Partition types (range, list, hash) in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is range partitioning in PostgreSQL?

Range partitioning divides a table into parts where each part holds rows with values within a specific range. For example, a sales table can be partitioned by year ranges like 2020-2021, 2022-2023.

beginner

How does list partitioning work in PostgreSQL?

List partitioning splits a table into parts based on a list of discrete values. For example, a table can be partitioned by country names like 'USA', 'Canada', 'Mexico'. Each partition holds rows matching those values.

intermediate

Explain hash partitioning in PostgreSQL.

Hash partitioning distributes rows into a fixed number of partitions using a hash function on the partition key. It balances data evenly without ranges or lists, useful when data distribution is unknown.

beginner

Which partition type would you use to split data by months?

Range partitioning is best for splitting data by months because months form continuous ranges of dates.

intermediate

What is a key benefit of hash partitioning?

Hash partitioning evenly distributes data across partitions, which helps balance load and improve query performance when data values are unpredictable.

Which partition type divides data based on continuous value ranges?

A Range partitioning

B List partitioning

C Hash partitioning

D None of the above

Range partitioning splits data into partitions based on continuous ranges of values.

If you want to partition a table by specific countries, which partition type should you use?

A Range partitioning

B Composite partitioning

C Hash partitioning

D List partitioning

List partitioning is used to split data by specific discrete values like country names.

What does hash partitioning use to assign rows to partitions?

A A hash function

B Lists of values

C Value ranges

D Random assignment

Hash partitioning uses a hash function on the partition key to distribute rows evenly.

Which partition type is best when you want to balance data evenly but don't know the data distribution?

A Range partitioning

B Hash partitioning

C List partitioning

D No partitioning

Hash partitioning evenly distributes data without needing to know value ranges or lists.

Which partition type would you NOT use to split data by date ranges?

A Hash partitioning

B List partitioning

C Both B and C

D Range partitioning

Date ranges are best handled by range partitioning; list and hash partitioning are not suitable for continuous ranges.

Describe the differences between range, list, and hash partitioning in PostgreSQL.

Think about how data is divided in each type.

When would you choose hash partitioning over range or list partitioning?

Consider data balance and predictability.

Practice

1. Which partition type in PostgreSQL is best suited for dividing a table based on continuous ranges of values, such as dates or numbers?

easy

A. HASH partitioning

B. LIST partitioning

C. RANGE partitioning

D. NONE partitioning

Solution

1. Step 1: Understand partition types

   RANGE partitions split data into continuous ranges, like dates or numeric intervals.

2. Step 2: Match partition type to use case

   Since the question asks about continuous ranges, RANGE partitioning fits best.

3. Final Answer:

   RANGE partitioning -> Option C

4. Quick Check:

   Continuous ranges = RANGE partitioning [OK]

Hint: Continuous values? Choose RANGE partitioning [OK]

Common Mistakes:

• Confusing LIST with RANGE for continuous data
• Thinking HASH is for ordered ranges
• Assuming NONE is a valid partition type

2. Which of the following is the correct syntax to create a LIST partitioned table in PostgreSQL?

easy

A. CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region);

B. CREATE TABLE sales PARTITION BY LIST region (id INT, region TEXT);

C. CREATE TABLE sales (id INT, region TEXT) PARTITION BY RANGE (region);

D. CREATE TABLE sales (id INT, region TEXT) PARTITION BY HASH (region);

Solution

1. Step 1: Identify correct PARTITION BY syntax

   PostgreSQL syntax requires PARTITION BY followed by partition type and column in parentheses after table columns.

2. Step 2: Check each option

   CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); uses correct syntax: columns first, then PARTITION BY LIST (region). Options A, B, C have syntax errors or wrong partition type.

3. Final Answer:

   CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); -> Option A

4. Quick Check:

   Correct syntax = CREATE TABLE sales (id INT, region TEXT) PARTITION BY LIST (region); [OK]

Hint: PARTITION BY type (column) after columns [OK]

Common Mistakes:

• Placing PARTITION BY before column definitions
• Using wrong partition type for LIST
• Missing parentheses around partition column

3. Given the following partitioned table and inserts:

CREATE TABLE orders (
  order_id INT,
  order_date DATE
) PARTITION BY RANGE (order_date);

CREATE TABLE orders_2023 PARTITION OF orders
  FOR VALUES FROM ('2023-01-01') TO ('2024-01-01');

INSERT INTO orders VALUES (1, '2023-06-15');
INSERT INTO orders VALUES (2, '2022-12-31');

What will happen when the second insert is executed?

medium

A. The row is inserted into orders_2023 partition

B. The row is rejected with a constraint violation error

C. The row is inserted into a default partition automatically

D. The row is inserted into the parent table without partition

Solution

1. Step 1: Understand RANGE partition boundaries

   The orders_2023 partition accepts dates from 2023-01-01 up to but not including 2024-01-01.

2. Step 2: Check the inserted date '2022-12-31'

   This date is before the partition range, so no matching partition exists for it.

3. Step 3: Behavior on no matching partition

   PostgreSQL rejects inserts that don't fit any partition unless a default partition exists (none here).

4. Final Answer:

   The row is rejected with a constraint violation error -> Option B

5. Quick Check:

   Out-of-range insert = error [OK]

Hint: Out-of-range insert without default partition causes error [OK]

Common Mistakes:

• Assuming automatic default partition insertion
• Thinking parent table stores unmatched rows
• Ignoring partition range boundaries

4. Consider this partitioned table creation:

CREATE TABLE employees (
  emp_id INT,
  department TEXT
) PARTITION BY LIST (department);

CREATE TABLE employees_sales PARTITION OF employees FOR VALUES IN ('Sales');
CREATE TABLE employees_hr PARTITION OF employees FOR VALUES IN ('HR');

Which error will occur if you try to insert INSERT INTO employees VALUES (1, 'Marketing');?

medium

A. No partition found for value 'Marketing', insert fails

B. Syntax error due to missing partition

C. Row inserted into employees_sales partition by default

D. Row inserted into parent table without partition

Solution

1. Step 1: Check defined partitions

   Partitions exist only for 'Sales' and 'HR' departments.

2. Step 2: Check inserted value 'Marketing'

   'Marketing' is not listed in any partition's VALUES list.

3. Step 3: PostgreSQL behavior on unmatched LIST value

   Without a default partition, insert fails with no matching partition error.

4. Final Answer:

   No partition found for value 'Marketing', insert fails -> Option A

5. Quick Check:

   Unlisted LIST value = insert failure [OK]

Hint: LIST partition needs matching value or default partition [OK]

Common Mistakes:

• Assuming insert goes to any partition by default
• Expecting parent table to store unmatched rows
• Confusing syntax error with runtime insert error

5. You want to evenly distribute a large table's rows across 4 partitions to improve query performance without caring about specific value ranges. Which partition type and setup is best in PostgreSQL?

hard

A. Use no partitioning and rely on indexes.

B. Use LIST partitioning with 4 specific values.

C. Use RANGE partitioning on a numeric column with 4 ranges.

D. Use HASH partitioning with 4 partitions.

Solution

1. Step 1: Understand partitioning goals

   The goal is even distribution across 4 partitions without caring about value ranges.

2. Step 2: Match partition type to goal

   HASH partitioning evenly distributes rows based on a hash function, ideal for this case.

3. Step 3: Evaluate other options

   RANGE and LIST require specific ranges or values, not suitable for even spread without criteria. No partitioning misses distribution benefits.

4. Final Answer:

   Use HASH partitioning with 4 partitions. -> Option D

5. Quick Check:

   Even distribution = HASH partitioning [OK]

Hint: Even spread without ranges? Choose HASH partitioning [OK]

Common Mistakes:

• Using RANGE or LIST when no value grouping needed
• Thinking indexes replace partitioning benefits
• Confusing HASH with LIST partitioning