACUUM does after deletes

   VACUUM frees space taken by deleted rows so it can be reused.

2. Step 2: Check other options

   VACUUM does not increase size, lock table fully (that's VACUUM FULL), or create backups.

3. Final Answer:

   The deleted rows' space will be freed for reuse -> Option D

4. Quick Check:

   VACUUM frees deleted space = D [OK]

Hint: VACUUM frees space from deleted rows, not increase size [OK]

Common Mistakes:

• Confusing VACUUM with VACUUM FULL locking
• Thinking VACUUM increases disk size
• Assuming VACUUM creates backups

4. You run VACUUM FULL on a large table but notice the table remains locked for a long time. What is the best way to fix this issue?

medium

A. Use regular VACUUM instead of VACUUM FULL

B. Restart the PostgreSQL server immediately

C. Run VACUUM FULL more frequently

D. Drop and recreate the table

Solution

1. Step 1: Understand locking behavior of VACUUM FULL

   VACUUM FULL locks the entire table, causing long waits on large tables.

2. Step 2: Choose a better approach

   Regular VACUUM does not lock the table fully and is better for large tables.

3. Final Answer:

   Use regular VACUUM instead of VACUUM FULL -> Option A

4. Quick Check:

   VACUUM FULL locks table; regular VACUUM doesn't = A [OK]

Hint: Use regular VACUUM to avoid long table locks [OK]

Common Mistakes:

• Restarting server unnecessarily
• Running VACUUM FULL more often without need
• Dropping table instead of vacuuming

5. You have a large table products with frequent updates and deletes. You want to reclaim disk space without locking the table for a long time. Which approach is best?

hard

A. Run regular VACUUM products; frequently and schedule VACUUM FULL during maintenance windows

B. Run VACUUM FULL products; daily during peak hours

C. Never run VACUUM and rely on autovacuum only

D. Drop and recreate the table every week

Solution

1. Step 1: Understand the impact of VACUUM FULL

   VACUUM FULL reclaims space but locks the table, so running it during peak hours is bad.

2. Step 2: Best practice for large tables with frequent changes

   Run regular VACUUM often to keep space reusable and schedule VACUUM FULL only during low-traffic times.

3. Final Answer:

   Run regular VACUUM products; frequently and schedule VACUUM FULL during maintenance windows -> Option A

4. Quick Check:

   Regular VACUUM often + VACUUM FULL off-peak = B [OK]

Hint: Use regular VACUUM often; VACUUM FULL only off-peak [OK]

Common Mistakes:

• Running VACUUM FULL during busy times
• Ignoring regular VACUUM
• Dropping table unnecessarily