[Answered] What are PostgreSQL partitioning strategies?

Answer

PostgreSQL supports table partitioning, which is an effective way to manage large tables by splitting them into smaller, more manageable pieces called partitions. Partitioning can greatly improve performance for certain types of queries and is also useful for purging old data. There are several partitioning strategies in PostgreSQL, each suitable for different scenarios:

1. Range Partitioning

This strategy involves dividing a table into partitions based on ranges of values of a partition key. It is often used with date or time columns.

CREATE TABLE measurement (
    city_id         int not null,
    logdate         date not null,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (logdate);

CREATE TABLE measurement_y2020 PARTITION OF measurement
    FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');

CREATE TABLE measurement_y2021 PARTITION OF measurement
    FOR VALUES FROM ('2021-01-01') TO ('2022-01-01');

2. List Partitioning

List partitioning allows you to map rows to partitions based on the specific values of a partition key.

CREATE TABLE customer (
    id              int not null,
    country         varchar not null,
    name            text
) PARTITION BY LIST (country);

CREATE TABLE customer_usa PARTITION OF customer
    FOR VALUES IN ('USA');

CREATE TABLE customer_canada PARTITION OF customer
    FOR VALUES IN ('Canada');

3. Hash Partitioning

Hash partitioning assigns rows to partitions based on a hash value of the partition key. This strategy aims to evenly distribute the rows across partitions.

CREATE TABLE product (
    id              int not null,
    name            text,
    price           numeric
) PARTITION BY HASH (id);

CREATE TABLE product_part1 PARTITION OF product
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);

CREATE TABLE product_part2 PARTITION OF product
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);

Choosing a Partitioning Strategy

Range partitioning is ideal for time-series data where queries often filter by date ranges.
List partitioning works well when you frequently query subsets of data based on discrete values, such as country codes or status codes.
Hash partitioning is best suited for distributing data uniformly across partitions, especially when no logical range or list distribution exists.

Considerations

Partitioning requires planning and understanding of your data characteristics and access patterns.
While partitioning can significantly improve performance for certain queries, it may add complexity to your database schema and operational processes.
Not all features and optimizations are available for partitioned tables, such as foreign keys referencing partitioned tables.

Using partitions effectively in PostgreSQL requires careful consideration of your use case, but when implemented correctly, it can offer significant performance improvements and ease of maintenance.