Question: What are the differences between PostgreSQL inheritance and partitioning?

Answer

PostgreSQL offers two powerful features for organizing data: table inheritance and table partitioning. Both mechanisms have distinct uses, advantages, and considerations. Understanding their differences is crucial for database design and optimization.

Table Inheritance

Table inheritance in PostgreSQL allows tables to inherit the structure of another table, which is referred to as the parent table. The inheriting tables are called child tables. This feature is derived from the concept of class inheritance in object-oriented programming.

Use Cases:

• Implementing table hierarchies.
• Sharing a common set of columns across multiple tables while allowing each child table to have additional columns specific to its context.

Example:

CREATE TABLE vehicles (
    vehicle_id SERIAL PRIMARY KEY,
    make VARCHAR(255),
    model VARCHAR(255)
);

CREATE TABLE cars (
    top_speed INT
) INHERITS (vehicles);

In this example, cars inherit from vehicles, meaning cars will have vehicle_id, make, model, and top_speed.

Considerations:

• Queries on the parent table can include records from all child tables, which might not always be desirable.
• Indexes, foreign keys, and unique constraints only apply to individual tables, not across the hierarchy.

Table Partitioning

Partitioning involves splitting a single table into multiple smaller tables (partitions) based on certain criteria, such as ranges of values or key hashes. Each partition contains rows that meet the specific criteria defined for that partition.

Use Cases:

• Improving query performance by enabling more efficient data access patterns.
• Managing large tables by breaking them down into more manageable pieces.

Example:

CREATE TABLE measurements (
    city_id INT NOT NULL,
    logdate DATE NOT NULL,
    peaktemp INT,
    unitsales INT
) PARTITION BY RANGE (logdate);

CREATE TABLE measurements_y2020 PARTITION OF measurements FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');

In this setup, data for the year 2020 will be stored in measurements_y2020.

Considerations:

• Requires careful planning of partitioning strategy to ensure efficient data distribution and access.
• PostgreSQL handles partitioning under-the-hood, making it transparent to queries, which can simplify application development compared to managing inheritance manually.

Conclusion

While both inheritance and partitioning can be used to organize data in PostgreSQL, they serve different purposes and come with their respective advantages and drawbacks. Inheritance is best suited for situations where there’s a clear hierarchical relationship between datasets. Partitioning, on the other hand, is geared towards performance optimization in scenarios involving very large datasets.